Study On The Migration Of Selenium And Cadmium In Soil-Rice System And The Human Health Risk In A High Geological Background Area

Biogeochemical cycling and health effects of trace elements in high geological background area are one of research focuses in the field of environmental health science presently.This study investigated the accumulation and migrate of selenium?Se?and cadmium?Cd?in soil-rice system in a high geological background area,analyzed the bioaccessibilities of Se and Cd in raw rice,cooked rice and freeze cooked rice,respectively,through in vitro PBET?Physiologically Based Extraction Test?method,and evaluated the risk of human health.The levels of?2-macroglobulin in urine?U?2-MG?,and Se and Cd concentrations in urine and hair were determined through a cross-sectional population survey.Subsequently,the realistic risk of population health in high geological background area was evaluated.The main results of this study were as follows:1.The average soil Se content was 1.42 mg·kg^-1,2.86%of the soil samples were Se excessive and posed high risk of selenosis.The contents of Cd in soil ranged from 0.90 to2.05 mg·kg^-1,which exceeded the risk screening values for soil contamination of agricultural land(0.3 mg·kg^-1).The average Se content in polished rice was below the upper limit of Se-enrich rice.Totally,71.43%of the polished rice were heavily polluted by Cd,and the source of soil Cd was endogenous.Se contents in soil were positively correlated to the contents in rice fractions?p<0.01?.Cd contents in rice fractions were highly related to each other.Cd in the soil was readily to be absorbed by rice root,but only 6%of the Cd in the root was finally transferred to the polished rice.Our results revealed that Se in the soil could not alleviate the accumulation of Cd in the rice,which was different to the results of previous pot experiments.This could be partly due to the differences in the contents and chemical forms of Se and Cd between natural environment and control experiments.2.For the three pretreatments,Se bioaccessibilities were consistently lower at the gastric phase than those at the intestinal phase.Se bioaccessibilities in raw rice were the highest?88%and 92%for gastric phase and intestinal phase,respectively?among three pretreatments.Se bioaccessibility in the digestive tract was positively correlated to Se contents in rice.Cooking tended to reduce the bioaccessibility of Se in rice.In contrast,Cd bioaccessibilities at the intestinal phase were lower than those at the gastric phase,which might be ascribed to the increase of pH value and organic components in intestinal fluid.Cooking reduced Cd bioaccessibility at the gastric phase but increased it at the intestinal phase.It the intestinal phase,the highest Cd bioaccessibility?44%?occurred in cooked rice.3.The Average Daily Dose?ADDba?values of Se from rice for adults and children were 1.21 and 1.57?g·kg^-1bw·d^-1,and those of Cd were 0.68 and 0.88?g·kg^-1bw·d^-1,respectively.The ADDba values of Cd for children were higher than the Provisional Tolerable Daily Intake?PTDI?value(<0.83?g·kg^-1bw·d^-1)specified by the Joint FAO/WHO Expert Committee on Food Additives?JECFA?,but the values for adults were below the standard.The Hazard Quotients?HQba?values of Se and Cd for adults and children were less than 1,indicating that the potential non-carcinogenic health risk was low.4.In the study area,the average concentrations of U?2-MG and U-Cd for male were 1.13 and 3.38 folders higher than those of female,respectively.However,the higher concentration of U-Se averaged at 44.13?g·g^-1 cr was observed in female participants.The percentage of exceedance of U?2-MG for males was 2.86%,while that for females and U-Cd for all the participants were below the standard.The contents of H-Se and H-Cd were consistently higher in females(0.63 mg·kg^-1,0.17 mg·kg^-1)than those in males(0.46 mg·kg^-1,0.13 mg·kg^-1),indicating that females were more likely to enrich Se and Cd than males.However,none of H-Se and H-Cd reached the disease threshold.In the population,U-Cd has a positively correlation?p<0.01?with U?2-MG?r=0.40?and age?r=0.35?,but U-Se?r=-0.39,p<0.01?decreased with age.Se is likely to resist the toxicity induced by Cd through stimulating the antioxidase system.Therefore,dietary Se tends to alleviate the adverse symptoms induced by Cd exposure.However,in contrast to Se,Cd accumulation tended to increase with age,which might increase the health risk.The results indicated that the soil in the study area was seriously polluted by Cd,and71.43%of the polished rice exceeded the limit of Cd in food.Nevertheless,no significant antagonistic effect between soil Se and Cd accumulation in rice was observed.For the three pretreatments,Se and Cd bioaccessibilities were consistently lower and higher at the gastric phase than those at the intestinal phase,respectively.The HQba values of Cd for adults and children were less than 1,suggesting low potential non-carcinogenic health risk for local residents.U-Cd and H-Cd were within the safety threshold,and there was no obvious symptom of renal dysfunction.Females were more likely to enrich Se in the body than males.