Induction and metal speciation of metallothionein in wood mice (Apodemus sylvaticus) along a metal pollution gradient.

We investigated the binding of Cd, Cu, and Zn to metallothionein (MT) and other metal-binding proteins in free-living wood mice (Apodemus sylvaticus L.) captured in four areas along a metal pollution gradient. We measured total and cytosolic Cd, Cu, and Zn concentrations in mouse liver and kidney by means of inductively coupled plasma-mass spectrometry (ICP-MS). Total (Cu, Cd, Zn)-MT levels were determined in the same tissues by means of the cadmium thiomolybdate saturation assay. Metal speciation of metalloproteins was studied by means of size-exclusion high-performance liquid chromatography-ICP-MS. Liver and kidney of wood mice from the site adjacent to the pollution source showed the highest Cd and Zn concentrations (total and cytosolic) and (Cu, Cd, Zn)-MT levels compared to the other sites farther away from the pollution source. No or only small site differences in tissue Cu concentrations were observed. Almost all the variation (85-95%) in hepatic and renal (Cu, Cd, Zn)-MT levels was explained by the total or cytosolic hepatic Zn and Cd concentration or the renal Cd concentration, respectively. An analysis of the cytosolic metal speciation showed that the Cd-MT, Cu-MT, and Zn-MT fractions in liver and kidney increased significantly with increasing cytosolic metal concentrations. Metals associated with the other cytosolic protein fractions did not increase with increasing exposure. These results illustrate the important role of MT in metal homeostasis and detoxification processes. We conclude that MT is a useful biomarker for environmental metal contamination in free-living wood mice.

Transfer and accumulation of metals in a soil-diet-wood mouse food chain along a metal pollution gradient.

We studied the accumulation and transfer of As, Cd, Cu, Pb and Zn in the compartments of a soil-diet-wood mouse (Apodemus sylvaticus) food chain at five sites located along a metal pollution gradient. We observed a clear gradient in metal exposure at increasing distance from the smelter in all compartments of the food chain for the non-essential metals. The gradient was less clear or absent for the essential metals in acorn and mice target tissues. Regression analysis showed overall strong relationships within the soil-diet and diet-wood mouse compartments for the non-essential metals, while relationships for the essential metals were weak or absent. Total metal in soil appeared as a better predictor for the diet metal content than the available metal fraction. Our results suggest a more important transfer of non-essential elements through the food chain than essential elements, which is probably a consequence of homeostatic control of the latter group.

Metal blood levels and hematological characteristics in wood mice (Apodemus sylvaticus L.) along a metal pollution gradient.

The present study evaluated whether blood could be used as a nondestructive tool for monitoring metal exposure and related hematological effects in wood mice (Apodemus sylvaticus L.) living along a metal pollution gradient. Soil concentrations of arsenic, cadmium, copper, lead, silver, and zinc decreased with distance from the emission source. Blood levels of cadmium and lead differed significantly among sites, whereas those of the other metals did not. Blood levels of cadmium and lead correlated with soil concentrations of cadmium and lead, respectively. No such significant relationships were found for the other measured metals. Hematocrit levels decreased in wood mice from the most polluted site (45.96% +/- 0.53% [mean +/- standard error]) compared to the reference site (48.04% +/- 0.47%). A negative correlation between hematocrit and blood levels of cadmium and lead was found. Erythrocyte count, leukocyte count, hemoglobin concentration, mean corpuscular hemoglobin (average wt of hemoglobin in a red blood cell in pg), and lysozyme activity did not differ among study sites. Mean corpuscular volume (average volume of a red blood cell in microm3) and mean corpuscular hemoglobin concentration (average proportion of hemoglobin in a red blood cell as a %) differed among study sites but showed no relationship with metal exposure. We conclude that whole blood from mice can be used for nondestructive monitoring of the exposure to nonessential metals under natural conditions. The present results indicate that decreased hematocrit levels may be an early warning signal for a negative impact of metal exposure on the oxygen-transport capacity of blood in wood mice in their natural environment.