Study On Pollution And Risk Of Heavy Metals In Farmland Soil Of Wuwei

The accumulation of heavy metals in the soil to a certain level will cause soil heavy metal pollution.In addition,heavy metals have high toxicity and are difficult to biodegrade,so the soil ecological environment will be seriously threatened.And the harm caused by polluting farmland soil is incalculable.After heavy metals pollute farmland soil,it may cause excessive accumulation of heavy metal concentrations in crops.If such crops are accidentally eaten,the health and safety of humans and other organisms will be infringed.Therefore,heavy metal pollution in farmland soil has become one of the environmental issues that are highly valued by all sectors of society.Wuwei,located in the eastern part of Hexi Corridor,is not only an important town on the ancient Silk Road,but also one of the typical oases in the arid region of Northwest China and an important grain production base in Northwest China.Its agricultural development plays a vital role in promoting the grain industry in Gansu Province.Hence,it is particularly important to understand heavy metal pollution situation of Wuwei farmland soil,identify priority pollution sources that posed ecological and human health risks and evaluate the risks of heavy metals scientifically and rationally.At the same time,it can also provide strong theoretical support for environmental protection managers to formulate detailed pollution control measures,so as to protect ecological health,food safety and human health.In this study,57 sampling sites were set up in Wuwei(Liangzhou district)farmland area and the heavy metal content of each sampling site was analyzed to explore the contamination situation of Wuwei farmland soil.In this study,the geochemical baseline values of Ti,V,Cr,Mn,Ni,Cu,Zn,As and Pb were determined in farmland soil of Wuwei.And the average concentrations of heavy metals were compared with the corresponding baseline values,it was found that human activities had a certain effect on the accumulation of heavy metals in the study area.The pollution assessment index and risk assessment model showed that the pollution degree of Pb was relatively serious in farmland soil of Wuwei,and As generated the highest ecological risk and non-carcinogenic risk.Therefore,the key point of heavy metal pollution prevention and control should be to control the emission of Pb and As in farmland soil of Wuwei.Positive matrix factorization(PMF)model determined the four different pollution sources of heavy metals(coal-related activities source,mixed source of mining and traffic emissions,industrial activity source,agricultural source related to the application of agrochemicals).Then the PMF model was combined with potential ecological risk index(RI)and human health risk assessment(HRA)model to carry out quantitative research on the ecological and human health risks caused by different pollution sources.According to the risk assessment results of pollution sources,it can be found that control of the discharge of heavy metals from coal-related activities can effectively reduce the human health risk.The priority pollution source should be identified as the mixed sources from mining and traffic emissions to protect the health of ecological environment.In general,the pollution degree and risk level of heavy metals were in an acceptable range in farmland soil of Wuwei,and none of the pollution sources posed significant threat to the ecological environment and human health.In order to evaluate the risk degree of heavy metals in Wuwei farmland soil more scientifically and reasonably,and focusing on risk control of heavy metals with high pollution levels.This study used the acute toxicity data of species to construct the species sensitivity distribution(SSD)curve of heavy metals to derive the predicted noeffect concentrations(PNEC)of heavy metals and carry out probabilistic ecological risk assessment.The study showed that the PNEC values of Cr,Ni,Cu,Zn,As and Pb were all lower than the corresponding contamination risk screening values(GB15618-2018),which indicated that the current soil environmental quality standards in China are not effective in protecting species diversity.Therefore,it is particularly important to carry out corresponding ecotoxicology studies of heavy metals.At the same time,the research results can provide a strong theoretical support for the establishment of environmental quality standards for heavy metals to meet the requirements of soil in China.By evaluating the probabilistic ecological risk of heavy metals,it was found that Cr had greater possibility to harm the ecological environment.Traditional risk assessment methods,such as single ecological risk factor,underestimate the harm caused by Cr to the ecological environment in farmland soil of Wuwei,which may be detrimental to the ecological environment protection in the study area.In addition,this study used Monte Carlo simulation to investigate the uncertainty of human health risk of heavy metals.It was found that the carcinogenic risks caused by Cr and As for adults and children had higher probability of exceeding the limit 1E-06,the total carcinogenic risk caused by heavy metals had the probability of more than 99% over 1E-06,while the non-carcinogenic risk was less likely to occur.Based on the sensitivity analysis results of exposure parameters,it was found that slope factor and reference dose had great impact on human health risk assessment results.Therefore,representative exposure parameters should be selected when carrying out health risk assessment,so as to reduce the uncertainty in the risk assessment process and obtain more reasonable and reliable risk assessment results.