Cadmium :: freshwaters ecosystems

Key concerns

The toxicity of cadmium to aquatic organisms is variable, and it depends on both the species and environmental factors such as water hardness, salinity, temperature, pH, organic matter content and the presence of other metal ions, especially calcium and zinc (WHO 1992). Toxicity to aquatic organisms generally increases with increasing temperature and decreasing salinity and hardness. Early life stages of organisms, especially embr yonic and larval stages, are more sensitive to the effects of cadmium than the adult stage.

Cadmium has been shown to be toxic to duckweed Lemna minor and the floating fern Salvinia natans at 0.05 mg/l. Toxicity was evident by reduced growth and chlorosis. Plant death was reported at 0.5 mg/l (Hutchinson and Czyrska 1975). Similar phytotoxicity was reported in water hyacinth (Eichhornia crassipes), with reduced biomass and chlorophyll a content following exposure to 0.4 mg/l (Nir et al. 1990). The toxicity of cadmium to freshwater invertebrates has been classified as ranging from moderately toxic to highly toxic, with acute LC50 values ranging from 0.02 to 520 mg/l (WHO 1992). Acute LC50 values for fish ranged from 0.001 to 72 mg/l (WHO 1992). Cadmium has also been shown to affect reproduction, with NOELs of 0.6 and 1.7 to 3.4 µg/l reported for daphnia (Daphnia magna) and brook trout (Salvelinus fontinalis), respectively (Eaton et al. 1978; Kuhn et al. 1989).