Study Of Speciation And Bioaccessibility Of Arsenic And Mercury In Food

Currently,the researches of health risk of heavy metals manily focused on the total concentration.However,only the bioavailable part will do harm to our body.Different chemical species of heavy metal have various toxicity.Thus,research on the bioaccessibility and chemical species is of great importance when we evaluate health risk of heavy metals.In our study,we sampled usual types of food?rice,seaweed,seafood,and fungus?from market in Guangzhou City.Change of arsenic?As?and mercury?Hg?speciation in food during cooking was investigated.We also have done the research of As and Hg bioaccessibility in cooked food through in vitro method?Physiologically Based Extraction Test,PBET?systematically in order to obtain the regularity of the influence of cooking.Then,the change of As and Hg chemical speciation during gastrointestinal digestion combined in vivo test and in vitro test was discussed.Finally,we selected some Cantonese complementary food,which could decease As and Hg bioaccesssibilty.With regard to determination,total As and Hg were obtained by ICP-MS and chemical speciation of the two elements were got by HPLC-ICP-MS.Our research results may have benefit on estimating health risk of contaminants more scientifically and amending our diatery more reasonable.After cooking processes and analysis of bioaccessibility of As and Hg in food,we found that cooking could reduce bioaccessibility of these two elements by about 9-32%and up to 65%,respectively.Combined with our research results,we found that there were two factors that influence bioaccessibility:?1?The releasing of As and Hg from food during cooking.Mass balance calculation results demonstrated that As and Hg would decrease after cooking and the main route of As releasing was through dissolving into cooking water or oil and volatilaztion was the main way which caused Hg lost.?2?Both As and Hg has strong affinity with SH in protein.Heating would degrade protein,which would make the food matrx shrink and lower the degree of protein attached As and Hg dissolving from food during digestion and thus reduce bioaccessibility finally.Results also demonstrated that the speciation of As in food would change during cooking:the transformation of AsB into DMA and the demethylation of DMA or MMA into iAs⁵⁺would occur.While,due to Hg is with high volatility,we still cannot judge Hg speciation would change or not.Through analysis of the speciation of As and Hg in gastrointestinal digestion,we fond that AsB in food would not change during gastrointestinal digestion,while DMA and MMA would demethylate into iAs⁵⁺.And methylation of As would also occur.However,demethylation reaction played a major role.For Hg,in vitro and in vivo gastrointestinal digestion with various chemical forms of Hg also showed that demethylation and methylation of Hg could take place.Methylation mainly occurred in the gastric tract,while methylation mainly occurred in the intestinal digestion.Additionally,we preliminarily discussed the demethylation mechanism,and showed that sodium cholate may determine the demethylation reaction during intestinal digestion,and pancreatin promotes demethylation in neutral or weakly alkaline environment.Further studies on the specific mechanisms of As and Hg demethylation&methylation during gastrointestinal digestion are essential.Speciation change of As and Hg would influence the health risk evaluation,especially As.Results showed that the target cancer risk?TR?values of clams,scallops and oysters were more than 10^-4,which was beyond the acceptable range and with carcinogenic risks.Relatively speaking,it is hard to reduce As bioaccessibility and we only found a reduction percent of 19-59%and 21-43%for rhizoma smilacis glabrae and abrus cantoniensis,respectively.The decreased percent of bioaccessibility of various species of As was as follows:MMA>DMA>iAs>AsB.The reduction of As bioaccessibility was mainly in the gastric digestion phase.For Hg,almost all the sampled co-ingested food?including flos lonicerae,flos chrysanthemi,glycyrrhrizae radix,prunellae spica,herba epimedii,rhizoma smilacis glabrae,vileplume and abrus cantoniensis?could decrease Hg bioaccessibility by 9-80%.The reduction of Hg was mainly in the intestinal digestion.Co-ingested food have stronger lowering effect on MeHg bioaccessibility that that of Hg²⁺.