Heavy Metal Pollution In Farmland Soil And Risk Assessment

With the development of industrialization and urbanization, heavy metal pollution problems in farmland soil caused by transportation, industrial emissions, sewage irrigation are becoming increasingly serious in china. Based on the domestic and foreign published papers about soil heavy metal contents(including mercury, arsenic, cadmium, chromium, lead, copper, zinc and nickel), the present study explored pollution situation and quantified the risks these pollutants pose to human health of heavy metals in farmland soil in China. Totally, 249 studies on heavy metal were collected, covering 31 provinces. Single factor index, Nemero index, geoaccumulation index and potential ecological risk index, human health risk assessment and GIS statistical methods were used to analyze the soil heavy metal pollution throughout the farmland. Furthermore, In order to understand whether the crops produced by the heavy metal accumulated soil have an effect on human health, soil and wheat samples were collected in Jinghui irrigated area, and the content of eight heavy metals in samples was analyzed to assess their geo-spatial distribution in soil. Multivariate statistics(Correlation analysis, principal component analysis and cluster analysis) and geostatistics methods(Arc GIS tools) were used to identify possible pollution sources of heavy metals. Potential human health risks of the HMs in local residents were also determined by evaluating the consumption of wheat flour. The results are shown as follows:1. The average content of soil heavy metals in farmland soil were higher than the background value of the China, except for As. The accumulation of heavy metals were arranged in decreasing order as follows: Cd > Hg > Pb > Cu > Zn> As > Ni >Cr, Which Cd and Hg exceeded the background value of 157.5% and 106.7%, respectively. However, the average content was significantly lower than Chinese standard(HJ/332-2006). The heavy metal accumulation in Southwest China, Yangtze River Delta and Pearl River Delta region are serious and can cause ecological risk. There was no human health risk by soil heavy metal intake inhalation pathway.2. The content of the Hg, As, Cd, Cr, Pb, Cu, Zn and Ni in soil of the Jinghiu irrigared area averaged 0.091, 15.4, 0.25, 74.4, 27.2, 28.1, 81.1 and 36.6 mg·kg-1, respectively. All of them were slightly higher than their natural background values of agricultural surface soil in Shaanxi, but below the threshold values of the National Environment Quality Standard for Soil(GB15618-1995). Geostatistical analysis showed that the nugget-to-sill ratio of Hg, Ni and As ranged from 25% to 75%, indicating the moderate spatial dependence among them. The nugget-to-sill ratio of Zn, Pb, Cd, Cu and Cr were all higher than 75%, indicating weak spatial correlations. Multivariate analyses suggested that soil contamination of Hg, Cd, Pb, Zn, Cu, As, Cr and Ni may be derived from anthropogenic activities, such as agricultural practices, transportation and industrial discharge. Therefore, there was a trend toward increased heavy metal accumulation in soil of Jinghui irrigated area and a comprehensive environmental management strategy should be strengthened.3. The total heavy metal concentrations in wheat flour were 0.0017 mg·kg–1 for Hg, 0.028 mg·kg–1 for As, 0.020 mg·kg–1 for Cd, 0.109 mg·kg–1 for Cr, 0.128 mg·kg–1 for Pb, 2.66 mg·kg–1 for Cu, 24.20 mg·kg–1 for Zn, and 0.20 mg·kg–1 for Ni. All of the mean concentrations were significantly lower than the tolerance limits of Chinese standards; however, 15% of Pb in the wheat flour sample exceeded the Chinese standard(GB2762-2012). This study highlighted human health risks both adults and children consume wheat flour grown in farmland soils. Non-carcinogenic risks caused by HMs were not observed in the area(HI<1) except in children at the Jingyang county, and Cd generated the greatest carcinogenic risk, which poses a potential health risk to consumers. Moreover, the government, as well as other institutions, should implement measures to prevent and control HM contamination in farmland soil and crops so that associated health risks will be mitigated.In conclusion, a large variation of heavy metal content was was observed in different area in China. Pollution mainly appeared in the southwest, Yangtze River Delta and Pearl River Delta region. Currently, thought soil heavy metal ingested by soil has no siginificant impact on human health, it can also enter the body through the food chain. Examples of Jinghui irrigatied area showed that the total carcinogenic risk by wheat comsunption was in the level of 10-4, which was higher than recommended maximum acceptable risk. There is an obvious potential harm to human health.