Risk Assessment And Thermal Desorption Of Organophosphorus Pesticide Contaminated Soils

With the rapid development of urbanization in China,recycling waste site which has been shut down or demolished has become an important issue in development plan of China,and toxic and harmful substances are more or less subsistent in the waste site.This will pose a potential hazard to the human health in the future,therefore,it is necessary to carry out site risk assessment before the secondary development and utilization of space.this study is based on the environmental health risk assessment methodology which has been referred to Technical Guidelines for Risk Assessment of Contaminated Sites,through six routes of exposure for the soil of a typical pesticide contaminated sites in North China with residual organic phosphorus pollutants to carry out human health risk assessment and to research on soil remediation technology.In order to provide reference for the effective remediation and rational development of polluted sites.By the analysis of sampling data,we can find that the content of the organic phosphorus pollutants within the site has been seriously excessive,and the concentration of phorate,terbufos and parathion were 1075 times,1866.7 times and 19.7 times that of the United States EPA common soil screening levels(residential land),respectively,which were the highest.Using spatial interpolation techniques on the overall concentrations of pollutants at different depths of the field to draw,it was found that the content of pollutants decreased obviously,inside the content of pollutants extend to the edge and the content of the production area was decreased under 7m depth.But sewage treatment,old line of phosphorus,new lines of phosphorus and fenitrothion phosphorus workshop remains contaminated until 12m depth.The results of health risk assessment show that the non-cancer risk levels phorate and other pollutants were bigger than 1,more than the acceptable level of risk in the contaminated sites.According to the different pollution degree,this paper adopts different repair technology to study.The higher concentration of contaminated soil was remediated by thermal desorption technology,using the uniform design experiments to researched on the factors of reducing organic phosphorus in contaminated soil,and it shows that The results showed that the dosage only affecting removal of parathion,temperature and residence time are the main parameters to affect the removal of three organophosphorus pesticides,and by plotting and superimposing the contour map of the logarithmic removal rate,the parameter values of requirements are obtained.Fenton oxidation and high-temperature treatment of off gas,respectively,show 1000? high temperature treatment can make the removal rate of three organophosphorus pesticides up to 99.99%in off gas and the two pollution is less.So this treatment effect is better.The lower concentration of contaminated soil was remediated by biological method,including microbial remediation technology and plant microbial combined remediation.11 strains which can degrade organophosphorus pesticides were selected and isolated from pesticide contaminated soil.we observe the bacteria morphology,physiological and biochemical characteristics of 11 strains.Then through the liquid culture experiments,getting the degradation ability of 11 strains of phorate,selected 4 degradation bacteria who's degradation rate is higher than others,and the growth curve and growth conditions were studied.4 strains of degradation bacteria were inoculated into the soil contaminated with organic phosphorus pesticide,and the effect of soil remediation was determined;The strain were inoculated into the contaminated soil with planting buffalograss,and the effect of plant microbial combined remediation was determined,too.The results indicate that four strains have good effect and large difference on degradation of the three organophosphate pesticides.TN7 is the best strain in phorate and parathion degradation,and TN8 is the best strain in terbufos degradation.Degradation rate was increased with the increasing of inoculation quantity.When 1.0×108CFU·g-1dry soil of strain have added into soil,biodegradation rate of the three pesticides were 23%,28%and 27%,respectively,after 40d.Plant microbial combined remediation can promote degradation rate into 34%,35%and 37%,which is higher than the inoculate of microorganisms and separate planing plants,obsviously.In summary,according to the differences of soil contaminated by organic phosphorus pesticides,it is advisable to adopt the combined technique of thermal desorption and plant microbial combined remediation,which can be used for reference for other contaminated sites,with strong pertinence,less investment and quick effect.