A summary of recent research shows climate change will increase our exposure to mercury, a toxic heavy metal that threatens fetal growth and development and targets the brains of children.
Pregnant women hear a lot about mercury from their obstetricians, who emphasize the need to limit tuna consumption during pregnancy. New moms hear a lot about mercury from their pediatricians, who warn against feeding too much tuna to their toddlers. So moms know that tuna can threaten the health of fetuses, babies, and children.
What many moms don't know is that most mercury in fish comes from coal fired power plants. Because coal contains trace levels of naturally occurring mercury, when it's burned that mercury goes up the smokestack and into the atmosphere. Power plants can install scrubber technology to prevent this, but many still spew massive amounts of the pollutant into the air.
The mercury "cycle" -- how mercury moves through our ecosystem -- is a complex atmospheric, geologic, and biochemical process. And it's precisely because of that complexity, that dependence on a myriad of other natural processes, that climate change will alter these pathways. What scientists are learning with their models of these cycles is that these pathways will change in ways that will worsen mercury pollution.
We are exposed to mercury largely through eating fish that have mercury in their bodies. So when scientists think about human exposure to mercury, they think about the amount of mercury getting into water bodies. Once mercury gets into the water, microorganisms can convert it into methylmercury, which fish absorb. When we eat those fish, we absorb it too.
How can climate change worsen mercury pollution?
- More mercury can get into the water from increased precipitation. A warmer atmosphere can hold more water, so rainfall may increase in some regions. Rain is what carries mercury out of the sky and makes it fall into the water. If rainfall increases, more mercury can be carried out of the atmosphere and into lakes and oceans.
- Increased rain can also increase the mercury falling on land, as well as the amount of runoff flowing into water bodies. This runoff will move more mercury from land sources into rivers, lakes, and oceans.
- Climate-related extreme weather events such as hurricanes and floods will increase soil erosion. More soil will be washed into water bodies. Because soil contains trace levels of mercury pollution, both naturally occurring and from human activity, there will be more mercury moving into water bodies from land sources.
- The thawing of the permafrost may release mercury locked in frozen northern soils into the ocean. Also, non-mercury components of the soil and organic matter that are released into the ocean as the permafrost melts will likely enhance the production rate of methylmercury in the oceans.
- Increased carbon dioxide levels in the atmosphere can alter the ocean ecosystem in ways that favor methylmercury production. Higher carbon dioxide levels can increase oxygen deficient zones in the ocean; this process can increase methylmercury production. This means that once the mercury is in the water system, it will be more likely to get converted into highly toxic methylmercury.
- Higher temperatures may increase the size of some fish. Because bigger fish accumulate more methylmercury in their bodies than smaller fish, there will be more of the toxic substance in these bigger fish.
If a changing climate increases our children's exposure to toxic mercury pollution, it's one more way in which climate change disproportionately harms children.