Runoff rates and ecotoxicity of zinc induced by atmospheric corrosion.

Initiated by regulatory restrictions on the use of zinc for various building and construction applications, together with a lack of knowledge related to the release of zinc induced by atmospheric corrosion, a major interdisciplinary research project was implemented to generate data to be used in future risk assessment. Runoff rates from a large number of commercially available zinc-based materials have been determined on panels inclined 45 degrees from the horizon, facing south, during a 1-year atmospheric exposure in an urban environment in Sweden. Possible environmental effects of runoff water immediately after leaving the surface of the various materials have been evaluated during two different sampling periods of varying season and zinc concentration, using the standard growth inhibition test with algae. Raphidocelis subcapitata (formerly Selenastrum capricornutum). Zinc-specific biosensors with the bacterial strain of Alcaligenes eutrophus, and computer modeling using the water-ligand model MINTEQA2 and the humic aquatic model WHAM, have been used to assess the bioavailability and chemical speciation of zinc in the runoff water. An excellent consistency between the different methods was observed. The results show considerably lower runoff rates of zinc (0.07-3.5 g m(-2) year(-1)) than previously being used for regulatory restrictions, and the concentration of zinc to be predominantly responsible for the observed toxicity of the runoff water towards the green algae. The majority of the released zinc quantity was found to be present as free hydrated zinc ions and, hence, bioavailable. The data do not consider changes in bioavailability and chemical speciation or dilution effects during entry into the environment, and should therefore only be used as an initial assessment of the potential environmental effect of zinc runoff from building applications. This interdisciplinary approach has the potential for studies on the environmental fate of zinc in soil or aquatic systems.

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