Heavy Metals Accumulation And Pollution Assessment Of Greenhouse Soils

Due to the high multiple cropping index,continuous cropping of long-term crops,long-term input of large amounts of fertilizer and its special environment,the greenhouse soil has caused a series of soil problems such as soil secondary salinization,soil acidification,continuous cropping obstacles,soil fertility decline and heavy metal accumulation.Among them,the accumulation of heavy metals in the greenhouse soil can cause soil pollution,affect the structure and function of the biomes in the soil;produce different degrees of toxic effects on the crops,affecting their quality and yield;and can also enter human body through the food chain by the enrichment of edible crops.These heavy metals can accumulate in the human body and cause harm to human health.Therefore,the accumulation and pollution of heavy metals in the greenhouse soil have attracted a lot of attention.The pollution assessment and risk assessment were carried out by single factor pollution index method,Nemero comprehensive pollution index method and potential ecological risk index method.Combined with the basic conditions of vegetable greenhouses at each sampling point,the pollution status of heavy metals in greenhouse soil under conventional production mode was analyzed.At the same time,based on the long-term located fertilization test of tomato greenhouse in Shenyang Agricultural University(built in 2009),this paper also studied the accumulation of heavy metals(Cd,Cr,Cu,Ni,Pb,Zn)in the greenhouse soil under different treatments with different combinations of chicken manure(M),straw(R),K2SO4(K),lime(Ca)and compound fertilizer while improving the soil quality.The effects of different fertilization methods on the heavy metal content of the greenhouse soil were analyzed,and the pollution assessment and risk assessment were carried out.In order to explain the heavy metal pollution status greenhouse soil in some regions of Liaoning Province from the perspective of the effect of fertilization on the accumulation of heavy metals in soil.The results showed as follow:(1)Among the soil samples from various regions of Liaoning Province,Cr,Ni and Pb did not exceed the standard pollution,while Cd,Cu and Zn had different degrees of pollution.Among them,the pollution situation of Cd was the most serious,and the pollution rate exceeding the standard was 59.02%.The Cd pollution status of Jinzhou was the most serious among these regions.The over-standard contamination rate of Cu was 41.0%,and the maximum single factor index value was 5.77.The Zn over-standard pollution rate was 24.6%,and its maximum single factor index value was 2.87.According to the comprehensive pollution situation,44.26% of the soil samples were safe and alert,and 47.54% of the soil samples were slightly polluted.Some soil samples were moderately polluted and heavily polluted.Among them,Jinzhou's comprehensive pollution situation was the most serious,and Shenyang was the slightest.(2)The single factor potential ecological risks of Cr,Cu,Ni,Pb and Zn in the soil samples of various regions in Liaoning Province were all low ecological hazards,while the ecological hazard of Cd was relatively high.Among them,the ecological hazard of Cd in Jinzhou soil was the strongest.From the perspective of the overall ecological risk of the soil,83.61% of the soil samples were low ecological hazards,and 16.39% of the soil samples were moderate ecological hazards.Among them,Jinzhou soil samples had the strongest ecological risk and were moderate ecological hazards.The other regions were all minor ecological hazards.(3)In this study,the treatment of different combinations of chicken manure,straw,K2SO4,quicklime and compound fertilizer could lead to different accumulation of heavy metals in the greenhouse soil,but Cr,Cu,Pb,Ni and Zn did not exceed the risk control standard for soil contamination of agricultural land t,Cd exceeded the standard value under all treatments except CK.The content and accumulation rate of Cd,Cr and Zn in soil were the highest under MRKCa treatment(the treatment of chicken manure,straw,K2SO4,lime and compound fertilizer were applied together).Cu,Ni and Pb have the highest content and accumulation rate in soil under MR treatment.According to the current accumulation rate of each heavy metal element,the content of each element in the soil would increase to varying degrees after 10 a and 20 a.Among them,the situation of Cd exceeding the standard would be more serious,and the soil Zn content under MRKCa treatment would also exceed the standard after 20 years.(4)From the results of single factor pollution index evaluation,under different long-term fertilization treatments,the soil was not polluted by Cr,Cu,Pb,Ni,Zn,and the ecological risk of these elements were small.Cd had different degrees of pollution except CK,all of which had low ecological hazards,among which MRKCa was the most polluted.From the perspective of comprehensive soil pollution,only the soil under the CK treatment had not been contaminated by heavy metals.Under other treatments,they were at alert level and the soils were still clean,all of which were low ecological hazards.Among them,the pollutiton under MRKCa treatment was the most serious and the ecological risk was the strongest.(5)According to the calculation of the current accumulation rate of heavy metals,the pollution and the potential ecological risks of the six heavy metal elements in the long-term fertilization facility would increase after 10 a and 20 a.Among them,the soil under each treatment was not polluted by Cr,Cu,Pb and Ni,and the potential ecological risk of these elements were small.The pollution status and ecological risk of Cd would be intensified under each treatment,and the soil Cd under partial treatment would have strong ecological damage after 20 years.In addition,the soil under MRKCa treatment would be contaminated with Zn after nearly 20 years.The overall pollution status of the soil would continue to deteriorate in the next 20 years,and the soil under the MRKCa treatment would reach moderate pollution.The ecological risk of the soil under each treatment would become moderate ecological hazard.