Study On Soil Copper Limit Standards In Farmland

As a nutrient element necessary for plant survival,Cu is also one of the common heavy metal pollution elements.Cu is absorbed by plants and accumulates in tissues from soil.Excessive Cu may cause toxicity to plants,herbivores and even humans.This study compared the physicochemical properties of copper-contaminated soils from different sources in Jiangsu,Anhui,Jiangxi and Zhejiang with the copper content in edible parts of Chinese cabbage;evaluated the ecological toxicology of copper in vegetable;and screened copper accumulation with Chinese cabbage.The closely related soil available copper extracting agent combined with the previous experimental results to propose the toxicity threshold of Cu in soil,in order to provide a certain theoretical basis for the revision of Cu pollution standards in soil.The 128 soil samples collected from the farmland of the four polluted mining areas were analyzed.The results showed that the soil copper content in the farmland of Tongling Mining Area was seriously exceeded,and the total amount of soil copper was 24.03-5470 mg/kg,with a mean value of 793.9±1032 mg/kg.The over-standard rate was 92.50%;the Cu content in farmland soil samples in Zhuji mining area exceeded all standards,the total amount of Cu was 102.0-752.0 mg/kg,and the average value was 259.0±145.1 mg/kg;the total Cu content in farmland soil in Dexing mining area was 11.28-2028 mg/kg,with a mean value of 440.6±565.2 mg/kg,and the over-standard rate was 75.00%.The total amount of Cu in the farmland soil of Tangshan mining area was 19.92-1641 mg/kg,with a mean value of 379.1 ±400.0 mg/kg,the rate is 70.73%.The soil at the sampling point is mostly acidic and the pH value is generally low.The soil pH of the farmland in Dexing Mine is as low as 3.9,with a mean of 5.9± 1.2.The soil organic matter content is mostly in the range of 10-40 g/kg.Soil organic matter content was the highest,and soil samples with organic matter content exceeding 30 g/kg accounted for 46.43%.The absorption of Cu by plants is related to the bioavailability of Cu in soil.It is affected by soil pH and organic matter content.Therefore,Cu pollution in farmland soil of Tongling mining area is the most serious,and the potential risk of farmland soil in Dexing mining area is high.The determination of Cu content in edible parts of pakchoi showed that with the increase of total Cu concentration in soil,the content of Cu in edible parts of Chinese cabbage increased gradually.The variation range of Cu in edible parts of Chinese cabbage was 0-120.0 mg/kg,and the mean value was 27.25 mg/kg,in which the content of Cu in the edible parts of Chinese cabbage was:Dexing>Tongling>Tangshan>Zhuji.Although the total Cu content of farmland soil samples in Tongling mining area is higher than Dexing mining area,the average Cu content in the edible parts of Chinese cabbage cultivated in Dexing mining area is the largest among the four soil samples,reaching 30.47 mg/kg.The linear relationship between total Cu content in soil and Cu content in edible parts of Chinese cabbage was weak,which was not enough to predict the transport of Cu from soil to edible parts of pakchoi.When the soil organic matter content is high,it can promote the transport of Cu from the soil to the edible parts of pakchoi.When the organic matter content is less than 20.00 mg/kg,the total Cu content of the soil is linearly correlated with the edible part content of pakchoi.When the total Cu content and the organic matter content in the soil are relatively constant and the pH is low,the transport of copper from the soil to the aerial part of the Chinese cabbage is promoted.The enrichment ability of pakchoi to Cu is weak,and it is affected by soil properties.The bioconcentration factors(BCF)of Chinese cabbage has great difference among different soils.In addition,due to the lower pH value and higher organic matter content of the soil in Dexing,the Cu in the soil is more easily absorbed by the Chinese cabbage,which has a greater potential risk.The use of snail as a diagnostic indicator of soil ecotoxicology measures the ecotoxicity of Cu.The results show that Cu can accumulate in snails after consumption of Cu-contaminated cabbage,but most Cu accumulates in the snail digestive gland with feces.Except for excretion,only part of Cu is digested and absorbed,and there is almost no accumulation of Cu in the shell.Taking the weight change during the feeding of snails as an ecotoxicological index,it was found that when the Cu concentration of edible parts of pakchoi was below 205.0 mg/kg,the snails could eat and grow normally,and almost no effect on the weight of snails;When the concentration is higher than 205.0 mg/kg,the snail’s eating desire decreases,the mobility is weak,and the body weight is reduced.Cu pollution in farmland farmland threatens human health through three pathways:direct exposure of soil Cu,edible vegetable food produced by contaminated land,and drinking water.This study focused on two parts,namely the direct exposure of soil Cu and the polluted soil-planted Chinese cabbage for human health risk assessment.It was found that when the soil total Cu content was used for human body risk assessment,all areas of Cu were non-carcinogenic.The risk(THQ)<1 indicates that the exposure of the soil Cu to the non-carcinogenic risk of adults and children is small through the oral cavity;the daily Cu of the human body is estimated according to the concentration of Cu in the edible part of the cabbage and the average daily intake of vegetables.Intake(EDI),the EDI value of children in all kinds of spots was significantly higher than that in adults,and the over-standard rate in Tongling and Zhuji areas was 100%.After the residents ingested the Chinese cabbage planted in the soil of each sampling area,Cu may have adverse effects on human health,especially children.The content of available Cu in soil plays an important role in the study of Cu transport in food chain,but the ability of different extractants to extract heavy metals from soil is often different due to differences soil properties.In this experiment,the soil extracting effect of eight extractants on soil available Cu was studied in four sampling areas.It was found that EDDS was used as a specific extracting agent for Cu,and the soil soluble Cu and cabbage were extracted.The Cu content of the edible part has the highest linear correlation.Then we explored the optimum concentration of EDDS extractant.The results showed that when 3.0 mmol/L EDDS was used as the extractant of soil-effective Cu,the effective Cu content of the extract and the edible part of Chinese cabbage were extracted.The Cu content has the best linear relationship(R2=0.9124).The use of EDDS as an effective extracting agent for soil Cu can simulate the transport of Cu from soil to pakchoi,and compared with soil total Cu,EDDS leached Cu is used as a measure to better reflect the toxic effects of Cu in soil.Finally,we used the EDDS leached Cu and the edible part Cu of Chinese cabbage to establish the Cu-absorption transport equation of soil-pakchoi,and calculated the soil Cu toxicity threshold based on EDDS leached Cu to 176.0 mg/kg.