Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) may be formed during the manufacture of chlorinated pesticides, and can remain in the products as impurities. However, the contemporary release of PCDD/Fs to the environment from pesticide use is poorly understood. For this study, 27 pesticide formulations were analyzed for PCDD/Fs (n = 23 registered for use in Australia). PCDD/F impurities were present in all samples, ranging from 0.020 to 2100 ng SigmaPCDD/F g(-1) active ingredient (AI). Among current use pesticides, pentachloronitrobenzene (PCNB) contained the highest impurity levels (up to 2000 ng SigmaPCDD/F g(-1) AI and 5.6 ng TEQ g(-1) AI). The quantity of pesticide used in Australia and associated release of PCDD/Fs was estimated for PCNB and phenoxy herbicides (2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4-dichlorophenoxybutyric acid (2,4-DB)) using a probabilistic approach. Input parameters to model pesticide use contributed the highest proportions to the variability of the estimated PCDD/F release, and were considered to have the highest uncertainty. Preliminary estimates of PCDD/F release suggest that contaminated pesticides represent an important ongoing PCDD/F source to the Australian environment (10th-90th percentiles for PCNB = 14-42 and 2,4-D/2,4-DB = 0.35-1.6 g TEQ annum(-1)). These results may have global relevance given that many of the pesticides analyzed were imported into Australia, and are used in high volumes in other countries.

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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.