Transfer of microcystin from freshwater lakes to Puget Sound, WA and toxin accumulation in marine mussels (Mytilus trossulus)

• First confirmation of microcystin entering Puget Sound from freshwater inflows.
• Microcystin was present in marine mussels exposed to contaminated freshwater inflow.
• Certain Puget Sound seafood consumers may be exposed to unsafe microcystin levels.
• Toxin presence indicates an unhealthy ecosystem and may impact food safety.

Many eutrophic inland freshwater lakes in the Puget Sound Washington region produce toxic cyanobacteria blooms annually. While such blooms in lakes tend to be viewed as a localized phenomenon, there is significant potential for downstream export of toxins to freshwater streams, and marine and brackish water environments. However, monitoring for cyanotoxins typically associated with freshwaters, such as the hepatotoxin, microcystin (MC) in marine receiving waters is rare. In 2013 we studied four eutrophic Puget Sound area lakes to assess both toxin transport to marine waters and its potential accumulation in marine shellfish, specifically mussels. Shellfish beds are extensive throughout Puget Sound, and recreational harvest occurs downstream of our study lakes, so a study goal was to also assess if shellfish consumption poses a human health risk for MC exposure. We confirm, for the first time, freshwater to marine transfer of MCs in Puget Sound with subsequent bioaccumulation of MC by 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 we found relatively low MC levels in mussels, our study implies that potential concern for human food safety is justified and warrants further investigation.