Factors influencing variability and potential uptake routes of heavy metals in black kites exposed to emissions from a solid-waste incinerator.

Exposure to heavy metals from emissions of the solid-waste incinerator (SWI) of Madrid (Spain) was assessed by determining the relationships between the distance from black kite (Milvus migrans) nests to the SWI and metal concentrations in nestling blood and failed eggs. Lead levels increased as the distance to the SWI decreased, while no significant relationship was found for the remaining elements. Analysis of frequency distributions showed that Pb was normally distributed, suggesting a generalized exposure to this contaminant. Variability in metal levels within and between nests indicated a differential nest exposure to contaminant metals with sibling chicks showing similar metal levels. Correlations between essential and contaminant metals suggested detoxifying mechanisms mediated by essential metals. The contribution of metal residues in blood coming from deposition in eggs was minimal compared with residues coming from posthatch exposure. Exposure to particulate volatile Pb in the form of dust from fly ash emitted to the air by the SWI is suggested to be the main route of uptake via inhalation, while both dietary and respiratory routes may contribute to Cd uptake. The increasing human population living close to the SWI may be increasingly at risk from exposure to air-borne contaminants depending on the emission standards from the SWI.