Is Eating Seaweed Dangerous?

Question:
I was wondering if you could tell me how safe eating seaweed is these days, pollution wise. I hear lots about fish, but nothing about seaweed. Our family consumes 6-12 ounces a week. We buy organic, but it's wild caught. I eat seaweed in salads, sandwiches, and sushi. Mostly we just snack on dulse. -which I believe comes from the Atlantic. And we use Kombu, kelp, when cooking soups and beans. I believe the Kombu is local. We're in Santa Cruz, Ca. Thanks so much for your time!

Response:
Edible seaweed is a marine algae that can come in many forms, including the type that you mention kombu, as well as the commonly eaten wakame and nori seaweeds. Although long part of the Asian diet, edible seaweed has increasingly become a part of Western diets due to its well-documented nutritional and often discussed medicinal qualities.

In comparison, there is little information about the possible negative effects of eating seaweed. A couple of years ago, several governments, including the Canadian and British governments, issued warnings advising people not to eat one type of seaweed – hijiki – because of concern over high levels of inorganic arsenic, a toxic element that has been linked to cancer, that was found in seaweed samples. Since little was known about the specific risks of arsenic in hijiki, hijiki was not banned. The warnings, which were intended to give the consumers a choice, explicitly stated that eating hijiki occasionally was probably not dangerous. Importantly, the warnings did not apply to other more commonly eaten seaweeds, including arame, nori, kombu, and wakame, which were found to be free of arsenic.

Based on these and other concerns, several scientific studies have been performed to measure the amount of metals present in seaweed. Results from these studies show that metal contamination of seaweed depends on three major factors, including where the seaweed was harvested, the type of seaweed, and the specific metal. For example, in a small Canadian study (Van Netten et al., Science of the Total Environment, 2000), seaweed grown in waters near British Columbia, Canada generally had lower amounts of heavy metals, especially of mercury, than seaweeds grown in Japan and Norway, possibly due to lower amounts of these metals in British Columbia waters. All seaweed samples – even those grown in Japan and Norway – however, had metal levels that are generally thought of as safe to eat.

What this means for you and your family is that you can continue to enjoy your seaweed salads, soups, and sushi (although given the governmental warnings I would probably stay away from hijiki). Given seaweed’s many nutritional benefits and relatively low pollutant levels, seaweed is probably not only a safe food but also one that is good for your health.