Atmospheric Progression of Microcystin-LR from Cyanobacterial Aerosols

The potential for exposure to aerosolized algal toxins during harmful algal blooms has not been well studied. A fundamental question about the longevity of algal toxins in the aerosol phase remains. In this study, the influence of environmental factors such as sunlight and atmospheric oxidants (e.g., ozone and OH radicals) on the lifetime of microcystin-LR (MC-LR), which is known to be the most toxic of the MCs produced by cyanobacteria, was investigated. A cyanobacterial culture aliquot (Microcystis aeruginosa and Dolichospermum sp.) spiked with MC-LR was nebulized into a large outdoor photochemical chamber and atmospherically aged in the presence and absence of sunlight or ozone. The concentrations of MC-LR in aerosol were measured using liquid chromatography/tandem mass spectrometry and the enzyme-linked immunosorbent assay (ELISA) for atmospheric aging of aerosols. With 61.5 nm(3) m(-3) gaseous ozone, the secondorder rate constant of ELISA-based MC-LR in M. aeruginosa aerosol was approximately (3.91 +/- 0.17) x 10(5) M-1 s(-1) (54 min lifetime). Because of the involvement of OH radicals, the daytime degradation of MC-LR was significantly faster than that at night with the same amount of ozone in the chamber air. We conclude that under natural sunlight, MC-LR in cyanobacterial aerosols quickly decays through heterogeneous chemistry with atmospheric oxidants but can still impact neighboring communities.