Distribution Pattern of Dioxins in Sediment Cores from the Xiangxi River, a Tributary of Three Gorges Reservoir, China

Sediment cores were collected from the Xiangxi River, a tributary of the Three Gorges Reservoir, the deposition time in the longest sediment core (90 cm) was measured by radiometry (Cs-137, Pb-210) activities and polychlorinated dibenzo-p-dioxins/furan (PCDD/F) concentrations in different depths of the sediment core were measured. The results indicated that the mean deposition rate was 1.01 cm/a. The total PCDD/F concentrations ranged from 19.28 to 70.07 pg/g d.w. with a mean of 35.06 pg/g d.w. PCDD/Fs in the 1960-1990s were higher than others, which were significantly different in the various layers and cores (p < 0.05). PCDD occupied 63.42-87.33% of PCDD/Fs, and octachlorianted debenzo-p-dioxin (OCDD) was the predominant congener. The ratio of PCDD to PCDF was 2.26-8.08. PCDD/Fs significantly correlated with total organic carbon (TOC) (p < 0.01). The toxic equivalent (TEQ) ranged from 0.15 to 0.98 pg/g d.w. No significant difference was found in TEQ (p > 0.05). It was concluded that the spatio-temporal heterogeneity determined by hydrodynamics and total organic carbon (TOC) was the distribution pattern of PCDD/Fs in the sediment cores of Xiangxi River, the concentrations of PCDD/Fs were low, with a low environmental pollution risk, and by-products of sodium pentachlorophenate might be the main source.

Automated summary

This study collected sediment cores from the Xiangxi River and measured the deposition time and concentrations of PCDD / F using radiometry and chemical analysis. The results showed that the mean deposition rate was 1.01 cm/a. The concentrations of PCDD/Fs varied significantly in different layers and cores, with higher concentrations in the 1960-1990s. PCDD accounted for 63.42-87.33% of PCDD/Fs, and the predominant congener was OCDD. The study concluded that the spatio-temporal heterogeneity and total organic carbon influenced the distribution pattern of PCDD/Fs in the sediment cores. The concentrations of PCDD/Fs were low, indicating a low environmental pollution risk. The main source of contamination may be by-products of sodium pentachlorophenate.