Serve a scientist a plate of fish swimming with mercury, and she will tell you not to eat it. Pass a nutritionist a fish high in fatty acids, and he’ll extol the health benefits of your meal. But if these fish were one and the same—high in both a well-known toxin and a well-known nutrient—neither expert could recommend the fish.
A paper published 14 September in the Journal of the Marine Biology Association of the United Kingdom, written by a cross-disciplinary group of scientists from around the globe, found that researchers rarely factor in the presence of both toxins and nutrients when studying fish.
“We very rarely study contaminants and nutrients at the same time in the same study,” explained Celia Chen, co-author and professor of ecolotoxicology at Dartmouth College. She and her colleagues performed the study, she said, because they “don’t have the right kind of information to give both risk-benefit and guidance at the same time.”
Doctors and dieticians have long touted the benefits of eating fish: improved blood pressure and heart function, weight loss, improved neonatal health, and even reduced breast cancer rates have all been linked with the nutrients fish contain.
At the same time, seafood can be potentially—and even lethally—toxic. Large fish, which tend to be at the top of the food chain and often at the top of menus, “bio-accumulate” chemicals, storing in their tissues the toxins gathered by every smaller fish they consume.
One particular case study demonstrates why scientists should consider both of these characteristics: research found that fish containing high levels of selenium, a metallic element with antioxidant properties, tend to have low levels of methylmercury, a form of mercury highly damaging to the brain. By studying both factors, researchers were able to connect that selenium allows fish to increase the rate at which mercury is eliminated from the body. Similar interactions could exist between other substances.
Yet, these compound studies are done infrequently. Mostly, Chen explained, this is due to logistics and funding.
“For example, labs with the capability to measure fatty acids are specialized; our program at Dartmouth, meanwhile, specializes in metals, and we don’t measure fatty acids,” she said. “We have the capability, but we tend to get funding to study one thing. Science can be kind of siloed that way.”
The paper also suggested that future studies consider the effect of geography and range on the chemicals found in seafood, the impacts of which are poorly understood. In particular, Chen and her colleagues believe that coming changes in the marine environment, such as ocean acidification and atmospheric warming, may impact the toxin and nutrient loads in fish populations in unexpected ways.
“Overall, we feel this will be a good reference, a summary of, ‘what does the literature really say?’” said Chen of the paper. “If you’re trying to communicate risk, you need to take a more multidimensional look. And we’re trying to encourage that…it’s a message to people who do risk assessment as well as to scientists that this is the kind of work we need.”