Identification and Atmospheric Transport of Microcystin Around Southern California Using Airborne Remote Sensing

Abstract:

Microcystin, a hepatotoxin produced by the cyanobacteria Microcystis, has been known to contaminate fresh water sources around southern California. Ingesting this toxin can cause death in animals and illnesses in humans, which has promoted the World Health Organization (WHO) and California to establish preliminary guidelines for microcystin concentrations in the water (1 µg/L in drinking water and 0.8 µg/L for recreational exposure respectively). However, very few studies have been done to assess the effects of this toxin when aerosolized, even though Fitzgeorge et al. (1994) describes the toxin as potentially 12x more deadly if inhaled rather than swallowed. This project aimed to identify areas with the potential for high microcystin concentrations using airborne data and then model the potential atmospheric transport of the toxin. After applying the Master Scattering Line Height (MSLH) and Aphanizomenon-Microcystis Index (AMI) algorithms to Airborne Visible/ Infrared Imaging Spectrometer (AVIRIS), multiple water bodies were identified as having the potential for Microcystis, although many of the observed water bodies had AMI values indicating the presence of Aphanizomenon-- a non-toxic cyanobacteria that is usually present before Microcystis. A relationship between toxins and biomass was developed and used to estimate the amount of phycocyanin and dissolved microcystin in the water. Brevetoxin, common in the Florida 'red tides', was used as a proxy to estimate the amount of microcystin that becomes aerosolized given a known water concentration (Kirkpatrick et al, 2010). These amounts were then run and averaged with the HYSPLIT dispersion model for 4 hours, 12 hours, and 24 hours. The final results show that most areas are exposed to less than 0.1 ng/m^3 after 4 hours. As a worst case scenario, one final model was run to show the exposure amount when Pinto Lake was observed to have the maximum amount of microcystin recorded in 2007. The results show that after 4 hours, some areas were exposed to values greater than 10.0 ng/m^3. These results highlight the potential widespread presence of freshwater toxins in populated areas of California, and the potential for chronic exposure at some distance from the source.