| Hexachlorocyclohexanes (HCHs), dichlorodiphenyltrichloroethanes (DDTs) andorganotins (OTs) are types of persistent organice pollutants (POPs) extensivelydistributed offshore all around the world, which could cause a series of adverse effectson various marine organisms at very low levels and cause harm to human health viamarine foodstuff. Due to the high levels of the HCH, DDT and organotin residuesoffshore in China, their potential risk to marine organisms and human health shoulddraw attention. Aquatic ecological risk assessment (ERA) is usually based on externalwater-borne exposure concentrations of the target pollutants, which could be definedas an external ERA (EERA). However, the exposure via diet and the toxicity kineticsof target toxicants are not taken into consideration in an EERA, which wouldunderestimate their true risk to organisms in the environment. Therefore, an ERAbased on biological tissue residue of target toxicants defined as an internal ERA(IERA), was addressed in the present study.The concentrations of HCHs, DDTs and OTs in the water and sediment of theJincheng Bay mariculture area (JBMA) were investigated in the present study, andaccordingly a fugacity-based foodweb bioaccumulation model was developed toestimate the tissue residue levels of these pollutants in various kinds of speciesbelonging to different function groups (FGs) of the JBMA foodweb. Besides, speciessensitivity distribution (SSD) curves were constructed for HCHs, DDTs and OTsemploying multiple models, and the safety levels (HC5) were derived based on thesecurves. By integrating the internal concentration (biological tissue residue levels)generated from the bioaccumulation model with the SSD curves based on internaltoxicity data, an ERA and human health risk assessment (HRA) were performed. Themain results are as follows: (1) The concentrations of the total HCHs (∑HCH),∑OT (ng Sn/L in sea waterand ng Sn/g in sediment), and DDTs (∑DDT) were2.98-14.87,23.88-44.82ng/L,and below the detection limit (<0.032ng/L), respectively, in the surface seawater and5.52-9.43,4.11-6.72, and4.11-6.72ng/g, respectively, in the surface sediment. Thesediment concentrations of γ-HCH and p,p’-DDE were0.64-3.13and1.36-4.02ng/g,respectively, which exceeded the TEL values (0.32ng/g for γ-HCH and2.07ng/g forp,p’-DDE) of the Sediment Quantity Guidelines by the frequency of100%and66.7%,respectively. And the aqueous concentrations of TBT were0.60-2.90ng Sn/L, whichwere comparable or above the critical levels (1-2ng Sn/L) that could deduce imposexfor female Nucella lapillus. The investigation primarily suggested that the HCH, DDTand OT residues were potentially detrimental to marine organisms and the safety ofaquatic products in the study area.(2) The goodness of fit of different SSD models for the toxicity data of HCHs,DDTs and OTs differed, among which the log-logistic models showed the bestgoodness. However, the log-logistic model did not fit well for toxicity with a largesample size as N>80. All the SSD models were well fitted with both the bootstrap andmodified bootstrap approaches for the toxicity data of these compounds, especially forthe toxicity data with a large data size. However, both the two methods depend muchon the original toxicity data, which would underestimate the toxicity to the potentialmore sensitive species not involved in the data assemblage with a small sample size(N<20). The bootstrap regression method could integrate the excellence of both thenon-parametric bootstrap and parametric approaches, with which a reliable HC5couldbe derived. However, this approach costs much more time and a computer with higherspeed is required.(3) A fugacity-based foodweb bioaccumulation model was constructed in thisstudy. Employing this model we stimulated the transportation and transformation ofHCHs, DDTs and OTs in the foodweb of the JMBA, estimated their tissue residuelevels in thirteen FGs. The estimated values were comparable with the observedvalues for validation. According to the simulations, the residue levels of∑HCH(2.54-3.24ng/g) in some FGs of higher level were significantly lower (P<0.01) than those (8.11-26.75ng/g) in FGs of lower level, suggesting no biomagnification in thefoodweb. And similar results were obtained from the simulations of OTs. In contrast,significant biomagnification in the foodweb for DDTs was predicted, with the meantissue residual level ranged from22.89to69.45ng/g in the FGs of higher level, whichwere significantly higher (P<0.01) than those (0.10-0.37ng/g) in the FGs of lowerlevel by2-3folds. These results were highly consistent with those experimented inboth the laboratory and the field, which had been reported in numerous references.(4) The potential ecological risk values of HCHs, DDTs and OTs to marineorganisms were estimated by integrating their biological tissue residue levels based onthe bioaccumulation model with the SSDs based on internal toxicity data. The overallrisk probabilities of∑HCH,∑DDT, TBT and DBT were0.029,0.086,0.09and0.06,respectively on non-conservative estimation basis, and0.070,0.13,0.21and0.017,respectively on one conservative estimation basis. And the results of anotherconservative estimation were similar to those of the former conservative estimation.These results showed that the risk level of∑HCH was higher than0.05based on theconservative estimations, a critical level for management control, whereas those of∑DDT, TBT and DBT were all higher than0.05based on both the conservative andnon-conservative estimations, suggesting potential detrimental effects on marineorganisms. Besides, based on external toxicity data, the overall risk was0.0087,0.0013,0.04, and0.01for∑HCH,∑DDT, TBT, and DBT, respectively evaluated bynon-conservative estimation, and0.021,0.0037,0.07, and0.36evaluated by the firstconservative estimation, similar to that evaluated by the second conservativeestimation. It is clear that slight differences of the risk values between the IERA andEERA were observed for both HCHs and OTs, with a factor of less than4, while therisk values based on IERA were much higher than those based on EERA byapproximately30to70folds. The comparison revealed that underestimate of trueecological risk would be performed for the POPs which presenting biomagnificationeffects such as DDTs, while an IERA based on an aggregate exposure viamultipahway including the food exposure was more reliable.(5) According to the EPA approaches, the consumption limits of the marine food in the JMBA were calculated based on the biological tissue residue levels of HCHs,DDTs and OTs. The maximum allowable consumption rate (CR) of marine food washigher than the domestic average consumption rate, suggesting little or no risk tohuman health from the exposure of OTs through marine food of this area. And similarresults were concluded for noncancer health effects from the exposure of HCHs andDDTs. However, considering the cancer health effects from the exposure of HCHsand DDTs, the CR was just1/5and1/6of the average consumption rate in China andthe average consumption rate in a typical coastal area with high consumption rate ofmarine food, respectively.In this study, the biological residue levels of HCHs, DDTs and OTs wereestimated via the fugacity-based foodweb bioaccumulation model, which wereemployed for ERA and HRA for the first time. This model could be applied toconduct an ERA in marine areas to determine whether the area was available foraquaculture anterior to the aquaculture performance, which could also serve as a basisfor the safety management in mariculture sea areas. |
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