Biomonitoring of lead in Antarctic lichens using laser ablation inductively coupled plasma mass spectrometry

Abstract

A method for direct determination of Pb by LA-ICP-MS in lichen samples collected in a heavily anthropogenically impacted area of Maritime Antarctica was developed. The lichen samples were cryogenically ground and digested with nitric acid and hydrogen peroxide. Lead determination by solution-based ICP-MS was validated by the use of 2 certified reference materials. Once the Pb concentrations were measured with adequate accuracy and precision, a method for its direct determination by LA-ICP-MS was developed. The laser ablation parameters were optimized by the use of a Doehlert design matrix. The final optimized conditions were: laser energy (60%), spot size (150 μm) and repetition rate (10 Hz). Lead concentration of the analyzed lichen samples were plotted against the intensity of the lead isotopes (²⁰⁸Pb, ²⁰⁷Pb and ²⁰⁶Pb) determined by LA-ICP-MS. Satisfactory linear correlation factors were obtained when ¹³C was used as internal standard. Lead distribution profiles in lichen thalli cross-sections were also obtained. By these results, LA-ICP-MS emerges as a potential analytical tool for Pb concentration estimation in lichen samples. Minimum amount of sample required, bioimaging capability, high analytical throughput, and minimization of waste generation are the major analytical features of this approach. The significant differences between the Pb concentration in the lichen samples from the control site (1.12 ± 0.05 mg kg⁻¹) and from the impacted points (mean = 5.03 ± 0.57 mg kg⁻¹) permitted qualify these organisms as good biomonitors. Elemental bioimaging of lichens demonstrated that the medulla region of lichen thalli is consistently the main atmospheric lead bioaccumulating lichen tissue.