Airborne particle accumulation and loss in pollution-tolerant lichens and its magnetic quantification

Abstract

Pollution-tolerant lichens are recognized ecological indicators of air pollution in cities, which can also collect airborne anthropogenic particles in their tissues. Harmful (sub)micron-sized magnetites are a ubiquitous component of air particle pollution, adversely impacting human health. In this work, in situ magnetic susceptibility κis of well-characterized ultrafine magnetite and lichen thalli were measured to quantify the amount of airborne magnetic particles (AMP) after calibration and to assess the lichen´s decontamination over time. Up to 2850 magnetic measurements were carried out in twenty-nine transplanted lichens (collected in urban and clean areas) from winter 2020 to winter 2021. Before the transplants, their initial κis values were 0.23 - 9.45 × 10−5 SI, representing AMP contents of 0.1 - 4.6 mg in lichen thalli. After lichens were transplanted to a shared site, the magnetic signals evidenced short-term increases and long-term decreases. After three, five and nine months, the AMP loss is more pronounced for transplanted lichens from polluted (e.g., AMP_5-months loss = 0.59 mg) than clean (= 0.08 mg) sites. Rainfall influenced the lichen´s decontamination between seasons. In situ measurements and lichens offer a valued and time-saving methodology for biomonitoring harmful airborne particles simply and effectively.