Bioaccumulation Of Persistent Halogenated Organic Pollutants By Insects And Insect-mediated Transport In Food Web

Halogenated organic pollutants（HOPs）are ubiquitous contaminants in the environment.Environmental pollution and ecological and health risks of HOPs have attracted wide attention,because of their persistence,bioaccumulation,long-range transport potential and toxicity.Bioaccumulation and biomagnification of HOPs are the basis for these risks.Insects are a dominant component of biodiversity in both aquatic and terrestrial food webs because of their biomass and the large number of taxonomic groups that exist.Due to metamorphosis of insects,the larvae and adults often live in different habitats and are the prey of different predators.Regulation of contaminants during metamorphosis may lead to different exposures to the different predators.At present,bioaccumulation and biomagnification of HOPs are more concern on the high trophic level organisms in aquatic and terrestrial ecosystem.However,the accumulation characteristics of HOPs in insects and the effect of metamorphosis on pollutions are still less studied.More studies on the bioaccumulation of HOPs in insects and the transfer along the food chain are necessary.Samples were collected from a pond located in Longtang Town,Qingyuan County of Guangdong Province and the surrounding region（within a 500 m radius）.The pond has been heavily polluted by chemicals associated with e-waste.Polychlorinated biphenyls（PCBs）,dichlorodiphenyltrichloroethanes（DDTs）,polybrominated diphenyl ethers（PBDEs）,dechlorane plus（DP）,decabromodiphenyl ethane（DBDPE）,and other brominated flame retardants（OBFRs）were measured.The insect samples（include odonata,lepidoptera,orthoptera,hemiptera,coleoptera and mantodea）,aquatic,amphibious,and terrestrial organisms（include fish,shrimp,toad,frog,watersanke,waterbird egg,lizard,long-tailed shrike,oriental magpie-robin and Eurasian blackbird）,and abiotic samples（include water from the pond,soil from the fields,and plant leaves）were collected.The concentration and composition of HOPs in various species and abiotic samples were analyzed.The accumulation characteristics of HOPs by insects and other organisms in different habitats were researched and assessed the effect of insect metamorphosis on HOP accumulation patterns.The bioaccumulation and biomagnification of HOPs in insect-mediated food web were investigated.The concentrations of DDTs,PCBs,PBDEs,DP,DBDPE,and OBFRs in insects were ranged from nd¹000,20¹6000,0.08²8000,nd⁵000,0.53⁵200,and0.12¹400 ng/g lipid weight,respectively.PCBs were the predominant contaminants in insects,followed by PBDEs,the contribution of DDTs was less in this study area.Principal component analysis（PCA）was conducted,and different contaminant composition patterns were seen among the different species of insects.PCBs and DDTs are predominant in lepidoptera and coleoptera,which are consistent with the profiles of their host plant.For orthoptera,PBDEs,DP,and DBDPE were predominant in grasshoppers which are similar with the grass,but most of crickets and mole-crickets were enriched with PCBs and DDTs.Four taxa of insects（odonata,lepidoptera,orthoptera,and hemiptera）collect the larvae and adults at the same time.The correlations between the ln A/L ratio and log K_OW of HOPs for the four taxa can be fitted by a cubical polynomial model.For compounds with low hydrophobicity(log K_OW<6.5),the ln A/L ratio was negatively correlated with log K_OW.Then,ln A/L increases with increasing log K_OW until log K_OW equals 8 or 8.5 and subsequently declines with further increases in log K_OW.This result implied that the regulatory mechanism of HOPs in insects during metamorphosis is common to the four taxa studied.The concentrations of PCBs and PBDEs in aquatic,amphibious,and terrestrial organisms were ranged from 990⁴50000 and 130⁸0000 ng/g lipid weight,respectively,were 1² orders of magnitude higher than that of insects,while the concentrations of other HOPs were in the same order of magnitude as insects.PCBs were the predominant contaminants in organisms and followed by PBDEs,which is consistent with the composition of HOPs in insects.The contribution of BDE 153 for?PBDEs was 12³7%in amphibious and terrestrial organisms.The selective bioaccumulation was found for BDE 153 by insects in the comparison between the insects and abiotic samples,indicating this selective bioaccumulation by insects may further affect the insectivorous predators.In addition,BDE 47,100,153,and 154 were the predominant homologues in PBDEs profiles in the watersanke egg,but BDE 209was the most abundant PBDE congener in the maternal body,indicated that there is selective bioaccumulation of PBDEs during the maternal transfer.A multi-linear relationship was found between the maternal transfer potential and log K_OW of HOPs.The compounds with log K_OW between 6 and 8 exhibited the same maternal transfer potential;when log K_OW was larger than 8,a negative relationship between the maternal transfer potential and log K_OW was observed.This suggested that the K_OW of HOPs may not be the main factor to control the maternal transfer efficiency of watersanke.Several insect-mediated food chains（web）were constructed through stable isotope and diet analysis.Biomagnification factor（BMF）values of PCB,PBDE and DP in aquatic,amphibious and terrestrial food chains were all greater than 1,suggesting biomagnification capacity.The BMFs of HOPs in insect-birds food chains were significantly higher than the food chains of insect-fish（toad or lizard）,indicating that the biomagnification potential of HOPs in the endotherm is higher than that in the poikilotherm.In insect-mediated terrestrial food web,trophic magnification factor（TMF）values of PCB,PBDE and DP were 4,2.9,and 1.7,respectively,suggesting their biomagnification in the present food web.Significant parabolic correlations between log TMFs and log K_OW and log K_OAA for HOPs,indicating that the K_OW and K_OA have a similar regulatory mechanism in present terrestrial food web.