Polycyclic aromatic hydrocarbons in urban tunnels of Guanajuato city (Mexico) measured in deposited dust particles and in transplanted lichen Xanthoparmelia mexicana (Gyeln.) Hale.

Sixteen priority PAHs were determined in five urban tunnels of Guanajuato city, through which about 4 % of population walks and about 25,000 vehicles pass daily. Xanthoparmelia mexicana (Gyeln.) Hale, highly abundant lichen in this region, was exposed during 6 months and then the samples were collected together with the wall dust; both materials were analyzed by gas chromatography-mass spectrometry. Total PAH concentrations in dust and in lichen samples were in the range 1392-7961 ng g(-1) (average per tunnel 4637 ng g(-1)) and 522-3571 ng g(-1) (average 2587 ng g(-1)), respectively. In dust, the highest concentrations corresponded to PYR, FLA, BaA, CHR, BaP, and PHE, whereas in lichens the most abundant were DahA, IcdP, BghiP, and PYR. The obtained results suggested passive deposition of PAHs on lipophilic lichen surface rather than phenomena associated with metabolic activity of the exposed organisms. Application of seven different molecular diagnostic ratios pointed to gasoline-operated cars as the principal source of PAHs. Based on the obtained results and their comparison with data reported for other geographical regions, Guanajuato tunnels were considered moderately contaminated with PAHs; however toxic BaP equivalent concentrations integrated for seven carcinogenic compounds presented relatively high values in four tunnels: 567-1051 ngBaPeq g(-1) as evaluated for dust samples. Since up to 7000 persons walk daily through tunnels, the obtained data call for more detailed study evaluating PAHs toxicity in Guanajuato population.