Technical Report No. 5
J Müller, R Muller, K Goudkamp, M Shaw, M Mortimer, D Haynes, D Burniston, R Symons and M Moore,
Department of the Environment and Heritage, May 2004
ISBN 0 642 54997 4
This study was a component of the National Dioxins Program that was tasked to quantify and assess the concentrations and relative chemical compositions of dioxin-like chemicals in Australian soils.
The project involved the systematic collection of several thousand soil cores by more than 50 individual sampling personnel using a standard sampling protocol. Samples were collected from 86 locations representative of airsheds and catchments based on the National Pollution Inventory. For the purposes of the study, the continent, including Tasmania, was divided into three geographic areas (Northern, South-Eastern, and South-Western), and soil samples were taken from locations in each geographic area that were representative of different land-uses (agricultural, urban, industrial, and remote). Further subdivisions were made of agricultural land-uses according to the predominant form of agriculture practice (grazing, cotton, vegetables, sugarcane, forestry, cereals). In addition, an archive of historical soil samples collected from a single location near Adelaide was assessed for evidence of changes in background levels of dioxin-like chemicals since the 1920s.
Chemical analysis of soil samples was primarily conducted by the Australian Government Analytical Laboratories, and a series of quality assurance/quality control checks were incorporated into the study including replicate sampling, replicate analysis and an interlaboratory comparison of analytical results using an overseas laboratory highly regarded for its experience in the analysis of dioxin-like chemicals in environmental samples. These checks showed high reproducibility in chemical analysis, and that the identification of individual dioxin-like chemicals and quantification of their concentrations in soil samples was reliable. However, the reproducibility of results from replicate sampling in the more highly contaminated locations was more variable, indicating the likelihood of historical or current point source contamination at or near some of the sites concerned.
Data was assessed both in terms of actual concentrations of dioxin-like chemicals as well as toxic equivalents. In addition, the patterns of component chemicals were evaluated, and assessments of contamination patterns were made in respect to geographic location and land-use differences.
Dioxin-like chemicals were found in most of the 116 Australian soils sampled, with middle bound concentrations ranging from the limit of detection 0.05 pg TEQ g-1 dm to 23 pg TEQ g-1 dm. Median concentrations of dioxin-like chemicals expressed as toxic equivalents in soils across all land-use types in the Northern and South-Eastern study regions were similar, but the median concentration in the South-Western study region was less. The greatest concentrations of dioxin-like chemicals were found in soils collected near centres of population within the South-East coastal area of Australia, whereas concentrations were consistently low in soils collected from locations in Western Australia and inland areas across all regions.
Data from the study showed that levels of dioxin-like chemicals in soils from urban and industrial locations were substantially higher relative to agricultural land-use and remote locations. This pattern was consistent regardless of whether levels were expressed as toxic equivalents or as concentrations. Across agricultural land-uses, concentrations of dioxin-like chemicals in soils were similar, with the exception of sugarcane growing, in which the concentration was substantially greater than other agricultural land-uses. However, other evidence suggests that contamination of sugarcane soils is not likely to be related to sugarcane cultivation since contamination extends throughout the coastal environment of Queensland. The formation process or specific source of the elevated levels of dioxins in these coastal soils remains unknown although natural formation processes may be involved.
Homologue and congener profiles for the PCDD/PCDF were strongly dominated by OCDD. Similarly, the tetra-heptachlorinated 2,3,7,8-chlorine substituted profiles are dominated by the highest chlorinated PCDD, 1,2,3,4,6,7,8-heptachloro dibenzodioxin. The source or formation processes by which dominance of higher chlorinated congeners could occur remains unresolved despite intensive studies by others. With regards to the TEQs, on average, more than 80% of the toxic equivalency across soil samples was attributed to 2,3,7,8-PCDD/PCDF.
Although there is no Australian guideline threshold for dioxin-like chemicals in soils, comparison of concentrations of dioxin-like chemicals in the NDP soil samples against a categorisation derived from German thresholds showed that only 15% of the Australian samples (all but one of which were from urban or industrial locations) exceeded the German derived target value of -1 dm.
The concentrations of dioxin-like chemicals in urban and industrial locations sampled as part of the NDP were similar to those reported in previous Australian studies and in the New Zealand Organochlorines Program. On the basis of toxic equivalents, concentrations of dioxin-like chemicals in Australian soils are on average much lower than those reported from many industrial locations internationally. On a global basis, they can be considered among the lowest background concentrations reported in soil from any industrialised nation.
Lower bound oncentrations of dioxin-like chemicals for the archived samples ranged from 0.54 to 3.8 pg TEQ g-1 dm. Interestingly, the oldest sample, collected in 1925, contained detectable concentrations of PCDD/PCDF as well as PCB. Also, the concentrations in the 1925 sample are greater than in the samples from the 1930s and 1940s. It is not clear how selective contamination of the oldest sample could have occurred and whether it is an artifact related to sampling or storage of the sample.