Investigate The Bioaccessibility Of PCBs In Soils Using An In Vitro Gastrointestinal Model

As a typical POPs extensively exsited in environment, polychlorinated biphenyls (PCBs) are shown to have strong carcinogenicity, teratogenicity, mutagenicity, which will bring potential and persistent harm to the health of human and environment. Due to its characteristic of semi-volatility and relatively high octanol/water partition coefficient, PCBs can be significantly detained in environment especially in soil environment. The contact and mis-ingestion of certain mount of soil through hands and mouth has become a major way for PCBs exposure to human body. In-vitro gastrointestinal model is considered to be simple, fast as well as freeing from ethical issues in evaluating bioaccessibility of pollutants which is an inevitable evaluation factor in human-health risk assessment. Therefore, using in vitro gastrointestinal model to investigate the bioaccessibility of PCBs is very important.In this study, seven representive PCBs were chosen as target pollutants and an analytical method including extraction, purification and determination of PCBs in the gastrointestinal solution was established. By applying in vitro gastrointestinal model, several influence factors such as pH value, incubation time, liquid/solid (L/S) ratios and the PCBs level in soil were investigated to assess the bioaccessibility of PCBs. The bioaccessibilities of PCBs from four typical soils in gastric and intestinal conditions were compared and the effects of different physical-chemical characteristics of PCBs and soils on bioaccessibility were examined. This study provide some references in evaluating the environmental quality of PCBs polluted soil and some scientific envidence for revealing the health risk of PCBs in soil.An analytical method including extraction, purification and determination of PCBs in gastrointestinal solution was established and optimazed as follows:firstly, gastrointestinal solution containing PCBs were extracted with 60 ml mixture of n-hexane and dichloromethane (2:1, v/v), then purified though concentrated sulfuric acid and muti-layer silica gel -alumina complex column. Finally, the eluent were dehydrated by anhydrous sodium sulfate, condensed to 1.0mL and determined by GC-MS-EI in the mode of SIM. This analytical method, quantitatively analyzed by internal standard, was found to be able to meet the requirement of the following experiments after evaluation of some indexes:method blank, the efficient of chromatographic separation, recovery, accuracy, precition and detection limits.The effects of pH value, digestion time, liquid-solid ratio and the PCBs level in soil on the bioaccessibility of PCBs by using in vitro gastrointestinal model were investigated. The bioaccessibility in neutral pH was much higher than that in acid pH.the bioaccessibility increased with the increase of digestion time and showed no change after six hours equilibrium, which can be described by pseudo-second-order kinetics equation.With the increase of liquid/solid ratio, the bioaccessibility of the seven chosen PCBs rised significantly at the beginning and had no obvious change when liquid/solid ratio reached 50. But PCBs level in soil was shown to have no effect on bioaccessbility.In the four typical soils, namly yellow blown soil, black soil, paddy soil and OECD soil, the bioaccessibilities of the seven chosen PCBs were all low and in the range of 0.34%-15.07%, which was found to have a negative correlation with logarithms of octanol/water partition coefficient. After fully reacted by gastrointestinal solution, the bioaccessibility of PCBs in the intestine turned to 11.4-66.2%. Furthermore, it increased as the number of chlorine increase, which followed biquadratic equations.The bioaccessibility of the seven chosen PCBs in intestine were all much higher than that in stomach.It is measured that the content of organic matter of yellow blown soil, black soil, paddy soil and OECD soil were 28.5g·kg-1,25.3g·kg-1,21.6g·kg-1,60.1g·kg-1 respectively. The bioaccessibility of PCBs in gastric and intestinal condition was negatively and linearly correlated with the content of organic matter, with an correlation coefficient above 0.9934. This suggested that content of organic matter play an important role in effecting the bioaccessibility of PCBs.