Metals and metallothionein in the liver of raccoons: Utility for environmental assessment and monitoring

The relationship between metallothionein levels and concentrations of sever al metals and radionuclides was examined in liver tissues of raccoons (Proc yon lotor, n = 47) from the Department of Energy's Savannah River Site in S outh Carolina to determine the applicability of metallothioneins as an init ial screening device for exposure assessment in free-living mammals and env ironmental monitoring. Using a fluorescent marker and a cell sorter to meas ure metallothionein, a significant positive correlation was found across an imals between levels of metallothioneins and concentrations of selenium (Pe arson's r = .30), mercury (Pearson's r = .31), and copper (Pearson's r = .3 0) in liver tissue. Arsenic, cobalt, silver, thallium, and tin were below d etection limits in most or all liver samples. Other metals, including cadmi um, chromium, radiocesium (Cs-137), copper, lead, manganese, strontium, and vanadium, showed only weak and nonsignificant correlations with metallothi onein. Concentrations of mercury were correlated with concentrations of sel enium (Pearson's r = .73), manganese (Pearson's r = .56), and strontium (Pe arson's r = .57). In an posteriori test, there was a still unexplained posi tive correlation between mercury (Pearson r = .56), selenium (Pearson r = . 54), and radiocesium (Pearson's r = .38) concentrations and background cell ular autofluorescence, and a negative correlation of strontium with the lat ter (Kendall tau = -.38). Background cellular autofluorescence may represen t a generalized cellular stress response, or a yet unidentified biomarker. To better understand which metals contribute to the induction of metallothi onein, principle component analysis (PCA) was performed. The first three pr inciple components explained 78% of the variance, with highest loadings bei ng from mercury and radiocesium. Metallothionein levels did not correlate w ell with the principal components from the metals and radiocesium, while au tofluorescent background levels tended to correlate better.