Toxicity test procedures forHyalella azteca, and chronic toxicity of cadmium and pentachlorophenol toH. azteca, Gammarus fasciatus, andDaphnia magna

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Abstract
Survival, growth, and reproduction ofHyalella azteca were determined under various test conditions. Reproduction by a cohort begins when the amphipods are 5 to 6 weeks old, peaks at 8 to 12 weeks, and then declines due to continuing adult mortality. Full life-cycle tests can be completed in 12 to 14 weeks at 25°C. Reproduction is poor when only artificial plastic substrate is provided. A substrate of cotton gauze results in dramatic improvements in both reproduction and growth. Better reproduction can be obtained by culturing the amphipods in some sediments, but this makes weekly enumeration difficult. Increased mortality during chronic exposure to cadmium was observed at 1 μg/L forH. azteca and 3.2 μg/L forGammarus fasciatus. Reproduction during longer exposure was not reduced at concentrations lower than those causing increased mortality within six weeks. Chronic toxicity of pentachlorophenol was observed at 100 μg/L for both species. Chronic toxicity toDaphnia magna was similar to that of the amphipods for cadmium, but lower for pentachlorophenol. Amphipods are at least as sensitive asDaphnia to a variety of toxicants during chronic exposure.