Levels Of Heavy Metals In A Zinc And Lead Mining Region Of Southern China

The decline of biodiversity is becoming more and more obvious with the rapid development of industrialization.A lot of research has shown that pollutants are a major driver of biodiversity loss.Heavy metals are important class of pollutants,arising from both local point sources and long distance deposition(in the case of Hg,specifically).China has a large number of heavy metal pollutions problems,and although much is known about levels of heavy metals in China in soil,water,air and human samples,less is known about levels in wildlife.Birds are a good indicator of heavy metal contamination.This study focused on multiple heavy metals(Hg,Cd,Pb,Zn,Cu,Sn,As)in historical lead-zinc and mercury mining areas in Guangxi Province,southern China.We measured concentrations of metals in soil,rice and bird feather samples near four polluted and one control(considered clean)rivers.We hypothesized that a hidden cost of mining for Zn,Pb and Sn would be Hg poisoning,particularly for high-trophic animals in which it would biomagnify.We found concentration levels of Hg varied according to the diet guild of the birds,in the direction of biomagnification,with carnivorous and insectivorous birds having higher concentrations than plant-feeders.Sn and Zn had opposite patterns,with plant-feeders having higher metal concentrations,although not at such a significant level.As to the location and extent of contamination,the largest river had highest levels of Cu and As.A small river near a Hg mine had relatively high Hg levels,and the location near the Hg mine was extremely high.Cd was very high near two lead and zinc mines.Most other metal concentrations were spread over the different sampling points on a river,with no clear-cut difference between sites near point source locations and those farther away.As far as correlations between the different metals across the 14 sites,we found a few significant positive associations between Cd and Pb,Cu and As,Sn and As.However,Hg was not positively correlated with the other metals,and even showed a(non-significant)tendency to be negatively correlated with Cu.This is a fortunate result for biodiversity,as Hg is the heavy metal with the most known adverse effects on wildlife.