Influence of Dissolved Humic Compounds on K. brevis Cell Viability, Intracellular Brevetoxin Concentrations and Brevetoxin Aerosolization

Karenia brevis, the dinoflagellate responsible for Florida red tides, produces a suite of potent neurotoxins called brevetoxins (PbTxs) which cause massive fish kills, marine mammal and seabird mortalities, and commercial shellfish bed closures. Brevetoxins can be aerosolized and carried by winds onshore, causing human eye irritation and respiratory symptoms. Dissolved humic substances (DHS), a form of dissolved organic carbon that dominate estuaries during periods of heavy rainfall and runoff, have been shown to stimulate growth of some dinoflagellate species and accelerate brevetoxin breakdown. We examined the impact of two different DHS, commercially-sourced DHS derived from leonardite, and natural DHS extracted from the Peace River, on K. brevis cell viability, intracellular brevetoxin composition, and brevetoxin aerosolization. A benchtop mitigation trial with K. brevis cultures in 1 L beakers exposed to 0, 5, 15 and 30 mg L^-1 DHS was conducted over a 48-hour period, and aerosolization was simulated with the Mote Aerosol Generator for a 30-minute period at t = 48 hr. Commercial and natural DHS both significantly (p<0.05) inhibited K. brevis survival and viability, with up to 39% cell removal efficiency, but had no significant impact on intracellular brevetoxin concentration or composition. The addition of DHS, however, significantly (p<0.05) reduced brevetoxin aerosolization: Peace River DHS additions of 30 mg L^-1 were 80% effective at preventing brevetoxin concentrations in aerosols. These data demonstrate that natural DHS are a potentially effective treatment for reducing brevetoxin aerosol during coastal K. brevis blooms.