Determination of polycyclic aromatic hydrocarbons extracted from lichens by gas chromatography-mass spectrometry

Abstract

Lichens are well-known biomonitors for semi-volatile pollutants, due to their ability to absorb and retain different chemical compounds such as Polycyclic Aromatic Hydrocarbons (PAHs), directly linked to levels in the atmosphere. Based on that, this paper proposes an analytical method capable of quantifying 16 EPA-PAHs from lichens found in an intertropical zone, as a natural alternative to typical capture methods, with the aim of monitoring atmospheres polluted by toxic compounds. An analytical protocol, including sample pre-treatment, followed by ultrasound extraction, clean-up in a chromatographic column, concentration and quantification by Gas Chromatography-Mass Spectrometry (GC-MS) using Selective Ion Monitoring has been developed. Additionally, a set of guidelines on lichen collection and sample handling is given, in order to achieve representative samples.•Limits of quantification (LOQ) and detection (LOD) varied from 2.0 to 16 µg/L and 1.0 to 5.0 µg/L, respectively. Calibration curves had correlation coefficients higher than 0.99 in all cases.•Validation of the method for determining PAHs concentration associated to 30 lichen samples collected along two roads, with high and low traffic volumes was carried out.•The method showed good performance according to the sources of PAHs, traffic patterns and gradient in roads.

Keywords: Biomonitors; Lichen; PAHs; Road characteristics; Road traffic emission; Traffic emissions.

Graphical abstract

Fig. 1

Location of sampling sites with coordinates in degrees, minutes and seconds (DMS) and photographs of lichen collected. Sp1: Hypotrachyna rhabdiformis (Kurok.) Hale; Sp2: Heterodermia obscurata (Nyl.) Trevis; Sp3: Parmeliella sp.; Sp4: Parmotrema perlatum; Sp5: Hypotrachyna sp.; Sp6: Punctelia colombiana Sérus. Species were deposited in the CAUP herbarium.

Fig. 2

Recovery percentage (% REC) and confidence intervals for each PAH.

Fig. 3

EPA-PAH sampling points and average concentration of in roads. a) PR and b) NR. Colors are directly related to average of PAH concentration found as associated to lichen in different transects. SSB: Small speed bumps, BSH: Big speed hump.

Fig. 4

Distribution of EPA-PAHs according to their number of aromatic rings. The black box inside the bars shows analyte percentage with three aromatic rings, and thus grey to four aromatic rings, sloping lines to 5 aromatic rings, and grid box to six aromatic rings.