Comparative Selenium Toxicity to Laboratory-Reared and Field-Collected Hyalella azteca (Amphipoda, Hyalellidae)

Selenium (Se) contamination of aquatic habitats is a global environmental issue. Although organic forms of Se are thought to represent the most bioavailable forms of Se, elevated concentrations of inorganic Se can cause toxicity in aquatic organisms such as benthic invertebrates. To assess the potential role of Se in mortalities observed during previous in situ invertebrate exposures, laboratory experiments on toxicity of inorganic Se (selenate) to Hyalella azteca were performed. Both a laboratory-reared and a field-collected H. azteca population were exposed to Se concentrations ranging from near 0 (control) to 21.79?mg/L, and survival of exposed individuals was monitored over 10?days. In the laboratory-reared H. azteca, significant changes in mortality pattern and reductions in mean survival time (MST) were noted in the test groups exposed to ??0.164?mg/L Se. In the field-collected animals however, significant changes in mortality pattern and reductions in MST were measured in H. azteca exposed to ??1.43?mg/L Se. The 10-day LC50s were 0.086 and 0.574?mg Se/L for the laboratory and field-collected H. azteca populations, respectively. The laboratory-reared group thus was about one order of magnitude more sensitive to Se exposure than the field-collected amphipods. Our results suggest that Se toxicity was likely not a major contributor to amphipod mortalities observed in earlier field studies. Furthermore, population-specific tolerances of the test organisms may need to be considered when extrapolating laboratory-generated data to field situations.