Study On Photodegradation,migration And Transformation Of Pyrethroid Pesticides In Soil Environment

Due to its high efficiency,low toxicity,wide pesticidal spectrum and easy degradation and other advantages,Pyrethroids are widely used in agriculture and forestry,family and health fields,which resulting it residue in soil,water,sediment and atmosphere,Even in human breast milk and urine,its metabolites were also detected.The degradation of pyrethroid pesticides can be divided into biodegradation and abiotic degradation,of which,photochemical degradation is the most direct and highly efficient way in the environment.By using the self-developed UV photodegradation instrument with small ecosystem simulation box,this article studies the influence of UV degradation of bifenthrin in the soil surface,and the migration and the degradation of four kinds of the pyrethroids among the sand/soil,plant and water,aiming at providing the basic support for the pyrethroids use and environmental safety assessment.The main conclusions are as follows:1.Discussion on pretreatment method of pyrethroid pesticide in soil.We discussed four important prerequisites: temperature(30℃,40℃,50℃);the proportion of extracting agent and eluent(n-hexane: acetone=1:1;3:1;9:1),and the times of ultrasounds(once,twice,three times;10min every time).By the method of recovery and repeatability,the pretreatment method of pyrethroid pesticides in soil was determined: the temperature is 40 ℃;the proportion of extracting agent and eluent is n-hexane: acetone=3:1;the times of ultrasounds are three times and 10 min every time.2.The invention of ultraviolet degradation instrument(Authorized patent number:CN201510836244.8).Due to the UV degradation instrument on the market failed to meet the experimental batch conditions and the price is expensive,and the public patents such as201220594735.8 and 201420156084.3 were unable to control the distance between the samples and UV lamp.Besides,the UV lamp power is too larger to simulate the natural light intensity of UV light conditions;and the experimental equipment of rectangular shape occupied a large space,and the sample space inside is small,so that people can not carry out many groups of experiments at the same time.Thus,it has little practical application significance.Therefore,we designed a UV degradation instrument and created it combined with manufacturing enterprises,the cost is 30% of which on the market with the same function,which can achieve large quantities and controlling several factors experiment,andthe UV lamp design in the center,so the batch samples can uniformly receive the adjustable ultraviolet radiation.3.The design of small ecological test box(Authorized patent number is CN201510753751.5).The operation of the ecological simulation box on the market is small,and the price is expensive,and it can not complete the migration and transformation of the chemical substances in the interface of plant-soil-water.The Publicly authorized biochemical incubator such as CN2015203418993,CN201510092127.5,CN2014206972924,and CN201520089789.2 are open when we need sampling.Therefore,the invention overcomes the disadvantages of the prior art,designed an ecosystem simulation instrument that can complete the simulation of rainfall,sunlight,the whole system can be closed or open,and we also created it combined with the manufacturing enterprises,and the cost is 40% of which on the market with the same function,is worthy of popularization of ecological simulation case.4.The study on photodegradation of bifenthrin on soil surface.the photodegradation of Bifenthrin fitted for pseudo first-order reaction.The rate photodegradation of Bifenthrin increased with the increasing of the granularity of the soil the decreasing of the distance of the light source;and the rate photodegradation decreased with the increasing of the moisture content,but the result should be further examined;the Bifenthrin is more likely to degradate in the strong acid and the alkaline medium;the initial concentration of Bifenthrin is inversely proportional to the rate photodegradation and proportional to the amount of photolysis.The humic acid(HA)has inhibitory effects on the photodegradation of Bifenthrin,The rate photodegradation of Bifenthrin increased with the increasing of the mass fraction of HA when it belows 1.5%,on the other hand,the rate decreased with the increasing of the mass fraction of HA when it is above 1.5%.5.The study of transformation and migration of four kinds of pyrethroid pesticides(bifenthrin,cyhalothrin,cypermethrin and beta cypermethrin)in plants-sand /soil-water.In the sand in the experiment,the change trend of four kinds of pesticides is positively related with molecular polarity(cyhalothrin > beta cypermethrin > bifenthrin >cypermethrin);In the soil experiment,due to the complex structure of soil,biological activities,the rich organic matter and mineral content,the change trend is different from which in the sand experiments(cypermethrin > beta cypermethrin > cyhalothrin >bifenthrin).The four pesticides in 3cm of sand or soil experiment showed first increased and then decreased under precipitation erosion.The main reason is because the Chinese cabbage growth enrichment and artificial precipitation leaching.At the depth of 11 cm of the two experiments of sand and soil,bifenthrin gradually increased and then stabilized,and the highest concentration is lower than 0.05mg/kg and the other three pesticides were not detected.The edible part of cabbage have a little pesticide residue that about 0.29% and 0.18%from the sand and soil.In the sand experiment,the average concentration in leafs of bifenthrin and beta cypermethrin are 32.4μg/kg and 25.6μg/kg;while the concentration in roots of which are 4.31mg/kg and 4.58mg/kg,and the root uptake is 133 times and 179 times as high as edible part of cabbage;in the soil experiment,the average concentration in leafs of bifenthrin and beta cypermethrin are 17.9μg/kg and 18.2 μg/kg,while the concentration in roots of which are 2.43mg/kg and 1.97mg/kg,and the root uptake is 135 times and 108 times as high as edible part of cabbage.Therefore,in this experiment,the edible parts of Chinese cabbage was much lower than the national limit standard GB-2763-2014(leaf vegetables:bifenthrin,0.5mg/kg;lambda-cyhalothrin,0.5mg/kg;cypermethrin,2mg/kg;beta cypermethrin,2mg/kg),which indicated that leaf vegetables could be eaten safely.Bifenthrin was only detected in the leaching and the highest concentration is 28μg/L.It indicates that Bifenthrin has bigger mobile ability in the case of 20 cm of sand or soil,and based on the distribution of the bifenthrin in Cabbage and soil,bifenthrin stability keep for a long time and it probably bring some problems about the organism safety and environmental threats compared with the other three kinds of pesticide.