Abstract:

Owing to their persistence, ease of accumulation in organisms, and high toxicity, the use of persistent organic pollutants (POPs) has been limited ever since the Stockholm Convention on Persistent Organic Pollutants was signed in 2001 by the United Nations Environment Programme (UNEP). As typical POPs, organochlorine pesticides (OCPs) and polychlorinated biphenyls (PCBs) can persist in the environment for long periods. They can enter human bodies through many pathways and pose a high exposure risk to humans. OCPs and PCBs can lead to endocrine disruption, neurotoxicity, immunotoxicity, reproductive toxicity, and cancer in human beings. Accurate quantification of pollutant load levels in vivo is crucial for the evaluation of health effects.

In this study, a rapid and sensitive method based on solid phase extraction-gas chromatography-tandem mass spectrometry (SPE-GC-MS/MS) was developed for the simultaneous determination of 35 OCPs and PCBs in serum. Accordingly, 100 μL of the serum sample was gently mixed with the isotope-labeled internal standard solution (10 μL) to obtain a final mass concentration of 10 ng/mL for each internal standard. After incubation overnight, the samples were mixed with 100 μL purified water for dilution. After protein precipitation with 100 mg urea, the serum samples were passed through preconditioned Oasis^® HLB cartridges, washed with 6 mL purified water, and eluted with 5 mL hexane-dichloromethane (1∶1, v/v). The SPE eluant was collected, evaporated to near dryness under a gentle nitrogen stream, and dissolved in 100 μL n-hexane. The reconstitution in the vial insert was injected into the GC-MS/MS instrument for analysis. The analytes were separated on an Agilent J&W DB-5MS capillary column (30 m×0.25 mm×0.25 μm) with temperature programming. The mass spectrometer was operated in the electron ionization (EI) mode. The optimal mass spectrometry conditions were realized by optimizing the instrument parameters such as ion pairs and collision energies. The analytes were detected in the multiple reaction monitoring (MRM) mode, and the internal standard method was used for quantitative analysis. The OCPs and PCBs had good linearities in the range of 0.05-50.0 ng/mL. The limits of detection (LODs, S/N=3) ranged from 1.2 to 71.4 ng/L. The recoveries of the 35 compounds were 72.6%-142% with relative standard deviations (RSDs) of less than 25% at the three spiked levels. The developed SPE-GC-MS/MS method was successfully applied to the simultaneous analysis of OCPs and PCBs in serum samples obtained from the general population in Wuhan. The results showed that the general population in Wuhan was widely exposed to OCPs and PCBs, especially the former. The detection frequencies of eight OCPs and seven PCBs were greater than 50%, and p,p'-DDE, p,p'-DDD, and methoxychlor were detected in all serum sample pools. Non-dioxin-like PCBs (NDL-PCBs) were the dominant PCB congeners, while PCB-28, PCB-153, and PCB-52 were the dominant PCBs in the general population of Wuhan. The concentration of OCPs increased with age. Moreover, the concentration of OCPs in individuals who were more than 66 years old was significantly higher as compared to that in younger individuals. The positive association differing by gender was significant in individuals over 60 years of age. There were no significant differences in PCB concentrations according to gender or age. There were no seasonal differences in the residue levels of OCPs and PCBs in the general population of Wuhan. The developed method is rapid and sensitive; it has the advantages of low limits of detection, satisfactory recoveries, accurate precision, and microsample volume, thus allowing for the simultaneous analysis of trace OCPs and PCBs in microserum samples in epidemiological studies. This robust analytical method also provides a powerful tool for the health risk assessment of OCP and PCB exposure.

Key words: gas chromatography-tandem mass spectrometry (GC-MS/MS), polychlorinated biphenyls (PCBs), organochlorine pesticides (OCPs), serum samples, concentration distribution