Characteristics And Safety Assessment Of Microplastics And Plasticizers From Plastic Mulch Film

The application of plastic mulch film has played an important role in Chinese agriculture to meet the increasing food supply requirement in China.While producing huge benefits,plastic film mulch technology has also brought on a series of pollution hazards,plastic film residual increase in soil is cancelling the benefits.In the past decades,scientists have devoted enormous effort on study of the features,damages and prevention technology of plastic residual pollution,and gained a series of important achievements.However,the study on microplastics,plasticizers and other potential pollution caused by residual plastic film in soil,as well as the potential impact on the safety of soil animals and agricultural products just began.In this thesis,the feeding experiment of earthworm was carried out by introducing different kinds of microplastics at different concentration levels in soil,the behavior and growth of earthworm were systematically studied to understand the effects of microplastics.And the thresholds of microplastics level on earthworm growth at different toxicity endpoint traits were proposed by generalized linear regression model.Further,the content and characteristics of PAEs in plastic mulch film from different region of China were analyzed,the transfer and retention rates of PAEs from plastic mulch film to soils and plants were also investigated.The main results are as follows:（1）The microplastic concentration rather than plastic type showed obvious impacts on regulating earthworm responses to soil contamination.The critical threshold for microplastic contamination was at40 g kg^-1,earthworms exhibited the microplastic avoidance behavior once the threshold was exceeded.A 10%reduction(EC₁₀)in number of cocoons and juvenile earthworms was observed at the concentration of 53 g kg^-1and 97 g kg^-1,respectively;and the reduction in number of cocoons and juvenile earthworms reached to 50%(EC₅₀)with increasing the concentration level to 207 g kg^-1and347 g kg^-1.No significant effect was found for survival of earthworm until microplastic level was as high as 500 g kg^-1.Compared with polyethylene microplastics,biodegradable microplastics（PLA and PPC）did not show obvious friendliness to earthworm growth.（2）A range of the plastic film products made in China were investigated,the detection rate of six kinds of phthalate ester（PAEs）was 100%.The average content ofΣ₆PAEs in polyethylene film was13.4 mg kg^-1,mainly DEHP and DBP.The average content ofΣ₆PAEs in biodegradable mulch films was32.5 mg kg^-1,significantly higher than that in polyethylene mulch.There were also small amounts of DMP and DEP in biodegradable mulch films apart from DEHP and DBP.The content of PAEs was related to the raw materials used to produce plastic film,but independent in the physical properties（color,thickness）or mechanical properties of the plastic mulch films.（3）When plasticizer content in the plastic mulch films were at or below the average level(13～33mg kg^-1),theΣ₆PAEs content in soil ranged from 0.0004 to 0.0010 mg kg^-1,much lower than the risk threshold of 10 mg kg^-1and background value(1.0 mg kg^-1)of plasticizer in the soil,the pollution risk of plasticizer in the soil was negligible.When the content of plasticizer in plastic mulch film is very high(77～400 mg kg^-1),the plasticizer content in lettuce increased by 3%～26%,which may have low dietary health risk to human body.On average,plasticizers in lettuce cause no risk to human health.In general,microplastic concentration rather than plastic type showed important impacts in regulating earthworm responses to soil contamination.The critical threshold for microplastic contamination was at 40 g kg^-1,above the threshold earthworms exhibit microplastic avoidance behavior.A significant reduction in number of cocoons and juvenile earthworms was observed at the concentration of 53 g kg^-1and 97 g kg^-1,respectively.Compared with polyethylene microplastics,biodegradable microplastics did not show obvious friendliness to earthworm growth.TheΣ₆PAEs content of plastic mulch films in China is generally in the safe range,and the plasticizer in soil is extremely low,which will not cause health risks to human.