Sources and deposition fluxes of PCDD/Fs in a high-mountain lake in central Taiwan

Abstract

Sun Moon Lake (SML) is located at 23°52'N, 120°55'E near the center of Taiwan Island. In 2009, deposition of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/F) in ambient air, water bodies and sediments were measured in SML in this study. The monthly atmospheric PCDD/F deposition ranged from 0.61 to 3.0 pg I-TEQm(-2)d(-1) in the vicinity area of SML. Average PCDD/F concentrations (0.008-0.012 pg I-TEQ L(-1)) in the surface water were uniform and sufficiently mixed at the center, outflow and south bay of SML. However, the PCDD/F content (2.42±0.5 ng I-TEQ kg(-1) d.w.) of surface sediments measured at the south bay of SML was significantly higher than the PCDD/F content at other sampling sites. To evaluate the anthropogenic pollution history in central Taiwan, PCDD/F concentrations were also analyzed at 1-2 cm intervals in three dated sediment cores collected at different locations of SML. The year dating by the sediment cores at different depths was estimated from the sedimentation rate (0.47±0.13-1.35±0.22 cm y(-1)) calculated by (210)Pb and (137)Cs analysis. Based on the results of isotope analysis of sediment cores collected from the center, outflow and south bay of SML, PCDD/F concentrations at different locations appeared to be quite similar. PCDD/F concentrations in sediment cores began to increase in 1964 and reached a peak (4.78 ng I-TEQ kg(-1) d.w.) in 1968. In addition, variation in PCDD/F content at different depth of the sediment cores appeared to correlate directly with the rate of organochlorine pesticides production in Taiwan.