PHYSICO-CHEMICAL SPECIATION OF ZINC, CADMIUM, LEAD AND COPPER IN URBAN STORMWATER.

Zinc and cadmium exhibit a preference for the dissolved phase whereas lead predominates in the suspended solid phase. Copper is distributed equally between both phases. The exchangeable fraction of the suspended solid phase exhibits unexpectedly high metal levels which may be easily released on contact with receiving waters and thus provide a major source of bioavailable metals. Both UK and Swedish catchments show consistently similar distributions of all four metals between the six experimentally determined fractions. The major differences are the higher lead concentrations found at the UL site and the considerably larger copper concentrations which are distinctive of the Swedish catchment. These higher copper levels accompany a free or weakly complexed copper contribution to the soluble phase which is absent within the UK catchment.