Study On Environmental Standard Value And Environmental Capacity Of Brick Red Soil In Typical Crop System Of Hainan Province

With the rapid development of commercial cultivation of tropical fruits and vegetables and cash crops in Hainan,and the modern agriculture characterized by a high-multi-planting and high-fertilization management model,it brings heavy metal pollution risks to Hainan's soil.Agricultural non-point source pollution pressure is a problem that needs to be solved urgently for the sustainable development of agriculture and ecological environment in Hainan Province.However,China has a vast territory,rich soil types,and many types of vegetation.The country has only issued standards for the management of soil pollution risks on agricultural land,and urgently needs a baseline value of soil environment for local soil types and planting characteristics.This is also the local soil environmental benchmark value encouraged by the current state.The establishment of soil environmental benchmark values and the determination of soil environmental capacity have extremely important value and significance.First of all,the establishment of the soil environmental benchmark value is the basic work of further formulating the soil environmental standard system,correcting and optimizing the farmland irrigation water and sludge application standards,and is also used for soil pollutant prediction and soil environmental quality assessment,and provides scientific basis for total pollutant control.Therefore,the establishment of environmental benchmark values for soil heavy metals in typical crop systems in Hainan is urgently needed and necessary before the development of Hainan's environmental quality standards and evaluation system.This paper takes brick red soil,the main soil type in Hainan Province as the research object.Through field investigations,pot experiments and soil column leaching experiments,and introducing human health risk assessment,the Cu,Cd,Cr,Ni,Pb,As and other six major heavy metals based on human health risk assessment,taking into account the safety of agricultural products,groundwater safety and soil ecological safety of the establishment of soil environmental benchmark values,and on this basis to estimate the environmental capacity of Hainan brick red soil.The implementation of this study will provide data support for the development of Hainan's environmental quality standard system,which is of great significance for the construction of Hainan International Tourism Island.The research conclusion is as follows:?1?According to the pot experiment,the enrichment coefficients of Cu,Cd,Cr,Ni,Pb,and As in the red bean soil are 0.0118,0.0245,0.0176,0.0194,0.0075,and0.0322 for the red bean soil,respectively.And based on China's latest food pollutant limit standards?Cu no relevant standards?,the safety thresholds of 6 typical heavy metals in brick red soil are Cd:4.08 mg/kg,Cr:28.41 mg/kg,Ni:51.55 mg/kg,Pb:26.67 mg/kg,As:15.53 mg/kg;for the pineapple system,the enrichment coefficients of Cu,Cd,Cr,Ni,Pb,and As in the brick-red soil are 0.0345,0.1197,0.003,0.0027,0.0017,0.0037.In addition to Cu,the safety thresholds of the six heavy metals in brick red soil are Cd:0.42 mg/kg,Cr:166.67 mg/kg,Ni:370.37 mg/kg,Pb:58.82mg/kg,As:135.14 mg/kg.?2?Based on the acceptable health risks of human body,for bean system,the safety thresholds for six typical heavy metals in brick red soil in Hainan Province are:Cd 0.598 mg/kg,Cu 1392.37 mg/kg,Ni 121.13 mg/kg,Pb 56.00 mg/kg,As 1.24mg/kg,Cr 188.30 mg/kg;for pineapple system,they are:Cd 0.982 mg/kg,Cu 548.99mg/kg,Ni 1003.70 mg/kg,Pb 276.47 mg/kg,As 8.05 mg/kg,Cr 150.00 mg/kg.?3?Cording to the effect of heavy metals on soil enzyme activity:With 20%inhibition of soil enzyme activity as the standard,for brick red soil in Hainan Province,the safety thresholds for the six typical heavy metals in the bean system are Cu:92.97 mg/kg and Cr:75.66 mg/kg,Cd:1.05 mg/kg,Pb:185.50 mg/kg,Ni:33.19mg/kg,As:21.64 mg/kg;6 typical heavy metal safety thresholds in the pineapple system are Cu:85.03 mg/kg,Cr:186.87 mg/kg,Cd:1.50 mg/kg,Pb:294.50 mg/kg,Ni:119.85 mg/kg,As:66.49 mg/kg.The difference in safety thresholds for the six heavy metals in the pineapple system and the bean system is mainly due to the different crop types.?4?The leaching experiment shows that Cu,Pb,and As are more easily adsorbed by the soil,and are more difficult to migrate in the countryside through leaching.The leaching losses of Cu,Cd,Cr,Ni,Pb,and As accounted for up to 1.693%,53.485%,23.846%,21.760%,2.069%,and 3.976%of the total,respectively.Assuming that the soil properties of the underground soil layer of brick-red soil are the same or similar to the surface layer,when the top and bottom are approximately homogeneous,the average depth of soil in the northern region with the best degree of brick-red soil development 2.85m.The concentration of heavy metals when they reach 2 meters below ground is:2.02×10^-12mg/kg?0.02 mg/kg?0.004 mg/kg?0.001 mg/kg?1.37×10^-10mg/kg?3.19×10^-1010 mg/kg;Calculated by the SLL model,when the contents of Cu,Cd,Cr,Ni,Pb,and as in the brick red soil reached 153.13 mg/kg,0.77 mg/kg,7.66 mg/kg,3.06 mg/kg,1.53 mg/kg,1.53 mg/kg,the concentration of the leaching solution reaches the national Class III standard of"Groundwater Quality Standard"?GB/T14848-2017?.Moreover,combined with the soil characteristics of the brick red soil in Hainan,Cr,Cd and Ni are more likely to cause downward migration through leaching,which has a great risk of causing groundwater pollution and needs people's concern.?5?Based on the acceptable health risks of the human body,taking into account the safety of agricultural products,groundwater safety,and soil enzyme inhibition rate,the benchmark values of 6 typical heavy metals in brick red soil of Hainan Province in the bean system and pineapple system were finally determined.For the bean system,the benchmark values are Cu:92.97 mg/kg,Cd:1.05 mg/kg,Cr:188.30 mg/kg,Ni:33.19 mg/kg,Pb:56.00 mg/kg,As:15.53 mg/kg;For the pineapple system,the benchmark values are Cu:85.03 mg/kg,Cd:0.42 mg/kg,Cr:150.00 mg/kg,Ni:119.85 mg/kg,Pb:58.82 mg/kg,As:66.49 mg/kg.?6?The soil dynamic capacity of several typical heavy metals in brick red soil in Hainan Province is significantly stronger than the soil static capacity,which indicates that on the one hand,brick red soil has a certain amount of pollution within the threshold range of soil environmental safety;on the other hand,has the ability of output migration?plant absorption,plant infiltration,etc.?to achieve self-purification effect.The soil environment has a certain capacity to regulate and control heavy metal pollutants,and as the control period increases,the environmental capacity will gradually decrease and tend to stabilize.For haricot soil,the ranking of element's static capacity in the soil is:Cr>Cu>Pb>Ni>As>Cd;the ranking of element's dynamic capacity in the soil is:Cr>Ni>Cu>Pb>As>Cd.For pineapple soil,the ranking of element's static capacity in the soil is:Ni>As>Cu>Pb>Cr>Cd;the ranking of element's dynamic capacity in the soil is:Cr>Ni>Cu>As>Pb>Cd.