Kaolinitic clays as a potential source of dioxins in the Noosa River catchment, Queensland, Australia

Abstract

Environmental context Dioxins have been found along the east coast of Australia in agricultural areas where there is no obvious source of dioxins. These dioxins have an unusual signature that does not match common industrial sources, but it has been suggested that they may be associated with pesticide use. This study found a strong correlation between dioxins with this unique signature and the amount of a kaolinitic clay in the sediments sampled. Abstract The presence, concentrations and profiles of 2,3,7,8-substituted polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) in sediment were investigated in this study with the aim of determining whether dioxin-like compounds were present and, if found, a likely source could be deduced. The sampled catchment lies within an area of high conservation value. Sediments from seven lake sites were sampled as possible sinks for any contamination from historical pesticide use. PCDD/Fs were measured in all the lake sediments. The 2,3,7,8-substituted congener profile was dominated by octachlorodibenzo-p-dioxin (OCDD) with furans at or below the limit of detection, a profile that has been associated with kaolinitic clays from around the world. A strong and significant correlation was found between the total dioxin concentration and the percentage of kaolinitic clay in the sediments. The lack of furans in the 2,3,7,8-substituted PCDD/F profile indicates pesticides or pentachlorophenol (PCP) are unlikely to be the source in the catchment. Further, the concentration of total dioxins and OCDD tended to be higher than those measured outside the study area, even though, overall, the study area is likely to have had less pesticide use than the other intensive agricultural areas previously studied. The results presented in this paper indicate that caution should taken when attributing the presence of dioxins in soil and sediment to anthropogenic sources.