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CHARACTERIZATION OF ARSENOSUGARS AND ASSOCIATED DEGRADATION PRODUCTS FOLLOWING AN AGGRESSIVE ACID/BASE EXTRACTION PROCEDURE
Citation:
Gallagher, P A., B. M. Gamble, A. Heck, C A. Schwegel, AND J T. Creed. CHARACTERIZATION OF ARSENOSUGARS AND ASSOCIATED DEGRADATION PRODUCTS FOLLOWING AN AGGRESSIVE ACID/BASE EXTRACTION PROCEDURE. Presented at International Symposium of Environmental Toxicology of Metals and Metallloids - Environmental Chemistry, Toxicology and Health, South Mole Island, Australia, July 1-5, 2001.
Impact/Purpose:
The goal is to develop an extraction protocol that mimics the human digestive tract and then to use it to assess the bioavailable fraction of arsenic from complex dietary mixtures such as a daily composite -- to move current methods toward a better human physiologically-based exposure estimate method which approximates the "true" bioavailability of arsenic within an environmental or dietary matrix.
Description:
The speciation of arsenic in seafood products is important for the determination of an improved toxicity based relative source (water vs. diet) contribution estimate. The two major sources of arsenic are drinking water and seafood ingestion. Drinking water contains predominately inorganic or toxic arsenic while arsenic exposures from seafood products are thought to be predominantly non-toxic. The daily dose of arsenic from drinking water is generally less than 20ug/day (i.e., 2L/day at 10ng/mL) while from a total metal standpoint, seafood ingestion of arsenic can easily exceed 1000ug/day (i.e., 227[8oz] seafood ingestion at 5ug/g; some fish contain 10-50ug/g). The toxicity from this arsenic dose is considered non-toxic. However, this generalization comes from speciation analyses of seafood products like Atlantic Cod, halibut and English sole. The arsenicals in these types of seafood are easily extracted once the sample has been freeze dried. The subsequent speciation analysis indicates that 99% of the arsenic is AsB. For these seafood products, the current assumption that arsenic in seafood is non-toxic is accurate. But in many types of seafood the extraction efficiencies may be as low as 50%. Thus, the subsequent speciation analysis can then only provide speciation-based information on one-half of the arsenic present. The speciated fraction can contain dimethylarsinic acid [DMA] (a suspected cancer promoter), As(V) (suspected carcinogen) and a variety of arsenosugars (which have been shown to degrade to DMA in the body, a potential conversion to a more toxic spcies). This in combination with the poor extraction efficiency creates considerable uncertainty in estimating the risk from these exposures. In this case, the assumption that arsenicals in these seafood types are non-toxic can produce a misleading risk assessment. Finally, there are seafood products (i.e., kelp, sushi, etc.) which produce extraction efficiencies of less than 50% and half of which is As(V). The saving grace here is that large quantities are not typically ingested, but even a 5g portion can easily exceed a typical exposure from drinking water. Again, the risk assessment with these seafood products should not be lumped together with the Atlantic cod, halibut and English sole analysis due to the fact that the extraction efficiencies are poor and that the species extracted are more toxic.
The objective of this research is to evaluate extraction techniques, which provide near quantitative extraction of the arsenicals from a wide variety of seafood products. Some "aggressive" extraction techniques have already been shown to produce by-products from arsenosugars. These by-products will be characterized chromatographically and identified using electrospray [ESI]-MS/MS. This poster will identify extraction conditions that tend to produce degradation products and describe analytical conditions that can be used to minimize their formation. Structural identfication of these degradation products in standard solutions will also be used to evaluate chromatographic recovery of the arsenicals extracted from seafood matrices.