Dioxins in food: Dietary exposure assessment and risk characterisation

(Findings released 28 May 2004)

Executive summary

'Dioxins' refers to a group of persistent chlorinated chemical compounds that have similar chemical structures and properties, and have similar biological characteristics, including toxicity. Food Standards Australia New Zealand (FSANZ) has conducted an analytical survey of dioxins in a range of food sampled in Australia with the purpose of assessing the level of risk to human health associated with the dietary exposure of the Australian population to dioxins.

The overall conclusion of this report is that, on the basis of the available data, taking into account all the inherent uncertainties and limitations, the public health and safety risk for all Australians from exposure to dioxins from foods is very low.

'Dioxins' includes the polychlorinated dibenzodioxins (PCDDs or dioxins), the closely related polychlorinated dibenzofurans (PCDFs or furans) and polychlorinated biphenyls (dioxin-like PCBs, or PCBs). These compounds can accumulate in the body fat of animals and humans and have a tendency to remain unchanged for prolonged intervals. Long term high levels of exposure to dioxins have the potential to cause a range of toxic effects in animals and humans, including skin lesions, reproductive disorders and cancer. Several hundred of these compounds exist, however, as evaluated by the World Health Organisation (WHO) in 1998, 29 of the compounds (congeners) were considered to have similar 'dioxin-like' toxicity. PCDD/Fs are predominantly generated as unintended by-products of combustion processes and are therefore most usually discharged into the air and then deposited on plant, soil and water surfaces. Environmental PCB contamination has come about through their manufacture for industrial purposes. Dioxins enter the food chain when animals eat contaminated plants. The dioxins are then absorbed into the animal fat, increasing in concentration as they migrate up the food chain. The consumption of animal products with high fat content, such as meat and dairy products, can increase human exposure to dioxins.

FSANZ conducted a survey of both PCDD/Fs and for dioxin-like PCBs in a range of foods representative of the total diet. The food survey analysed composite food samples for each of the 29 PCDD/F and PCBs, for which the WHO developed toxicity equivalency factors (TEFs) to the most toxic dioxin congener TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin). Results are reported for PCDD/F and PCB concentrations and used, with dietary information from the 1995 National Nutrition Survey, in the determination of the dietary exposure. The concentrations of all of the PCDD/F and PCB congeners were summed to give overall dioxin levels. Overall, the concentration of dioxins in the surveyed foods was very low with the highest mean PCDD/F concentrations being found in peanut butter (0.035-0.235 pg TEQ/g fresh weight, lower to upper bound), butter (0.010-0.20 pg TEQ/g fresh weight) and fish fillets (0.08-0.13 pg TEQ/g fresh weight). Highest mean PCB concentrations were found in fish fillets (0.51 pg TEQ/g fresh weight, at the lower and upper bound), although much of this was contributed by a single sample.

The dietary exposure assessment was conducted using FSANZ's dietary modelling computer program, DIAMOND. The results provide information on the mean and 95th percentile dietary exposure to dioxins for various age groups: toddlers aged 2-4 years; children aged 4-15 years; young adults aged 16-29 years; adults aged 30-44 years and 45-59 years; and older adults aged 60 years and above. The results also provide information on lifetime exposure (2 years and above). Separate and combined dietary exposures were determined for PCDD/Fs and PCBs. A dietary exposure assessment was also conducted for infants aged 9 months using a constructed diet based on infant formula.

For all age groups as well as for the lifetime exposure, the mean and 95th percentile monthly dietary exposures were below the Australian tolerable monthly intake for dioxins of 70 pg TEQ/kg body weight (bw)/month. For the population group aged two years and above, representing a lifetime of exposure, mean estimated exposure to dioxins was 3.7-15.6 pg TEQ/kg bw/month (lower to upper bound). Estimated mean 95^th percentile exposures for this group was 16.1-40.6 pg TEQ/kg bw/month (lower to upper bound). Toddlers aged 2-4 years were estimated to have the highest exposure to dioxins (mean 6.2-36.7 and 95^th percentile 12.1-66.2 pg TEQ/kg bw/month, lower to upper bound respectively) due to their higher food consumption relative to body weight. The mean estimated dietary exposure to dioxins calculated for infants aged 9 months was 11.8-60.8 pg TEQ/kg bw/month (lower to upper bound).

The major foods contributing to PCDD/F exposure and to PCB exposure for the general population (2 years and above) were fish (including crustaceans and molluscs) and milk and dairy products. For toddlers and children, the major foods contributing to both PCDD/F and PCB exposure were milk and dairy products.

In characterising the risk associated with dioxin exposure through food, the uncertainties and limitations in many aspects of the data need to be considered, both in relation to the characterisation of the hazard and determination of the tolerable monthly intake, as well as in relation to the survey data and dietary exposure assessment. In particular, it needs to be recognised that potential adverse effects have only been associated with an elevated dioxin body burden following long-term exposure. Taking these factors into account, it is concluded that the public health and safety risk for all Australians from exposure to dioxins from foods is very low.

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SUPPLEMENTARY INFORMATION to the Dioxins in food: Dietary exposure assessment and risk characterisation report containing summaries of analytical data.

Dioxins in Australia: A summary of the findings of studies conducted from 2001 to 2004