| Objective:Wanshan is a city in southwest China that has several inactive mercury(Hg)mines.The local population are exposed to methylmercury(Me Hg)due to the consumption of Hg contaminated rice.The relationship between Hg exposure and the cognitive functions of local children is unknown.Methods:244 rice samples(including 235 rice samples from children home and 9 rice samples from school canteens)and 506 hair samples were collected in Wanshan Hg mining area.Intelligence quotient(IQ)test were carried out on 314 children from Wanshan Hg mining area.Direct mercury analyzer(DMA-80)was used to measure the total mercury(THg)concentration in rice and hair samples.Results:The median of THg concentrations in rice samples from children home was 21.6(12.9,34.7)ng/g(with a range of 2.29?234 ng/g),and 54.0%exceeded national limit of 20.0 ng/g.The median of rice THg concentration in school canteen was 8.50(7.68,11.5)ng/g(with a range of 7.53 to 12.0?g/g),which all were lower than 20.0 ng/g.The closer the school was to the mercury slag heap,the higher the average THg in the rice of the pupils.The Hg concentration of rice in the home of children in primary school C was significantly higher than that in the home of children in other two schools(p<0.01),and there was no significant difference between the mercury concentration in the home of children in primary school A and that in the home of children in primary school B(p>0.05).The median of hair Hg concentration in Wanshan children was 1.11(0.79,1.61)?g/g(with a range of 0.12 to 12.6?g/g).58.5%(328/561)exceeded the reference value of1?g/g set by the United States Environment Protection Agency(USEPA).11.2%(63/561)exceeded the reference value of 2.3?g/g suggested by the Joint Expert Committee on Food Additives(JECFA).The mean value of the total IQ scores was91.0±10.2(with a range of 51 to 122)in the children,which is lower than the average intelligence level(100)of Chinese children.The average IQ scores of primary school children in A and C were 90.3±10.6 and 91.7±9.87.The median IQ scores of primary school children in B was 89.0(85.0,96.5).However,there was no statistically significant difference in IQ scores between the three schools(p>0.05).Results of logistic regression analysis showed that children with hair Hg?1?g/g were 1.58 times more likely to have an IQ score<80,which is the clinical cut-off for borderline intellectual disability(R~2=0.20,p=0.03).The regression coefficients between IQ and hair Hg were stable between-0.9?-1.0 in multiple linear regression analysis,but no significant association was found between hair Hg and IQ(p>0.05).The total economic cost of IQ loss due to Hg exposure was estimated to be?424million per year in the Wanshan area.If the hair Hg in Wanshan people reduce 0.1?g/g due to the pollution control and remediation,the economical value was estimated to be?29 million per year in Wanshan area.Conclusion:Mercury mining activities have caused Hg contamination in rice in Wanshan mining area,and the children in Wanshan area are at health risks of Hg exposure. |
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