Uranium mining in relation to impacts on inland waters

8/18/2019 Uranium mining in relation to impacts on inland waters

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E c o t ox i c o l ogy 1 , 75-88 (1992)

ranium mining in relation to

impacts on inland waters

toxicological

D O U G L A S A . H O L D W A Y

Key Centre or Applied and Nutritional Toxicology Royal Melbourne Institute of Technology Melbourne

Victoria 3001 Australia

Rec eive d 22 April 1992; accep ted 10 June 1992

Protec tion of tropical rivers from m etal pollution requires that mining wastewaters be b iologically

tested for aquatic toxicity before release from the site into natural ecosystems occurs, and that a

'safe' dilution which incorporates a minimum 10-fold safety factor applied to the lowest NOEC

threshold value be util ized. Ap plication of these test methods to wastewaters from an operating

uranium mine has shown that pre-release toxicity testing provides accurate information on the

toxicity of metal-contain ing wastewaters with a high d egree o f confidence. Field validation o f the

labo ratory results was obta ined w hen wastewaters which were field diluted through a release into a

billabong gave similar results to laborato ry-diluted wastewaters. N o o ne species is always the most

sensitive to exposure to complex wastewaters. Changes with time in wastewater chemistry,

toxicity, and in the physiological capacity of specific organisms to survive in a contaminated

env ironm ent (toleranc e), can result in differen t species having varying sensitivities ov er time to

exposure to complex wastewaters collected from the same location. As a result of the remote

likelihood o f finding the 'most sensitive species', it is necessary to te st the tox icity of comp lex

wastewaters to a batter), of organisms, representing differen t trophic levels of the ecosy stem, und er

physical conditions represe ntative of the specific enviro nm ent needing prote ction. U se of a natural

billabong as a 'biological filter ' for releasing mine wastew aters did n ot result in toxicity mitigation

and preve nted controlled dilution from occurring during periods of high creek f low.

Keywords: uranium mining; inland waters; pollution

ntroduction

T h e u r a n i u m m i n i n g a n d o r e - p r o c e s s i n g i n d u s t r y p r o d u c e s c o m p l e x wa s t e wa t e r s i n v o l v -

i n g m a i n l y m i x t u r e s o f m e t a l s , b u t a ls o c o n t a i n i n g p e t r o l e u m p r o d u c t s a n d o r g a n i c

chemica l s used on s i t e (ARRRI , 1987a ,b , 1988 , 1991) . I n the t r op ics , these can inc lude

c h e m i c a l s u s e d i n t h e m a n a g e m e n t o f m i n e - s i te in s e c t a n d n o x i o u s we e d p o p u l a t i o n s

( Ho l d w a y , 1 9 91 ). I n n o r t h e r n Au s t r a l i a , wh e r e t h e R a n g e r Ur a n i u m M i n e is l o c a t e d

(F ig . 1 ), a mo nso on a l c l ima te r esu l t s in the majo r i ty o f annua l r a in f a ll ing be t we en

D e c e m b e r a n d M a r c h ( Au s t r a l i a n s u m m e r ) . T h i s is r e f e r r e d t o a s t h e we t s e a so n , w i t h

t h e r e m a i n d e r o f t h e y e a r b e i n g g e n e r a l l y d r y .

L a r g e q u a n t i t i e s o f wa t e r fa l l o n t o a m i n in g o p e r a t i o n a t th i s t i m e o f y e a r a n d m u s t b e

h a n d l e d e f f ic i e n tl y t o p r e v e n t m i n e c l o s u re . M a n a g e m e n t o f wa t e r i n e x c e ss o f p r o c e s s in g

r e q u i r e m e n t s d u r i ng t h e w e t s e a s o n c a n b e a c c o m p l i sh e d i n o n e o f t w o m a j o r w a y s. O n e

m e t h o d i s t h r o u g h s t o r a g e a n d e v a p o r a t i o n o f wa t e r i n l a r g e r e t e n t i o n p o n d s . A s e c o n d

a n d o f t e n c o m p l e m e n t a r y m e t h o d i s t o p r o v i d e f o r t h e r e l e a s e o f wa t e r i n t o t h e l o c a l

s t r e a m s a n d r i v er s d u r i n g p e r i o d s o f h i gh f lo ws. R i v e r a n d s t r e a m f lo w d u r i n g t h e d r y

0960-3123 © 1992 Chap man Hall


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76 oldway

r . . . . . . . . . . . . . .

32 ° :~4 °

t

°

Fig. 1. Map of the Alligator R ivers region o f the Northern Territory, Australia, with insert

showing its location within the continent.

season is low or nonexistent . Thus, the re lease of any wastewater with high dilut ion is

restr ic ted to high f low per iods in the wet season, per iods which are notor iously unpre-

dic table and of ten of extremely l imited durat ion.

The complex chemical and biochemical interact ions involved when biological organ-

isms are exposed to chemical mixtures of two or three individual metals are not ful ly

unders tood. The s imple chemica l measure ment of every chemica l wi th absolu te ce r-

ta inty is next to imp ossible and extremely exp ensive, s ince mos t analyses require

a priori

knowledg e of the chemica ls to be assayed. As the impac t of complex and varying

wastewate rs on f reshwate r ecosys tems cannot b e predic ted accura te ly f rom s imple

chemica l knowledge of the indiv idua l components of the wastewate rs (which typica l ly

are no t ful ly kno wn w ith regard to e i ther their identi ty or toxicology) , testing the toxici ty

of the mine wastewater on l iving aquatic organisms is an essentia l requirement for the

control of wastew ater impacts. The comb ination o f synergist ic, antagonist ic and addit ive

effects of chemicals on l iving organisms, and the changes in concentra t ions and chem ical

consti tuents with t ime, prevent the accurate predict ion of toxicological effects of com-

plex wastewate rs on aqua t ic organisms (U SE PA , 1980). The toxic ity of Range r U ranium

Min e s R eten tion Po nd N o. 4 (RP4 ) wastew ater discussed in this paper is an excellent

example of a wastewater toxici ty that great ly exceeds the addit ive toxici ty of i ts k nown

chemical com ponents .


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Uranium mining

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In o rder to en sure correct interpretation o f toxicity test results regarding the potential

impact of the release of uraniu m mine wastewaters , knowled ge is required regarding the

ma jor physical, chemic al and biological mod ifying factors of aqu atic toxicity which exist

in the local environm ent. Som e of the mo re impo rtant modifying factors which can be

recognized as affecting the toxicity of min e wastewaters in softwater seasonal intermit-

tent s treams such as those which flow out o f the A rnh em Land escarpm ent (e.g. M agela

Creek) are thus discussed. The application of toxicity testing methods to minimize

deleterious effects of uranium mining in tropical Australia is discussed in detail with

respect to Rang er Ura nium M ine which is located within Kakadu N ational Park, a World

Heritage area of high conservation value.

biotic modifying factors of toxicity

Thre e imp ortan t abiotic factors that affect the toxicity of xenobiotics in tropical Austra-

lian freshwater ecosystems are: continuously high water te mpe ratures (generally 28 °C or

greater); in termitte nt or greatly reduced flows; and unusual water chem istry ( in the case

of Magela C reek, extremely soft , low buffering capacity, low pH water) . O f these three

factors , high water temperature is common to all tropical Australian waters , while

interm ittent f low and water chemistry depe nd o n site-specific circumstances of geology,

climate and hydrology.

Water temperature alters the toxicity of chemicals by affecting their chemistry e.g.

solubility, mo lecu lar kinetics (speciation), rate of volatilization, rate of brea kdo wn , etc.

(Sprague, 1985). T em pera ture can also indirectly affect the toxicity of com pou nds via

effects on the physiology of aquatic organisms (Fry, 1971). High water tem pera ture

affects the bioenerg etics of aquatic organism s by altering the efficiency of digestion , the

basal and active metabolic rates and the activity levels (Fry, 1971; Holdway and

Bea mish , 1984). T he m etabo lic rate of fish can double for every 10 °C rise in tem pe rat ure

(Fry, 1971), so that at hi gher tem per atur es ther e may be significantly less energy

available for detoxificafion and/or active removal o f a substance, modifying the toxic

impact o n th e organism. Consequ ently, survival time during exposure to rapidly lethal

concen trations of toxicants decreases roughly by a factor of two or three for each r ise of

10 °C (MacLeod and P essah 1973; Hod son and S prague, 1975; Sprague, 1985). How ever,

the manner in which temperature modifies overall toxicant impact ( including chronic

toxicity) canno t be p rejud ged , and the l i terature em phasizes unpredictabili ty in this

respect (Lloyd and Herb ert , 1962; Picketing and H ende rson, 1966; Brown, 1968; Cairns

et al. 1975; Hod son and Sprague, 1975; Smith et al. 1978; Kovacs and Le duc , 1982a,b).

The vast majority of th e scientific l i terature deals with toxicant exposures at te mpe ra-

tures in t he 5-25 °C range, making li terature-based toxicity predictions of chemicals at

the high tem pera tures of tropical freshwater ecosystems (generally 28 °C or greater)

unreliable at best.

In th e A lligator Rivers region, the inte rmittent f low of man y of the r ivers and creeks

co mb ine d with the acid sulfate soils on th e floodplain result in the first flush of water

into the per ma nen t f loodplain bil labongs having a low pH and high aluminium conten t

(Noller and Cusbert, 1985). These billabongs act as important refuge areas for a large

portion of the aquatic fauna over the dry season (Bishop

et al.

1986). During the dry

season, mo st of the s tanding-water habitats shrink and beco me mo re saline, du e to large

evaporative losses of water . Consequently, resident populations of aquatic organisms


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Hol dw ay

exper ience inc reased levels of compet i t ion for both space and food resources, decreased

condit ion o f individuals , increased incidence of disease, and increased mo rtal i ty (Bishop

et al. 1986).

Th e influx of low qual i ty acid wate r (which would possibly be tolerated by a heal thy

nonstressed populat ion) into bi l labongs containing already stressed and weakened

populat ions of organisms can have a severe impact . Natural f ish kil ls a t the onset of the

wet season are not uncommon in Austra l ian t ropical freshwater ecosystems. Pulses of

water containing elevated a luminium concentrat ions (especial ly ionic AI) a long with

reduced dissolved oxygen levels have been correla ted with fish ki l ls occurring in the

All igator Rivers region (A RR RI , 1984; Noller and Cusb ert , 1985). This is not unl ike the

spring thaw of winter snow and ice in Nor th Am erica , which resul ts in a pulse of water

conta in ing accumu la ted a tmospher ic pollu tants a t concent rat ions much higher than those

found dur ing the rem ainder of the year (Je ff r ies

et al.

1979; Hulsman

et al.

1983; Dillon

et al.

1984). Th e m ost co mm on m ajor contam inant in post-winter pulses is sulfuric acid,

and the resul ting low pH can cause reproduct ive fa i lure and de ath of aquat ic organisms

both direct ly or indirect ly, through the increased mobil izat ion and toxici ty of metals ,

part icularly a luminium (Driscol l

et al.

1980; Bro wn , 1983; Mills, 1984; Hu tchin son and

Sprague, 1986).

The condit ion of s t ressed aquat ic organisms has important implicat ions for the

labora tory testing of mine wastewaters and subsequent predict ion of safe di lution levels

for re lease into the natural environment , part icularly i f any re lease were to take place

early in the wet season (which is not l ikely under the present regulatory regime).

Popula t ions of labora tory-rea red f i sh a re genera l ly mainta ined under opt imal and

control led condit ions. Measured abi l i t ies of heal thy laboratory-reared organisms to

withstand various levels of effluent exposure m ay thus not necessarily be an indicator of

the abi l i ty of natural populat ions of aquat ic organisms recovering from dry season

stresses ( including exposu re to frs t f lush water) to conten d with similar exposures. The

t iming of any appropria te ly regu lated re lease of mine wastew ater should be such that th e

ecosystem has been flushed with c lean water for a s ignificant period o f t ime prior to any

release being al lowed.

Rain water in the Jabiru area o f the All igator Rivers region is natural ly acidic , with an

averge recorded pH of 4 .3 ( range = 3 .5-5 .2) be tween 1983 and 1986 (A RR RI , 1985,

1987a). This natural ly acid ra in is coupled with a ver y low buffering capaci ty of the cree k

wate r owing to the loca l geochemis try . Conduc t iv i ty of Mage la C reek w ate r in M arch

1989 averag ed 13.0/zS cm -1 (A RR RI , 1991), while the long-term average pH of Magela

Creek water is approximatley 6.0 (range 4.5-6.4). High concentra t ions of dissolved

calcium and magnesium in water s ignificant ly reduce the toxici ty of many substances,

particu larly dissolved metals (Mo unt, 1966; Ho wa rth an d Spragu e, 1978; Sprag ue, 1985).

In th e condit ions prevai l ing in the M agela Cre ek and in oth er s imilar ul tra-soft waters,

the concentra t ion s of such cat ions are so low that l i tt le mit igation of metal toxici ty can

occur. C onseq uently , there is potent ia l for any uncon trol led re lease of mining wastewa-

ters to have a s ignificant toxicological impact o n th e aquat ic environ men t .

Biotic factor s in tropical ustralia

Differences in sensi t ivi t ies between temperate and t ropical species are re la t ively

unknown and unquantif ied. This was of importance when at tempting to re la te aquat ic

toxicological information from other species and countries to the Austra l ian t ropics.


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U r a n i u m m i n i n g

79

M u ch o f t h e av a i l ab l e aq u a t i c t o x ico l o g ica l d a t a r e l a t e t o t em p er a t e s p ec i e s s u ch a s t h e

c o l d w a t e r R a i n b o w T r o u t

O n co r h yn ch u s m yk i s s )

o r w a r m w a t e r F a t h e a d M i n n o w

P i m ep h a l e s p r o m e l a s ,

an d i s o f u n k n o w n r e l ev an c e to A u s t r a l i an t r o p ica l s p ec i es .

P r e l i m i n a r y d a t a ex i s t to s u g g es t t h a t a t l e a s t s o m e s p ec i e s o f t h e i n d i g en o u s A u s t r a l i an

aq u a t i c f au n a a r e s i g n if ican tl y m o r e s en s it iv e t o ce r t a i n p e s t ic i d e s s u ch a s D D T an d

d i e l d r in t h an a r e R a i n b o w T r o u t ( A l l en an d B ac h e r , 1 98 6) i f n o t me t a l s ( B y w a t e r

et al . ,

1991).

S i ze , f eed i n g s t a t u s an d l if e - s tag e can g r ea t l y mo d i f y t h e s en s i ti v it y o f aq u a t i c o r g an -

i sms t o t o x ican t s ( S p r ag u e , 1 98 5; H o l d w ay an d D i x o n , 1 9 8 5 ; H o l d w ay

et al . ,

1987).

La r v a l an d j u v en i l e l i f e s t ag es a r e amo n g t h e mo s t s en s i t i v e t o t o x i can t ex p o s u r e , an d

of t en g ive i n fo rmat ion r ep resen t a t i ve o f fu l l ch ron ic t ox i c i t y t es t s (Wol t e r ing , 1984) .

Th u s , i t is i mp o r t an t t h a t t o x i c i ty t e st s b e p e r f o r m ed o n e m b r y o , la r v a l an d ea r l y j u v en i l e

l i f e - s t ag es o f aq u a t i c o r g an i s ms w h en ev e r f u l l ch r o n i c o r r ep r o d u c t i o n - r e l a t ed t o x i c i t y

t e s t s c an n o t b e r u n .

r o t e c t io n f r o m e r r o r

C o n t r a r y t o m an y co m m o n mi s co n cep t i o n s ab o u t t o x ic i ty t e st s , l ab o r a t o r y - d e r i v ed d a t a

d o n o t a l w ay s e r r o n t h e s i d e o f cau ti o n . Th i s v i ew i s b a s ed o n a w i d e l y h e l d a s s u mp t i o n

t h a t n a t u r a l ch emi ca l an d p h y s i ca l p r o ces s e s w h i ch can n o t b e r ep r o d u ced ea s i l y i n t h e

l ab o r a t o r y t en d t o mi t i g a t e t h e t o x i c i mp a c t o f an e f f l u en t o r w a s t ew a t e r in t h e f i e ld . A s

d i s cu s s ed p r ev i o u s l y , l ab o r a t o r y an i ma l s a r e n o r m a l l y h ea l t h y an d w e l l- f ed , w h i l e w i ld

a n im a l s m a y b e h i g hl y s t re s s e d a n d m a l n o u r is h e d . I n h e r e n t e r r o r c a n t h u s b e i n e i t h e r

d i r ec t i o n an d p r o t ec t i o n f r o m e r r o r mu s t b e max i mi zed , e s p ec i a ll y t y p e I I e r r o r .

Ty p e I I e r r o r i n aq u a t i c t o x i co lo g y i n v o lv es d e t e r m i n i n g th a t a p a r t icu l a r ch em i ca l o r

e f f l u en t is s a f e w h en i n r ea l it y it is h aza r d o u s . Ex p e r i m en t a l e r r o r can b e b o t h s y s t ema t i c

an d s t at is t ic a l i n n a t u r e . P r o t ec t i o n f r o m s y s t ema t i c t y p e I I e r r o r is max i m i zed b y t e s ti n g

a n u m b e r o f d i f f e r en t s pec i e s, b y u s i n g f u ll ch r o n i c an d r ep r o d u c t i v e t e st s an d , p e r h ap s

mo s t i mp o r t an t l y , b y ap p l y i n g a co n s e r v a t i v e s a f e t y f ac t o r t o t h e l o w es t n o - o b s e r v ed -

e f f e c t - c o n c e n t r a t io n ( N O E C ) o r t h r e sh o l d v al u e w h e n d e ri v in g a p r e d i c t e d s a f e c o n c e n -

t r a t i o n .

S a f e t y f ac t o r s a r e r eq u i r ed o w i n g t o t h e p o s si b il it y o f s i g ni fi cant d e l e t e r i o u s e f f ec t s t h a t

w e r e n o t l o o k e d f o r in t h e l a b o r a t o r y , u n k n o w n d i f f e re n c e s b e t w e e n s p e c ie s , t h e

ex i s t en ce o f mo r e s en s i t i v e s p ec i e s i n t h e w i l d t h a t w e r e n o t t e s t ed , t h e r e s t r i c t ed

ex p o s u r e t i mes an d ex p e r i men t a l d u r a t i o n s i n t h e l ab o r a t o r y t e s t s , an d o v e r a l l ex p e r i -

m en t a l e r r o r , b o t h s y s t ema t i c an d s t at is ti c al ( B r o w n , 1 9 8 8; H o l d w a y , 1 9 91 ). S e l ec t i o n o f

t h e s a f e t y f ac t o r d e p en d s o n t h e t y p e o f e f f lu en t b e i n g t e s t ed ( e . g . e x t r em e l y t o x ic ,

m o d e r a t e l y to x i c , h i g h ly li p o p h il ic e t c . ) , b u t s h o u l d n o t n o r m a l l y b e l es s t h an a f ac t o r o f

t en , t o g u a r d ag a i n s t u n k n o w n o r u n d e t ec t ed ad v e r s e e f f ec t s , i n te r s p ec if i c d i f f e r en ces

( b ea r i n g i n m i n d t h e n eed t o ex t r ap o l a t e t o a l l s p ec i e s ) , an d s ta t is ti c al e r r o r . W h er e

t h e r e a r e v e r y l a r g e d i f f e r en ces i n r e s p o n s es b e t w een s p ec i e s t e s t ed , a s a f e t y f ac t o r o f 1 00

shou ld be used (Bro wn , 1988), s i nce it is li ke ly t ha t s imi l a r l a rge d i f f e re nce s wi ll occur

b e t w e e n t h e m o s t s e ns it iv e s p e ci es t e s te d a n d t h e m a n y m o r e u n t e s t e d o r ga n i s m s f o u n d

i n th e n a t u r a l aq u a t i c eco s y s t em . Ex t r em e l y t o x i c s u b s t an ces , e . g . , p e r s i s t en t o r g an i c

co mp o u n d s w i t h h i g h b i o l o g i ca l a c t i v i t y , c an r eq u i r e s a f e t y f ac t o r s ex ceed i n g 1 0 0 0 .

H o w ev e r , an y r e l ea s e s o f t h e s e k i n d s o f p r o b l ema t i c ch emi ca l s s h o u l d b e co n t r o l l ed t o

t h e l o w e s t li m i ts p o s si b le , an d ch em i ca l an a l y s e s may b e m o r e s u i tab l e f o r p r o v id i n g t h e

m o s t a p p r o p r i a t e d a t a f o r r e g u l a t o r y p u r p o se s .


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Holdway

The val idi ty of this ' safe ' concentra t ion can then only be verified as having no

detectable effect on the aquat ic ecosystem by monitoring the aquat ic ecosystem into

which the wastewater is being re leased (Hodson, 1986a; Humphrey

et al.

1990). This

mo nitoring must as a matte r of design include the assessment of impact both within and

outside the mixing zone, an arbi t rari ly defined area outside which the wastew ater wil l be

at or below the defined 'safe ' concentra t ion. Since the quest ion of whether or not an

effect can be observ ed in the fie ld before serious i rreversible damage o ccurs outside th e

mixing zone is un certa in, i t is essential that lab ora tory tests be as rigorous and applicable

as possible . I t was thus desirable to s tudy an assemblage of animals from th e A ll igator

Rivers region represent ing different t rophic levels , and nineteen species of t ropical

freshwater organisms were assessed for sui tabi l i ty as toxici ty test organisms, many of

which hav e be en ut i lized since in s tandardized toxici ty test meth ods (Holdw ay, 1992).

Protect ion from a sta t is t ical type II error is afforded by increasing sample size or

accepting a larger probability of type I err or ( Co hen , 1973, 1977; Fair wea ther , 1991). In

toxicology, type I erro r is mo re tolerable tha n type II error, s ince i t involves error o n the

side of caut ion (Hay es, 1987). T her e is less danger to society from incorrect ly restric t ing

the re lease of a safe wastew ater than fro m wrongly al lowing the re lease of a dange rous

wastewater. Thus, for aquat ic toxicology experiments ut i l iz ing twenty individuals or

fewer per test concen tra t ion (which includes the majori ty of s tand ard toxici ty tests), th e

statistical significance of th e resu lts should be assessed at the p


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Uranium mining

81

xample of uranium mine wastewater toxicity testing results

Ran ger U ranium Mines P ty. L imi ted is loca ted on a leased a rea com ple te ly surrou nded

by Kakad u National Park, and proxim ate to Mag ela Creek. M agela Creek flows into an

extensive area of wetlands which are a s ignificant habi ta t for thousands of birds. The

retent ion ponds of Ranger are designed to re ta in the excess water which fa l ls on the

mine-si te and pi t during the w et season and which are s l ight ly to m od erat e ly contam in-

ated with metals and some organic materia ls .

The dom inant m eta l of concern in these was tewate rs is uranium, but mangan ese and

zinc levels are a lso e leva ted re la t ive to the natural Mag ela waters as are sulfa te levels of

the re te nt ion pond s waters . Du ring y ears of high ra infal l , it is sometimes necessary for

the min e to re lease excess wastew ater contained in these re tent io n ponds into the M agela

Creek to prevent having to s top mining operat ions. To ensure the heal th of the aquat ic

ecosys tems of the Al l iga tor Rivers region and ensure tha t the Mage la Cree k and

f loodpla in a re not a f fec ted by uranium mining, the Commonweal th Government of

Austra l ia establ ished a s ta tutory autho ri ty, the Office of the Supervising Scient is t , as an

envir onm ental protecto r of the region (OSS, 1979).

As part of this role , a s t ra tegy of pre-re lease biological test ing of an y wastewaters with

potential for release from the mine site was adopted (OSS, 1987, 1988, 1989). Toxicity

tes t s were conduc ted for a number of years on the major re tent ion pond wate rs .

Re tent io n Pon d 4 (RP4) rece ives runoff wa te r only f rom the waste rock (overburden )

stockpile , but has consistent ly been foun d to be toxic during the wet season for unkn ow n

reasons (i t has very low metal contaminat ion). Authorizat ion, however, has been given

by the Northern Terr i tory Depar tment of Mines and Energy ( the regula t ing body) for

the d isposa l of Re tent ion Pond 4 (RP4) wate r in to Mage la Creek in recent years ,

irrespective of its tested toxicity.

Th e o rganisms used in the pre-re lease and post-re lease toxici ty tests included several

species of local f ish, water-fleas (Cladocera n), shrimp, freshw ater snai ls , two species of

hy dra (Ph ylum Cn idaria), tadpoles, larval freshw ater mussels , and a species of duck wee d

(Holdw ay, 1992). Test m etho ds were standard ized and test cri teria included mortal i ty,

reproduct ion, behaviour, and physiology, and sought the most sensi t ive response for

each species. Resul ts of tests showed that water from RP4 was qui te toxic to nine

differen t species of aquat ic organisms throug hou t the ent ire 1988-1989 w et season, and

the toxici ty exceeded tha t which would be expec ted f rom the kn own m eta l content of the

wastewate r (Holdway

et aI.

1991). Four bat teries of tests were undertaken before any

wastewater re leases on RP4 water col lected: 12 December, 1988; 16 January, 1989; 7

February , 1989; and 21 February, 1989. Two representat ive sets of these toxici ty test

resul ts for RP4 wate r a re g iven in Tables i and 2. An y NO EC 's of


8/14

82

H o l d w a y

Tab le 1. Toxicity test results for RP 4 wa ter collected Janu ary 16, 1989 given as RP 4 wa ter

(p ~< 0.1). W he n endpoints differed in sensitivity, the m os t sensitive endpoint (underlined)

was used to determ ine the respective L O EC and N O EC values a

Testspecies Test Endpoint LO E C NO EC

time ( ) ( )

d )

Larval Gu dgeon s 14 Mortali ty 0.3


9/14

Uranium mining 83

Table 2, Toxicity test results for RP4 water collected February 21, 1989 given as RP4

water (p 32 32

Mogurnda mogurnda

Juvenile Perchlet t4 Mortality >32 32

Ambassis macleayi Weight

Cladoceran 6 Adult mortality 0.3


10/14

84 oldway

CREEK

WATER SAMP LING SITES

FEB 22 1989

1 UpstreamMagela UM)

Downstream Magela 009)

3 RPI Spillway overflow RPI)

4 Djalkmara/Magela Confluence C)

5 ,Middle Djalkmara M)

6 Mid-Upper Djalkmara MU)

7 Upper Djalkmara U)

IIII

RETENTION

POND 1

DJALKMARA

RP4 OUTFLOW

SWAMP

POND4 RP4) RETENTION

POND 2 RP2)

/

Fig. 2. Map of water sampling sites utilized during wastewater releases from Retention

Pon d 4 on 22 February, 1989. The size of the back-flow billabong, Djalkm ara Billabong,

is only an approximation at one point in time. Size dramatically increases and decreases

depending on Magela C reek flow, with large size during filling high creek flow) and small

size after draining low creek flow), respectively.

onclusion

The problems associa ted with assessing the toxici ty of mining wastewaters in the

Alligator Rivers region of the Northern Terr i tory are discussed in re la t ion to the major

abiotic and biotic factors operat ing in the region. These include high water tem peratu re ,

seasonal in te rmi t ten t f low as a consequence of the w et-d ry monsoo na l c l imate, low pH,

low buffer ing capacity, ul tra-sof t water and re la t ively unk now n biota . The abiotic factors

wo uld general ly increase the toxicity of metal-containing mine wastew aters beyo nd that

which might be predic ted in a tempera te e .g . , Nor th A mer ican) envi ronment . T he

rela t ive sensi t ivi t ies of t ropical aquatic organisms to dif ferent toxicants are general ly

unknown .

Predict ion of the potentia l impact of complex mixed wastewaters on tropical f resh-

wat er bi ota is not possible without actually determining their toxic i ty to sensit ive aquatic

organisms fro m several dif ferent trophic levels . Protect ion o f an aquatic ecosystem is an


11/14

Uranium mining 85

Table 3. Djalkmara Billabong toxicity test results for water collected February 22, 1989, two days

after a water release from Retention Pond Number 4 into the billabong began. When endpoints

differed in sensitivity, the most sensitive endpoint (underlined) was used to determine toxicity to

each test species (p ~< 0.1)a

Test species Tes t Endpoint Toxic Non-

time water toxic

d) water

Cladoceran 5 Adult mortality C,MU,U UM ,0 09

Moinodaphnia macleayi Reproduction M

Juvenile mortality

Green Hydra 6 Tentacle morphology C,M,MU UM,009

Hydra sp. A Population reproduction U

Pink Hydra 6 Tentacle morphology Cb UM,009

Hydra sp. B Population reproduction U M,MU

Duckweed 14 Frond propagation C, UM,009

Lemna aequinoctialis Root growth M,MU,U

Plant dry weight

Frond condition

aWaters tested were upstream Magela (UM: pH 6.36, conductivity24/~S cm- 1), downstreamMagela (009: pH

6.40, conductivity16/zS cm-1), the confluence of Djalkmara billabong and the Magela Creek (C: pH 6.83,

conductivity60 ktS cm-a), middle Djalkmara Billabong (M: pH 7.52, conductivity220/~S era-l), mid-upper

Djalkmara Billabong (MU: pH 7.45, conductivity380 ktS cm-l), and upper DjalkmaraBillabongwater (U: pH

7.52, conductivity520 pS era-l).

u= stimulationof reproduction.

extremely difficult goal to achieve if any policy other than no detectable impact is

pursued. It is thus essential that pre-release testing be undertaken, and nontoxic

dilutions be determined, before any wastewater release into aquatic environments is

permitted. Should a wastewater release be approved as being safe , a biological

monitoring programme must be implemented to ensure that unlooked-for or unobserved

deleterious effects do not occur. Only in this manner can the biological integrity and

health of the receiving aquatic ecosystem (in this case a World Heri tage National Park)

be ensured.

cknowledgements

The pre-release biological testing research discussed in this paper was under taken during

my tenure as a Senior Research Scientist with the Office of the Supervising Scientist. I

am grateful to Ms Helen Allison, Ms Magda Wiecek, and Mr Michael Mannion for their

technical support. I also wish to thank the now retired Deputy-Director of the Institute,

Mr Vince M. Brown, and the Supervising Scientist of the past ten years, Mr Robert M.

Fry, for their advice and support. Constructive criticism resulting in an improved

manuscript was gratefully received from Dr David J.H. Phillips of Acer Consultants

Limited, UK, and Dr A. J. Stewart of the Oak Ridge National Laboratory , USA.


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86 H o l d w a y

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