Oxidative stress on domestic ducks (Shaoxing duck) chronically exposed in a Mercury-Selenium coexisting mining area in China.

The Wanshan mercury mine is the largest mercury deposit in Guizhou Province, China. Few attempts have been made to study the toxic effects of mercury on biota in this mining area. This study was the first to investigate the oxidative stress on domestic ducks (Shaoxing duck) chronically exposed to mercury in the Wanshan mining area. Chemical analyses revealed higher concentrations of both, mercury and selenium in samples from the Wanshan area. Total mercury and selenium concentrations in duck tissues varied from 0.073 to 4.465 mg/kg and from 1.073 to 6.35 mg/kg, respectively. Analysis of covariance revealed that there were significant effects of zone on accumulation of mercury and selenium in all duck tissues (P<0.01). Moreover, analysis of covariance indicated that mercury content significantly affected the accumulation of selenium in duck muscle, brain, and liver (P<0.01). Mercury and selenium were also highly correlated in Wanshan duck liver, muscle, brain, and lung. The statistical analysis suggested that selenium might be an interactive factor in mercury toxicity. As for the biochemical analyses, it was observed that selenium-dependent glutathione peroxidase and superoxide dismutase activities and glutathione (GSH) content were significantly increased in the livers and brains of Wanshan ducks (P<0.01, 0.05). However, no significant changes were observed in malondialdehyde content (P>0.05). Although the results indicated that adaptive responses of the redox-defense system are associated with the increased enzyme activities and GSH content, the most likely explanation is that selenium plays a critical role. Therefore, the effects of the interaction environmentally occurring selenium and mercury on public health in the Wanshan area should be examined in further studies.