Pollution of crops and pastures by a smelter

T h e study area.

T h e Sou th Austra l ian t o w n

o f Port Pir ie is domina ted by

a metal-ref ining c o m p l e x ,

incorpora t ing the wor ld ' s

largest lead smelter.

T h e c o m p l e x a lmost ho lds

another record : its 205 -m-

h i g h c h i m n e y , c o m p l e t e d

last A u g u s t , is the s econd-

tallest man -made structure

in Austral ia, surpassed on ly

by a stack at M t Isa.

T h e smelters refine lead

and z inc f rom ore m i n e d at

Broken Hi l l . T h e s m o k e

c l i m b i n g the c h i m n e y

conta ins traces o f these

heavy metals — and o f other

e lements , such as c a d m i u m ,

that o c c u r in smaller

amounts in the ore .

N o w a d a y s these traces are

very small , but f rom 1889,

w h e n the first smelter began

operat ing, until 1925, w h e n

emis s ions were greatly

r educed f o l l o w i n g a R o y a l

C o m m i s s i o n report, an

e n o r m o u s quantity —

perhaps 4 0 000 tonnes — o f

Smel ter 'fall-out' l and ing

o n the leaves and stems o f

whea t plants d id no t

apparently cont r ibute to

con tamina t ion , even in crops

g r o w n nearby. W a s h i n g

wheat plants m a d e n o

difference to their metal

con ten t ; this was no t

surprising, as the

concen t ra t ions o f heavy

metals in the fumes f rom the

smelters have b e e n kept very

l o w for years.

W i n d - b l o w n soi l dust

c o u l d in theory con tamina te

plants, but wheat grain is

we l l protected wi th in the

head as it deve lops , and the

scientists found n o ev idence

that dust had cont r ibuted to

the h igher levels o f heavy

metals found in grain g r o w n

near the smelters.

A l l this may c o m e as a

rel ief to l oca l farmers, but

what o f the pastures that

fo rm an essential part o f c r o p

rotat ions? A r o u n d Port Pirie

the m a i n pasture spec ies are

annual m e d i c and various

annual grasses, w i th native

c h e n o p o d s ( spec ies o f g o o s e -

foot) and in t roduced w e e d s .

In p laces s tock graze over

former wheat lands that have

reverted to saltbush and

b luebush , or o n samphire

g r o w i n g o n salty so i l s .

M r Mer ry and D r T i l l e r ,

w h o carried out the study o f

pasture con tamina t ion ,

found that different plant

spec ies t ook u p w i d e l y

differing quantit ies o f metal

pol lutants , and in different

ways . C a d m i u m and z inc , it

appears, are absorbed by the

roots , but mos t o f the lead is

depos i ted o n shoo t s , f rom

dust and c h i m n e y fall-out.

T h e scientists be l i eve that

soi l dust plays little part in

pasture po l lu t ion excep t

wi th in about 5—10 k m o f the

smelters.

Ward ' s w e e d recorded the

h ighes t c a d m i u m and z inc

concen t ra t ions , and potato

w e e d topped the list for lead,

w i th Ward ' s w e e d no t far

beh ind . A t the other end o f

the scale , the least-

27

potential ly tox ic metals

b e l c h e d out o f the smelter 's

c h i m n e y . Wha t g o e s u p mus t

c o m e d o w n , and the metals

eventual ly fell to earth,

where they persist.

A t least 3 4 0 0 sq k m o f

land are con tamina ted by

lead, and in 2 7 0 sq k m the

soi l con ta ins 10 or m o r e

t imes the general

' background ' level o f 10

parts per m i l l i o n (p .p .m.) .

C a d m i u m and z inc pol lu te

s imilar areas. W e k n o w the

concen t ra t ions o f the

contaminants in soi l and

vegetables (see Ecos 7 ) . T o

what extent are cereals and

pastures affected, and is the

heal th o f h u m a n s and

l ives tock at risk? A team o f

researchers f rom the CSIRO

With increasing distance from the smelter, pollution falls to a 'background ' level. Z inc is shown here; lead and cadmium curves are similar. C o p p e r is a negligible c o m p o n e n t o f smelter smoke .

D i v i s i o n o f So i l s has been

tackl ing these ques t ions .

M r R i c h a r d Merry , D r

K e v i n T i l l e r , M r Paul de

Vr i e s , and D r Brian

Cartwright t ook samples o f

whea t and pasture plants

f rom sites at var ious

dis tances f rom Port Pirie,

i n c l u d i n g poin ts o n a l ine

stretching m o r e than 30 k m

south f rom the smelters. T h e

scientists c o l l e c t e d bo th

grain and w h o l e tops o f

whea t plants, as we l l as

spec imens o f s o m e 30

pasture species and samples

o f the soi ls in w h i c h all

these plants g rew.

T h e y then analysed the

plants and soi ls to find out

Heavy metal uptake is illustrated here by cadmium: the more there is in the soil , the more will contaminate a plant. M o s t pasture species take up less cadmium than Ward ' s weed but more than bluebush. Soil metal values were obtained by extraction with a standard reagent, EDTA.

h o w m u c h lead, z inc , and

c a d m i u m these con ta ined .

A s a c h e c k , they also

measured the concen t ra t ions

o f metals that are very m i n o r

c o m p o n e n t s o f the smelter

s m o k e , s u c h as coppe r .

T h e y found a g o o d

corre la t ion be tween the

degree o f con tamina t ion o f

m o s t plants and the

con tamina t ion o f the soi ls

they grew in. T h e m o r e

c a d m i u m that pol lu tes the

g round , for example , the

m o r e there wi l l be in a whea t

stalk or a paddy m e l o n leaf.

T h e farther the scientists

travelled a long their south­

b o u n d transect, the less

con tamina t ion they found ,

unti l , about 35 k m f rom the

smelter , the pol lutant

concen t ra t ions had d ropped

to ' background ' levels

similar to those f o u n d

e l sewhere in the State.

T h e levels o f heavy metals

in whea t c a m e we l l wi th in

the l imits set by State health

authorit ies. What ' s m o r e , the

pol lutant metals b e c o m e

di luted dur ing bu lk hand l ing

and mi l l i ng , w h e n

con tamina ted grain is

b l ended wi th wheat f rom

unpo l lu ted areas. T h e

researchers be l ieve that

h u m a n heal th is un l ike ly to

be endangered by the heavy

metals in whea t grain

harvested near the smelters .

con tamina ted plants were the spec ies o f b luebush . T h e scientists c o l l e c t e d their samples at three t imes o f year, and i n c l u d e d plants at var ious stages o f their life c y c l e s , and this m a y at least partly a c c o u n t for the variations b e t w e e n spec ies .

S h e e p and cattle graze o n these pastures; are they b e i n g ha rmed by their Saltbush is grazed o n s o m e former wheatlands.

c h e m i c a l diet? T h i s is a t o u g h ques t ion . It seems that the risk depends to s o m e extent o n w h i c h spec ies they eat. B y c h o i c e , the s tock take the m a i n pasture plants, but w h e n these are in short supply the animals turn to saltbush and b luebush , and finally the burrs (fruits) o f m e d i c .

In the semi-arid c l imate o f Port Pir ie , the g r o w i n g season lasts for o n l y 5 m o n t h s and d rough t c o n d i t i o n s o c c u r frequently. T h i s m e a n s that sheep are often dr iven to r u m m a g i n g for m e d i c burrs, inevi tably garnished wi th a s ignif icant quanti ty o f so i l , w h i c h con ta ins h ighe r metal levels than d o the plants. T h e animals ' intake o f lead, in particular, w i l l r ise, s ince lead is abou t 10 t imes as concen t ra ted in so i l as in pasture.

Scient is ts d o n o t k n o w all the ways in w h i c h heavy metals may affect an imals . Cer ta inly t o o m u c h o f any o n e metal w i l l be t ox i c . Wha t ' s m o r e , s o m e pol lutant meta ls antagonize essential e l emen t s : for e x a m p l e , an an imal that s w a l l o w s s o m e c a d m i u m wi l l absorb less o f the c o p p e r in its f o o d than i f its mea l had been unpo l lu ted .

Ward ' s w e e d , w h i c h was in t roduced f rom the Medi te r ranean r e g i o n , con ta ins relatively large amoun t s n o t o n l y o f c a d m i u m but a l so o f sulfur, another e l em en t that antagonizes coppe r .

T h e risk is particularly hard to assess because several metals are invo lved , and they interact.

Z i n c , for e x a m p l e , aggravates lead toxic i ty . O n the other hand, c a l c i u m and p h o s p h o r u s he lp to offset the t o x i c effects o f bo th lead and z inc . T h e Por t Pir ie r e g i o n has ca lca reous so i l s , w h i c h perhaps offer s tock s o m e measure o f pro tec t ion .

Bluebush is less contaminated than most plants examined, but stock turn to it only when the main pasture species are in short supply.

A n i m a l s vary in their p h y s i o l o g i c a l r e sponses , t o o . S h e e p and cattle tolerate lead in their diets at concen t ra t ions u p to 3 0 0 p .p .m . w i thou t s h o w i n g any i l l effects, a l t hough they d o accumula t e the metal . ( T h i s concen t ra t ion is m a n y t imes h igher than any the scientists found in plants near Por t Pir ie .) Other n o n -ruminants c a n n o t pu t u p wi th lead levels nearly as h i g h as this: horses , for e x a m p l e , c a n tolerate o n l y about 80 p .p .m.

T h e scientists f o u n d lead concen t ra t ions o f 2 0 0 0 p .p .m . o r e v e n m o r e in soi ls in the t o w n , and wheat and pasture soi ls near Por t Pir ie often con t a ined 3 0 0 - 5 0 0 p .p .m. Because the m o s t con tamina ted soi ls g r o w the m o s t con tamina ted

vegeta t ion, the researchers be l i eve that the animals at greatest risk are those wi th in about 5 k m o f the smelter c o m p l e x .

M r Mer ry and D r T i l l e r feel that this ques t ion o f animal health needs further invest igat ion. A study be ing carr ied out at the Institute o f M e d i c a l and Veterinary S c i e n c e in A d e l a i d e is p rov id ing valuable informat ion . T h e r e , M r T e e -S iaw K o h and D r G e o f f Judson are test ing the idea that the c o p p e r de f i c i ency observed in sheep grazing near the smelters c o u l d b e caused by the levels o f heavy metals i n the diet.

T h e scientists se lec ted s ix propert ies f rom 6 to 4 0 k m sou th o f the smelters , and o n t o e a c h farm m o v e d 14 sheep f rom the State's unpo l lu t ed south-east. Ass is ted by M r W a r w i c k H a c k o f the S o u t h Austra l ian Depar tmen t o f Agr icu l tu re , they t ook samples o f b l o o d and faeces every 3 m o n t h s , and every 6 m o n t h s they k i l led three sheep o n e a c h property and r e m o v e d liver, k idney , m u s c l e , and b o n e samples .

T h e analyses s h o w h o w m u c h o f the heavy metals the sheep are s w a l l o w i n g and absorb ing into their t issues, and enab le the researchers to k e e p an eye o n the animals ' levels o f c o p p e r and other essential e lements .

T h e faecal samples to ld a

\t

Ward's weed, an introduced annual, takes up relatively large amounts of cadmium and zinc in polluted areas.

clear story o f increased heavy metal intake near the smelters. F a e c e s f rom the sheep nearest Port Pir ie con ta ined 4 0 t imes as m u c h lead as faeces f rom the sheep o n the m o s t distant property, w h e r e the animals were e x p o s e d on ly to ' background ' levels o f heavy metals . T h e co r r e spond in g ratio for c a d m i u m was 30 , and for z inc 4 .

W e mus t e x p e c t s o m e o f these addit ional heavy metals to f ind their way in to the sheep 's o rgans . M r K o h and D r Judson have found three to five t imes as m u c h lead and c a d m i u m i n the b l o o d and tissues o f the sheep near the smelters as in the ' background ' sheep .

T h e sheep c o n s u m i n g the largest quantit ies o f heavy metals also had the l o w e s t concen t ra t ions o f c o p p e r in their livers — on ly o n e -twent ie th the ' no rmal ' value.

T h e scientists c o m m e n t that the exper imenta l sheep near the smelters m i g h t have approached or even reached a state o f c o p p e r de f i c iency . T h e faecal analyses s h o w that o n all proper t ies the sheep inges ted the same amoun t s o f c o p p e r , so it s eems l ikely that the absorpt ion o f copper - f rom the gut into the b l o o d is impaired, p robab ly by h i g h leve ls o f o n e or m o r e o f the heavy metals .

Clear ly a ques t ion that wi l l n e e d answer ing is whe ther the metals accumula t i ng in l ives tock raised near Port Pir ie may , w h e n the meat reaches the d inner table, present a hazard t o h u m a n health.

Con tamina t ion o f whea t c r o p s a round a l e a d - z i n c smelter. R . H . Mer ry , K . G . T i l l e r , M . P . C . d e Vr i e s , and B . Cartwright . Environmental Pollution (Series B), 1981 , 2 , 3 7 - 4 8 .

T o x i c metals a round Por t Pir ie . Ecos N o . 7, 1976 , 2 7 - 3 1 .

28