PAH and PCB determination of the concentration gradient in moss Pleurozium schreberi near a highway, and seasonal variability at the background reference site

摘要

Moss (Pleurozium schreberi) was investigated as biomonitor of atmospheric polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs). Samples were collected at a distance of 10, 50 and 100 m from a highway and were seasonally collected in a forest stand near a regional background air pollution station situated approximately 30 km from the highway. The samples from the background area were dried using two different techniques in parallel, air-drying and freeze-drying. Simultaneous pressurised liquid extraction of PAHs and PCBs was performed, followed by purification using gel permeation chromatography of the crude extract. The concentration of the 15 most important Environmental Protection Agency (EPA) PAHs was determined by gas chromatography coupled with ion-trap mass spectrometry with a selected ion storage acquisition programme, and the PCB concentrations were determined using a mass spectrometer operated in tandem mass spectrometry (MS/MS) mode. Acceptable recoveries and quality parameters for PAHs and PCBs were achieved with the use of pressurised liquid extraction followed by gel permeation chromatography. The detection limit was ＜0.76 ng g~(-1) for PAHs and ＜0.04 ng g~(-1) for PCBs. Possible contamination of the moss samples by 3-ring PAHs and PCBs in the atmosphere was found during air drying. Increased PAH and PCB concentrations caused by car engine exhausts and by asphalt and oil evaporation were found near the highway. Generally, the PAH and PCB concentrations in moss decreased exponentially with distance from the highway. The organic compound concentrations close to the background station showed seasonal fluctuations corresponding to the fluctuations in the local air temperature and particle concentration.