Historical trends of dioxin-like compounds and heavy metals in sediments buried in a reservoir in central Taiwan.

Polychlorinated dibenzo-p-dioxin (PCDD), polychlorinated dibenzofuran (PCDF), polychlorinated biphenyl (PCB) and heavy metal concentrations were analyzed at 1-2 cm intervals in a sediment core collected from a reservoir to evaluate anthropogenic pollution history in central Taiwan. The age of the sediment core was estimated from the sedimentation rate (0.44-0.52 cm year(-1), calculated by (210)Pb and (137)Cs analysis). The highest PCDD/F (4.10 ng TEQ(WHO)kg(-1)d.w.) and PCB (0.345ngTEQ(WHO)kg(-1)d.w.) concentrations occurred around 1985 (i.e. at a downcore depth of 10-12 cm). Our results also demonstrated that PCDD/F and PCB concentrations in the reservoir sediment core started to decrease at a depth of 8-10 cm (estimated year: 1989). This may be attributed to the fact that the Taiwan Environmental Protection Administration (EPA) proposed the regulation of pentachlorophenol (PCP) production and PCB manufacture in 1983 and 1988, respectively. In addition, a linear increasing trend in metal content with time (towards the core top) was observed for several metals (Zn, Cr, Cu, Cd and Pb). Results of the enrichments rates of anthropogenic metals indicated that the metal/alumina (M/Al) ratios of Zn, Cd and Pb in sediment cores exceeded those in crust compositions by 47%, 59% and 78%, respectively. The results revealed that considerable amounts of heavy metals were carried into the reservoir following significant immigration during the Chinese civil war (1950).