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SPECIES SPECIFIC DIETARY ARSENIC EXPOSURE ASSESSMENT: THE NEED TO ESTIMATE BIOACCESSIBILITY AND ASSESSING THE IMPLIED PRESYSTEMIC METABOLISM IMPLICATIONS
Citation:
CREED, JOHN T., T. PINYAYEV, M. Mantha, P. A. CREED, J. Trent, E. A. Yeary, C. A. SCHWEGEL, J. XUE, M. J. KOHAN, K. HERBIN-DAVIS, D. J. THOMAS, K. Kubachka, T. Hanley, N. Shockey, D. Heitkemper, AND J. Caruso. SPECIES SPECIFIC DIETARY ARSENIC EXPOSURE ASSESSMENT: THE NEED TO ESTIMATE BIOACCESSIBILITY AND ASSESSING THE IMPLIED PRESYSTEMIC METABOLISM IMPLICATIONS. Presented at 57th International Conference on Analytical Sciences and Spectroscopy and the 3rd Canada-China Analytical Chemistry Conference, Toronto, ON, CANADA, August 28 - 31, 2011.
Impact/Purpose:
The chemical form specific toxicity of arsenic dictates the need for species specific quantification in order to accurately assess the risk from an exposure. The literature has begun to produce preliminary species specific databases for certain dietary sources, but a quantitative risk assessment requires that these estimates be limited to the physiologically relevant component of the exposure. This remains a shortcoming for most speciation based data sets. Another shortcoming, at least from a risk assessment / modeling perspective, is that the sampling protocol needs to be representative of the harvest demographics and reflect the associated consumption habits of the population. In order to address the physiological relevance, a synthetic gastrointestinal extraction has been coupled with speciation analysis to provide species specific bioaccessibility estimates. To facilitate broader population based exposure estimates, the samples are collected based on USDA harvest demographics and import estimates. The result is a distribution of bioaccessible inorganic arsenic concentrations associated with a dietary source which can be combined with dietary survey data within a probabilistic model to predict population based exposures. The application of this approach to carrots and rice will be discussed with an emphasis on the remaining sources of uncertainty associated with the model estimates. A second component of this presentation will discuss the potential need to incorporate the presystemic biotransformation of ingested arsenicals in order to differentiate between ingested arsenicals and those available for uptake in the intestine. To estimate the extent of these conversions, arsenic oxides were incubated in the presence of the microflora from the cecum of a mouse. The biotransformation observed in standard solutions was extended to dietary commodities by incubating the synthetic gastrointestinal extracts from the commodity within the same cecum assay. These results will be discussed in the context that estimating the ingested arsenicals may not provide the correct metabolic precursor for the species specific systemic exposure.
Description:
The chemical form specific toxicity of arsenic dictates the need for species specific quantification in order to accurately assess the risk from an exposure. The literature has begun to produce preliminary species specific databases for certain dietary sources, but a quantitative risk assessment requires that these estimates be limited to the physiologically relevant component of the exposure. This remains a shortcoming for most speciation based data sets. Another shortcoming, at least from a risk assessment / modeling perspective, is that the sampling protocol needs to be representative of the harvest demographics and reflect the associated consumption habits of the population. In order to address the physiological relevance, a synthetic gastrointestinal extraction has been coupled with speciation analysis to provide species specific bioaccessibility estimates. To facilitate broader population based exposure estimates, the samples are collected based on USDA harvest demographics and import estimates. The result is a distribution of bioaccessible inorganic arsenic concentrations associated with a dietary source which can be combined with dietary survey data within a probabilistic model to predict population based exposures. The application of this approach to carrots and rice will be discussed with an emphasis on the remaining sources of uncertainty associated with the model estimates. A second component of this presentation will discuss the potential need to incorporate the presystemic biotransformation of ingested arsenicals in order to differentiate between ingested arsenicals and those available for uptake in the intestine. To estimate the extent of these conversions, arsenic oxides were incubated in the presence of the microflora from the cecum of a mouse. The biotransformation observed in standard solutions was extended to dietary commodities by incubating the synthetic gastrointestinal extracts from the commodity within the same cecum assay. These results will be discussed in the context that estimating the ingested arsenicals may not provide the correct metabolic precursor for the species specific systemic exposure.