Magnetic biomonitoring of airborne particles using lichen transplants over controlled exposure periods

Abstract

Lichens are able to retain airborne pollution-derived particles in their thalli for a long time, and therefore, their use in assessing atmospheric pollution may be suitable and beneficial. In this study, we transplanted species of Parmotrema pilosum in bags and exposed them to atmospheric pollutants at different sites over the course of 1 year. The exposed lichen retained anthropogenic ferrimagnetic Fe oxides that were identified and characterized by environmental magnetism methods, X-ray diffraction analysis (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). The ubiquitous magnetite, released by metallurgical factories and vehicular sources, had small grain sizes (< 0.1–1 μm) falling in the range of harmful particulate matter PM2.5 and PM1.0. According to the anhysteretic ratios (χARM/χ, ARM/SIRM), magnetic grain size tends to increase (ratios decrease) over time. Concentration-dependent magnetic parameters evidenced the cumulative presence of anthropogenic magnetite-like particles which reached high values during the study period, increasing from an initial mass-specific magnetic susceptibility χ value (mean ± S.D.) of 24.1 ± 5.0 × 10−8 m3 kg−1 to higher values up to 51.2 ± 23.0 × 10−8 m3 kg−1. Joint analysis of meteorological data and magnetic susceptibility indicated a magnetic enhancement (χ/χinitial) during the austral winter season when mean temperatures were lower; moreover, relative decreases in χ values after rainy periods are observed. This simple and low-cost methodology allowed us to study, in controlled exposure periods of 1–11 months, the ability of transplanted lichens to retain fine and ultrafine airborne particles that may have impacts on human health.