Metal speciation in separate stormwater systems

Biochemical processes affecting metal speciation in a roadside gullypot and at storm water outfalls were investigated. Ionic lead and copper species released from road sediments by acid rain are scavenged by dissolved organic material and suspended solids. Cadmium and zinc tend to remain in the dissolved phase. Bacterial activity and acid dissolution produce increases in dissolved metal. Metals in basal gullypot sediments are readily mobilized during storms. The resulting storm water contains dissolved ionic forms of cadmium and zinc, while lead is mostly absorbed into suspended solid surfaces. Copper also binds to solids, although approximately 50% is transported by dissolved organic material. For the separation of directly toxic metal species, anodic stripping voltammetry at polymer coated electrodes is preferred. Lead and copper are present as iron/humic colloids and organic complexes respectively, which are not directly toxic to algae. Cadmium is predominantly ionic and inorganically complexed and therefore directly toxic. It is recommended that the highly toxic lipid soluble metal species should be analysed in storm water. (from authors' abstract)