Review of impact of heavy metals on stream invertebrates with special emphasis on acid conditions

Studies of the accumulation and toxicity of Cd, Zn, Fe, Pb and Cu under acid conditions to stream invertebrates are reviewed. The influence of pH on metal speciation decreases in the following order: Cu > Pb > Cd > Zn. The free metal ion is one of the most toxic species and is generally taken up directly from the water by organisms. The role of food in the uptake of metals depends mainly on feeding habits of the species, body size, life span and duration of the exposure. Surface adsorption can be regarded as a form of metal ‘uptake’ which increases at high pH. Biomagnification of metals along aquatic trophic food chains has not been proved for many metals. Toxicity of Cd, Fe, Zn and Pb increases at low pH, however not for all invertebrates. More knowledge is needed concerning sublethal effects of metals on invertebrates at different pH values and uptake, bioconcentration and biomagnification of metals at different pH values. Future studies should include experiments in artificial streams or in the field instead of short term tests and simple recording of field data.