WHO has recommended a Tolerable Daily Intake (TDI) of 1–4 pg/kg body weight per day for TCDD, and the TDI is applied to mixtures of dioxins and PCBs (IOM, 2003). Based on its estimate of cancer potency for DLCs, the US EPA concludes that intakes should not exceed 1–4 pg TEQ/kg/day in the general population (IOM, 2003).
DLC Exposure Limits in Foods With the exception of Canada and the United States, most countries utilize the TDI for assessing adverse health effects from exposure to DLCs and for setting acceptable limits in foods. The TDI represents an index for a contaminant similar to the adequate dietary intake (ADI) used for food additives. These limits are based on the assumption of an experimental threshold dose level below which no toxic effect is found in animal models, and include an additional uncertainty factor for extrapolation to humans.
The FDA and US EPA utilize probabilistic models to derive a Risk Specific Dose (RsD) for a contaminant. This model assumes the lowest dose that could result in a specific risk to humans, i.e., the dose with a lifetime cancer risk of 1 in 1 million. The use of the RfD, as previously described for methylmercury, was not applied to DLCs by the US EPA in its Draft Reassessment; the margins of exposure in the range of 100–1000 are generally considered inadequate to rule out the likelihood of significant effects occurring in humans, based on sensitive animal responses within the TEQ (US EPA, 1994; Foran et al., 2005a). Guidance on the development of risk-based meal consumption limits for 25 high-priority contaminants and analytes has been described by the US EPA (US EPA, 2000b). As described by the US EPA, a cancer slope factor (CSF) for carcinogenic risk can be calculated for DLC exposure of 1 × 10−3/pg TEQ/kg/day (US EPA, 2000c). These risks are described later for analyzing benefits and risks associated with consuming farmed salmon (Foran et al., 2005b).
Exposure to DLCs from Seafood In 2002, the IOM Committee on the Implications of Dioxin in the Food Supply commissioned an exposure estimate for DLCs using intake estimates from the Continuing Survey of Food Intake by Individuals (CSFII) imputed to data from the FDA’s Total Diet Study (Source: http://www.cfsan.fda.gov/~lrd/dioxdata.html). This analysis estimated that for all males and females in the general population, 1 year of age and older, the percentage contribution of fish and fish mixtures to the total DLC exposure from all foods was approximately 8 percent (IOM, 2003). When the data was analyzed for specific subgroups within the general population, the estimated contribution from fish and fish mixtures for pregnant and lactating women and for children (both males and females) aged 1 to 5 years was approximately 4 percent. By comparison, the estimated