| Mercury is a highly toxic heavy metal.Mercury emitted from coal-fired power plants(CFPP)accumulates into the food chain through crops,posing considerable potential health risks.Therefore,it is of great significance to study the distribution and accumulation characteristics of mercury in crops and rhizosphere soils around the CFPP for the native agriculture activities.Crops and rhizosphere soils around the CFPP were sampled to analyse the distribution and bio-accumulation characteristics of mercury in crops and rhizosphere soil.With pots experiment,the addition of nitrogen element,sulfur element and phosphorus element was to explore the mechanism of the distribution and accumulation characteristics of mercury in crops and rhizosphere soils.These samples of crops from native farmland were mainly divided into vegetables and rice.The Vegetables were divided into group A with leaves vegetables and group B with fruit vegetables.And the Rice was divided into group C with elongating stage and group D with ripening stage.Based on this study,the following are several results:(1)The distribution characteristics of mercury in crops and rhizosphere soils.The concentration of total mercury(THg)in rhizosphere soil ranged from 0.03 mg/kg to 1.05 mg/kg,of which 11.90%sample sites were over the risk screening value(0.3 mg/kg)of agricultural land in China,but did not exceed the risk control value(4.0 mg/kg)of agricultural land pollution in China.As for rice rhizosphere soil,the risk value of total mercury content was lower than the risk screening value of agricultural land in China.Methylmercury(MeHg)content in rice rhizosphere soil was higher than that in vegetable rhizosphere soil.Besides,the distribution of MeHg denpends on the environments of crops.The content of MeHg in Group C rhizosphere soil(0.95±0.32 ug/kg)was higher than that in Group D rhizosphere soil(0.85±0.27 ug/kg).Different tissues from all crops species were classified in the order of decreasing accumulation of THg as follows:root>leaf>stem>fruit,and the content of THg in vegetables was higher than that in rice.And roots from 4 groups were lassified in the order of decreasing accumulation of MeHg as follows:C>A>D>B.(2)The characteristics of mercury accumulation in crops and rhizosphere soils Bioaccumulation factor(BF)values of allium tuberosum and capsicum annuum were 0.68 and 0.70,higher than other vegetables.And the BF values of green gralic was 0.30.The BF of Group D was 0.31,higher than Group C.Vegetables and rice have better MeHg accumulation ability,BF of which are greater than 1.Green gralic has the stongest ability to accumulate MeHg,BF value reached 53.81,and the BF values of other vegetables varied from 2.48 to 8.73.Group C can absorb more MeHg than Group D.(3)The mechanism of mercury distribution and accumulation in crops and rhizosphere soil.Total mercury and methylmercury in vegetable rhizosphere were positively correlated with total mercury,methylmercury,organic bound mercury and residual mercury in rhizosphere soil,and negatively correlated with soluble and exchangeable mercury,indicated that the Hg accumulated in crops was closely related to the Hg content in rhizosphere soil.The concentration of methylmercury in vegetable rhizosphere soil was positively correlated with total mercury in soil.The distribution of methylmercury in rice roots was positively correlated with soil methylmercury(P<0.05),negatively correlated with soluble and exchangeable mercury(P<0.05).In addition,the growth of crops also affects the speciation distribution of mercury in soil.With the rice and green garlic growing,the portion of residual mercury was decreased.The pots experiments showed that the addition of nitrogen element could attribute to the THg and MeHg accumulation in green garlic To the contrast,the addition of sulfur element inhibited MeHg accumulated by green garlic,maybe sulfur element decreased the bioavailability of Hg. |
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