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

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-TEQ m−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 210Pb and 137Cs 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.

► PCDD/F concentrations in surface water were sufficiently mixed in SML.
► PCDD/F contents in sediments changed significantly at different locations of SML.
► PCDD/F concentration at sediment core increased in two major phases (1960s and 1980s).
► Accumulation rate of PCDD/Fs in sediments of SML was higher to atmospheric deposition.
► Major source of PCDD/Fs in SML after 1960 was from pesticide residue of PCP and CNP.