Typical Organochlorine Pesticides Residues In The Topsoils And Atmosphere Of Hexi Corridor And Lanzhou Area

Organochlorine Pesticides(OCPs)are categorized as a group of persistent organic pollutants(POPs),which share some specific characteristics,such as semi-volatility,persistence,bioaccumulation and high toxicity.In China,OCPs have a long history and large quantity of usage for the control of agricultural pests,resulting in contamination of soil,water and air because of their high stability,long residue periods and lipophilicity.China has banned or restricted the use of some pesticeds since 1983,however,some researches showed that the residue levels of OCPs in environment and human milk of some areas still remain high due to OCPs have been heavily used in these regions.It is well known that the soil has high affinity for hydrophobic organic pollutants and can act as a natural sink,and the atmosphere is the major medium for human exposure to OCPs pollution,so it is very important to study the residue levels of OCPs in soil and atmospheric environmrnt.In this paper,topsoil and air samples obtained by PUF disk passive air samplers were collected in Hexi Corridor and Lanzhou area of Gansu province.The typical OCPs residues including HCHs and DDTs of these samples were determinated using Agilent 7890-5975C GC-MSD.Spatial distribution characteristics and contamination levels of HCHs and DDTs were studied,meanwhile,the possible sources of them were appointed.The aim of this papaer is to understand the pollution status of OCPs in the environment,as a result,to provide a strong basis for further study of their transportation,transformation and fate characteristics in environmental media of this study areas.In addition,the research results will fill the data gaps of OCPs residues in the environmental media of Gansu province in China.The study results are as follows:(1)The OCPs residue levels were in the range of 0.22-53.69 ng-g-1 for DDTs and 0.07-9.16 ng·g-1 for HCHs,respectively,in the topsoils of both Hexi Corridor and Lanzhou regions.And the average concentration of OCPs was 8.58 ng·g-1 for DDTs and 1.32 ng·g-1 for HCHs.Moreover,DDTs was dominant in both topsoils of areas,accounting for 87%of the total residues of HCHs and DDTs.(2)Among the isomers of HCHs,?-HCH residues accounted for 61.1%of the total residues of HCHs.The a-HCH/y-HCH ratio ranged from 0.64 to 15.5,indicated that HCHs residues were mainly from both historical application of technical HCHs and Lindane.For DDTs,p,p'-DDT residues accounted for 65.4%of the total residues and the DDT/(DDE+DDD)and o,p'-DDT/p,p'-DDT ratios which ranged from 0.12 to 0.48 and from 0.11 to 0.79 respectively,denoted that DDTs residues sources should be mainly from technical DDTs.(3)In this study,there was no obvious relationship between OCPs residues and organic matter content in topsoils,while HCHs residues showed significant negative correlation with soil pH,which suggested that soil pH has a great impact on HCHs residues of topsoils in this study area.Comparing with Chinese Soil Environmental Quality Standard(GB 15618-1995),the topsoil burden of HCHs and DDTs in Hexi Corridor and Lanzhou area was relatively lower.(4)The OCPs residue levels were in the range of 12.82-490.69 pg-d-1 for DDTs and 35.03-939.29 pg-d-1 for HCHs,respectively,in the atmosphere of study regions.And the average content of OCPs was 131.38 pg-d"1 for DDTs and 317.59 pg·d-1 for HCHs.This study also showed that HCHs residues were generally higher than that of DDTs.Furthermore,?-HCH and p,p'-DDE accounted for the maximum percentage of the total residues of HCHs and DDTs(5)Both HCHs and DDTs concentrations in atmosphere decreased from north to south along latitude and from west to east along longitude,as a result,exhibited significant positive correlation with latitude and negative correlation with longitude.From these results,it could be deduced that HCHs and DDTs in atmosphere came from long-range transportation due to the northwest wind is the dominant wind direction in winter of study area.Comparing with those in other world regions and Chines provinces,the air concentrations of OCPs in study areas were at a lower pollution level.