BEWARE: High Levels of Freshwater Toxin Found in Shellfish from San Francisco Bay

A team of researchers from University of California, Sta. Cruz has detected high levels of freshwater toxin in mussels extracted from San Francisco Bay.

Their discovery, described in a paper published in the journal Harmful Algae, was made after low levels of microcystin were detected in the water samples from San Francisco Bay. Microcystin is a toxin produced by a type of freshwater algae known as cyanobacteria. If consumed, the toxin could result to serious liver damage.

"We found that this freshwater toxin accumulates in shellfish, both mussels and oysters, and that in San Francisco Bay, the toxin levels in some mussels exceed the recommended guidelines for consumption by quite a bit," said Raphael Kudela, the Lynn Professor of Ocean Health at UC Santa Cruz and co-author of the study, in a press release.

For the study, the researchers tested mussels collected from five sites in San Francisco Bay. Additional experiments with mussels and oysters in the tank were conducted to determine how quickly the shellfish absorbed the toxin and how long it takes to be cleared from their tissues.

Analysis of mussels from the San Francisco Bay revealed high levels of microcystin. In the additional experiment, the researchers found that particulate absorbed by mussels could take more than eight weeks to be cleared out of their system. On the other hand, dissolved toxin can also be absorbed by the shellfish but can be cleared out of their system at faster rate.

With their findings, the researchers recommend the addition of microcystin to the list of toxin being monitored in shellfish harvested from the coastal waters of California. Usually, a state quarantine on harvesting of mussels for human consumption is in effect from May to October to prevent poisonings from marine toxins.

Cyanobacteria, or also known as blue-green algae, thrive in warm, nutrient-rich water conditions. The warming temperature and recent droughts in California is promoting the growth of cyanobacteria.