Study On Contamination Distribution Of Inorganic Arsenic In Rice From China And The Associated Risk Assessment

Arsenic (As) is a toxic element and considered to be one of the most serious pollutants. In additionto the contamination of As in environment background, As pollution has become a global environmentaland food safety issues with the rapid development of industry, especially the unrestrained mining andthe "three wastes" discharge. As can enter the food chain through enrichment in the edible parts of plant,which leads to the accumulation of As in the body and put a threat to human health. As exists in theform of various compounds with different toxicities, of which the highest toxicity is inorganic As,causing possible bladder, lung and skin cancers, skin lesions, cardiovascular disease, neurotoxicity, anddiabetes under long term exposure, and classified as classⅠhuman carcinogen by the InternationalAgency for Research on Cancer (IRNC). Moreover, recently rice and its products have been alsoidentified as one significant dietary source of inorganic As in areas where rice as staple food, becauserice and its kernels are more efficient in As uptaking and accumulation from soil and water than otheragricultural plants. Rice is the staple food for more than60%of Chinese and has been one of the maininorganic As dietary exposure in China. The current researches about As in rice mainly focus on theuptaking and accumulation of different As species in the rice and the preliminary risk assessment,therefore it is necessary to carry out a risk assessment for the inorganic As exposure from rice intakes onthe basis of a large sample size, and an investigation of inorganic As pollution and its distribution frommain rice producing areas in China.Firstly, the high performance liquid chromatography coupled with hydride generation atomicfluorescence spectrometry (HPLC-HG-AFS) method for detection of inorganic As in rice was optimized,in which the effects of particle size, extractants, temperature and extracting methods on the extractionefficiency for arsenic and different mobile phase materials for chromatography column were studied.The optimized conditions of sample pre-treatment and chromatography column were as followed: ricesample was grinded and sieved by0.45mm mesh, then extracted with the methanol/water solution (v:v=50:50) containing0.02mol/L HNO3in a water bath at95℃for60min;5mmol/L malonate or15mmol/L (NH4)2HPO4could be chosen as the liquid phase. The results showed that the extractionefficiency was more than85%, and the recovery were85%-110%with the RSD≤10%, and the LOQof the method was24μg/kg.A total of1653paddy rice samples were obtained from top11producing provinces of China in2012, with sample quotas depending on the rice output proportion of each province. The results wereshowed: The mean levels of inorganic As and total As were90.9μg/kg and116.5μg/kg respectively,about1.15%samples exceeded the maximum contaminant levels (MCL) for inorganic As in polishedrice. Data obtained were used for estimating the potential risks for consumers in China associated withthe dietary exposures to inorganic As using RAMA model, and non-carcinogenic risk assessments weretypically performed to estimate the potential population’s health risks of contaminations using the targethazard quotient (THQ)(there is a chance of non-carcinogenic effect when THQ exceed one). As a result, at the P97.5exposure level, the risks of any age and gender categories in our country were acceptable(THQ <1), suggesting that there were low potential risks.By analyzing the total As, inorganic and organic As levels in the samples, the distribution ofinorganic As in rice from China, and the effects of different rice cultivar groups on As and speciated Asin rice were studied. There were significant differences among the rice inorganic As concentrations fromthe11provinces (P <0.001). The concentrations of inorganic As in rice from Jiangxi, Hunan, Sichuan,Guangxi were more than100μg/kg, and Jiangsu, Anhui, Zhejiang and Heilongjiang had a relativelylower levels. The effects of various rice cultivar groups on grain Asiwere significant (P <0.001), ofwhich the indica and early rice cultivars were apt to accumulate Asiin rice grain rather than thejaponica and intermediate-late rice, however, there was no significant difference between the hybrid andconventional rice in the aspect of indica rice (P>0.05). For the concentrations of speciated As in ricesamples, Asiwas the most dominant As speciation account for78.3%in rice produced from China, andDMA followed as the second dominant one for18.9%, but MMA was only detected in few samples;besides, there was a significant positive correlation between Asiand total As (P <0.001, r=0.81) inrice samples. The order of Asiconcentrations in fractions of rice grain was: rice hull> rice bran> brownrice> polished rice, and the ratios of Asiconcentration in rice hull, rice bran and brown rice to polishedrice were19.66,4.81and1.65, respectively.