Determination And Exposure Assessment Of Dioxin-like Compounds In Molluscacide Niclosamide

Schistosomiasis is a serious infectious disease endangering the health of the Chinese population.Despite preventive measures and treatment over the years,the epidemic continues to be serious.As the oncomelania snail is the only intermediate host of schistosoma japonicum katsurada,the eradication of oncomelania snail could be an effective measure to control the spread of schistosomiasis.In 2002,sodium pentachlorophenate(Na-PCP)as a previously used molluscacide was banned in China since it contained a large amount of dioxins.Presently,the only permitted chemical molluscacide in China is niclosamide,a new type of molluscacide instead of Na-PCP,which is,used around 3,200 tons annually.Its environmental and biological toxicity questions have attracted extensive attention.Dioxinlike compounds include polychlorinated dibenzo-p-dioxins/furans(PCDD/Fs)and dioxinlike polychlorinated Biphenyls(DL-PCBs).These compounds are a class of persistent organic pollutants(POPs)with bio-accumulative and have high toxicity.In this paper,the method for simultaneous determination of dioxins in niclosamide and serum samples by isotope dilution-HRGC/HRMS method is respectively established.Levels and fingerprints of dioxins in niclosamide samples were analyzed by isotope dilution-HRGC/HRMS method.The load levels of dioxins in serum samples of people living in schistosomiasis endemic area were also studied.Principal methods and results are as follows:The method for simultaneous determination of dioxins in niclosamide samples by isotope dilution-HRGC/HRMS method was established for the first time.We also establish and optimize the method for simultaneous determination of dioxins in serum samples.All samples met the requirements of EPA 1613 B and 1668 A methods for purification and separation effect,method recovery and detection limit.The reliability and accuracy of the experimental method are substantiated with the analysis of standard reference and actual samples.Levels and fingerprints of dioxins in niclosamide samples were analyzed by isotope dilution-HRGC/HRMS method for the first time.2,3,4,7,8-Pe CDF and 2,3,7,8-TCDF are important characteristic factors of PCDD/Fs,while PCB 126 are important characteristic factors of DL-PCBs.Concentration of dioxin in niclosamide was found only to be 0.8% of Na-PCP and the toxic equivalent level(TEQ)was only 0.4%,an indication that the content of dioxin in niclosamide was of low level.Both the toxicity of the chemical and the concentration of its by-products showed that niclosamide was a safer molluscacide.Levels and fingerprints of dioxins in serum samples collected from people living in schistosomiasis endemic area were analyzed by isotope dilution-HRGC/HRMS method.OCDD was the dominant of PCDD/Fs,followed by 1,2,3,4,6,7,8-Hp CDD and OCDF,the fingerprint of PCDD/Fs in serum samples is consistent with that in Na-PCP samples.This indicates that PCDD/Fs in Na-PCP could be the main source of exposure of local residents.The concentration fingerprint characteristic of DL-PCBs in serum samples is penta-PCBs.This is consistent with the fundamental reality of our country production and usage of PCBs.The study indicates that the exposure of Chinese population to PCBs may have been caused primarily by the production and use of PCBs in China.However,through comparisons of fingerprint characteristics of PCDD/Fs and DL-PCBs in serum and niclosamide samples,there are noticeable differences between them.It indicates that the pollution of dioxins in niclosamide samples is not the main local pollution route.Hence,the dioxin pollution caused by using niclosamide in our province has little impact on the health of the residents living in schistosomiasis endemic areas;in other words,niclosamide is relatively safe.The load levels of dioxins in the serum of local residents in this study were found to be lower when compared with other domestic and foreign studies.