Toxicity and bioaccumulation of arsenic and chromium in epigean and hypogean freshwater macroinvertebrates.

Lethal toxicity levels of two inorganic water pollutants, chromium (Cr6+) and arsenic (As3+), were determined toward six freshwater macroinvertebrate species collected from a single field site. Crustaceans were represented by two amphipod species, an epigean one (Gammarus fossarum) and a hypogean one (Niphargus rhenorhodanensis), and by an isopod species (Asellus aquaticus). There were two insect larvae, Heptagenia sulphurea (Ephemeroptera) and Hydropsiche pellucidula (Trichoptera) and a snail, Physa fontinalis. Median lethal concentrations (LC50s) were determined over 96-h and 240-h periods for chromium and over a 240-h period for arsenic. Arsenic bioaccumulation was studied, too. The macroinvertebrates tested showed a wide range of sensitivity and bioaccumulation. A comparison between 96-h and 240-h experiments demonstrated that there was an increase in toxicity values following a longer time exposure for chromium. Also chromium was more toxic toward crustaceans than arsenic; conversely, arsenic was more toxic for the insect larvae and snail tested here. The lethal concentrations determined for the two metals were discussed and compared to results from other toxicity studies. The use of such macroinvertebrates, collected in the field and tested for longer exposure periods than within the standardized 96-h tests, should provide more suitable results for monitoring the general environmental quality of freshwater systems.