Tracing anthropogenic imprints on polybrominated and polychlorinated dibenzo-p-dioxin/furans in soil: A comprehensive field study in an urban agglomeration of China

Abstract

Polybrominated and polychlorinated dibenzo-p-dioxin/furans (PBDD/Fs and PCDD/Fs) are primarily generated through anthropogenic thermal and chemical processes involving bromine and chlorine, respectively. However, the differential impacts of these anthropogenic activities on their environmental occurrences remain incompletely characterized yet. We conducted a comprehensive field soil study in the Pearl River Delta (PRD), a representative urban agglomeration in South China, to investigate the occurrence, sources, and risks of PBDD/Fs and PCDD/Fs. Compared to PCDD/Fs, PBDD/Fs in the PRD soils demonstrated comparable ubiquity and enrichment potential in organic-rich soils, but exhibited distinct compositions, inverse spatial distributions, and concentrations one to three orders of magnitude lower. PBDD/Fs in these samples were predominantly derived from bromine-involved industries (particularly those related to polybrominated diphenyl ether (PBDE)), thermal-related activities, and vehicular emissions. Consequently, they showed higher levels in highly industrialized/urbanized regions of the PRD and displayed positive correlations with local industrial/urban-related socioeconomic parameters, including gross domestic product (GDP), industrial output, population density, and volumes of vehicles, wastewater, waste gas, and waste incineration. In contrast, PCDD/Fs in these samples were primarily contributed by local agricultural activities (particularly the historical use of pentachlorophenol (PCP)/PCP-Na), thereby exhibiting significant positive correlations with local grain acreage, grain yield, and consumptions of pesticides and agricultural films. The contributions from biomass/waste open-burning and metalworking-related industries were three times lower. Unlike organic carbon content, the particle size of the PRD soils demonstrated insignificant influences on the distributions of PBDD/Fs and PCDD/Fs. PCDD/Fs and PBDD/Fs collectively exhibited notable carcinogenic risks in ≥50 % of the PRD soils and unacceptable non-carcinogenic risks in approximately one-quarter of the PRD soils. Most of these high-risk samples were collected from sites located in rural agricultural regions of the PRD, warranting continuous attention.

Keywords: Carcinogenic risks; Kriging algorithm; Persistent organic pollutants (POPs); Polybrominated dibenzo-p-dioxin/furans (PBDD/Fs); Polychlorinated dibenzo-p-dioxin/furans (PCDD/Fs); Positive matrix factorization (PMF).