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While it is increasingly being recognized that biotic ligand models (BLMs) are valuable in the risk assessment of metals in aquatic systems, the development of chronic BLMs has been less advanced for lead than for other metals. The authors investigated the univariate effects of Ca and pH on the chronic reproductive toxicity of Pb to Ceriodaphnia dubia at 4 levels. Calcium influenced chronic Pb toxicity to C. dubia only to a relatively small extent, whereas a high pH (8.2) provided strong protection against Pb toxicity (compared with lower pH levels). Based on this data set, a chronic Pb BLM for C. dubia was developed. The effect of pH was modeled as a single biotic ligand site competition by H(+) with a log stability constant for binding of H(+) to the biotic ligand (K(HBL)) of 7.6, while no other competitive constants were needed. The developed BLM was shown, in an independent validation with 3 other data sets, to be capable of predicting chronic Pb toxicity to different clones of C. dubia by an error of less than a factor of 2 in most synthetic and natural waters considered. The results add to the growing evidence that BLM-based risk assessment or water-quality criteria for Pb are likely to be more appropriate relative to hardness-based assessments or criteria.

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1989. Lethality of low pH and Al to early life sta inhabiting PieCambrian Shield waters in Ontario. Can. 8. Fish. Aqslat. Sei. 46: 1 Lethality of low pH and A[ to egg and fry stages of common shiner (Notropis csrwutus), white sucker (Catostornus cornrnersoni), wal leye (Stizsstediosa vitseum), lake whitefish (Coregonus ~Bupeafmrnis), small mouth bass (Micropterm dobrnie~i), and largemouth bass (M. salmoides) was determined in a series of laboratory tests in soft (Ca water. Low pH was lethal to cleavage eggs in the first 4 d of exposure, to eye eggs in the immediate iod and to fry following their transition to branchial respiration. ly life stage response ts Al was determined by their sensitivity to low pH. Al prolonged survival of cleavage at pH = 4.2, was detrimental to eyed eggs and fry at pH 4.4-5.4 and was most lethal within 8.3 pH units of the pH which was lethal in the absence of AI. In situ distribution of four sf the six species was adequately explained by lethality sf Bow pH abne to cleavage eggs or fry. Sensitivity to low pH and Al produced estimates of pH >5.9 (common shiner), pH >5.4 (lake whitefish, white sucker, walleye), and pH B5.9 (smallmouth and [argemoutk bass) for survival of early life stages in acidified waters. Ow a mesur6 experimentalement la mortalit6 de l'oeuf et de l'alevisp du m$ne 2 nageoires rouges (Notrspis eomutus), du meslnier noir (Catosesrnus cornersmi), du dor6 (Stizostedion vitseurn), du coregone de lac (Coregonus clupadosmis) et des achigans (Micrcyterus BTol smEeuE et M. salrnoides) %I ['acidite et 3 Al en eau douce (4'0 mg de CdL). Lfacidit6 ktait mortelle aux oeufs en clivage durant les 4 premiers jours, aux oeufs oeilles durant la periode pr6cedant irnmediatement l'&losion et aux alevins apr&s le passage 3 la respiration branchiale. La reaction 2 l'aluminium etait conditionn6e par la sensibilite 3 Ifacidit& L'AI a prolong6 la survie des oeufs en clivage 3 pH<4,2, rnais il a nui aux oeufs oeil$s et aux a h i n s pH 4'4-5,4 et atteint sa l&alite maximale %I moins de 0'3 unit& pH de Ifacidit$ morklle en Ifabsence dfAI. La distribution En-situ ( 4: quatre des six esp$ces s'explique assez bien par la I6talit6 de Ifacidit& seule aux sehafs en clivage et aux alevins. A partir de nos r4suttatsf on estime que les stades jeunes du men6 peuvent suwivre en milieu aeide A pH>5,9, ceux du csr6gonef du meunier et du dore, 3 pH>5,4 et cehax des achigans, 2 pH>5,4 . (1982) demonstrate a dominant role of Al in oversaturated solu-'Present address: B. A.R. Environmental9 Nicholas Bmck Road, R.R. #3, Guelgh, Owt. NIH %u&or to whom cr>nespowdence should be addressed.Al toxicity are not so straight forw A1 toxicity to fish is limited ters and Vanderborght 1987 such as cyprinids may show di action. In addition, species mQ early development rates v or episodic exposure differ description of losses of indi be based on laboratory estimates of survival of a single life stage. blem confounding prediction is relating field suromelate fish presence to pH, with controlled laboratory studies demonstratin...