As climate change impacts food webs, California researchers want to help make seafood safer

With the help of $7.35 million in funding, UC San Diego is establishing a research center focused on the connection between human health and ocean contaminants — like mercury, which gets into the seafood we eat. 

Amina Schartup, a marine biogeochemist, will be one of a team of researchers at the center focused on analyzing how mercury seeps into marine ecosystems and how climate change is impacting that. She said she’s specifically looking at methylmercury, which is the form of mercury you’d find in fish. 

“So when people tell you [to] be careful with swordfish or tuna … What people actually mean is that they have high methylmercury levels,” Schartup said. 

Schartup said the funding, which came from the National Science Foundation and the National Institutes of Health, will allow researchers like herself to better understand mercury contamination and how to ensure seafood safety. 

She told CapRadio that the contaminant she studies is a good example of how human impacts on the environment can get personal. 

This interview has been edited for clarity and length. 

Interview Highlights

How does mercury get into the food we eat? 

One of the characteristics of it is that it … enters an organism much faster than it leaves it. Over the life cycle of an organism, it will accumulate in the body, so the concentrations will increase over time. That’s one aspect of it. The second aspect is that an animal that consumes that animal that accumulated that mercury over time will accumulate even more because it starts out by ingesting a lot more through that animal.

Over time and over that food chain of these prey to predator relationships, those concentrations increase exponentially. You end up with concentration at the top of the food chain being much much higher than at the bottom of the food chain

Humans love eating [fish] on top of the food chain. So there's an exposure aspect there.

Can you tell me where this excess mercury is coming from?

A lot of these chemicals are emitted through our industrial activity. So they're actually highly connected to greenhouse gas emissions. 

In some of our models, we were trying to estimate how much mercury, for example, is being emitted on the planet. We kind of piggyback on the work that greenhouse gas researchers do because, in the particular case of mercury for example, one of the biggest sources is coal burning. So when you burn coal, you emit mercury, you also emit greenhouse gasses, so the two are related. If you curb carbon emissions or methane emissions, we also will curb our mercury emissions.

Another large source [is] artisanal gold mining. Artisanal gold mining is also, in part, increasing because of climate change. Because of the uncertainty due to climate and rainfall, people in some countries that are farming normally end up going from farming to artisanal gold mining. That is resulting in the use of mercury during that gold mining process, [because it’s used] to clean that gold and remove all the other metals and minerals in the gold, and purify the gold. 

How does the mercury then get into the ocean? 

You've noticed that a lot of it is related to burning, right? We are burning coal. We are burning that amalgamated gold. It gets emitted and then it kind of sits and floats around the atmosphere. It can float around for about six months to a year, which means that it can cover most of the planet quite rapidly, which is why we can find mercury in even pristine ecosystems. 

It starts moving into rain, into water, and then it deposits. So you get these deposit events where it just falls on the ground or falls in the ocean.

How much mercury naturally exists in the fish we eat?

There has always been a little bit of mercury that has been present in the environment. However, the concentration that we are seeing right now is not normal. They're not typical, this is not something that animals have been exposed to for a very long time.

At what level does this contaminant start to have an impact on humans? 

Well, that's highly debated. It's really hard to tell exactly what's the minimum amount that is not going to have a health impact. Generally in the community, we agree that we are trying to bring those numbers as low as possible because it's really hard to tell, especially when they are compounded with other types of exposure to many other chemicals. 

A lot of toxicologists and epidemiologists are trying to figure those numbers out, but what I've heard from that community usually is there's no such thing as safe levels of mercury just like they say there's no such thing as a safe level of lead. Our goal is to bring those [levels] as low as possible and limit the exposure. By reducing industrial emissions of mercury, we can do our best to reduce the exposure.