Are freshwater clams toxic?
They can be. The freshwater clams of North America (also called freshwater mussels) are bivalves belonging to the super-family Unionacea. Many different species inhabit Ontario’s lakes and rivers and were eaten for centuries by First Nations peoples, particularly when game was scarce. There’s no doubt that early Europeans also learned to appreciate them when times were tough. Clams are not normally anyone’s first food choice because their flavour can be iffy. Unlike a nice, big bowl of PEI marine mussels, clams tend to taste like whatever bottom they came from.
Back when our ancestors were eating clams as survival food, however, there was no pollution to speak of. The real problem with eating freshwater clams is that they are “filter feeders,” constantly ingesting the water around them, filtering out whatever is in it, and accumulating a variety of substances, including pollutants and toxins, in their own tissues. Clams can live for years – some species for decades – and even distant sources of pollution can produce high levels of toxins inside them. They may also feed on species that produce toxins of their own, so eating clams from water without evident pollution could still be problematic.
Unfortunately, freshwater clams are on the decline all over the world from pollution, habitat destruction, and the decline of the fish species that serve as hosts for their larvae.