Visualization Of Heavy Metal Health Risk In Farmland Based On Sequential Indicator Simulation

Farmland,the carrier of food and the production activity place of farmers,is one of basic land use.Human is adversely affected by inhalation,ingestion,skin contact with heavy metals in topsoil and ingestion of heavy metals in crops.With the development of social economy in China,heavy metal pollution of farmland has been paid more and more attention by administrators and the public.In order to divide accurately heavy metal health risk area of farmland soil-crop,find the risk source,identify the priority heavy metal,reduce the possibility of excessive environmental management,provide suggestions for controlling the heavy metal pollution of soil-crop from the source,and offer important basis for soil remediation,the following work was carried out.This will contribute to the construction of ecological civilization and the sustainable development of our society.In this study,72 soil samples and 12 rice samples were collected from a town in Chongqing to analyze the concentrations of Cd,As,Pb,Hg and Cr.Based on the health risk assessment model,the sequential indicator simulation(SIS)was used to construct the spatial distribution of heavy metals and human health risk in farmland soil.The Positive matrix factorization model(PMF)was used to analyze the source of heavy metals in soil,and the spatial distribution of health risk under the single source was visualized by ArcGIS.Through field investigation,some local exposure parameters and rice self planting condition were obtained,and the spatial distribution of soil-rice heavy metal health risk was constructed.The main results were as follows:(1)In 72 soil samples,Cd(43.06%)and As(6.94%)exceeded the corresponding risk screening values.The spatial distribution trend of five heavy metals in farmland soil was not the same,among which Cd-Cr,Cd-As and As-Hg showed a moderate positive correlation significantly.Compared with the Ordinary Kriging method(OK),the sequential indicator simulation(SIS)could take full account of the original data and was more suitable for constructing the spatial distribution of heavy metals in soil.(2)In some areas,there was a non-cancer risk for children in farmland soil heavy metal(414.72 hm2 farmland).And the contributions of As in children non-cancer risk was significantly different in space;in the northwest of the areas'farmland soil,non-cancer risk of As for children had the largest contribution,and the probability of children's non-cancer risk(HIAs>1)was high(0.85).(3)There were three sources of heavy metals in regional farmland soil.In the mixed source of agricultural activities and transportation(38.57%),factor load values of Cr,Pb,Cd were 54.4%,51.7%,44.9%;In the industrial emission source(29.33%),factor load values of As,Cd were 81.3%,44.3%;In the natural source(32.10%),factor load values of Hg were 70.4%.Due to the impact of industrial emissions,the non-cancer risk value of children in some areas exceeds 1(86.4 hm~2 farmland).(4)The sample Cd(33.33%),As(25%)and Pb(16.67%)of rice exceeded the standard in the area.Some of the exposure parameters obtained from the survey were different from the recommended parameters in the guidelines.In the farmland soil-rice heavy metal system,health risk of adults and children mainly came from the ingestion of heavy metals in rice,and industrial activities may had a serious impact on the quality of rice in some areas.The biological availability coefficient of heavy metals(Cd,As)in rice was introduced to make the total health risk closer to the reality.The use of sequential indicator simulation combined with positive matrix factorization model could effectively divide the health risk areas of heavy metals and the priority control areas of pollution sources,and realize the management of pollutants and pollution sources at the same time.