Accumulation Characteristics,Ecotoxic Responses And Bioavailability Of Phthalic Acid Esters In Soil-Vegetable System

Phthalate acid esters?PAEs?are a class of artificially-synthesized compounds that are widely used,and they can be released into soil via plastic mulching,application of fertilizer,wastewater irrigation,land application of sewage sludge,and atmospheric deposition.Then PAEs could be taken up and accumulated by crops,affecting the quality and safety of agricultural products,and they can harm human health through the food chain.Brassica chinensis L.as one of the leaf vegetable with large consumption,its quality and safety have attracted much attention.However,only few studies were conducted about the characteristics of absorption,accumulation and toxic effects of Brassica chinensis L.under PAEs stress.Up to now,the risk assessment of PAEs are mostly conducted based on the total soil concentration.However only the bioavailable fraction has environmental and health risks.Therefore,the total amount of PAEs may lead to overestimation of the degrees of pollution and environmental risk.In this study,Di-n-butyl phthalate?DBP?and di?2-ethyl hexyl?phthalate?DEHP?which are the serious contaminants in soil were used as target pollutant,and the typical vegetable Brassica chinensis L.were used as research object.The accumulation characteristics and toxic effects of Brassica chinensis L.under PAEs stress were investigated and the chemical extraction methods for predicting PAEs bioavailability in soil were established in order to provide the theoretical basis and technical support for the assessment and control the quality and safety of agricultural products,and for rapidly assessing the risk of PAEs to the environment.Main contents and conclusions are as follows:1.The accumulation of PAEs in Brassica chinensis L..The pot experiment was conducted to study the accumulation and translocation of PAEs in Brassica chinensis L.,and risk assessment of PAEs in vegetables was evaluated.The results showed that the amounts of DBP and DEHP remaining in the edible parts and roots of Brassica chinensis L.increased with increasing their concentration in soil.Moreover,DBP and DEHP accumulation in the root was higher than that in the edible parts.The enrichment factors and translocation factors of DBP in Brassica chinensis L.are higher than that for DEHP,which indicates that DBP is easier to accumulate and migrate in Brassica chinensis L..Translocation factors of DBP and DEHP were less than 1.0,which indicated that they were not easy to transfer from root to the edible parts.Dietary exposure risk assessment showed that the risk index of DBP and DEHP in the edible parts of Brassica chinensis L.to human body is less than 1.0?except for DBP6 treatment?,indicating that the health risk was lower.In addition,the health risk of DBP in edible parts of Brassica chinensis L.to human body under the same concentration of soil treatment is higher than that of DEHP.2.Toxic effect of PAEs on Brassica chinensis L..The toxic effects of soil DBP and DEHP on Brassica chinensis L.were studied taking the growth,physiology,biochemistry and quality of Brassica chinensis L.as evaluation indicators.The results showed that the growth,chlorophyll content and soluble sugar content of Brassica chinensis L.were slightly promoted by low concentration of DBP treatment.With the increase of DBP treatment concentration,it gradually inhibited the growth,chlorophyll content and soluble sugar content of Brassica chinensis L..As for DEHP,the inhibitory effect on the growth,chlorophyll content and soluble sugar content of Brassica chinensis L.increased with the increase of DEHP treatment concentration.With the increase of soil DBP and DEHP concentration in soil,the content of malondialdehyde?MDA?in Brassica chinensis L.increased significantly,and the activities of total superoxide dismutase?T-SOD?,peroxidase?POD?and catalase?CAT?increased first and then decreased.The content of vitamin C gradually decreased with the increase of DBP and DEHP treatment concentrations in soil.The EC₁₀ values of each index were calculated by fitting the dose-response curves between the treatment concentrations of DBP and DEHP and each index.The results showed that the EC₁₀values of DBP for each index were less than those of DEHP,indicating that the toxicity effect of DBP on Brassica chinensis L.was greater than that of DEHP.3.Establishment of chemical extraction techniques of bioavailability for PAEs.Four kinds of chemical extractants were used to extract PAEs from aged soil.Based on the accumulation and its physiological indexes of Brassica chinensis L.,the extraction effects of different extractants were evaluated and the optimal extractants were screened.The results showed that the extracted concentration of the four chemical extractants were significantly lower than the total concentration of DBP and DEHP.The order of extraction ability of each extractant to soil DBP was Tenax extraction>low molecular weight organic acids extraction>hydroxypropyl-?-cyclodextrin extraction>n-butanol extraction.The order of extraction ability of each extractant to soil DEHP was n-butanol extraction>hydroxypropyl-?-cyclodextrin extraction>Tenax extraction>low molecular weight organic acids extraction.The DBP content extracted by each extractant was lower than accumulation in Brassica chinensis L.,which underestimated the bioavailability of soil DBP,while the DEHP content extracted by each extractant was higher than accumulation in Brassica chinensis L.,which overestimated the bioavailability of soil DEHP.Among the extractants,only the DBP and DEHP content in soil extracted by Tenax was significantly correlated with the accumulation and physiological indexes of Brassica chinensis L.,and the correlation coefficient was the highest.And the amount of Tenax extraction is closer to the accumulated concentration in Brassica chinensis L..Therefore,Tenax extraction was a more appropriate and reliable chemical extraction method for predicting the bioavailability of DBP and DEHP in soil.