Human exposure to dioxins from food, 1999–2002

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Abstract

In response to aggressive attempts to control dioxin emissions over the last 35 years, human exposures to dioxins from the environment have declined significantly. The primary source of human exposure to dioxins at present is food. The sources of dioxins in food are not well understood and are probably varied. Data on the levels of dioxins measured in various foods for samples collected from 2000 to 2002 have recently been released by the US Food and Drug Administration as part of its Total Diet Study. Data on samples collected in 1999, and released in 2002, are also available. Based on those data and on the US Department of Agriculture’s most recent food consumption survey (1994–1996 & 1998 Continuing Survey of Food Intakes by Individuals), estimates of dioxin intake for the total US population and for three age groups of children were obtained. Results show that the most recent mean dietary exposures for all groups are below 2 pg TEQ/kg BW/day, the tolerable daily intake established for dioxins by the World Health Organization. Between 1999 and 2002 mean dioxin intakes from food appear to have decreased, but when estimates are adjusted based on a standardized limit of detection and evaluating only those {congener × food} combinations common to all 4 years, no trend is apparent. When dioxin concentrations below the limit of detection are represented by one-half the limit, approximately 5% of the intake estimates for 2-year-olds and 1% of the intake estimates for 6-year-olds exceed the tolerable daily intake by about 10%, although such upper-percentile estimates should not be equated with excess risk. When non-detectable dioxin values are set to zero (i.e., when only dioxin values actually measured are used), only 1% of intake estimates exceed the tolerable daily intake for 2-year-olds. As expected, about 50% of daily dietary dioxin intake by the total US population is attributable to meat and dairy products, based on the same food group classifications used by the National Academy of Sciences’ Committee on the Implications of Dioxin in the Food Supply. This information may be useful for targeting future risk management activities.

Introduction

Potential public health risks from environmental exposures to chlorinated dioxins and related compounds continue to be the subject of much research, regulation, and debate. Available data on emissions, environmental and food levels, and human body burdens of dioxins indicate a several-fold reduction in exposures and body burdens since 1970 (Hays and Aylward, 2003), suggesting that efforts to control dioxin emissions and to reduce exposures are succeeding. For example, the US Environmental Protection Agency (EPA) reported that emissions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) from quantified sources decreased from more than 14,000 g TEQ1/year in 1987 to about 3300 g TEQ/year in 1995 and are expected to decline an additional 60% by 2005 (USEPA, 2004). Human body burdens of TCDD in the US decreased 10-fold and dioxin TEQ decreased 4–5-fold between 1972 and 1999, which, due to the long elimination half-lives of dioxins, implies a decrease in exposure of more than 95% (Hays and Aylward, 2003). EPA has estimated that more than 90% of the remaining human exposures to dioxins occur through food consumption, primarily from animal fat (USEPA, 2004). Dioxins are not deliberately added to food or created during food processing. Natural sources of dioxins, such as forest fires, contribute to a background level of dioxin exposure from food (USEPA, 2004), as may unregulated anthropogenic sources such as uncontrolled burning of household waste in barrels (Lemieux et al., 2003).

To help evaluate human exposure to contaminants such as dioxins from food, the US Food and Drug Administration (FDA) conducts an ongoing market basket survey of approximately 280 core foods in the US to determine levels of various pesticide residues, contaminants, and nutrients. Data on dioxin concentrations are available for the years 1999–2002. The foods analyzed represent the major components of the diet of the US population, based on results of food consumption surveys conducted by the US Department of Agriculture (USDA). The USDA surveys provide consumption data on more than 3000 individual foods. Using the USDA survey data, FDA derives summary consumption data for representative foods in the US diet. For example, “apple pie” in FDA’s summary represents all fruit pies and pastries in the USDA survey. FDA most recently updated its consumption summaries in May 2004.

For this study, we combined FDA’s 2004 food consumption summaries with FDA’s dioxin TEQ analyses for the years 1999–2002 to obtain annual estimates of average daily dioxin intakes for the total US population and for three age groups of children: 2 years, 6 years, and 14–16 years. We estimated both mean and upper-percentile intakes and evaluated whether there were trends in average daily dioxin intake over time. We compared the results to the tolerable daily intake (TDI) for dioxins, 2 pg TEQ/kg BW/day (EC, 2001, JECFA, 2001), which is considered the amount of dioxin equivalents that can be ingested over a lifetime without appreciable health risk. Finally, we determined which food groups make the largest contributions to dietary exposure.

Section snippets

Dioxin levels in foods

The Total Diet Study (TDS) is an ongoing market basket survey of approximately 280 core foods in the US food supply to determine levels of various pesticide residues, contaminants, and nutrients in foods. Four market baskets are generally collected each year, one in each of four geographic regions of the US (i.e., West, North Central, South, and Northeast). FDA’s Dioxin Monitoring Program analyzed TDS samples from one market basket each year to determine levels of polychlorinated dibenzo p

Results

Mean dioxin intake estimates during 1999–2002 for the total US population and for each age group evaluated are presented in Fig. 1. As the figure indicates, none of the daily dioxin intakes exceed 2 pg TEQ/kg BW/day, the TDI for dioxins established by the World Health Organization, with the exceptions of those for 2-year-olds in 1999 and 2000 and 6-year-olds in 1999 when non-detects are assumed to equal LOD/2. It is notable that the LODs for 2,3,7,8-TCDD in 1999 and 2000 were about an order of

Discussion

Since risk management actions aimed at reducing dioxin emissions were initiated in the 1970s, substantial decreases in environmental dioxin levels and in body burdens have been observed. Risk management of dioxin emissions was initiated because of concerns about its potential carcinogenicity, but concern remains due to other potential human health effects, such as developmental toxicity. The US EPA has been debating the appropriate exposure limit for dioxins since 1990; no risk estimate or

Acknowledgement

The authors wish to thank Leila Barraj, Lesa Aylward, and Carolyn Scrafford of Exponent® for their useful comments and for performing the calculations used as the basis for this analysis and Linda Abbott and James MacGregor for their helpful review and comments.

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