Experimental factors that may affect toxicity of cadmium to freshwater organisms.

The effects of exposure duration, test organism, and test endpoint on the toxicity of cadmium to a variety of freshwater species were evaluated. Toxicity of cadmium was assessed by monitoring the survival and reproduction of Ceriodaphnia dubia Richard; the survival of Daphnia magna Straus; and the survival and growth of Hyalella azteca Saussure, Chironomus tentans Fabricius, and Pimephales promelas Rafinesque. Organisms were exposed in static systems for 48 h, 96 h, 7 d, 10 d, and 14 d to determine acute and chronic toxicity. Relative sensitivities of test organisms exposed to aqueous cadmium varied with test duration and test endpoint. In general, H. azteca was the most sensitive organism tested, followed in decreasing sensitivity by P. promelas, C. dubia, D. magna, and C. tentans. Mortality of C. dubia and D. magna was consistent up to 7 d, after which little additional mortality occurred. Effects of test duration on cadmium toxicity were most pronounced for H. azteca and C. tentans, with mortality and growth becoming increasingly sensitive with increasing test duration.

Trophic transfer and biomagnification potential of contaminants in aquatic ecosystems.

This review summarizes information obtained from published literature to determine to what degree biomagnification of organic compounds and metals occurs in freshwater and marine food webs. This review was conducted by: (1) examining data from studies conducted in laboratory experiments to establish body burden ratios between trophic levels (trophic transfer coefficients; TTCs); (2) comparing laboratory-derived TTCs with data obtained from field studies; and (3) comparing biomagnification predictions described by published aquatic food-web models with data obtained in this review. It was determined that: (1) the majority of chemicals evaluated (both organic and metals) do not biomagnify in aquatic food webs; (2) for many of the compounds examined, considerable trophic transfer does occur in aquatic food webs; (3) DDT, DDE, PCBs, toxaphene, methyl mercury, total mercury, and arsenic have the potential to biomagnify in aquatic systems; (4) the lipid fraction of receptors directly influences biomagnification of lipophilic compounds; (5) the food web model reviewed provided similar estimates for most of the organic compounds examined (log Kow values between 5 and 7), with model predictions falling within the range of values of all compounds except dieldrin; (6) for many organic compounds, lack of information precludes assessing the relative importance of biomagnification for these contaminants; and (7) even those compounds for which evidence for biomagnification is strongest show considerable variability and uncertainty regarding the magnitude and existence of food-web biomagnification in aquatic systems.