| Exposure assessment is one of the key parts of the risk assessment process in foodsafety,which is especially important to developing countries.Exposure assessmentmodels include such as point estimate and probabilistic assessment,etc.Applicationsof models rely on the assessment data obtained,variability and uncertainty analysis ofassessment parameters.In this study,the dietary exposure assessments for lead andcadmium,as representative heavy metal contaminations,were carried out by the pointestimate and probabilistic assessment models,on the basis of establishing of the Chinafood contamination monitoring database,Chinese food consumption database andexposure assessment models,and the contrastive studies of different models werefinished to obtain the parameters of mean exposure level and high exposure level,andalso to obtain the results of variability and uncertainty of the parameters.Threeresearch programs of lead and cadmium were carried out in details which include inthe analysis of contamination monitoring data of them in food and food consumptiondata,and the dietary exposure assessments for lead and cadmium.Ⅰ.Study on point estimate parameters of lead and cadmium by establishingfood contamination monitoring databaseIn this part,national food contamination data were collected strictly and normatively,and checked up.Uniform food classification and food coding of the data werecoordinated with Chinese food consumption data.As a result,the largest foodcontamination database of lead and cadmium in China was built,including 31883 dataon content of lead and 29580 data on content of cadmium in main foods.Lead and cadmium contamination were explored in 36 groups of foods in China andanalyzed statistically by SAS software to establish a series of parameters for pointestimate.Lead:Average level of lead contamination in preserved egg was the highest (1.782mg/kg),followed by tea (1.762 mg/kg) and dried edible fungus (0.392mg/kg).Average levels of lead in ten groups of foods exceeded 0.1mg/kg,but the contamination in the other 23 groups of foods were lower.It showed that the violatedrate of foodstuff exceeded 7.9%,among them the rice and its product was 11.5%.Except that the violated rate of leaf vegetables,bulb vegetables and berries wereunder 10%,the violated rate of milk and its products,beverages,fruits andvegetables were 11%～23%.The violated rate of preserved egg,meat of poultry andlivestock exceeded 11%,while the violated rate of the rest foods were all under 10%.The result of analyzing for high percentile showed that there were 28 groups offoods whose lead contamination exceeded the national limit,while the rest wereunder the standard.Cadmium:Average levels of cadmium in animal kidney was the highest (2.691mg/kg),followed by bivalve mollusks and dried edible fungus,crustaceans,offal oflivestock and poultry and fresh edible fungus separately with concentration of0.534mg/kg,0.362 mg/kg,0.350 mg/kg,0.213 mg/kg and 0.114 mg/kg.Averagelevels of cadmium in four groups of foods exceeded 0.05 mg/kg,but thecontamination in the other 26 groups of foods were lower.Cadmium contamination inanimal kidney exceeded the national limit standard,and the violated rate of sampleswas 30.49%.The violated rates of the edible fungus,crustaceans,and bivalvemollusks were separately 19.22%,16.07% and 12.1%,and those of the rest foodswere all under 10%.The result of analyzing for high percentile showed that therewere 20 groups of foods whose contamination exceeded the national limit standard,while 9 groups of the rest were under the standard.At present,there are not limitstandards about beverages,confects,spices,tea and milk and its products in China,and it should be paid more attention.Ⅱ.Study on point estimate parameters of food consumption by establishingfood consumption databaseAfter collection and verification of food consumption data from the national survey ofthe nutrition and health status of the Chinese people in 2002,food classification andfood coding for 1390 foods were carried out in accord with national foodcontamination database,and the largest Chinese food consumption database was built,including 1643859 data of food consumption.Analysis for dietary pattern and food consumption of different population from urban and rural areas were carried out by SAS software,and a series of pointestimate parameters of food consumption were established such as mean bodyweights of population,mean values and high percentiles of food group’sconsumptions.The result of analyzing for mean value showed that daily consumptions of cereals,potatoes and vegetables of rural population were higher than urban population,andby contraries,daily consumptions of fruit,meat,aquatic product,eggs,dried beanproduct,and beverage of urban population were higher.For all groups of the Chinesepopulation,the consumptions of cereals,such as rice,flour,as well as potato andpulse was the highest,and followed by vegetables,and then meat egg and milk,fruitand aquatic product,while the consumptions of other foods were very low.The result of analyzing for food consumptions percentiles showed that there wereonly the consumptions of foodstuff in P50 of children from 1-6 year old,and formale population above 18 year old,only a little leaf vegetable and a little meatconsumption was increased,and for other age group population,only a little leafvegetable consumption was increased.In P90,P95,and P97.5,the consumptionvarieties and amounts of foods gradually increased.High percentiles in main foodswere about 2-5 times of mean values,and those in low consumption foods wereprobably over 10 times of mean values.Ⅲ.Point estimate for dietary exposure of lead and cadmiumOn the basis of above two parts of work,dietary intakes of lead and cadmium fromsingle food group and all food groups about 9 age-sex groups in national,urban andrural populations were calculated by the formula of point estimate model.The resultsshowed as following:1.The smaller was the age,the higher was the dietary intake of Pb and Cd.Childrenwere more sensitive and their dietary intakes were very high.The dietary intake ofrural populations was usually higher than that of urban populations,and the dietaryintake of male was usually higher than female.The mean value of dietary intake wasusually 2-3 times higher than median,and the high percentiles of dietary intakeswere very high,which for most of populations greatly exceeded PTWI. 2.The result of analyzing for dietary intakes from mean contamination-meanconsumption combination showed that the dietary intakes of lead of children under10 years old were between 70% and 98% of PTWI,and those of children over 11years old were between 40% and 60% of PTWI.The dietary intakes of cadmium ofchildren under 10 years old greatly exceeded PTWI,those for male over 11-14 yearsold was 101% of PTWI and those of other age-sex populations were between 70%and 90% of PTWI.3.The result of analyzing for contribution of food group to dietary intakes showedthat the dietary intake of lead in staple foodstuff such as rice,flour,as well as potatoand pulse was the highest,which was about 50% of total intake,and those ofvegetable was about 25% of total intake.The dietary intake of lead in meat,egg andmilk was about 12%,and that in fruit and aquatic product was about 6%,and thosein all of other food groups were under 4%;The dietary intake of cadmium infoodstuff was also the highest,which was about 65% of total intake,and that invegetable was about 14% of total intake,and that in meat,egg,milk and aquaticproduct was all under 10%,and those in all of other food groups were under 5%.Ⅳ.Study on probabilistic assessment for dietary exposure of lead andcadmium1.The total database of probabilistic assessment model,including three parts of data,i.e.food consumption data,chemical concentration data and bridge data forconnecting food consurnption data with chemical concentration data was established.2.The distributions of the rnean and percentiles of dietary intakes about lead andcadmium of different age-sex groups in national,urban and rural populations werecalculated by Monte Carlo simulation,and obtained the medians of thosedistributions.The results showed that mean dietary intakes of lead and cadmium ofChinese children were high and unsafe,and moreover,the percentiles of dietaryintakes were higher.To protect most of populations’ safety,the essential measures tocontrol the food contaminated by heavy metals should be carried out as quickly aspossible.Variability of dietary intakes of sensitive children aged 1-10 were quantified by Monte Carlo methods.The basic statistics of the dietary intakes distributions of themean and the percentiles about lead and cadmium of children aged 1-10 showed thatthe medians of those distributions were basically accordant with their mean values,and standard deviation were small.The quartile spaces and the rate of P95:P5suggested that the variability of dietary intakes were also small.These resultsshowed that the variability of dietary intakes was quantified well by Monte Carlomethods,and the mean and the percentiles were stable.The relation of the dietary intakes distributions and PTWI were analyzed for childrenaged 4-6.For lead,the dietary intakes distributions of the mean weren’t normal,whose high percentile exceeded PTWI in urban children,but whose middlepercentile exceeded PTWI in rural children.The dietary intakes distributions of P75exceeded PTWI in urban children at high percentile,but at low percentile exceededPTWI in rural children.For p90,p95 and p99,their whole distributions all exceededPTWI.For cadmium,the dietary intakes distributions of the mean were normal forurban and rural children,which entirely exceeded PTWI.The dietary intakesdistributions of P75,p90 and p95 all exceeded PTWI too.3.The reliable spaces and quartile spaces of the mean and the percentiles of the leaddietary intakes of children aged 1-10 were obtain by Monte Carlo method andBootstrap method,which showed that the mean and the percentiles were stable andtheir distributions were concentrative,which suggested that the variability wasquantified well by Monte Carlo simulation.Simultaneity,the higher was thepercentile,the broader were the reliable spaces of 95%,and the larger was theuncertainty too.The uncertainty of the mean was larger than P50,and the 95%reliable space of the mean for rural children was almost equivalent to that of P97.5,which suggested that the uncertainty of result calculated from the mean might belager.4.Comparing with the results of point estimateThe trend of the dietary intakes from two assessment models was basically accordantfor different group’s populations.The mean values from two models were basicallyaccordant,but the results of point estimate model were a little lower than probabilistic assessment model.The dietary intakes from low percentiles were lower,but that from high percentiles were higher in point estimate model,which indicatedthat the results of probabilistic assessment model were relatively suitable to reality.To protect most of populations’ safety,the results of point estimate might be as initialreference,but the results of probabilistic assessment should be more taken intoaccount when establishing standards and policies.ⅤSummaryIn this study,the systematic analysis on the lead and cadmium contaminationsituations in various groups of foods in China,the dietary intakes of different group’spopulations in China,point estimate model and probabilistic assessment model ofdietary exposure were carried out.On the basis of establishing of the China nationalfood contamination monitoring database,and Chinese food consumption database aswell as exposure assessment models,point estimate and probabilistic assessment fordietary exposure of lead and cadmium in Chinese people were finished.The resultsfrom this study showed the dietary exposures of lead and cadmium in parts ofpopulations in China,especially children,were high and unsafe,to which should bepaid enough attention.The results of the dietary intakes from point estimate andprobabilistic assessment was basically accordant,but the variability and uncertainty ofpoint estimate were larger.Therefore,the results of point estimate might be as initialreference,but the results of probabilistic assessment should be more taken intoaccount when establishing maximum limits and control policies.The results of thisstudy can provide the important science base for comprehensively and accuratelyassessing the health risk of lead and cadmium in Chinese people and putting forwardeffective and precautionary measures. |
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