Transfer of the Harmful Algal Toxin, Microcystin, from Freshwater Lakes to Puget Sound, Washington, and Toxin Accumulation in Marine Mussels Mytilus trossulus

Cyanobacteria toxins, such as the hepatotoxin microcystin (MC), are well known to contaminate freshwater ecosystems. However, monitoring for MC in marine environments has been minimal, despite evidence that MC can contaminate marine receiving waters. Freshwater organisms, such as finfish and shellfish, can accumulate MC, but due to minimal monitoring in marine environments, poisonings of marine biota have only occasionally been reported. Eutrophic inland waters produce annual toxic cyanobacteria blooms that drain into Puget Sound, an inlet of the Pacific Ocean. Puget Sound shellfish are important economic resources that are commercially distributed worldwide and are harvested by many residents as a locally available, inexpensive protein source. We confirm, for the first time, the freshwater to marine transfer of MCs and subsequent bioaccumulation of MC by Puget Sound mussels. ELISA analysis estimated maximum MC concentrations in source lakes of 2700 μg/L, up to 0.34 μg/L in marine waters and 6.5 μg/kg in mussels. Confirmatory analyses by LC-MS/MS on water and mussel samples identified MC-LA as the major toxin. Although relatively low levels of MC were found in mussels, toxin presence is indicative of an unhealthy ecosystem, and may impact food safety, especially for populations reliant on consuming Puget Sound shellfish.