arsenic and the · arsenic compounds have long been infamous as very potent poisons, a well-known...

SFUND RECORDS CTR

AROOO4,COLORADO SCHOOL OF MINES n* ^COLORADO SCHOOL OF MINES RESEARCH INSTITUTE

MINERAL INDUSTRIES BULLETINVolume 17 May 1974 Number 3

SFUND RECORDS CTR

88222353

R. Wayne Whitacreand

Carlton S. Pearse

Arsenicand the

environment

IT-

CONTENTS

Introduction _ 1

Natural occurrence of arsenic 2

Land _ „ _.. 2

Water _ _ _ 2

Freshwater _ _ _ 2

Seawater . _ 2

Air __ _ '. _ 2

Living organisms _ 5

Plants _ _ 5

Animals _ _ __ 5

Summary _ '. _ _ _ 5

Cultural contributions of arsenic to the environment — _ - _ 6

Basic chemistry _ 7

Toxicolotrv „ 10"*••* O/ ••••••-——-——• - - •-• ,........_.... .... ...........——•"———• •————— •—— *- --•-

Analytical methods for arsenic determination _ — 11

Qualitative analysis _ _.. 12

Macro _ _ _ _ _ __ -_ 12

Micro _ _ _ _... 12

Quantitative analysis _ _ 12

Macro „ 12

Micro _ _ 12

Standards ". _ 13

Abatement methods — _.. 15

Removal of arsenic from water _ 15

Removal of arsenic from air _ _ '. 17

Acknowledgments __ _ 18

Bibliography _ 18

Co-editon: Jon W. Ra«< and Donald A. Paist

Cover notes: Illustration from Agricola's De Be MetaJlica, first published in J556. Medieval furnace (A) isshown below vaulted dust-chamber (D). As ores were smelted, smoke and fumes were collected and saved in the dustchamber and in the chimney (F). Workers removed soot and 7inc deposits from the chamber. The products probablycontained arsenical oxides, used extensively by the ancients for medicinal purposes. Agricola's description would in-dicate one of man's earliest attempts to preserve the environment while at the same time conserving a useful by-product.

Colorado School of Minrs Mineral Industrim Rutirtin, v. 17, no. J, May 1974. Published bi-monthly by the Colorado Schoolof Mines at Golden, Colorado 80401. Second-claw pottage paid at Golden, Colorado. Copyright © 1974 by Colorado School ofMines. Subscription $4.00 a year. Single copy or back issue $1.00.

Arsenicand the

environment

R. Wayne Whitacreand

Carlton S. Pearse

INTRODUCTION

Arsenic compounds have long been infamous asvery potent poisons, A well-known portrayal of theuse o£ arsenic as a poison is given in Joseph Kcssel-ring's contemporary drama "Arsenic and Old Lnrc"which opened in New York in 1941. In it, twoelderly ladies relieved lonely, troubled men fromthe burdens of the world by poisoning them, whichcame as somewhat of a surprise to their youngnepBew:

Martha: Well, dear, for a gallon of elderberrywine I take one tcaspoonful of ar-senic, then add a half tcaspoonful ofstrychnine and then just a pinch ofcyanide.

Mortimer: (appraisingly) Should have quite akick.

Abby: Yes! As a matter of fact one of ourgentlemen found time to say "howdelicious!"

Throughout history, however, man's uses for ar-senic have been ambivalent, i.e., while in some sit-uations arsenic resulted in poisoning, in other sit-uations arsenic compounds were thought to havegenuine medicinal value and were even used asvitality potions. As recently as 1901, Professor ].

R. Wayne Whitacre, research chenwt, and Carlton S.project engineer, are with the Colorado School of MinesResearch Institute.

Alfred Wanklyn (1901), in his book Arsenic, stated,"Recent medical experience points to arsenic as oneof the most potent medicinal agencies at the dis-posal of the physician." In Styria, a province insoutheastern Austr ia , arsenic was consumed regular-ly in large quantities by the peasants and theiranimals for two reasons:

"First, to give plumpness to the figure, clean-ness and softness to the skin, and beauty andfreshness to the complexion. Secondly, to im-prove the breathing and give longncss of wind,so that steep and coniinuous heights may beclimbed without di f f icul ty and exhaustion ofbreath" (Wanklyn 1901).

The use of arsenic as a pharmaceutical today israther limited, but when used judiciously, it liasmany other constructive applications. In spite ofits rather notorious reputation, the incidence of anyacute arsenical poisoning from natural causes, atleast in the United States, has been rare. Sincemuch less is known about its distribution, there isno current furor over potential damage of arsenicto the environment, as is the case with mercury,cadmium, and even phosphates. The mining in-dustry, however, should not underestimate the mag-ni tude of die potent ia l threat arsenic poses to theenvironment . The purpose of the authors of thisMID is to provide a basic knowledge of arsenicand how it rcaltcs to a healthy, balanced environ-ment.

Mineral Industries Bulletin

rNATURAL OCCURRENCE OF ARSENIC

Arsenic is an clement thai occurs in relat ivelylow concentrations almost everywhere in nature .Long before man's activit ies had any effect on thebalance of nature, arsenic was distr ibuted ub iqu i t -ously throughout land, water, air, and living organ-isms.

LANDN Arsenic is a rare crustal clement comprising

about five hundred-thousandths of 1 percent(0.00005 percent) of the earth's crust (Gulledgcand O'Connor 1973) and having an average terres-trial concentration of about 5 ppm (Carnpclla1963). Its distribution in various gcochcmical ma-terials is listed in table 1.

TABLE 1.— Arsenic concentration of variousterrestrial materials

(Bowcn 1966; Guahieri 1973; Onishi 1969)

Material As (ppm)

IgneousSedimentary

ShalesSandstonesLimestones and dolomitesPelagic claysCoal

Metamorphic

1.5

1311

I I25

0/1-18

Arsenic naturally occurs in over 100 .differentmineral forms (Mellor 1930), but only certain ofthese are commonly encountered in s ignif icantamounts. A few of the more commonly occurringarsenic minerals with notes on their na ture and oc-currence are listed in table 2.

Arsenic in its most recoverable form is found invarious types of metalliferous deposits. The majordeposits of this type are catcgori/cd inio seven majorgroups which are listed in table 3. Also listed arcthe arsenic minerals contained, the weight percentof arsenic present and the locations where thesetypes of deposit are found.

The amount of arsenic present in these metal-liferous deposits is vast and should be more thanadequate to meet any demand for the clement inthe foreseeable future. The distribution of thesedeposits in various geographic locations is shown intable 4 where the known deposits as well as esti-mated hypothetical deposits are included.

As in rock, arsenic is a normally occurring traceconstituent of most soils. Data on worldwide soilconcentrations is limited, but data on United Statessoils are summarized in Onishi (196P). It was re-ported that 30 percent of the soils tested contained

less than 5 ppm of arsenic, about 50 percent con-tained 5 to 10 ppm, and the remaining 20 percentcontained more than 10 ppm. The average valuefor arsenic concentration in American soils then liessomewhere between 5 and 10 ppm.

WATERFresh Water

As on land, arsenic is found at low concentra-tions in vir tual ly all natural waters. It is even atrace constituent of various forms of precipitation.A few statistics of arsenic concentrations measuredin 'precipitation gathered all over the world arelisted fn table 5. Values range from 0.0006 to 0.025mg/litcr and the accepted average is 0.001 mg/liter (Onishi 1969).

Precipitation then, containing an average ofabout one-thousandth of one mg/litcr of arsenic,falls on the land and begins its course to the sea,inevitably exchanging various quan t i t i es of arsenicwith the minerals it contacts on its way. Sincerocks and soils contain varing amounts of arsenic,the exchange is one that depends strongly on therelative arsenic concentration at any given location.Bowcn (1966) lists an average arsenic concentra-tion for fresh waters at 0.000-1 mg/litcr, whileFerguson and Gavis (1972) list 0.001 mg/litcr asan average for rivers free from arsenic pollution.Ru t , as can be seen from the data in table 6, thevariance of concentrations throughout the worldis great indeed. In certain places in New Zealand(Schneider 1971) and Taiwan (Shcn 1973). high

na tu r a l concentrations of arsenic in drinkingsources have been linked to black-foot disease andeven death.

Seawatcr

Scawater also contains measurable concentra-tions of arsenic, ranging from less than 0.001 mg/liter along the Aleutian Islands in the Pacific to0.006 mg/litcr along the coastal waters of Japan(Onishi 1969). The accepted worldwide average ar-

senic concentration in the seas is taken as 0.002 to0.003 mg/liter (Onishi 1969; Schneider 1971; Bow-en 1966). While this concentration is rather low(two or three ten-millionths of a percent), whenthe waters of all the oceans in the world arc con-sidered, the amount of arsenic contained therein isimmense. If we take the mass of all ocean watersto be 1.42 x 10=1 kg (Bowen 1966), the total amountof arsenic in them is then estimated to be betweenthree and five billion tons.

Am

The amount of arsenic in the air is minute, av-eraging less than O.OI/tg/cu m, or approximately7.7 x 10-" ppm (Bowcn 1966). Studies in the

Safff

2 Colorado School of Mines

southern Lake Michigan area indicated arsenic par-ticulate concentrations ranging from 0.002 to 0.012

/ig/cu m with only moderately weak pollutionsources in (lie area (Harrison and others 1971).

TAUI.F 2—.SV/^r/rv/ nr.irnie minerals(mostly from Oimhi 1909)

Name Composition N f a n n c r of Occurrence

Adamite

Arsenic

Arsenolite

Arsenopyrite

Claudetite

Cobaltite

DomeykiteEnargite

Loellfngite

Niccolite

Orpiment

Pharmacosiderite

Proustite

Rammelsbergite

Realgar

Zn2(OH) (AsO<)

As

Safflorite

SeligmanniteSmaltiteTennantite

FeAsS

CoAsS

Cu3AsCu3AsS4

FeAs2

NiAs

Fes (AsO<) , (OH) 3-5H2O

Ag3AsS3

NiAsj

AsS

(Co.Fe) As2

PbCuAsSgCoAsj(Cu.Fe) As

Secondary mineral.

Found in hydrothermal veins.

A secondary mineral formed by the oxidationof arscnopyritc. native As, and other As min-erals.

The most abundant and widespread As min-eral; it occurs in diverse types of deposits,usually as one of the earliest minerals to form.

A secondary mineral formed by the oxidationof realgar, arsenopyritc, and other As minerals.

Found in high-temperature deposits and asdisseminations in metamorphic rocks.

Found in vein and replacement depositsformed ni moderate temperatures.

Found in mcsothermal vein deposits.

Frequently occurs in norites or ore depositsfrom them; also found in vein deposits withCo and Ag minerals.

Found in hydrothermal veins, as a hot springdeposit, and as a volcanic sublimation pro-duct.

Oxidation product of arsenopyrite and otherAs-rich minerals.

Generally one of the late Ag minerals in thesequence of primary deposition.

Commonly in mesothermal vein deposits.

Occurs commonly as a minor constituent ofcertain ore veins associated with orpiment andother As minerals; also found in certain lime-stones or dolomites, in clay, and as a volcanicsublimation product or a deposit from hotsprings.

Generally in mesothermal vein deposits.

Occurs in hydrothermal veins.


TABI.F 3—Ar.trnir deposits of the world(mostly from Gualt icri 1973)

Type of Deposit As Minerals (s) Contained

AverageArsenic

Concentrate(ppm) Location

(1) Enargite-bearingcopper-zinc-leaddeposits

(2) Arsenical pyriticcopper deposits

Enargite

Arscnopyrite. tenn.mtite

(3) Native silver and Smnliiic, domcykite, snfflor-nickel-cobah arsenide- ite, rammcisbcrgite. cobnl-bearingdeposits lite, niccolitc, locllingite,

arscnopyrite, et al.

(4) Arsenical golddeposits

Arscnopyritc, locllingiic

(5) Arsenic sulfide and Realgar, orpimcntarsenic sulfide golddeposits

(6) Arsenical tin deposits Arsenopyrile

(7) Arsenical quartz, silver Arsenopyritcand lead-zinc deposits

1000 (0.1%) United States, Argentina, Chile,Peru, Mexico, Republic of thePhilippines, Spain, Yugoslavia,USSR

40000 (4%) United States, Sweden, FederalRepublic of Germany, Japan, jjFrance, USSR ' (

i25000 (2.5%) Canada, Norway, Germany Dem- \

ocratic Republic, Czechoslovakia i

<5000 (0.5%) United Stales, Brazil, Canada,Republic of South Africa, Aus-tralia, USSR

20000 (2%) United States, People's Republicof China

2000 (0.2%) United States, Bolivia, Australia, IIndonesia, Malaysia, Republic of |South Africa ;

6000 (0.6%) United States, Canada, et al. j

TABLE •!.—ll'orW resources of arsenic—identified and hypothetical(Gualtieri 1973)

Region

United StatesNorth America exclusive of United StatesSouth AmericaEurasia (including insular areas of

southeastern Asia)AfricaAustralia

World total

IdentifiedResources

(short tons)

1,300,000500,000

3,000,00010,100,000

2,300,000400,000

17,f)00,000

HypotheticalResources

(short tons)

650,000300,000

2,700,0008,450,000

1,850,000350,000

11300,000

TotalResources

(short tons)

1 ,950,000800,000

5,700,00018,550,000

4,150,000750,000

31,900,000

\?>I\-

\j*

t

>t

Colorado School of Mines

TABLE 5.— Arsenic in precipitationthroughout the world

(from data recounted in Onishi

Location

Average ArsenicConcern™ I ion

mg/liicr

Bern, SwitzerlandJapanNorth Pacific OceanAntarctica

0.00250.001(50.00060.0006-0.00067

TABLE 6.—Arsenic in various freshwater sourcesthroughout the world

{from various data recounted in Onishi, 1969;Ferguson and Gavis 1972; Koehoe and others 19-M)

AsConcentrations

Freshwaters (mg/litcr)

Rivers in SwedenElbe River, GermanyRivers and lakes, JapanWaiknto River, New ZealandRivers and lakes, U.S.A.Ground Waters:

U.S.A. (GA.,IL.,MI.,MO.,OH.)Skelleftea, SwedenOrsk, Ural, USSRJapan

0.0002-0.000-10.02-0.0250.00016-0.00770.000-1-0.0050.0016-1.1

<0.0010.0009-0.0022

<0.0020.00021-0.00042

LIVING ORGANISMSPlants '

Arsenic is an element which is found to becumulative in living tissue, i.e., once ingested by anorganism, it is passed out of the organism only veryslowly if at all. The amount of arsenic in a plant,then, depends almost solely on the amount of ar-senic it is exposed to. Values as low as one-tenthppm or less for tomatoes and as high as 10,000 ppmin Douglas Fir needles have been found in planttissue (Onishi 1969). Averages for various plantslisted by Bowen (1966) are as follows: 30 ppmfor marine plants with the highest concentrationfound in brown algae, and 0.2 ppm in land plants.

Animals

As in plant tissue, arsenic is cumulative in an-imal tissue, allowing for a wide variation in con-centration due to the variance in arsenic ingestedin different areas. Among marine animals, arsenichas been found to accumulate to levels of from0.005 to 0.3 ppm in coelenterates, some molhisks,

and crustaceans (Bowcn 1966). These levels occurin aqua t ic animals inhabi t ing natural waters, andthere is no indication of any abnormalities in theseorganisms. McKec and Wolf (1963) reported thatsome shellfish may contain over 100 ppm of arsenic.There is, therefore, significant arsenic in the diet offreshwater and marine fish who feed on these lowerforms of water organisms. Ellis and others (19-11)reported an average arsenic content in freshwaterfish of 0.5-1 ppm on the basis of total wet weight, butsome values reached as high as 77.0 ppm in the liveroil of freshwater bass.

In land animals, an average value for arsenicconcentration of less than 0.2 ppm is listed by Bow-cn (1966). In mammals it has been found that thearsenic accumulates in certain areas of the ecto-dermal tissue, primarily the hair and nails (Vallceand others 1960). Normal values for human arsenicconcentrations in various tissues are given in table7.

TABLE 7.—\ormal arsenic content of tissues andfluids of man (TaUee and others I960)

Tissue orFluid

Whole BodyUrineBloodHairNails

Arsenic Content(ppm)

0.2-0.30.003-0.1500.01-O.fvl0.036-0.880.087-1.0

SUMMARY

A summary of average arsenic concentrations asthey occur throughout nature is given in table 8.

TABLE 8—Arsenic throughout nature

Natural AreaAs Concentration

(ppm)

Land (including soil) 5.0-10.0

Water

PrecipitationFreshwaterOceans

Air

Natural organisms

Nfarine plantsLand plantsMarine an imalsLand animalsFreshwater fish

0.0010.0004-0.0010.002-0.003

7.7 x 10-* (0.012/ig/cum)

300.20.005-0.3

<0.20.54


CULTURAL CONTRIBUTIONS OFARSENIC TO THE ENVIRONMENT

Man contributes an estimated 50 (o 70 percentof the arsenic entering the world's wmcrs, much ofwhich comrs as a direct consequence of some of itsend uses. The use of arsenic-containing pesticidescontributes the majority of the arsenic pollution inthe United Slates today. Some arsenic, however,enters the environment because of smelting opera-tions, from waters from mines and mineral proces-sing activities, and other sources.

Arsenic is produced as a by-product from ihcsmelting of arsenic-bearing ores, chiefly copper,lead, and zinc ores, and the entire production ofarsenic for use in commercial arsenic compounds inthe United States is from this source. Smelter opera-tions of American-owned companies produced (>,100short tons of arsenic in 1968: 2,900 short tons in theUnited Slates, 600 short tons in Peru, 500 short tonsin Canada, and 2,100 short tons in the Phil ippines(Paone 1970). Sweden contributed the most of the

world output of 56,500 short tons by producing17,900 short tons of arsenic in 1908. The UnitedStates' demand for arsenic in 1%8 was 23.900 shorttons and about 97 percent of th is was in the formof arsenic trioxide ("while arsenic:") and the other5 percent in the form of metallic arsenic (Paone1970). About 75 percent of the arsenic trioxideused in this country is for the manufac ture of in-secticides.

The most common arsenic-containing insecti-cides manufactured in the United States arc ca lc iumand lead arsenate, arsenic acid, sodium arscnatc andarsenite, and some organic arsenicals. Calciumarsenate is an excellent insecticide for com roll ingboll weevils. It was used extensively before 1919and then regained popularity after 1950 when itwas discovered that the boll weevil had developeda resistance to many of the chlorinated hydrocar-bons that were being used (Carapclla 1963). Theuse of lead arsenate is diminishing because of thegreater effectiveness of calcium arsenate. Lead ar-senate, however, is still a widely used insecticide inthe apple growing industry. Both sodium arseniteand arsenate are used as soil sterilizers and for landand aquatic weed control. After years of sprayingwith arsenic pesticides, soil concentrations of ar-senic have been reported to rise to many hundredparts per million which may result in an unpro-ductive soil (Vallee and others I960).

Much of the environmental impact of arsenic-containing pesticides is controversial. Sodium ar-senate and sodium arsenite arc both freely solublein water, which is a primary reason for their use asaquatic weed control agents. They can also enicrlakes and streams from water runoff because of theirhigh solubility in water and because arsenic tends

to remain in the top layers of the soil (Vallcc andothers 1960).

The solubility of commercial lead arscnalcwas found by Linkc (1958) to be 3.0 mg (As)/liter in distilled water and 33.8 mg (As) /l i ter inlap water which contained dissolved calc ium andmagnesium bicarbonates. McKce and Wolf (1963)do not consider lead arscnatc soluble enough topose a threat of contamination to local waters. Cal-cium arsenate (CaHAsO4) is soluble to the extentof 3.10 g/liier, whereas in the form of Cas (AsO4),it is soluble to the extent of only 130 mg/litcr.Therefore, the compound CaHAsO4 can contributeabout 20 limes more arsenic lo solution thanCa;, (AsO4) 2- These solubilities arc determined un-der laboratory conditions in distilled water and arconly indicative of potential solubilities that mightoccur in the far more complex waters occurring innature.

Geologic formations that contain pyrite andother sulfides in sufficient quan t i t y generate acidin the presence of oxygen and water. Some typicalreactions involved are as follows:

(1) 2FeS2 + 7O2 + 2H2O -> 2H2SO4 + 2FcSO4.This reaction occurs ai a temperature of about52°F. At higher temperatures the following oc-curs:

(2) 4FeSO« + O2 + 2H2SO4 -» 2Fe,, (SO4) 3 +H2Ofollowed by

(3) Fe2 (S04), + 6H20 -» 2Fc (OH)., +3H2SO4

The pyritc can also react with ferric sulfatc.

' (4) Fc2 (SO4) 3 + FcS2 -» 3FeSO4 + 2SThe sulfur can then produce acid

(5) S + 1-I/2O2 + H2O -» H2SO4.

Although not studied in detail, it would beanticipated that the decomposition of arsenic sulfideminerals, particularly those containing iron, mightproceed in a similar manner. These reactions takeplace in pyritic and other sulfide-coniaining ge-ological formations, but generally so slowly as notto result in detrimental contamination of watersources and supplies. Once the formalion is ex-posed by mining, however, the reaction may pro-ceed rapidly as exemplified by the acid mine waterproblems in Pennsylvania, Illinois, West Virginiaand other parts of the country. Evidently arsenicis seldom a problem in the acid mine waters of theeastern United States, and acid mine waters are nottoo prevalent in the western United States. Wherethey exist, however, there is a potential for dissolu-tion of some of the arsenic present. Arsenic contentof some acid mine waters from abandoned mines inColorado is shown in table.9.


TABLE 9.— Water quality surveillance program ofUSEPA, 1966 to 197!

Name ofMine

Red MtnAdit

GenesseeMine

RouvilleAdit

JokerTunnel

KoehlerTunnel

Location and Typeof Opening

North of Silvcrtonat Red Mtn Town(Adit)

Near Idorado(Adit)

At Guston (Adit)

Near Ironton(Adit)

North of Silverton(Adit)

pH

2.-1-3.6

2.4-3.1

2.7-3.2

2.6-3.2

<2.0-3. 1

As(mn/litcr)

0.27-0.50

0.77-l.O

0.05-0.08

0.038-O.l

•l.O-22.0

Water from underground mining operations isgenerally used in the mill or mineral processingplant. Most flotation processes are conducted inalkaline pH ranges, and many of the heavy metalswould be precipitated to negligible concentrationsin the flotation system. The chcmi.sjry ol arson iras discussed herein would indicate that arsenic pre-cipitation to an acceptably low level would be un-likely in the average flotation system. Arsenic com-pounds, however, are frequently adsorbed on pre-cipitates that might be present in many f lo t a t ionsystems. At this time little information is avai lableon the concentration of arsenic in the waters ofmineral processing plants.

Acid formation also takes place on tail ings damscontaining substantial quantities of pyritc. and ar-senic, if present, would be expected to dissolve 1.0some degree.

The mineral industry in the past has been asignificant contributor to emissions of arsenic to theatmosphere. An example was a base metal roastingoperation in South America where there were about20 cases reported daily of arsenic dermatitis fromthe approximately 500 workers at the mine's man-ufacturing departments (Oyanguren and Perez1966). People in the area reported that animalssuffered from ulcers of the feet which is a conditionarising from prolonged dermal contact with arsenictrioxide. This situation was corrected by installa-tion of suitable pollution abatement equipment.There have been similar examples in early UnitedStates' smelting practice. Harkins and Swain (1908)reported cases of atmospheric arsenic pollution thatkilled several hundred animals.

Arsenic can also enter the atmosphere from theburning of fossil fuel. Ferguson and Gavis (1072)estimated conservatively thai appro*imale)} 2.5grams of arsenic can be released to the atmosphere

for every ton of coal that is burned. They calculat-ed the amount of arsenic released during the 71-year period between 1900 and 1971 to be 290,000tons. Tliis is an average of about '1,000 tons peryear from the burning of coal, and the impact ofth i s is yet lo be determined.

Not all of man's uses of arsenic prove lo be adetriment to his environment. Metallic arsenic isused chiefly as an alloy. It is used in copper to in-crease corrosion resistance. Arsenical copper is alsoused for products that are subjected to heat, such asautomobile radiators, to increase the annealingtemperature. Metallic arsenic is used in lead-tinalloys to refine the grain and increase the compres-sion strength. Metallic arsenic is added to brass tominimize season cracking and de/incification. It isalso used as an alloy in the manufacture of leadshot to improve the roundness of the shot, and inother lead-base materials to improve hardness.

Tlie most recent use of metallic arsenic, and one(hat requires a high purity (99.999%-f), is for usein semiconductors (Doak and others 19fi3). Thearsenic is alloyed with a luminum, gall ium, andindium. Gal l ium and indium arsenide have bothbeen used in experimental lasers.

Compounds of arsenic have been used in medi-c i n e for over 2,500 years (Campbell 19(50). Romanphysicians used arsenic compounds for d ie ' t r ea t -ment of leprosy, tuberculosis, and asthma. Hippoc-rates recommended using arsenic trisulfidc fort rea t ing skin diseases.

The early use of arsenic compounds in medicineinvolved only the inorganic compounds, but mostof the modern medicines containing arsenic arcorganic arsenicals. Since arsenicals can cause toxicreactions, they arc becoming obsolete in medicinethough they are still used widely in the treatment ofamcbic dysentery and African trypanosomiasis (Af-rican sleeping sickness) (Doak and others 19fi3).

BASIC CHEMISTRY

Arsenic belongs to group VA of the periodictable as do nitrogen, phosphorus, antimony, andbismuth. The atomic number of arsenic is 33 andit has an atomic weight of about 75. There is onlyone stable isotope, therefore, the natural isotopicabundance of "As is 100 percent (Onishi I9f>9).The electron configuration of the atom is [Ar] 3d1"4s2 'lpa. The five electrons in the outer shell giverise to the three principal oxidation states of arsenic-winch arc —3, +3, and +5.

Elemental arsenic is not a true metal. Arseniclies in the nonmctal section of the periodic tablebordering on the division line between the metalsand the nonmetals. Although there are several allo-iropic forms of the element, the most common formis gray or "metallic" arsenic. Metallic arsenic is


brittle, lias a crystalline nature, and exhibi ts a lowelectrical conductivity. It is stable in dry air binoxidizes in moist air. am! when heated it docs noimelt but sublimes. A molten form of metall ic ar-senic can be produced at a pressure of L'K .itm. Someof the physical properties of arsenic (Carapclla1963) are summarized in table 10.

TABLE 10.—Physical properties r>f arsenic

Atomic number 33Atomic weight ("C = 12.0000) 719210Melting point at 28 aim, °C 817Boiling point, °C 013 (sublimes)Density at 20°C, g/cm'Specific heat, cal/gram/°CElectrical resistivity at 20°C,

microhm-cmCrystal system

5.720.082233.3

Hardness, Mobs' scale

hexagonal(rhombohedral)3.5

The most important commercial arsenic com-pound is arsenic (III) oxide (arsenic trioxidc, ar-senous oxide, "white arsenic," and live misnomer"arsenic"). It occurs as an octahedral crystal ofAs4O|) molecules. The dissociation to AsoO3 can bedetected at temperatures of about fiflO°C. At ;itemperature of 1800°C the molcculnr weight is thruof As2O3 (Doak and others 1963). The formulaAs2O8, however, is generally the one used for thiscompound.

Arsenic trioxide is a white solid thai lias a melt-ing point of 275°C under its own vapor pressure,but it does begin to sublime at a temperature of135°C. It is amphoteric and therefore is soluble inboth acids and bases, and is moderately soluble inwater. Solubilities at various temperatures arelisted in table 11 (Linke 1958).

TABLE 1 \.—Solubility of As,O, in water at varyingtemperatures

Temp., °C Solubility, g/liter

015257598.5

12.116.620.556.281.8

Arsenic trioxide is slightly less soluble in 0.1MH3AsO4, H3P04, HjSO,, HC1, and HCK>4 than inwater; but more soluble in sodium hydroxide solu-tions.

When As2O3 is dissolved in water it forms ar-senous acid, the exact nature of which is not known.

HaAsOs, HAsO.,, and As2O., (aq) have all beenused as representative chemical formulas of the acid,which is a weak acid with a dissociation constant of8 x 10-'" at 25-C. HsAsO9 is also thought to existas the hydroxide As (OH) 3 which would help toexplain the amphoteric ab i l i ty ol the compound toneutralize both acids and bases. The followingequations illustrate this behavior (Sienko andPlane 1960).

As (OH) 3 (s) + H+ -» As (OH),+ + R.OAs (OH) 3 (s) + OH- -» H2AsOa- + H2O

The fact thai only one dissociation constant is givenfor arscnous acid supports the postulaic that threeOH groups are attached to the arsenic atom in thefree acid (Doak and others 1963). The salts ofarscnous acid are known as arsenitcs.

Arsenic trioxide is generally obtained as a metal-lurgical by-product. ^Vhcn arsenic-bearing ores,such as suJfide ores of copper and lead, arc roastedthe arsenic is volati l ized and oxidizes to arsenic tri-oxide.

Another oxide of arsenic that is of commercialimportance is arsenic (V) oxide (arsenic oxide,arsenic pentoxide), The empirical formula ofAsjO-i is the one generally used because the struc-ture of arsenic pentoxide is not known. The com-pound begins to decompose into a vapor as As2O3

and O2 at a temperature of about 300°C. Arsenicpentoxide is very soluble in water though it dis-solves slowly. The solubility is about 2300 g/literat 20°C.

In water, arsenic pentoxide forms arsenic acid(orthoarscnic acid), H3AsO«. It is a triprotic acidwith three dissociation constants like phosphoricacid. The three are Kt = 2.5 x 10-*, K2 = 5. 6 x10-", and K3 = 3 x 10-" (Sienko and Plane 1966).The salts of arsenic acid are known as "arscnates"and are very good oxidizing agents.

Arsenic acid is commercially prepared by crys-tallization from, a solution of arsenic (III) oxide(arsenic trioxide) and nitric acid. The dehydrationof crystalline arsenic acid at temperatures of about200°C is the best method for preparation of arsenicpentoxide since the pentoxide cannot be obtainedby the reaction of the elements nor by the reactionof arsenic trioxide with oxygen (Doak and others1963).

The most common arsenjc hydride is arsine(hydrogen arsenide, arsenic trihydride). Its chem-

ical formula is AsH3. It has a melting point of-116.3°C and a boiling point of -62.4°C (Doakand others 1963). The solubility of arsine in wateris 200 ml/liter at room temperature. Arsine is acolorless gas which has an odor that resembles gar-lic, and is the most toxic of arsenic compounds.

Arsine is the product of the reaction between


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atomic hydrogen and arsenic though it is not pro-duced by their direct union because arsinc is notstable at high temperatures (above 300°C). Arsineis formed whenever any inorganic arsenic-contain-ing material is reacted with zinc and strong acids.Pure arsine can be condensed at low temperaturesfrom a dried gas steam produced by a reaction ofarsenic pentoxide with hydrochloric acid and /inc.One dangerous aspect of storing commcrd;il acidsin mental tanks is that arsine may be produced fromthe arsenic impurities in the acids.

The three arsenic sulfides are arsenic ( I I I ) sul-fide (arsenous sulfide, arsenic scsquisulfidc, arsenicred), aresenic sulfide (arsenic monosulfidc, arsenicdisulfide), and arsenic (V) sulfide (arsenic pcnta-sulfide).

Arsenic (III) sulfide (As4S . AszS3) has a melt-ing point of 320°C and a boiling point of 7(>7°C.It, like many other arsenic compounds, starts to sub-lime before melting. It is insoluble in acid and al-most insoluble in water (only 0.52 mg Asa.Ss/literat 18°C), but docs dissolve in many basic solutions.When heated it will burn in air, forming arsenictrioxide and sulfur dioxide. Arsenic ( I I I ) sulfidecan be oxidized by nitric acid.

Arsenic sulfide (As4SH, AsoS2, AsS) occurs n;ii-urally as the mineral realgar. This compound has amelting point of 307°C and a boiling point of565°C. Arsenic sulfide is listed as insoluble in waterby Hodgman and others (1959) and in hot concen-trated hydrochloric acid by Doak and others (I%3).It will dissolve in warm alkali hydroxide and sulfidesolutions. The compound can be oxidized by n i t r icacid and will react vigorously with chlorine.

Arsenic (V) sulfide (As^,) is a stable com-pound at room temperature but dissociates intoarsenic (III) sulfide and sulfur at a temperatureabove 95°C. Its solubility in water at 40'C is Smg/liter (Linke 1958), and it is liydrolyzcd in boil-ing water, yielding sulfur and arsenous acid.

Arsenic (V) sulfide is soluble in basic solutionsand in nitric acid. It can be precipitated at lowtemperatures from strong acidic solutions whichcontain arsenates by bubbling hydrogen sulfidethrough the solution at a rapid rate (Doak andothers 1963).

Arsenic (III) forms fluorides, chlorides, brom-ides, and iodides. The only simple pcntahalidcknown for arsenic (V) is the fluoride. Hodgmanand others (1960) list an arsenic pentachloridc andan arsenic pentaiodide but consider them to be ofquestionable existence.

Arsenic (III) fluoride (AsF,,) and arsenic ( I I I )chloride (AsCla) are both colorless liquids at 25°C,whereas arsenic (III) bromide (AsBr3) is n yellowsolid and arsenic (III) iodide (Asls) is a red solid.Arsenic (V) fluoride (AsF5F) is a colorless gas at25 °C.

All of the arsenic halides dissociate or hydrolyzein water with the exception of arsenic peniafhioridc.The pcntafluoridc is soluble in water though nosolubili ty data are listed by either Hodgman andothers (1959) or Linke (1958).

Arsenic (III) chloride is the most common ofthe arsenic halides. It can be prepared by severalmethods, including the spontaneous combination ofthe elements.

Arsenic generally behaves as an anion in theform of arscnitcs and arsenates. There arc noarsenic carbonates, bicarbonatcs, or phosphates.The only m.ijor inorganic compounds in whicharsenic acts as a cation are the halides and sulfidcs.There is an arsenic monophosphidc (As?) whichdissociates in water and an arsenic (III) sulfate(Asa (SO4) „) which is formed by the reaction ofarsenic trioxide and SO.-, at a temperature of 100°C.Arsenic (III) sul fn tc is soluble in water, but it isnot listed by either Hodgman and others (1959)or l.inkc (1958).

Arsenic also forms arsenides with most mctnls.Cxjbalt and iron, for cxnmple, form CoAs= andFeAs2, respectively. Arsenides are compounds inwhich arsenic is the negative element (anion).Arsenides can be decomposed by water or diluteacids with the formation of arsinc.

There nre a great many organic compounds ofarsenic, the two most common being the arsonicacids and the arsinic acids. In general, the organicarsenic compounds were synthesized in search ofcompounds of medicinal value. The arsonic acidsnrc of the type R AsO (OH) 2 where the R groupmay be aliphatic, aromatic, or heterocyclic. Theyarc used extensively in analytical chemistry and arcdibasic, forming botli acid and neutral salts. Thearsinic acids are of the type R8AsO (OH), wherethe R group may be aliphatic or aromatic.

Arsenic can be fairly easily separated from otherelements, and can be removed from solutions byadsorption and coprccipitation. Arsenic cnn be pre-cipitated in the elemental state by reducing agentssuch as hypophosphite or stannous chloride. Hypo-phosphite has been used to precipitate arsenic fromsolutions of 1:1 hydrochloric acid, with a recoveryof about 95 percent when copper is present to cata-ly/c the reduction (Sandcll 1959).

Arsenic in the +5 state, which includes the ar-scnatcs, can be coprecipilated with ferric hydroxideor magnesium ammonium phosphate. In the for-mer case, it is believed that the arsenates adsorbonto the surface of the hydrous iron oxides. Shn-yukov (in Ferguson and Gavis 1972) reported thatiron ores arc always enriched with arsenic, anil at-tributes this to the high adsorptive capacity of thehydrous iron oxides. Iron oxide has a positive sur-face charge in nature and therefore adsorbs anions.Since arsenic exists primarily as anionic arscnate

Mineral Industries Bulletin 9

and arsenitc species in solution, it cm be adsorbedon the positively charged iron oxide surfaces. Ar-senaies can also be adsorbed by a l u m i n u m hydrox-ide and clays (Ferguson and Gavis M)72) . Stove (inFerguson and Gavis 1972) reports that the arseniccontent of Florida phosphate pebbles is proportion-al to the iron content and inversely proportional tothe phosphate content. The above relationshipexists even though arscnatc and phosphate havesimilar chemical characteristics.

Arsenic in its +3 state, which includes the ar-senites, has a strong aff ini ty for .sulfur and A v i l lcoprccipitate with metal sulfldcs. The arsenic IIIsulfide (As-jSg) precipitate is insoluble in hydro-chloric acid and for that reason precipitat ion byhydrogen sulfide from a 25 percent lid solution isused as a method of qualitative analysis for thepresence of arsenic in a solution. The technique ofadsorption of arsenites onto hydroxides and clays isa promising candidate for arsenic water pollutionabatement and merits more investigation.

The application of some of the above-mentionedmethods for removal of arsenic from aqueous solu-tion will be covered in the abatement section ofthis MIB.

TOXICOLOGY

A substance is usually defined as being toxic i(it injures the growth or metabolism of an organismwhen supplied above a certain concentration. Thisdefinition of toxicity would embrace almost any Mib-stance if supplied in excess. Toxicity, however, isgenerally a question of mechanism rather than oneof concentration, although most substances that pro-duce a toxic mode need only be present in smallquantities.

The most common toxic mode of an clement isthe inactivation of enzyme systems. Enzymes serveas biological catalysts, and, like inorganic catalysts ,serve to accelerate chemical reactions by loweringthe free energy of activation. Chemically, enzymesare proteins that are structured as long chain aminoacids placed in specific order. Of the over 150amino acids known to exist, only 20 common aminoacids generally form all of the proteins (Lclmingcr1970). Any one of the 20 common amino acids cnnbe used several hundred times in different locationsalong the chain, and any change in order, addi t ionor omission of one amino acid can result in loss ofspecificity of the enzyme.

Arsenic in its +3 state reacts wi th the s t i l fhy-dryl groups of the amino acid cysicinc (Fergusonand Gavis 1972). Since the disulfidc bridge (-S-S-)is a very important covalcnt linkage in proteins(Lehninger 1970), enzyme inact ivat ion can resultfrom destruction of the chain.

Arsenates [salts of As (+5)] can subs t i tu te for

phosphate in a living organism (Vallec and othersIW(1) and can also be reduced to a (+3) state byl iving organisms (Ferguson and Gavis 1972). Therearc many needs for phosphate in l iving organisms,and arsenate, being chemically similar, can substi-tute for phosphate in many instances. Followingarsenate substitution, however, the biomolerulescannot carry out their highly specialized functionsand there is subsequent interference with enzymefunctions, energy transformations, and reactions ofcarbohydrates.

The other major oxidation state of arsenic (—3)is found in the compound arsinc (AsH3). The toxicmode, of arsine occurs as hemolysis (the breakingdown of red blood cells), and the reason for thiseffect is uncertain (Vallce and others 19f>0).

Arsinc is by far the most toxic of the arseniccompounds. Hodgman and others (1959) list thetoxicity of many gases and vapors and of these onlyphosphine (PH3) is listed as more toxic. The toxi-ci ty of arsine in air is listed at 0.000] mg/litcr or0.05 ppm. There can be no specific value assignedin regard to toxicity as to the minimum quantityrequired to manifest specific symptoms, includingdeath—toxic levels must be considered on relativerather than absolute bases. Although arsinc posesmore of an industrial hygiene rather than an envir-onmental problem, it deserves mention due to thefact that arsinc generation is the major industrialrisk posed by arsenic (Vallec and others 19(50).Poisoning by arsine can be minimized if employeesare made aware of the problem and instructed toavoid creating conditions for its generation.

Arsenic is more toxic in its irivalcnt reducedstale (+3) than its oxidized pentavalent state (+5).Ferguson and Gavis. (1972) reported that arscnilcis about 60 limes more toxic to man than arsenateand the possibility exists that arsenatcs can be re-duced to arsenites in areas where the dissolvedoxygen of streams and lakes approaches zero(Angino and others 1970).

Vailee and others (I960) report that the fataldose of arsenic trioxide for humans is between 70and 180 mg. Toxic symptoms and reactions, though,can occur at much lower doses. Arsenic is a cumu-lative poison in living tissue, and therefore chronicpoisoning by arsenic compounds can occur. Oehme(1972) states that up to 70 days may be requiredfor complete elimination even though excretion ofarsenic begins 2 to 8 hours after administration.

The toxic dose of arsenic to some farm animalshas been listed by the Federal Water PollutionControl Administration (1968) and summarized intable 12.

Harkins and Swain (1908) listed the results ofanalyses of various organs in a horse that sufferedfrom chronic arsenic poisoning. Somc^pf the resultsappear in table 13.


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TABLE 12.—Toxic doses r>f arsenic

Toxic Do.scAnimal g/animal

TARI.K \-\.—Arsenic concentrations harmful toaquatic life

PoultryDogsSwineSheep, goats, horsesCattle

0.05-0.10.1-0.20.5-110-1515-30

TABLE 13.—Distribution oj arsenic intissues of a horse

Organ or Area As.,0;, in |>pin

Ulcer in noseContents of wet stomachContents of stomach (dried)UrineHair of tailLiverThyroid glandStomachSpleenPancreasSmall intestines

65825

39851)58664.1•1.64 A4.0

The horse that was found to contain 20 to •!"> ppvnof As2O3 had been eating hay for several months.An analysis of dust shaken from the hay was foundto contain 9,190 ppm of As2O3.

Lead arsenate administered in doses from 1.3 to56.7 grams per day has been reported to have ki l led18 out of 31 chickens with the survivors manifestingno symptoms of arsenic poisoning. Also, the LD.(quantity which proves fatal to 50 percent of a testgroup) of lead arsenate for male rats is reportedto be 1,050 mg/kg of body weight (McKce andWolf 1963).

The use of sodium arsenite for aquatic weedcontrol has prompted studies on its effect on aquaticlife. McKee and Wolf (1963) reported concentra-tions of sodium arsenite shown in table 14, whichare lethal, toxic, or harmful to aquatic life.

Of greater probable importance than the above-reported harmful concentrations to fish is the factthat organisms used by fish for food can only toler-ate 1.4 to 2.3 mg (As)/liter of sodium arsenite.

Arsenic is considered as only moderately toxicto plants (Bowen 1966), and many lower forms ofplant life such as fungi, yeasts, and bacteria canexist in very high concentrations of arsenic. Ccriainstrains of the lower plants are known to mcthylatcarsenic to gaseous derivatives of arsinc such astrimethylarsine (Vallee and others I960). McKcc

Organism

Pink salmonFingcrlingChannel catf ishRainbow troutMinnowsMinnowsMinnows

mg/1

5.015

20272945

Time ofExposure

lOdnvs18&72hrsTLm«

36 hours72 hour TLm•18 hour TLm24 hour TLm

*Tlic TLm (median tolerance l imit) is the con-centration that an organism is subjected to whichresults in a 50 percent fatal i ty of the test group.

and Woll (1963) reported-that 5 mg/litcr of arse-naic and 10 mg/litcr of arsenite arc toxic to growthof lemon plants in solution cul ture . In this oneexample the arsenate is more toxic than the ar-senite.

One of the main symptoms of arsenic toxicity toplants is chlorosis, the yellowing or blackening ofleaves, which results from the destruction of chloro-phyll . Since chlorosis is a symptom for a great manyplant a i lmen t s , including a lack of certain n u t r i e n t s(Levitt 1%!)), its occurrence is not a reliable indica-tion of the presence of arsenic toxicity in plants.McKee and Wolf (1963) reported tha t plantsgrown in water which contained one mg/litcr ofAsoO.t have shown a blackening of the vascu la rbundles (plant conductive tissue analogous toiiricrics and veins in animals) . The presence ofexcessive amounts of soluble arsenic in irrigationwater can have detrimental effects on crops. Or-chard soils t ha t have become unproductive havebeen found to contain between -1 and 12 mg As.,O:,/kg of topsoil (McKce and Wolf 1963). It is esti-mated tha t IO7 kg of arsenic are taken up annuallyby grasses and crops (Norman 1968).

ANALYTICAL METHODS FORARSENIC DETERMINATION

There are many techniques available to deter-mine the presence of arsenic in a medium. Some ofthe tests, qualitative analyses, give an indicationonly to the existence of arsenic in the medium,while others, quant i ta t ive analyses, give the analystan estimate of the actual amount of the elementpresent. Different methods also exist for determi-nation of arsenic in micro amounts, which are con-centrations less than 0.01 percent or 100 ppm, andin mncro amounts, jj-hich are concentrations largerthan tha t amount.

ties Mineral Industries Bulletin 11

In the discussion (hat follows, ihc methods usedmost predominantly today arc described. Since gooddata on the distribution of arsenic in the environ-ment nre possible only with accurate analysis, theimportance of llicse techniques cannot be mimi/cd.

QUALITATIVE ANALYSIS

Macro

Arsenic can be precipitated as arsenic trisulfidcfrom a strongly acidic solution of hydro-

chloric acid by bubbling hydrogen sulfidc throughthe solution. The solution should contain at least25 percent HC1 to prevent precipitation of othersulfides that can be formed from reactions wi th

(Furman 1962; Carapella 1903).

Micro

Trace quanti t ies of arsenic can be determinedby the Marsh test in which the arsenic is. convertedto arsine from the action of /inc and acid followedby thermal decomposition of the arsine .in a smalltube to form an arsenic mirror. As l i t t l e as onemicrogram of arsenic in the sample can be detectedusing this method (Furman 1962) .

QUANTITATIVE ANALYSIS

Macro

Titrimetric methods are generally preferred formacro quanti tat ive analysis because of their simplic-ity, accuracy, and rapidity. Furman (I9(>2) gives theprocedures for many litrimctric methods includinginformation on possible interferences and how theycan be eliminated or minimized.

Atomic absorption can be used for arsenic anal-ysis although this method is subject to many inter-ferences. In addition to chemical interferences thereare spectral interferences from flame gases and solu-tions in the ultraviolet region of the spectrumwhere the most sensitive lines for arsenic occur.Atomic absorption, though probably one of themore useful analytical tools available today, re-quires more mollification of technique and matrixcorrection for arsenic determinations than is con-sidered desirable by some analysts.

Micro

There are three satisfactory micro methods forthe determination of arsenic based on the genera-tion of arsine; two of these methods require aspectrophotometcr. The classical procedure for thedetermination of arsenic has been the Gut7citmethod. This method is rapid, sensitive to about ±5 jig, and is still widely used as a micro qualitativeand semiquantitative method. The arsine, which is

generated by the action of zinc and hydrochloricacid, is passed through a scrubbier of glass woolimpregnated with lead acetate to remove HMSwhich, if present, causes interference. The arsinethen reacts with mercuric bromide (coated on a stripof paper) forming a colored compound. Thelength and intensity of the colored stain is com-pared to standard stains and an estimate of theamount of arsenic present can be obtained. Theprocedures for this method are reported in Furman(1962).

The hetcropoly molybdenum blue and the silverdiethyl dithiocarbamate (SDDC) methods, bothcoloritnetric, involve the generation of arsine froma reaction Mask by the action of zinc and hydro-chloric acid. In the hetcropoly blue method theevolved arsine gas passes through a lead acetatescrubber and into the absorber solution where itforms a strongly colored "molybdenum blue" com-pound suitable for photometric determination.Phosphate if present will cause significant interfer-ence because it reacts in the same manner as arsc-nate and with approximately the same sensitivity.Both Furman (1962) and Sandcll (1959) give pro-cedures for the hetcropoly molybdenum bluemethod.

The SDDC method uses the same apparatus andprinciple for arsine generation as docs the hctcro-poly blue method, the difference being that thearsine reacts with the SDDC reagent forming n redcomplex. The only significant interference encount-ered when using the SDDC method is from anti-mony, which produces slibinc gas (SbH3) under (hereaction conditions. The stibine reacts with theSDDC to form a colored compound which has amaximum absorbance very near that of the arsenic-SDDC complex. If antimony is present in signifvcant quantities, the heteropoly blue is the methodof choice.

The SDDC method is the recommended methodfor arsenic analysis in the Thirteenth Edition of theStandard Methods for the Examination of Watrrand Walcrwaste (American Public Health Associa-tion and others 1971) and in Methods of Air Samp-ling and Analysis (Intersociety Committee 1972).Procedures for the SDDC method can be found inthe above and in the Annual Book of ASTM Stand-ards (1972).

The literature describing the SDDC methodgenerally recommends that pyridine be used as thesolvent for the silver diethyl dithiocarbamate. Kopp(1972) reports on a study describing the use of

/•ephcdrine in chloroform as a solvent system forthe SDDC. The procedures for analysis arc present-ed as well as a discussion of the solvent system andits comparison to pyridine. The major differenceis that the absorbance of the red complex is meas-ured 520 nm when using /-cphedrine in chloroform


rather than the 535 or 540 nm wavelength used forpyridine.

Shen (1973) compared the results obtained fromanalyses of several standard solutions using theSDDC, heteropoly blue, and Guueit methods. Hefound the standard deviation to be ±0.01 for theSDDC method, ±0.02 for the hclcropoly blue mci li-ed, and ±0.03 for the Gutzeit method.

A typical arsinc generation apparatus is shownin figure I. An admonition when using the ap-paratus, either for the SDDC or the hcteropoly bluemethod, is that care must be taken not 10 allow theabsorbing solution to back up into the si-rubber.The reaction apparatus must be placed at an anglein a beaker so that it is tilted toward the absorber.The beaker also contains water for control of thetemperature of the reaction flask so that uniformbubble rates between samples and standards can bemaintained.

STANDARDS

One of the earliest arsenic standards on recorddates back to 1903 when the Royal Commission on

FIGURE 1.—Arsine generator.


Arsenical Poisoning in England published recom-mended standards for food and drink. These stand-ards were designed to cut down on the rash ofhuman poisonings in the early part of the twentiethcentury. An excerpt from this report gives theirrecommended tolerance levels for arsenic:

"In our view it would be entirely proper thatpenalties should be imposed under the snlc ofFood and Drugs Acts upon any vender of beeror any oilier l iquid food or of any liquid enter-ing into the composition of food if that liquid isshown by an adequate test to contain I/100 ofa grain or more of arsenic in (he gallon [appx.0.129 ppm]; and witli regard to solid food . . .if the substance is shown by an adequate test tocontain l/10()ih grain of arsenic or more in thepound [1.08 ppm]."

(Final report Royal Commission on ArsenicalPoisoning, 1903 in Harkins and Swain 1908.)

The Food Standards Committee for Englandand Wales published a set of regulations for foodand beverages in 1959. The maximum allowablel imit for ready-to-drink beverages was set at 0.1 mg/liter and 1 ppm for all food—standards not signifi-cant ly different from those suggested by the RoyalCommission on Arsenical Poisoning some 56 yearsearlier (McKec and Wolf 1965).

In 1958 the World Health Organization(WHO) published a standard for the maximum

allowable concentration of arsenic in potable waterof 0.2 mg/liier. By 1971, however, the WHOstandards had been upgraded substantially and in-cluded a "tentative limit" for the arsenic concentra-tion in drinking water of 0.05 mg/liter. Printedbelow the figure was this somcwhat-less-than-neces-sary postscript: "It would seem wise to keep thelevel of arsenic in drinking-water as low as possible"(World Health Organization 1971).

In this country, the United States Public HealthService has been enforcing regulations limiting theamount of arsenic in drinking water since 1942.From that time until the present, the standard formaximum permissible arsenic in drinking water hasremained 0.05 mg/liter (Title 42, Federal Code ofRegulations, October 1, 1973). Concentrations inexcess of this quantity constitute grounds for rejec-tion of supply. In 1962, the USPHS new recom-mendations staled that when, in the judgment ofreporting agencies and certifying authorities, othermore suitable supplies are or can be made available,arsenic in potable water should not be.in excess of0.01 mg/liter.

Certain states, notably California, have publish-ed recommended arsenic concentrations for all typesof waier. These recommendations, as listed in table15, go farther than the federal regulations in thatthey include all waters associated with man's variousnatural food sources.

13

TABLE \5.—Suggested tnnxitinitn arsenicconcentrations for various waters

(MrKcc :md Wolf l!)f>3)

Maximum ArsenicConcentrations

Water Use mg/litcr

Domestic water suppliesIrrigationStock and wildlife wateringFish and other aquatic life

0.051.01.01.0

In the area of food and beverages, the UnitedStates Federal Government currently enforces threebasic types of arsenic standards aimed at l imi t ingthe three major sources of possible contamination.In order to reduce the possibility of human poison-ings due to arsenic-containing pesticides used onfresh fruits and vegetables, the Environmental Pro-tection Agency currently enforces the following al-lowable residues on raw agricultural commodities(table 16).

TABLE 16.—Arsenic-containing pesticide tolerancelevels for raw agricultural commodities

(Code of Federal Regulations, January 1, 1972)

PesticideAllowable PesticideResidue

Calcium arsenateCopper arsenateLead arsenate

Magnesium arsenateSodium arsenate

3.5 ppm As2O3

3.5 ppm As2O3

1 ppm lead on citrus f rui ts7 ppm lead elsewhere3.5 ppm As2O33.5 ppm As2O3

The second area of federally enforced arsenicstandards for food is in pork and poultry wherearsenic-containing animal feed is used to encour-age rapid growth. These standards are summarizedin table 17.

The third type of food regulation governs thearea of horse and cattle products where sodiumand potassium arsenite insecticides are often applieddermally to control ticks. Legal tolerance levels forthese substances are given in table 18.

In the area of air-borne arsenic pollution, thereare no federal regulations restricting its emission.As participates, however, most forms of air-bornearsenic compounds do fall under the ambient airquality standards. To protect the public's healthand welfare, respectively, primary and secondaryambient air standards were passed in 1071 and are

currently on record under the jurisdiction of theEnvironmental Protection Agency. These standardsare listed in table 19.

TABLF 17.—Tolerances for total arsenic residuesin poultry and pork

(Federal Register, October 2, 1970)

Allowable ArsenicTissue Residue (ppm As)

Uncooked turkey and• chicken muscle tissue 0.5

Uncooked turkey and chickenedible by-products 1.0

Eggs 0.5Uncooked swine liver and kidney 2.0Uncooked swine muscle tissue and

by-products other than liverand kidney 0.5

TABLE 18.—Tolerances for residues of sodium andpotassium arsenite insecticides in horses and. cattle

(Federal Regulations, June 6, 1973)

TissueAllowable Arsenic Residue(expressed as ppm As2O3)

Kidney and liver 2.7Meat, fat, and meat by-products 0.7(except kidney and liver)

TABLE 19.— Primary and secondary ambientair standards

Maximum24-Hour

ConcentrationAnnual Allowable Not to beGeometric Mean Exceeded

Paniculate More ThanConcentration Once a Year

i m) (p8/cu m)

PrimarySecondary

7560

260150

These standards (table 19) in conjunction witheach state's authority to "prevent construction,modification, or operation of any stationary sourceat any location where emissions from such sourcewill prevent the attainment or maintenance of anational standard" arc the only present safeguards


of thendards

idues

rsemcm As)

and•ittle

idue

-vithion,urceurce>f airds

ines

against arsenic-containing air pollution in thiscountry (Title -10, Federal Code of Regulations,January 1,1972).

Certain other countries have ambient air qual i tystandards specifically designed for air-borne arseniccompounds, including Czechoslovakia and theUSSR where tlic maximum allowable average 24-hour arsenic concentration is 3 fig/cu m (Stern1968).

ABATEMENT METHODS

REMOVAL or ARSENIC FROM WATER

Sources of reliable data on the removal of ar-senic from water are limited due to the fact thatarsenic pollution is not widespread at th is time. Inmost areas, potable waicr supplies contain a levelof arsenic well below current standards, and therehas been little necessity to develop methods for ar-senic removal. Fully developed technology forarsenic removal from water is sparse if even existent.

One region of the world where abatement isimportant,.however, is in an area of southwest Tai-wan where groundwatcr arsenic levels range be-tween 12 and 40 times the current health standardof 0.05 mg/litcr. To reduce this high arsenic levelwith its a t tendant incidence of the dreaded black-foot disease (linked to arsenic ingestion), Y.S. Slicnof the Taiwan Institute of Environmental Sanita-tion spent five years developing a process which nowserves to purify the drinking water in that location.In his work, a great deal of data was generated on(lie efficacy of various arsenic-removing processes(Slien 1973).

Shell tested five basic techniques in initial lab-oratory work in an effort to reduce the arsenic levelsof the loral well water. Various selected data fromhis results appear in table 20. Based on these andother da ta , Shcn arrived at the following conclusion:

"If the arsenic-containing water is oxidized withchlorine, coagulated with ferric chloride, and isthen (slow-) filtered, the finished water can bekept free from arsenic for a long period withoutsaturating the filter medium" (Shcn 1973).

TABLE 20.—Selected results nf fivr techniques for loweringarsenic conce.iitrntions in well water

(Shcn 1973)

Method

Sedimentation (15 days)

Ion exchange bed (lonac A-260) :

do.do.

Arsenic inRaw Water

mg/liter

0.8

0.84

0.901.06

% ArsenicRemoved

48.7

-100J

~ioo)5.6-34

Comments

Too time-consuming

{Excellent, but notpractical for large-scalePoor results

Coagulation by various agents:

20 rng/1 aluminum sulfate20 mg/I lime20 mg/1 ferrous sulfate20 mg/1 ferric chlorideSO mg/1 ferric chloride

Oxidation by various agentsfollowed by coagulation by FeG3:

2 mg/1 KMnO4 + 40 mg/1 FeCl35 mg/1 KMnO4 + 70 mg/1 FeCl35 mg/1 C12 + 50 mg/1 FeCla

20 mg/1 CIg + 50 mg/1 FeCls

Filtration using sand and anthracite:

Fast (168. 1 cu m/ sq m/day)Slow (0.4-2.0 cu m/ sq m/day)

1.01.01.01.01.0

0.80.80.80.8

0.330.85

32 Poor20 Poor24 Poor82 Good92 Best results in coagulation

72.5 Good88.8 Better85.098.7 Optimum results

26 Poor-100 Good but time consuming


Based on his preliminary results, Shcn tlicnbuilt a 1,585 gal/day pilot plant to tcsi th is premise.Many operating parameters were varied in an effortto develop optimum process characteristics for pro-ducing potable water from water com;imin;ttc(! wi tha high level of arsenic (in excess of 0.6 mg/liicrAs). After considerable pilot-scale testing, a systemwas proven consistent with that which hntl shownthe most promise in bench-scale cx]>criments, i.e.,initial aeration and C12 addition followed by coag-ulation with Fed, and slow-filteration through sandand anthracite. As shown by the data in table 21,water was produced averaging less thnn 0.10 mg/liter of arsenic for a continuous period of 59 dayswithout regenerating the sand and anthracite fi l ter.Later it was shown that nearly 90 percent of thearsenic in the filter media could be removed by-leaching with high concentrations of sodium hydrox-ide followed by an arsenic-free water rinse.

Based on the results of laboratory and fieldexperiments, a water plant was constructed to serve1,500 people in 1969. The plant has a capacity of40,000 gal/day of purified water and includes anareation tower, a mixer, a sedimentation tnnk,two slow sand filters, a storage tank, and a sand-washing basin. The estimated cost of chemical re-quirements based on current prices is shown intable 22.

Rosehart and Lee (1972) also published resultson various methods of removing arsenic from pro-cess water streams. They studied the use of variousschemes designed to remove arsenic from gold minewaste streams, and their results are summari/cd intable 23. Of the effective methods tested, the use ofCaO exhibited the most attractive economics, butan effluent water pH of 12 might pose problems; inmost areas of the United States the maximum pHallowable in effluent waters is from 8.5 to 9.0.

Bellack (1971) reported on studies he made onthe removal of arsenic from potable water using

sorption columns. The test columns were filled withactivated a lumina (AI2Oa) or bone char, both ofwhich have been used for removal of fluoride. Itwas discovered that both materials also reducedarsenic concentrations in water, however only thealumina could be regenerated and thus reused. Thearsenic sorption evidently changed the basic chem-ical structure of the bone char irreversibly, leavingit fit only for disposal.

In subsequent work with the alumina medium,Bellack was able to reduce the arsenic concentrationof an aqueous solution containing 0.06 Trig/literarsenic to 0.005-0.007 mg/liter at a pH of 7.1. Theloading capacity of the alumina at this inlet con-centration was about 1 mg As per gram of aluminaor 0.1 percent. Meanwhile, the alumina retainedits efficacy for fluoride removal. To regenerate thecolumn a scries of four rinses was used as follows:

(1) four bed volumes of 1 percent NaOH;(2) eight bed volumes of raw water;(3) one bed volume of 0.05 N H2SOi;(4) one bed volume of raw water.

TARLF. 22,-Chcmical costs far -JOflOO gal/dayarsenic-removal water treatment plant*

Total PriceChemical Used (S/mil gal)

FeCl3:270 Ib Feds/mil gal x

$0.04/lb FeCl;, $10.80C12 (Assume in the form of C1O2) :

lOOlbCl j /mi lga lx1.901bClO2/lbCl2xS0.40/lb CIO2 76.00

Total $86.80

•Price data as of November 1973.

TABLE 21.—Continuous operating data from arsenic removal pilot plant(Shcn 1973)

Arsenic concentrations (mg/1)

Time in Days

24 40 59

Dosage of C12 (Ib/ 1000 gal)Dosage of FeCls (Ib/ 1000 gal)Residual C12 in water effluent (mg/1)pH of water effluent

0.3170.7932.07.2

0.0870.8511.57.1

0.2201.190.37.4

0.2971.402.57.4

Raw waterAfter sedimentationFinished water effluent

Percent arsenic removal

0.60.050100

0.580.090100

0.880.130.1088.5

0.790.080.0791.2


ofItdie>en-

n,•n:rien->adies:

TABLE 23.— Efficacy of various processes used to remove arsenicfrom gold mine waste waters

(Roschart and Lee 1972)

Method

Precipitation with:

FeS04 - 7HaO

FeCI, * 7HS0

A12(S04)8-

NajS

CaO

NaOH

Sorption processing withactivated carbon

Initial AsConcentration

(mg/litcr)Optimal

PHPercent AsRemoval

1320.5

1320.5

1320.5

1320.5

1320.5

1320.5

0.5

98

7-87-8

1212

10

94none

9095

9095

80none

9595

80none

40

Chemical CostPer Pound ofAs Removed*

(5)

1.05

3.183.18

1.951.95

0.45

0.070.07

0.33

•Cost data as of 1968.

Bellack estimated that operating costs of sim-ultaneous fluoride and arsenic removal from waterat $15 to $50/mil gal treated.

Gulledge and O'Connor (1973) found that bothhydrated alum (Al2(SO4)j • 18H2O) and hydrousferric sulfate (Fea (SO4) s • 3H2O) were effectiveadsorbants for arsenic (V) at an initial level of0.05 mg/liter in water. They found that both thedose of sorbent added and the pH of the solutionaffected the removal characteristics significantly. Inthe pH range of 5 to 8, it was reported that ferricsulfate removed arsenic much more efficiently thandid the alum. The amount of arsenic removed froma solution containing 0.05 mg/liter arsenic was re-ported to be almost exclusively in the 95 to 100percent range, and it was also concluded thatarsenic was more readily removed in the pH rangebetween 5.0 to 7,0.

Nilsson (1971) was able to remove As (V)effectively from solutions containing 4.2 to 23 mg/liter As (V) by precipitation using aluminum sul-fate at pH 6.5 to 7.0 and calcium hydroxide atpH 9.5. Jn most cases, after settling and centrifuga-tion, the solutions contained less than 1 mg/literAs (V) . The reduced species, As (III) , however,

seemed to respond very little if at all to this treat-ment.

A review of chemical abstracts over the past sev-eral years shows a reasonable amount of foreignand domestic research on the removal of arsenicfrom aqueous solutions of varying natures. Severalof these methods are listed in table 24.

In none of the papers was there any discussion ofmethods planned for the ultimate disposal of thearsenic removed from the contaminated water. Anytechnique that does not include this provision mustbe considered incomplete as regards coping withcurrent environmental requirements.

REMOVAL OF ARSENIC FROM AIR

In the United States, arsenic air pollution is al-most exclusively abated by removal of arsenic-con-taining dusts from smelter and other process emis-sions with fabric filters and electrostatic precipi-tators.

A number of techniques have been investigatedfor removal of specific arsenic compounds from gasstreams and these arc summarized in table 25.


TTABI.F. 24.—Methods of removing arsenic from aqueous solutions

stu died in recent years

Year Method Author (s)

1967 FeSO4 addition + filtrationF968 Addition of FeSO4 & Ca (OH) 2 or CaOClo1968 Addition of CaO and FcCI3

1969 Addition of C12 and FcSO4

1970 Addition of H3PO4 and Ca (OH) „1972 Addition of H3PO< and Ca (OH),1971 Ozonation followed by coprccipitation wi th

Fe hydroxides1973 Contacting with Fe (OH), gel1972 Milk of lime treatment1973 Addition of H2SO4 and CaO1973 Adsorption on hair or feathers1973 Contacting with disintegrated rubber wasic

Hedlich and othersShabunin and othersHollo and othersKcrmcrNikolaev and MazurovaNikolaev and others

Alimzhanov and othersPakholkov and Ul'yanovaAchkinadziGladyshcva and othersUeda and othersAlbenesius and others

TABLE 25.—Methods of removing arsenic from gaseous streamsstudied in recent years

Year Method Author (s)

1970 As2Os adsorption on zinc oxide1971 As2Os absorption in H!!SO< containing sus-

pended As2O8

1973 AsH3 adsorption on a molecular sieve column1973 As2O3 removal by cooling and condensation1973 Arsenic removal from hydrocarbons by con-

tacting with spongy Pd or Pd on a porousA12O3 carrier

1973 Arsenic powder, vapor, AsHs and organic ar-senic removal by Cu, Fe, Ni or Co in a silicatube at 700°

1973 As2O3 removal by cooling and circulationthrough a purifying column containingH2S04

Polukarov and othersMelkersson

Kellcher and othersTercbcnin and BykovDeutsche Texaco

Shinohara and Ito

Ojima

Country

Germany (East)USSRHungaryGermany (East)USSRUSSR

USSRUSSRUSSRUSSRJapanUSA

Country

USSRSweden

USAUSSRGermany

Japan

Japan

IV

V.

El

F<

F<

F

C

C

C

I

I

J

1

I

ACKNOWLEDGMENTS

The authors thank Mr. F. T. Davis, director ofthe Environmental Technology Division, and Dr.David E. Hyatt, senior environmental scientist,both at the Colorado School of Mines Research In-stitute, for their kindness in comprehensively re-viewing the manuscript for this MIB and for theirmany helpful suggestions.

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arsenic and the · arsenic compounds have long been infamous as very potent poisons, a well-known...

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