Histopathology related to cadmium and lead bioaccumulation in chronically exposed wood mice, Apodemus sylvaticus, around a former smelter.

The ceasing of industrial activities often reduces the emission of pollutants but also often leaves disturbed areas without remediation and with persistent pollutants that can still be transferred along the food chain. This study examines the potential relationships between non-essential trace metals and histopathology in target tissues of wood mice (Apodemus sylvaticus) collected along a gradient of contamination around the former smelter, Metaleurop Nord (northern France). Cadmium and lead concentrations were measured, and histological alterations attributable to chronic trace metal exposure were assessed in the liver and the kidneys of 78 individuals. Metal concentrations quantified in the present study were among the highest observed for this species. Some histological alterations significantly increased with Cd or Pb concentrations in the soil and in the organs. Sixteen mice from polluted sites were considered at risk for metal-induced stress because their Cd and/or Pb tissue concentrations exceeded the LOAELs for single exposure to these elements. These mice also exhibited a higher severity of histological alterations in their organs than individuals with lower metal burdens. These results indicate that the Metaleurop smelter, despite its closure in 2003, still represents a threat to the local ecosystem because of the high levels and high bioavailability of Cd and Pb in the soil. However, among the mice not considered at risk for metal-induced stress based on the metal levels in their tissues, a large percentage of individuals still exhibited histological alterations. Thus, the present study suggests that the evaluation of toxic effects based only on the LOAELs for single metal exposure may result in the underestimation of the real risks when specimens are exposed to multiple stressors.