Residues And Enantiomeric Fractions Of Organochlorine Pesticides In Agricultural Soils From Zhejiang

Large quantities of organochlorine pesticides(OCPs) were historically and currently introduced into soils of Zhejiang,yet very limited information is publicly available for the present level of OCPs in the district.Past studies revealed that residues of chiral OCPs in soils were generally nonracemic.This work found the pollution level of OCPs in Zhejiang was moderate and enantiomeric fraction(EF) of chiral OCPs in nearly all samples significantly deviated from 0.5 at the present.The order of residue level and detectable ratio of OCPs is DDT＞HCH＞Endosulfans＞any one of other target OCPs,this linked with the usage and characteristics of OCPs.Residues of most of OCPs and were log-normally distributed.The spatial distribution showed that the residues in soils from mountain area were always higher than those in soils from plain in the same district.Besides usage and characteristics of OCPs,land use,climate conditions,and topography were also important factors which affect spatial distribution of OCPs.A significantly positive correlation between residues ofα-HCH andγ-HCH implied transformation fromγ-HCH toα-HCH in the region,this is consistent with the fact that soils in Zhejiang was under anaerobic conditions in most of times.Since a new input of dicolof-type DDT occurred in the region,the residues of DDT was positively and negatively correlated with the ratio of o,p'-DDT/p,p'-DDT and DEVrac of o,p'-DDT(defined as absolute value of EF subtracted from 0.5),respectively.The combination of isomeric and enantiomeric ratio is thus useful tool to identity "new" or "old" source.It is interesting to note that residues of HCH and DDT were significantly correlated with TOC and biomass of soils,respectively,and significant correlation between EF and properties of soils was also observed in this study.The two characteristics, significant correlation between residues of OCPs and TOC or biomass and derivation of all chiral OCPs from racemic,made the contamination of OCPs in Zhejiang be different that in previously studied regions, indicated the contamination is complex and should be received more concern in future.The residues of total HCHs in agriculture soils ranged from nondetectable to 50.56μg/kg.The levels of HCHs in all samples were lower than the first grade of guidelines of "Environmental Quality Standard for Soils in China(GB15618-1995)(50μg/kg),except HZ 10 Levels for DDTs in this study ranged from 3.27 to 529.08μg/kg with a geometric mean(GM) of 34.41μg/kg,Of the 46 soils analyzed in this study,two soils(HZ10 and JH 2) had levels of DDTs above 500μg/kg which is the maximum permitted concentration of DDTs in agriculture soils(the second grade of GB15618-1995,China).Residue of HEPT were above LOQ in only 3 of soils.HEPX had a higher detection ratio than HEPT and was found in 13 samples with levels ranging from 0.21 to 3.25μg/kg,aldrin and dieldrin were detected in 8 and 18 samples, respevtively,TC and CC had nearly similar detection frequence and were found in 19 and 18 of the soils analyzed with the concentration range of 0.13-28.61μg/kg and 0.90-17.55μg/kg,respectively,endosulfans had wider distribution than the other 6 OCPs in soils with a detection ratio of 70%and levels range of 0.52-39.43μg/kg.