ESTIMATING THE HAZARD OF CHEMICAL SUBSTANCES TO AQUATIC LIFE

John CAIRNS, Jr .*, Kenneth L. DICKSON* & Alan W. MAKI*

Biology Department and Center for Environmental Studies, Virginia Polytechnic Institute and State University,Blacksburg, Virginia 24061 ; Environmental Safety Department, Procter and Gamble Company, Cincinnati, Ohio 45217

Received May 24, 1978

Keywords : Toxicity testing, hazard evaluation, bioassay, toxic chemicals

Abstract

The assessment of the hazard associated with the introduction ofchemical substances into the environment is receiving consider-able attention in current ecological, political, and public forums .The purpose of this paper is to identify and evaluate the basic con-cepts involved in assessing the hazard of chemical substances toaquatic life . A conceptual framework for conducting a hazardassessment is elaborated . In addition, several proposed proce-dures for conducting aquatic hazard assessments are comparedand contrasted . A discussion of the decision criteria currentlyutilized in hazard assessment procedures is included. The use ofsafety factors or 'uncertainty factors' as a central concept in a se-quential testing approach is presented . An assessment of the'state-of-the-art' in aquatic hazard assessment and recommen-dations for succeeding steps in the development of proceduresconstitute the conclusion of the paper .

Introduction

With President Ford's signature on October I I, 1976, theToxic Substances Control Act (TSCA) became law . Thislaw provides that no person may manufacture a newchemical substance or manufacture or process a chemi-cal substance for a new use without obtaining clearancefrom the Environmental Protection Agency. TSCA re-presents an attempt to establish a mechanism wherebythe hazard to human health and the environment of achemical substance can be assessed before its introduc-tion into environment . After reviewing pre-marketingtesting results on the potential effects of the chemical sub-

Dr. W. Junk b. v. Publishers - The Hague, The Netherlands

Hydrobiologia vol. 64, 2, pag . 157-166, 1979

stances on human health and the environment, theAdministrator of EPA must judge the degree of risk as-sociated with the extraction, manufacturing, distribution,processing, use, or disposal of the chemical substance . Ifthe chemical substance presents an unreasonable risk ofinjury to health or the environment, the Administratorof EPA may restrict or ban the chemical substance .The enactment of TSCA provides a powerful new sti-

mulus to the development of testing procedures to eval-uate the hazard to human health and to the environmentassociated with potentially toxic chemical substances .Both those businesses responsible for the pre-marketingtesting of chemical substances subject to the law and theEnvironmental Protection Agency responsible for assess-ing the risk or hazard associated with the chemical sub-stances must develop testing and decision making proce-dures if the intent of the law is to be fulfilled . Thesehazard assessment procedures must represent a systema-tic and comprehensive approach to the problem . Becauseresources (both competent personnel and adequate facili-ties) for such testing are limited and the number of in-sufficiently testing compounds is extremely large, withmany more generated each year, it is essential to developa system for establishing testing priorities . This systemwould ensure that an accurate hazard assessment, con-sidering potential risks associated with the new chemical,can be estimated with the most efficient use of personnel,money, and time .

Safety, Hazard, and Risk DefinedThe terms safety, risk, and hazard are closely allied, and

* Co-authors

15 7

an understanding of the differences in their use is impor-tant . There is a compelling need to make judgments anddecisions concerning the risk associated with the manu-facture, transport, use, and disposal of chemicals . Thisneed has stimulated great interest in a process called`hazard assessment,' the objective being to provide infor-mation from which a judgment can be made regardingthe safety of the chemical . The initial attempts to de-scribe, define, and implement the hazard evaluation pro-cess as it relates to aquatic environments have often re-sulted in confusion and disagreement. Two principalsources for this confusion and disagreement exist . First,the meaning of the word safety, and the process by whichone comes to a judgment concerning safety, apparently isnot well understood . As a consequence, the distinctionbetween matters of empirical fact, scientific judgment(or what might be called conclusion), and value judgmentis not appreciated or preserved . For purposes of this dis-cussion, it is useful to define safety as a value judgment ofthe acceptability of risk . Risk, in turn, is defined as ascientific judgment regarding the probability of harm tothe aquatic environment resulting from known or poten-tial environmental concentrations . Thus, a chemical issafe if its attendant risks are judged to be acceptable . Thisdefinition implies that two very different activities are re-quired for measuring the risk to the aquatic environment :(1) an objective but probabilistic pursuit requiring empi-rical facts (data) and scientific judgments (conclusions) ;and (2) a value judgment regarding the acceptibility ofthat risk must be made . The second source of the confu-sion, disagreement, and inaction which has heretoforecharacterized the subject is society's failure to recognizethat science is not yet capable of precisely assessing risksto the aquatic environment in the quick, economical,reliable manner that is desired .

Conceptual framework for conducting a hazard assess-ment

In performing a hazard assessment to measure risk, onemust begin with facts that can then be utilized to makescientific judgments regarding: (1) toxicity -the inherentproperty of the chemical which will produce harmfuleffects in an organism after exposure of a certain durationto a specific concentration; and (2) environmental con-centrations -those actual concentrations resulting fromall point and non-point source inputs, as modified by thephysical, chemical, and biological processes active in the

15 8

environment . The toxicity of a substance, defined fromthe results of laboratory exposures, can then be assessedagainst projections or estimates of actual environmentalconcentrations and would enable a quantitative estimateof risk. Figure i illustrates the conceptual framework fora hazard assessment . Thus, the aquatic toxicologist willuse exposure and toxicity data to arrive at a scientificallybased judgment regarding the impact of a chemical onaquatic life . This judgment will consider the relationshipbetween the exposure concentration and the inherenttoxicity of a chemical . The acceptability of a hazard isdetermined by the risk society is prepared to accept . So-ciety's standards for acceptance or rejection of the riskassociated with the use of a chemical are set by publicdemands, legislation, and judicial decisions which maybe influenced by scientific information but rarely aredetermined solely by it .

Predicting the environmental fate of a chemical can beaddressed through both physical and mathematicalsimulation approaches (Baughman & Lassiter, 1978 ;Branson, 1978 ; Metcalf, Kapoor, Lu, Schuth & Sher-man, 1973) . While both the microcosm and environ-mental rates approaches have utility, the later approachoffers greater flexibility. The environmental rates ap-proach is based on the development of differential equa-tions. The equations would describe the dominant modesof transport and transformation of the chemical sub-stance as well as the potentially significant sources of thesubstance together with the conditions that represent theaquatic environments that the chemical may enter .Generally, a deterministic mathematical model is used .In this model, the differential equations describe both theindividual rates of transformation and the transport pro-cesses, thus permitting a description of the environmentalchemistry and fate of the chemical. Typical properties ofa chemical substance which are important in the pre-

Knowledge of theEnvironmental Fateof the Chemical

HazardAssessment

Fig. i . Components of a hazard assessment .

Knowledge of theInherent ToxicologicalProperties of the

Chemical

diction of environmental concentration using the en-vironmental rates approach follow :

Propertiesmolecular structurevapor pressureparticle sizewater solubilityabsorption spectra (UV, visible)

Rate Constantsphotodegradation (UV, visible)biological degradationchemical degradationevaporationsediment bindinguptake by organismsdepuration by organisms

Partition Coefficientsoctanol: waterair : watersediment : waterSimilarly, one should recognize that measurements of

several physical and chemical properties of the aquaticenvironment are needed to derive accurate estimates ofexpected environmental concentrations of a substancefollowing use. Typical properties of the environment usedto make these predictions of environmental fate and con-centration are :

Property

surface areadepthpHflow turbulencecarbon sediment (%)temperaturesalinitysuspended sediment concentrationtrophic statusabsorption spectra (UV, visible)A third factor, rate of chemical substance input, must

be used in conjunction with the properties of the chemi-cals and the environmental characteristics to develop ameaningful environmental fate and concentration pre-diction .

Determining the effects of chemical substances onaquatic life requires the application of an array of toxicity

tests. At the workshop on Application of Aquatic Toxi-city Testing Methods as Predictive Tools for AquaticHazard Evaluation, held at the University of MichiganBiological Station in June 1977, the various types ofaquatic tests were evaluated to determine which canproduce useful data regarding the toxicity of most chemi-cals to most aquatic organisms and to assess the valueand limitations of each test in estimating toxicity to aqua-tic organisms . In order to evaluate various methods, theparticipants developed a concensus matrix whichprovided a numerical evaluation of the present relativeutility of several types of tests on the basis of weightedevaluation criteria (Table i) . The relative importance ofeach criterion was rated numerically with i being the cri-terion of lowest significance and 6 the criterion of highestsignificance . The criteria, in order of relative importanceas determined by the workshop participants, were theecological significance of the effects measured by the test,the scientific and legal defensibility of the test, the avail-ability of routine acceptable methods for conducting thetest, the utility of the test results in predicting effects inaquatic environments, the general applicability of the testto all classes of chemicals, and the simplicity and cost ofthe test . The participants then rated each type of test (o toio in increasing value) under each evaluation criterion .The numerical rating in the matrix is a weighted meanrepresenting the product of the mean rating for each typeof test and the mean rating for each criterion. The presentrelative utility was determined by summing the weightedmeans for each type of test and expressing these summa-tions as a percent of the highest value (i .e ., acute lethalitytests received the highest numerical ranking, and this testwas assigned a present relative utility rating of too) . Aparticular test could receive a low or high rating under asingle, several, or all criteria ; therefore, the summationsmay not necessarily be indicative of overall value andtheir utility . For example, residue accumulation tests re-ceived a relatively high overall rating possibly because ofthe high ratings given to the ecological importance andlegal defensibility associated with legally established resi-due tolerances in aquatic organisms, and the fact that thesetwo evaluation criteria were considered the most impor-tant of all the criteria . Similarly, field studies received afairly high overall rating because the ecological signifi-cance of such studies is high (and this was the most im-portant evaluation criterion) while simplicity and cost,significant drawbacks of such studies, were rated the leastimportant evaluation criteria . Predictive utility was ratedlower than several other evaluation criteria, possibly be-

1 59

Table

1-Concensus

Eval

uati

onOf

The

Pres

ent

Rela

tive

Util

ity

ofSimple

And

Comp

lex

Toxi

city

Tes

tsUsed

InAs

sess

ing

The

Risk

Asso

ciat

edWith

The

Occu

rren

ceOf

Chemicals

inAq

uati

cEn

viro

nmen

tsMade

ByPa

rtic

ipan

tsAt

The

Work

shop

On

aFro

m Br

ungs

and

Mou

nt,

in p

ress

.

The

Appl

icat

ion

Of A

quat

ic T

oxic

ity

Test

Met

hods

As

Pred

icti

ve T

ools

For

Aqu

atic

Hazard Evaluation, Held In

Pellston, Michigan, June 1977.a

Scie

ntif

ic

EVALUATION CRITERIA

Availability

Simp

lici

tyPr

esen

t

Test

Ecol

ogic

alSignificance

and Legal

Defe

nsib

ilit

yof

Rou

tine

Meth

ods

Pred

icti

veUt

ilit

yGe

nera

lApplicab

ilit

yan

dCost

Rela

tive

Util

ity

Acut

e Le

thality

3336

Simp

le S

yste

ms

3522

2426

100

Embr

yo-L

arval

3330

2320

2514

82

Reproducti

on36

3021

2724

882

Residue Ac

cumu

lati

on27

3222

2417

1477

Alga

l As

say

3023

2618

1420

74

Orga

nole

ptic

1425

2527

1315

67

Stru

ctur

e/Ac

tivi

ty18

2123

1716

2266

Behavorial

2113

109

169

44

Histologic

al10

1020

1013

1041

Phys

iolo

gical

and biochemical

1210

138

198

40

In vitro

45

94

1111

25

Fiel

d34

24

Comp

lex

Syst

ems

1821

213

69

Diversity

2619

2515

2010

65

Benthic

2118

1218

1712

56

Micr

ocos

m19

1015

1417

948

cause few, if any, tests are considered to have a `high' pre-dictive utility . The present relative utility of such tests wasrated, and it was concluded that toxicity tests such asacute lethality tests, embryo-larval toxicity tests, testsassessing the effects of chemicals on reproduction(chronic tests), and tests on residue accumulation canprovide meaningful information for assessing the hazardassociated with the occurrence of a wide variety of chemi-cals in aquatic environments . Other tests were identifiedwhich provide information that can be particularly usefulin assessing the hazard associated with specific classes ofchemicals or the hazard to specific biological groups .

Hazard assessment procedure

A hazard assessment procedure should consist of a se-quential series of tests . Progression through the seriesshould be governed by decision criteria applied at frequentintervals in the sequence of testing . These decision criteriashould allow one of the following decisions to be made :(i) use the chemical ; (2) ban use of the chemical ; or (3)more testing is required before a final decision can bemade on use. Sound scientific judgment should be usedin the establishment of these criteria and in their applica-tion to decisions regarding progression through the se-quential series of tests .Several hazard assessment procedures are being

developed which conform to the basic design of sequentialtesting to evaluate the hazard to aquatic life associatedwith the use of chemicals . Two committees working in-dependently under ASTM (American Society for Testingand Materials) and AIBS (American Institute of Biologi-cal Sciences) authorization have produced drafts ofhazard evaluation programs, each with a specific and in-tended purpose. ASTM Committee E-35 on Pesticidesand its Subcommittee E-35 .21, Safety to Man and theEnvironment, have organized a Task Force under thechairmanship of Mr. J . R. Duthie. The Task Force willdevelop a standard practice for a laboratory testing planto evaluate hazard to non-target aquatic organisms . Thelatest draft being reviewed (dated March 1, 1977) de-scribes a stepwise laboratory testing plan to develop datato evaluate the hazard to non-target aquatic organismsresulting from intended and unintended release of essen-tially any material into the aquatic environment. Theessence of this procedure was presented at the First Sym-posium on Aquatic Toxicology last year (Duthie, 1977) .

The AIBS Committee entitled `Aquatic Hazards of

Pesticides Task Group' operates under the chairmanshipof Dr. C. H. Ward and was organized at the request of theCriteria and Evaluation Division, Office of PesticidePrograms, U . S . Environmental Protection Agency . Thegroup was organized to review and analyze available in-formation on test methods and protocols designed toevaluate aquatic hazard testing in order to facilitatepesticide registration . The procedure produced by thisgroup was discussed in detail during this symposiumby Dr. Ward and is published in the book Estimatingthe Hazard of Chemical Substances to Aquatic Life(Cairns, Dickson & Maki, 1978) .

A third hazard assessment procedure which utilizes thesequential testing design was developed by Monsanto In-dustrial Chemicals Company to systemetically evaluatethe hazard to aquatic life of new materials prior to theircommercialization. The basic concepts of this procedurewere presented to this symposium last year, and furtherelaborations of the procedure can be found in theproceeding of the workshop on The Application ofAquatic Toxicity Testing Methods as Predictive Tools forAquatic Hazard Evaluation (Cairns, Dickson & Maki,1978; Kimerle, 1977) .

It is not our intent to make a detailed comparison ofthe three procedures . However, an analysis of their basicstructure provides insight into the design of hazard assess-ment procedures in general. Although relying on severalcommon data requirement inputs, the proposed hazardassessment procedures developed by the ASTM E-35 .21Group, Monsanto, and the AIBS Special Task Grouprespectively have widely differing objectives and purposes .A listing of features common to each procedure ispresented in Table 2 . The ASTM and the Monsantohazard evaluation plans are targeted for broad spectrumuse with essentially any potential contaminant reachingor possibly reaching surface waters . The AIBS planfocuses on pesticide usage and its associated hazards .While the ASTM and Monsanto criteria lead ultimatelyto a use (or abandon use) option, the AIBS procedure wasdesigned to identify the need and type of additional long-term safety data which might be required .

The ASTM and Monsanto programs outline the scopeof a hazard assessment plan based on the use and prop-erties of a candidate compound, and the AIBS plan as-sumes availability of safety testing results for review .Decision criteria are related to projections of environ-mental concentrations under the ASTM and Monsantomethods, whereas the AIBS program outlines specifictest data in relation to environmental concentrations

1 6 1

1 62

Table 2--Characteristics of the three representative procedures for evaluationof aquatic hazard

which, if exceeded, spotlight the need for additionaltesting .

Decision Criteria

An effective plan for aquatic hazard assessment necessari-ly involves a hierarchial testing program in which theresults from a particular test series lead to decisions re-garding use of the material or the requirement for addi-tional testing. It is not reasonable to assume that a single,rigid hazard assessment procedure will apply equally wellto the broad range of test materials which might enter theaquatic environment. As a consequence, each testing planprovides the investigator with the flexibility to tailor thetesting program to the informational needs dictated bythe properties of the test material . A successful testingplan does not automatically dictate a series of tests whichmust run in sequence regardless of information generatedbut instead provides the opportunity to make appropriate

safety decisions when sufficient evidence is available .An operational hazard assessment procedure should alsoprovide a means for increasing the degree of certaintyupon which safety decisions are based as the volume useof the material increases .

In each of the three proposed procedures for aquatichazard assessment, a variety of decision criteria is used inarriving at judgments of the need for additional tests andthe risk associated with the decision to terminate testing .These specific decision criteria and the respective actionindicated are listed for the purpose of comparison inTable 3 . One should recognize that these decision criteriataken out of the context of an integrated hazard assess-ment program are by themselves meaningless . They aresummarized here only to give the reader a feeling forsome of the concrete decision points and their implica-tions used in these testing protocols . Although soundscientific judgment is the most important factor in any

PARAMETERS ASTM AIBS MONSANTO

1 . Application Broad spectrum Pesticides only Broad spectrum

2 . Purpose Leads to use or Identifies need Leads to use ordiscard decision for additional discard decision

testing and type

3 . Program Outlines priority Largely prescribed Defined testingdesign and scope series

4 . Baseline None Prescribed basic Nonedata tests

5 . Decision Relation to Provides specific Related to calculatedcriteria calculated numerical criteria environmental levels

environmentallevels

6 . Program 3 phases 2 phases 4 phasesoptions

7 . Environmental Requires calcu- Assumes avail- Requires calculationlevels lation and ability of accept- and refinement

refinement able estimates

8. Uncertainty Decreases as Unspecified Decreases asmargin assessment assessment proceeds

proceeds

Tabl

e3-

-Dec

isio

n cr

iter

iaus

edin

the

ASTM

, AI

BS,

and Monsanto

prop

osed

proc

edur

esfor

aqua

tic

hazard

assessment

and

thei

rim

plic

atio

ns f

or m

ater

ial

use

and

addi

tion

al t

esti

ng.

Risk

Una

ccep

tabl

e;

Term

inat

e Plans to Use

EEC>LC50

Part

itio

ning data make

bioc

once

ntration likely

to a

degr

ee k

nown to be

detr

imen

tal

EEC

1> M

ATC2

Chem

ical

/phy

sica

l

Broa

d, l

arge

vol

ume

Broa

d, l

arge

Biological half-life

data show no cause

use

patt

ern

volu

me u

se p

atte

rn

> 4

days

to suspect significant

partitioning data

bioaccumylation

indi

cate

bio

conc

entr

atio

rEEC<

.05

(MA

TC)

coul

d be

sub

stan

tial

1. E

stim

ated Environmental Concentration

2. M

axim

um A

ccep

tabl

e To

xica

nt C

once

ntra

tion

(fo

llow

ing

a ch

roni

c te

st)

3. B

ioco

ncentration Factor

No Further Tests

Addi

tion

al A

cute

Full

or

Part

ial

Bioconcentration

Required for Use

Test

ing

Life

Cyc

le C

hron

icTesting

EEC<

.002

(LC50)

LC50

< 1.0

mg/

lLC

50<

1.0

mg/

lWater Solubility

< .5mg/ or

EEC<

.01

(LC5

0)EE

C>.O

1 (L

C50)

EEC>

.01 (LC50)

BCF3

< 10

0So

lids

/HOH

P>1

000

LC50<EEC>.0

02 (

LC50)

Octanol/HOH P >1000

hazard assessment decision, these specific criteria serve tosharpen judgment regarding ultimate safety of materialsin the environment .

Safety factor concept

A central concept underlying the use of a sequentialtesting approach to hazard assessment is that as testingproceeds through succeeding tiers, estimates of expectedenvironmental concentrations and of the concentrationsproducing biological effects can be made with an in-creasing degree of accuracy and confidence. From thisgreater understanding and confidence in the accuracy ofthe knowledge about the relationship between environ-mental concentration and concentrations productingbiological effects, a more accurate risk assessment results .Thus, in the initial stages of a hazard assessment, a some-what arbitrary and numerically small safety factor (i.e .,I / 1000, 1/ goon, etc.) must be applied to the concentrationshowing some biological effects since the confidence inthe estimated environmental concentration and in theconcentration causing biological effects are both low .This definition of the safety factor implies a numericalquantity by which the known biological effect concentra-tion is to be multiplied in order to define a `safe' environ-mental concentration as in the following equation :(B. E .) X (S.F.) = E . C .whereBE = an estimate of the concentration causing no biolog-

ical effects determined from laboratory toxicitytests,

SF = safety factor with a typical range from i / loon to1 / 10, and

EC = a projected environmental concentration causingno effects on aquatic life .

As a chemical substance proceeds through evaluationin a sequential testing procedure, confidence in both esti-mates of biological effects and expected environmentalconcentration increase, and, thus, the margin of differ-ence between the two levels becomes increasingly welldefined. This in turn reduced the contribution of un-certainty to the safety factor and typically allows one toincrease the safety factor .

As a chemical substance proceeds through evaluationin a sequential testing procedure, confidence in both para-meters increases, and, thus, the numerical value of thesafety factor due to uncertainty increases (i .e ., i / Iooo to1 / 10o to 1 / 10) . During a hazard evaluation procedure, in-

164

increasingly accurate estimates are obtained of concen-trations of the chemical substance that do not cause ad-verse biological effects and the concentration that will re-sult from intended use of the chemical substance . Thesequential evaluation procedure should be carried out tothe point where the accuracy of the information is suffi-cient to allow a considered judgmental decision about thehazard. This process is further illustrated in Figure 2 .

Conclusions

Estimating the hazard of chemical substances to aquaticlife is a challenging task. The number of chemical sub-stances which alone have to be evaluated complicates thejob. The diversity and complexity of aquatic life furthercompounds the difficulty . Nevertheless, some procedureshave been developed which may very well accomplishthis task .

The realization that the hazard of a chemical substancemay be defined as the relationship between the environ-mental exposure concentration and the concentrationcausing a biological effect opened the door for the devel-opment of hazard assessment procedures . The ASTM,AIBS, and Monsanto approaches seem to be satisfactoryexamples of hazard assessment procedures . However, allof these procedures need to be rigorously tested . Old andnew chemicals need to be used to determine the efficacyof the procedures. The decision criteria used in the proce-dures to make decisions on the need for addtional testingneed to be critically scrutinized to firmly establish theirscientific credibility .

While it is easy to be critical of the hazard assessmentprocedures currently available, one should recognize thatthese scientists developing the procedures were pioneeringa complex and emerging area. To them we owe credit foridentifying the urgent need that exists for developmentsin the area of predicting the environmental concentrationof chemical substances . Likewise, their evaluation of themethods used to evaluate the biological effects of chemi-cal substances on aquatic life has stimulated the develop-ment of simplier, more reliable, and more cost effectivemethods .

In conclusion, we have the basic framework for es-timating the hazard of chemical substances to aquaticlife . It needs to be applied and refined based on the ex-periences of use. Likewise, efforts should be made tomake the hazard assessment as cost effective as possible .

mC0tN

U)

Em

U

0

C00

C0C0U

Acknowledgements

The authors are deeply indebted to the participants in theworkshop on The Application of Aquatic ToxicityTesting Methods as Predictive Tools for Aquatic HazardEvaluation held at the University of Michigan BiologicalStation, June 13-17, 1977, for many of the ideas presentedin this paper .

°ce\ \Inter,,,,

r

r

X/ ~Cohf deuce

\

t

Highest test concentrationproducing no biologicaleffects .

Highest expected environmentalconcentration .

1

I

I

II

2

3

4

5Sequential Tests of Hazard Assessment

ProcedureFig. 2 . Diagrammatic representation of a sequential hazard assessment procedure demonstrating increasinglynarrow confidence limits for estimates of no biological effect concentration and actual expected environmental

concentration .

References

Baughman, G. L. & Lassiter, R. R. 1978 . Prediction of environ-mental pollution concentration. Pages 35-54 in : J . Cairns, Jr.,K . L . Dickson, and A. W. Maki, eds ., Estimating the Hazardof Chemical Substances to Aquatic Life. American Societyfor Testing and Materials, STP 657, Philadelphia, Pa .

Branson, D. R . 1978. Predicting the fate of chemicals in theaquatic environment from laboratory data . Pages 55-7o in :J . Cairns, Jr ., K . L . Dickson, and A . W. Maki, eds ., Estimating

1 65

the Hazard of Chemical Substances to Aquatic Life . AmericanSociety for Testing and Materials, STP 651, Philadelphia, Pa .

Cairns, J ., Jr ., Dickson, K. L. & Maki, A . W . eds . 1978 . Esti-mating the Hazard of Chemical Substances to Aquatic Life .American Society for Testing and Materials, STP 657, 278 pp .Philadelphia, Pa .

Duthie, J . R . 1977 . The importance of sequential assessment intest programs for estimating hazard to aquatic life . Pages 17-35in : F. L . Mayer and J . L. Hamelink, eds ., Aquatic Toxicologyand Hazard Evaluation . American Society for Testing andMaterials, STP 634, Philadelphia, Pa .

Kimerle, R . A. 1977 . An industrial approach to evaluating envi-ronmental safety of new products . In: F . L . Mayer and J. L .Hamelink, eds., Aquatic Toxicology and Hazard Evaluation .American Society for Testing and Materials, STP 634, Phila-delphia, Pa.

Metcalf, R. L., Kapoor, I. P., Lu, P . Y., Schuth, C . K . & Sher-man, P. 1973 . Model Ecosystem studies of the environmentalfate of six organochlorine pesticides . Environ . Health Perspec-tives, Exp . Issue 4 : 35- 44 .

1 66