Study On The Toxic Effects And Thresholds Of Polycyclic Aromatic Hydrocarbons (PAHs) In Different Soils On White-spotted Springtai

Soil ecological standard is the basis and scientific basis for setting soil environmental standard.At present,the soil ecological reference study in our country mainly focuses on heavy metals,while the ecological reference study of organic pollutants such as polycyclic aromatic hydrocarbons（PAHs）is still in the early exploration stage.Due to the lack of basic biological poison data and scientific prediction model,the ecological reference value of soil PAHs can not be accurately derived.As a result,the determination of PAHs screening value of agricultural land soil in the existing national quality standards is not scientific,rational and applicable.Based on this,this study selected 15 representative soil species,took Folsomia candida,a soil invertebrate,as the subject species,and selected two groups of individual level evaluation indexes,namely survival rate and reproduction number,to study three PAHs in soil:The acute and chronic toxic effects of phenyrene（Phe）,Pyr（Pyr）and benzo pyrene（BaP）and ecological thresholds were determined.The main controlling factors affecting the toxicity threshold of PAHs were determined,and the prediction model of toxicity threshold was derived based on the physicochemical properties of soil.The toxic effects of different aging time on exogenous BaP and the changes of PAHs content in different soils with aging time were preliminarily investigated.The test results show that:（1）The acute toxicity to Phe,Pyr and BaP was significantly different in different types of soil.The variation range of LC₅₀ for acute survival of springtails was 57～240 mg·kg^-1,68～210mg·kg^-1 and 310～10000 mg·kg^-1,respectively.by comparison,the acute toxicity of Phe and Pyr showed the strongest acute toxicity in Jiangxi red soil,and the weakest acute toxicity in Ningxia lime soil.Although BaP did not have a obvious toxic effects in some soils,the toxicity of the three PAHs in the fifteen soils was Pyr>Phe>BaP,by comparing the threshold values.（Since BaP is less ecotoxic,it is not possible to calculate toxicity thresholds for comparison）Soil physical and chemical properties affect the toxicity of PAHs in soil,and soil p H has a significant negatively correlated with the toxicity threshold of PAHs,which is the main controlling factor affecting the acute toxicity of PAHs in soil.In the filter paper contact experiment,with the increase of exposure concentration and exposure time,the abnormal behavior of Folsomia Candida appeared earlier,and the toxic effect of PAHs on springtails was mainly on the movement behavior and appearance morphology.（2）There were significant differences in the chronic toxicity of Phe,Pyr and BaP in different types of soil.The LC₅₀ of Phe,Pyr and BaP were 36.8～116 mg·kg^-1,25.4～94 mg·kg^-1and 372～10000 mg·kg^-1 respectively.The EC₅₀ of Phe,Pyr and BaP to the chronic survival of springtails were 21.09～99.5 mg·kg^-1,18～101 mg·kg^-1and 230.64～10000 mg·kg^-1 respectively.Phe showed the strongest chronic toxicity in the Hebei tidal soil and the weakest chronic toxicity in the Heilongjiang black soil.The chronic toxicity of Pyr was the strongest in Anhui yellow brown soil and the weakest in Guangdong red soil.Soil ecological standard is the basis and scientific basis for setting soil environmental standard.Current studies on soil ecological benchmarks mainly focus on the effect of heavy metal soil physical and chemical properties on the toxicity of PAHs in soil,in which soil organic matter and soil clay have a significant positive correlation with the toxicity threshold of PAHs,and soil p H has a significant negative correlation with the toxicity threshold of PAHs.Three soil physical and chemical properties are main controlling factors affecting the chronic toxicity of PAHs in soil.The prediction model of PAHs toxicity threshold based on soil physicochemical properties showed that organic matter content and soil p H could better predict the toxicity threshold of Phe and Pyr in different soils.And for organic pollutants such as polycyclic aromatic hydrocarbons（PAHs）The toxicity of PAHs with different ring numbers was significantly different.In this study,the toxicity of the three PAHs was in the order of Pyr>Phe>BaP.The factors affecting the bioavailability of PAHs were the molecular size of PAHs and the physical and chemical properties of the soil.（3）Aging effect is an important factor affecting soil exogenous PAHs toxicity.With the increase of aging time,the content of PAHs in soil decreased significantly,the survival number and reproduction number of springtails increased significantly,hence,the toxicity of PAHs was significantly weakened,and the bioavailability of BaP showed a downward trend.Therefore,in order to avoid overestimating the ecological risk of PAHs and to provide scientific and practical basic data for subsequent studies,the effects of aging process must be taken into account when evaluating the ecological toxicity of PAHs in soil.The aging process of exogenous PAHs after entering soil varies with soil type and is affected by soil physical and chemical properties,such as soil organic matter and organic carbon content.The amount of BaP extracted from soil decreased most obviously in the early aging period（0-30 d）,and gradually leveled off in the late aging period（30-210 d）.Organic carbon（OC）content did not affect the bioavailability of BaP,but was negatively correlated with the extractable amount of BaP.