Assessment Of Cadmium Bioavailability In Rice And Its Health Risk To Humans

Cadmium(Cd)is a ubiquitous environmental pollutant which can be easily transferred from soil to plants and accumulated in rice,wheat,and vegetables.Increasing attention has been paid to food safety due to elevated Cd concentration in dietary staples.However,previous studies have focused on the transfer of Cd from soil to plants and Cd accumulation in food,Cd bioavailability in food is still unknown.Besides,there is a paucity of direct evidence showing the relationship between food consumption and Cd body burden,due to the lack of paired food Cd and urinary Cd data for a cohort.Studies have shown that nutritional status of the individual may affect Cd absorption in the gastrointestinal tract,but there is a lack of information on the influence of dietary minerals on Cd bioavailability in staple foods such as rice.Thus,first morning urine samples and food samples from residents of Cd contaminated areas were collected and analyzed for Cd concentration,an in vivo mouse bioassay was used to determine Cd bioavailability in food samples.Cadmium bioavailability was then incorporated into Cd intake to refine human exposure associated with food consumption,the relationship between food Cd intake and urinary Cd status was also studied.An in vivo mouse bioassay was developed to evaluate the effects of mineral nutrients on Cd bioavailability in rice,which can give implications for developing effective dietary strategies to reduce Cd exposure and its associated health risk in humans.Furthermore,the contribution of dietary and non-dietary pathways to metal exposures was assessed by coupling metal bioavailability with lead(Pb)stable isotope techniques to accurately identify the source of metal exposure as well as their potential health risk assessments.The main findings are as follows:(1)Elevated Cd concentrations were found among local food samples(rice,wheat,and vegetables)from Cd contaminated areas,which was presumably due to soil irrigation with Cd contaminated river water.Cadmium relative bioavailability(RBA)in rice based on a steady state mouse bioassay was 17-57%,a strong positive correlation was observed between Cd-RBA and Cd concentration in rice.Unlike rice,Cd-RBA in wheat was 37-68%.The most variation in Cd-RBA was observed for vegetables(courgette,long bean,loofah,okra,eggplant,radish,potato,pumpkin vines,amaranth,water spinach,taro,pakchoi,and leek),being 18-78%among different vegetables.Applying Cd bioavailability in foods to aggregate Cd intake calculation,rice was the largest contributor(71%),followed by wheat and vegetables(19.9%and 8.41%),with little contribution from non-dietary exposure pathways(0.5%).The study highlighted that rice was the main source of Cd exposure for residents in the local area,incorporating Cd bioavailability to assess dietary Cd intake is a valuable tool to accurately estimate human Cd exposure and associated health risk.(2)Urinary Cd concentration ranged from 0.2 to 5.41 ?g g-1 creatinine in local residents(n=119)from Cd contaminated areas,with an average being 1.20 ?g g-1 creatinine.It showed an increasing trend with age and was higher in females than males(1.17 vs.0.90 ?g g-1 creatinine).Predicted urinary Cd in nonsmokers from rice consumption with or without incorporating Cd-RBA in rice using a toxicokinetic model(TK model)were compared.For 63 participants providing paired urine and rice samples,predicted urinary Cd was 4.14 ?g g-1 creatinine based on total Cd in rice,the predicted urinary Cd at 1.07 ?g g-1 creatinine after incorporating Cd bioavailability was much close to the measured value at 1.20 ?g g-1 creatinine.The result indicated that incorporating Cd bioavailability to assess dietary Cd intake is a valuable tool to accurately estimate human Cd exposure and associated health risk.To extend cohort findings to a national scale,the TK model after incorporating Cd bioavailability in rice was utilized to predict urinary Cd for nonsmokers at a national scale of China to identify the national spatial distribution for Cd exposure.Predicted urinary Cd concentrations at province level showed considerable variation,with populations in southern China having significantly higher urinary Cd than those living in northern China.Significantly higher urinary Cd concentrations were predicted for Hunan province,where locally grown rice was contaminated by mining and smelting activities.(3)To determine the effectiveness of mineral dietary supplements to modulate Cd exposure,an in vivo mouse bioassay was conducted to evaluate the effects of mineral nutrients(Zn,Fe,and Ca)on Cd bioavailability in rice(0.8 mg kg-1 Cd).Without mineral supplements,Cd-RB A was 43%based on a mouse bioassay.Among Zn(NO3)2,Fe(NO3)3 and Ca(NO3)2 supplements,Ca(150-5000 mg kg-1)was the most effective in reducing rice Cd-RBA to 8.5-29%.Followed by Fe(6-200 mg kg-1),which decreased Cd-RBA to 27-47%,while Zn(30-1000 mg kg-1)supplements were ineffective,with Cd-RBA being 32-57%.Compared to Ca(NO3)2 supplements,Cd-RBA determined with CaCl2 supplements were significantly higher(25-67%),suggesting that chloride enhanced Cd bioavailability.The study suggested that adequate nutrition and low-salt diets may be used to alleviate human Cd exposure from rice consumption and the associated health risks.(4)Besides Cd contaminated area,typical mining-impacted areas with arsenic(As),Cd,and Pb co-contamination were selected as the study area.Rice and housedust samples were collected and analyzed for As,Cd,and Pb concentrations,an in vivo mouse assay was conducted for the first time to determine As,Cd,and Pb bioavailability in rice and housedust samples.Results showed that As,Cd,and Pb concentrations in rice were 0.29,0.48,and 0.20 mg kg-1,respectively;As,Cd,and Pb concentrations in housedust were 453,65.4,and 3725 mg kg-1,respectively.Arsenic,Cd,and Pb-RBA in rice were 34,59,and 31%,respectively;As,Cd,and Pb-RBA in housedust were 17,46,and 25%,respectively.Estimated daily intake of As,Cd,and Pb after incorporating of metal bioavailability showed that for both adults and children,rice was the main source for Cd exposure,while housedust was the predominant contributor to Pb exposure.For As exposure,rice intake was the main source for adults,whereas incidental ingestion of housedust was the main source of As exposure for children.Furthermore,stable Pb isotope ratios(207Pb/206Pb and 208Pb/206Pb)of hair(n=27,0.8481 ± 0.0049 and 2.0904±0.0102)were compared to housedust(n=27,0.8485±0.0047 and 2.0885±0.0107)and rice(n=27,0.8369±0.0057 and 2.0521±0.0119),showing an overlap between hair and housedust,but not rice,confirming that incidental housedust ingestion was the main source of Pb exposure.This study coupled bioavailability and stable isotope techniques to accurately identify the source of metal exposure as well as their potential health risk.