Biomonitoring of airborne magnetic particles over time: an in situ magnetic susceptibility-based methodology

We introduce a novel methodology that utilizes in situ magnetic susceptibility (κ_is) measurements through transplants of Tillandsia capillaris, which facilitates the quantification of (sub)micron-sized magnetite particles that may pose health risks. Scanning Electron Microscopy with Energy Dispersive Spectroscopy analysis reveals the presence of iron-rich spherical, semi-spherical, and irregular particles, along with potentially toxic elements such as chromium, cobalt, and manganese. Over one year, we tested two in situ measuring protocols—direct-contact methodology (DCM) and Petri-wood methodology (PWM)—on thirty-nine samples. The κ_is values obtained were comparable; however, the DCM exhibited a higher coefficient of variation (CV ≈ 1–97 %) compared to the PWM (CV ≈ 0–10 %). The PWM demonstrated low dispersion in its results, with a standard error of the mean of 0–3 × 10⁻⁷ SI, which is comparable to the instrument's sensitivity of 1 × 10⁻⁷ SI. The maximum change in κ_is observed in the transplants during the year of exposure across various sites ranged from 2.8 to 13.1 × 10⁻⁶ SI, indicating an accumulation of airborne magnetic particles (AMP) between 0.13 and 0.63 mg on the transplants. The analysis over one year suggests that traffic avenues corresponded with high AMP accumulation, while most other sites exhibited moderate accumulation. This insight is crucial for developing more accurate in situ measurement protocols and for understanding the role of epiphytic plants as biomonitors of air particle pollution.