Assessment Of Selenium Bioavailability And Human Health Risk Of Shuang'an Area Of Ziyang

In this study,a systematic investigation selenium in environmental media such as soil food,water,and hair of residents was conducted for the first time in the 30 years after the occurrence of Se poisoning in Ziyang County,Shaanxi Province.The daily Se intake and risk assessment of the local residents were estimated and evaluated.In order to set up a suitable method for evaluate soil Se availability,traditional chemical extraction methods and new DGT technology were conducted and comaaaredin study area.In addition,four gastrointestinal simulation methods were applied in-vitro experiment for both soil samples and food samples to evaluate Se poisoning risk faced by residents of study area.The main results are as follows:1.The distribution of Se in the environment of Shuangan and the health status of local residents were clarified.The Se content in the soil of Shuangan was extremly high and unevenly distributed.About 72%of the soil samples belonged to Se toxic level.The Se content in crops varied significantly and showed a great ability to absorb and accumulate Se,with a geometric mean of 0.76±2.51 mg/kg.The Se content of the soil and crop samples in Nangre Village was significantly higher than that of the Linbenhe Village and Shuanghekou Village.Se levels in streams were highest among water samples with a geometric mean of 12.35±10.46?g/L.The Se content in drinking water?7.85±6.04?g/L?is lower than the WHO and EPA standards.The high Se content in residents'hair and the high daily Se intake indicated that the Se poisoning risk is high for the residents in the Shuangan area of Ziyang County,especially for residents living in the downtown area.2.Compared with the traditional chemical extraction method,it was confirmed that the DGT method can be used as a better indicator of bioavailable Se in natural Se-enriched soil.The ability of the test method to predict the bioavailability of Se was as follows:DGT method>pore water method>PBS>KCl>water>NaHCO3>EDTA>DTPA>NaOH.The Se extracted by the leaching method consisted mainly of Se⁴⁺,Se⁶⁺and Se^2-,except for NaOH(Se⁶⁺was not detected).The Se measured by the DGT was mainly derived from the soluble Se fraction and exchangeable Se,indicating the DGT method can accurately reflect the bioavailable Se pool and potentially bioavailable Se pool.The DGT method has advantages over other measurement methods used in this study.Overall,the DGT method can be considered as the best method for evaluating the bioavailable Se in natural Se areas among the selected methods.3.By selecting the most suitable gastrointestinal simulation method,the health risks faced by local residents were further clarified.For plant samples,the extraction efficiency of the four methods showed PBET>UBM>SBRC>IVG.The extraction efficiency for soil samples was:PBET,IVG was the worst,and the extraction efficiency of UBM was higher than that of SBRC.However,the bioaccessibility of the gastric and intestinal phase of the soil samples was lower than that of the gastric and intestinal stages of the crop samples,and there were significant differences in the bioavailability of the soil and the crops using the SBRC method in the intestinal liquid stage.In addition,the content of Se^2-in gastrointestinal fluid obtained by crops was generally high,while the content of Se⁶⁺was relatively low.It showed that there is a great difference between the research materials of the soil sample and the crop materials,and the use of crop samples can accurately reflect the real absorption level of the human body.However,the soil and crop samples showed that the bioavailability of selenium in the gastric stage was significantly higher than the intestinal liquid stage,and the correlation between the bioaccessibile Se extracted by PBET method and the selenium of the crop was the strongest,so the PBET method could be more effective and conservative for the determination of bioaccessibile Se in the crop and soil samples.Based on the in-vitro experiment results of corn,vegetables and fruits,the daily Se intake of local residents was 402?g/d per day,which was most contributed by cereals.According to the NOAEL?400?g/d?set by the American Medical Association?U.S.Institute of Medicine,IOM?,the risk of Se poisoning for local residents was low,which is contrary to the conclusion of the total food assessment,indicating that the traditional human health risk assessment method will overestimate the actual risks faced by the human body.In summary,according to the Se content in the hair of the residents and the daily average Se intake calculated by the traditional methods,the local residents were facing high risk of Se poisoning.But the real daily average selenium intake calculated via in-vitro experiment showed that the risk of Se poisoning was no longer exist,which reflected the traditional health risk assessment method will overestimate the risk.In addition,the DGT method is a promising technique for the determination of Soil Available Selenium.