Assessing Dioxin Precursors in Pesticide Formulations and Environmental Samples As a Source of Octachlorodibenzo-p-dioxin in Soil and Sediment

Abstract

An as yet unidentified origin of elevated concentrations of polychlorinated dibenzo-p-dioxins (PCDDs) in soil and sediment has repeatedly been described from different locations around the world, including Australia. Natural sources have been hypothesized to account for such contamination, which is characterized by a distinctive dioxin profile, in particular, elevated levels of octachlorodibenzo-p-dioxins (OCDD) as well as relatively low contributions of polychlorinated dibenzofurans (PCDFs). The present study investigated whether OCDD formation via anthropogenically derived precursors represents a possible source in such samples. Soil and sediment from Australia and Hawaii were screened for known pesticide derived dioxin precursors. Two pesticide formulations containing pentachlorophenol (PCP), which are well-known to contain predominantly OCDD impurities, were also analyzed. Polychlorinated phenoxyphenols (PCPPs), common byproducts of pesticide production, were detected at parts-per-billion (ppb) levels in two PCP formulations and in five environmental samples. Of particular interestwasthe presence of the PCPP isomer 3,4,5,6-tetrachloro-2-(2,3,4,5,6-pentachlorophenoxy)phenol (nonaC2PP), often also termed predioxin, in these samples. This compound readily undergoes ring closure to form OCDD under a range of conditions and environments. In addition, the pesticide PCP itself, which also represents a potent precursor to OCDD formation and is known to contain OCDD impurities, was detected in some environmental samples. The evidence from this study indicates that pesticides and their impurities play an important role in the dioxin contamination of Australian soils and sediments, as well as other locations with similar PCDD/F patterns. The results further suggest that formation of OCDD from pesticide derived precursors may be a possible past, present, and future pathway for contamination of environmental samples.

Understanding bioavailability and toxicity of sediment‐associated contaminants by combining passive sampling with in vitro bioassays in an urban river catchment

“…Note, however, that there are some slight variations between relative effect potencies in AhR‐CAFLUX and international toxic equivalency factors that were applied in a previous study. Holt et al found that such high concentrations of dioxin‐like chemicals in soil and sediment were a result of the extensive use of pesticides in agriculture and that pesticides and their impurities play an important role in the dioxin contamination of Australian soil and sediment.…”

Refractory organic pollutants and toxicity in pulp and paper mill wastewaters

“…Dioxins can be formed via degradation of carbon species in the presence of a chlorine source at temperature range 200-600 °C. On the other hand, they can be formed via precursor compounds, such as pentachlorophenol chlorinated diphenylethers and polychlorinated biphenyls or chlorobenzenes which are used as fungicidal and bacterial agent in wood treatment (Weber 2007;Holt et al 2008).…”

Photodegradation of dioxin in contaminated soil in the presence of solvents and nanoscale TiO2particles

“…[30][31][32] Im et al [32] also found OCDD in soil samples from a remote mountainous area and suggested that it was dominantly deposited from the air as that study area was not directly influenced by human activities. Besides, it was reported that pesticides of pentachlorophenol (PCP) and related chlorinated phenoxyphenols (PCPPs) that have previously applied to soil may serve as potential precursors [33] for the OCDD formation in the presence of UV or natural sunlight. [34] This may explain the higher levels of OCDD detected on top soils as compared with those of lower soil layers in our UV-exposure experiments.…”