Sources and fate of dioxins in (sub)tropical environments: a case study from Queensland, Australia

Abstract:

Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are considered priority pollutants for global reduction and elimination. Their key sources, fate and toxic potencies have been researched extensively over the past decades, predominantly in temperate, industrialized Northern Hemisphere regions. With ratification of the Stockholm Convention, numerous other countries with limited or no information on the local sources and fate of PCDD/Fs can draw on this knowledge to establish monitoring and regulation. However, particularly in (sub)tropical regions some environmental and economic conditions differ from those in temperate industrialized countries. These may have the potential to considerably impact on contaminant fate, distribution and risk.

In (sub)tropical coastal Queensland, Australia, elevated concentrations of PCDD/Fs, predominantly octachlorodibenzo-p-dioxin (OCDD), are present in soil and sediment. Some differences have been observed with respect to the sources, distribution and fate of PCDD/Fs in this environment compared to those generally described from more industrialized and temperate regions. For example, a consistent source profile, suggesting the same origin, occurs within an exceptionally large area of Queensland (approximately 300,000 km2). This PCDD/F profile could not be satisfactorily matched with emission sources known from industrialized countries; recent research indicates that this contamination may be associated with impurities (PCDD/Fs and their precursors) in pesticides. In addition, despite the extremely low mobility of PCDD/Fs, elevated concentrations have been found up to several meters deep in Queensland soils and sediments, potentially providing extensive future contaminant reservoirs for erosion associated transport to the marine environment. OCDD has the lowest toxic potency among PCDD/Fs and thus sediment toxic equivalencies (TEQ) in Queensland are relatively low. However, TEQ in Queensland’s near-shore marine biota are comparable to some of the more industrialized regions. These findings from Queensland are considered to arise from a combination of various regional-specific conditions, activities and processes related to chemical production, land-use, as well as climatic factors. This case study highlights the importance of considering such regional factors when evaluating contaminant sources and environmental fate.

Dr. Caroline Gaus presently spends part of her sabbatical at Eawag in the department of Environmental Toxicology. She will be at Eawag until end of December. Please fee free to contact Caroline ( c.gaus@uq.edu.au or Caroline.Gaus@eawag.ch)  for a discussion.