| Rice is the dominant crop in China and its quality affects human health directly.Among the factors influencing the rice quality,soil heavy metal contamination has become one of the main sources,which has been accepted more and more concerns.Heavy metals can easily accumulate in the soil and impede the growth of crops due to their non-biodegradability,persistence and high toxicity,which could cause biomagnification effects in human body through the food chain.The spatial variation information and transfer characteristics of heavy metals in soil-rice system plays an important role in protecting the soil environment quality and food safety.Up to date,research related to heavy metal transfer in soil-rice system is lacking.Due to the spatial variation of soil environment,in the practical production area,the impact factors are countless.Therefore,it is necessary to carry out the research related to heavy metal transfer in soil-rice system under practical production area.,which could provide important information for safe rice production and guaranteeing agricultural products safety.In this study,a total of 95 topsoil samples and rice samples,respectively,from Shengzhou rice production area were collected.Based on geostatistics,Moran's I and GIS technique,the spatial variation and spatial relationship of heavy metals in soil-rice system were studied.The main results were summarized as follows:(1)The mean concentrations of total cadmium(Cd),copper(Cu),lead(Pb),Zinc(Zn)and nickle(Ni)were 0.21 mg kg-1,28.65 mg kg-1,27.02 mg kg-1,38.50 mg kg-1,98.75 mg kg-1,respectively.In addition,14%of samples were mildly polluted while 2%were moderately polluted The Cd had the maximum ecological risk parameter.However,the overall potential ecological risk of the study area is low.Local Moran's I results showed that the high-high values patterns of soil Cd,Ni,Cu and Zn were mainly distributed in the northern and central parts of the study area,while the high-value area of Pb was mainly located in the northwest.And the Low-low values patterns were distributed in the southeastern and southwestern areas.The spatial distribution maps of soil Cd,Cu,Ni and Zn showed similar spatial distributions with low values in east and west parts,and high values in central part.Especially for Ni,a large high value area was located in the central part.Industrial activities were main factors for the accumulation of heavy metals in paddy soils in the study area(2)Compared to the national food safety standards,the maximum value of Cd in rice was 0.64 0 mg kg-1,which was 3 times higher than the threshold,indicating that parts of the rice samples had Cd pollution risk.Based on the single factor pollution index(SFPI),the SFPI values of heavy metals were lower than 1,representing that the overall status of rice was safe in the study area.Meanwhile,the child had higher exposure risk to heavy metals than adult,especially for Cd and Cu which were higher than the EPA of U.S.A.limit.The Ni and Zn in rice had strongly spatial correlation.And the Cd and Cu had moderately spatial correlation.The spatial distributions of heavy metals in rice were similar with the heavy metal distribution in soils.It indicated that the concentration of heavy metals in soil affects the accumulation of heavy metals in rice to some extent.(3)The heavy metal enrichment factors in the soil-rice system was generally in the order of Cd>Zn>Cu>Ni,which indicated that Cd has strongest uptake ability so that there was potential risk of Cd contamination in the study area.The spatial distribution patterns of heavy metal enrichment index(EI)indicated that Ni,Zn and Cd in soil-rice system were the most effective in the western part of the study area.Soil properties,soil type,rice variety and other factors can influence the bioavailability of heavy metals to rice.Based on analysis of variance,the enrichment ability of hybrid rice to Cd and Zn was stronger than that of Japonica rice varieties.Principal component analysis showed that soil physical and chemical properties had certain effects on the migration and accumulation of heavy metals in soil-rice system,indicating that the bioavailability of heavy metals were related to soil physical and chemical properties and rice varieties.The linear and logarithmic model could be used to fit the transfer characteristics of heavy metals in soil-rice system.However,the practical paddy field is a complex and variable system,which had obviously spatial variation of soil physico-chemical properties and production models.Therefore,the model revealed in this study should be further improved in the future. |
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