The Combination Of Toxicity Identification Evaluation (TIE) And Effect-Directed Analysis (EDA):Screening The Toxicants In Sediment In Urban Waterways In GuangZhou

In the process of social development,a large number of chemicals have been released into aquatic environment,and sediment thus became an important reservoir of many hydrophobic contaminants.These contaminants not only threaten the indigenous organisms,but also endanger the aquatic ecosystem and even human health via food-chain transfer.It is impractical to analyze all the contaminants in complex sediment matrices.In addition,chemical analysis alone cannot provide the information on the joint effects(antagonism,synergism and additivity)among contaminants and bioavailability of these contaminants,and therefore it is hard to assess the toxicity of complex sediment samples just through chemical analysis.On the contrary,the bioassay can directly monitor sediment toxicity,but it fails to identify the major toxicants.Developing scientific and practical methods for toxicant screening is imperative for the identification and management of toxicants in complex environment.Toxicity identification evaluation(TIE)which was developed by U.S.EPA and effect-directed analysis(EDA)which was widely used in European countries become increasingly popular in recent years as a result of their outstanding ability in toxicant screening.Combining biological testing with chemical analysis,these two methods not only evaluate the toxicity of test samples,but also identify the contaminants responsible for the observed toxicity.As a consequence,they overcome the challenges in the evaluation with chemical analysis or biological testing alone.This dissertation developed a tiered toxicity identfication method by combining TIE and EDA techniques,with the consideration of bioavailability.Then,the developed the method was applied to identify the major toxicants in sediments of urban waterways in Guangzhou,China.In sediment TIE,the sediments showing toxicity in screening test were characterized with coconut charcoal,cation resin and zeolite.The results suggested that the mortality of Chironomus dilutus was mainly caused by organic contaminants and heavy metals,and ammonia contributed little to the mortality.Chemical analysis using exhausive extraction suggested that the possible toxic metals were Cr,Cu,Ni,Pb and Zn,and the possible toxic organics were cypermethrin,lambda-cyhalothrin,deltamethrin and fipronles.The bioavailability of heavy metals and organic contaminants were further assessed with BCR(CommunityBureau of Reference)sequential extraction and Tenax extraction,respectively.With the consideration of bioavailability,the major toxic metals were finally identified as Zn,Ni and Pb,and toxic organics were cypermethrin,lambda-cyhalothrin and fipronles.As the toxicants were identified by the target anlysis,other contaminants played a role in the toxicity might be overlooked.In the tier 2 eveluation,therefore,sediment EDA was used for screening organic toxicants using a non-target analysis method.For consideration of bioavailability of organic contaminants in EDA,the sediment samples were extracted with XAD resins.Results showed that sediment toxicity to Chironomus dilutus was significantly decreased after XAD extraction.The XAD extracts were cleaned with gel permeation chromatography(GPC),and separated with normal phase high performance liquid chromatography(NP-HPLC)and reversed-phase high performance liquid chromatography(RP-HPLC),sequentially.Meanwhile,the toxic fractions were tracked with in vivo bioasssay with the midges.Finally,organic toxicants were identified with gas chromatography/mass spectrometry(GC/MS)and liquid chromatography/mass spectrometry(LC/MS)and their toxicity was confirmed with dose-response curves.The results suggested that versalide contributed significantly to the mortality of Chironomus dilutus in urban waterways of Guangzhou,China.Another un-identified compound may also play a role in the toxicity,which needs further identification and confirmation.In conclusion,by developing the tiered screening method with the consideration of bioavailability,we found that sediment toxicity to Chironomus dilutus in urban waterways in Guangzhou,China was caused by heavy metals and organic contaminants.The major toxic metals were Zn,Ni and Pb.The predominent toxic organic compounds included versalide and pesticides(cypermethrin,lambda-cyhalothrin and fipronles).In addition,an unidentified compound may also contribute to sediment toxicity.The present research suggested that the combination of TIE and EDA,in addition to integrating bioavailability,could effectively handle toxicity evaluation in a complex environment with multiple stressors,improve the accuracy in identifying the main toxicants,and eventually provide useful suggestions for contamination management and remediation.