Global climate change can make fish consumption more dangerous

Hundreds of thousands of babies are born in the U.S each year with enough mercury in their blood to impair healthy brain development. As they grow, these children’s capacity to see, hear, move, feel, learn and respond can be severely compromised. Why does this happen? Mostly because a portion of mercury emitted from local power plants and other global anthropogenic sources is converted to methylmercury, a neurotoxic and organic form of mercury that accumulates in fish.

In addition to poisoning human diet, mercury continues to poison the Arctic. Despite a lack of major industrial sources of mercury within the Arctic, methylmercury concentrations have reached toxic levels in many arctic species including polar bears, whales, and dolphins because of anthropogenic emissions at lower latitudes.

Relationship between mercury exposure and climate change: In its latest report to policymakers, the International Governmental Panel on Climate Change (IPCC) has made it clear that climate change and local high temperatures will worsen air pollution by increasing concentrations of ozone and PM2.5 in many regions. However, no scientific body has collectively assessed the potential impact of changing climate on mercury, a dangerous pollutant that contaminates not just our air but our soils and waters (and as a result human and wildlife’s food supply).

After attending this summer’s International Conference on Mercury as a Global Pollutant (ICMGP) in Edinburgh (Scotland), I don’t have good news. In the past few months, I have talked to several leading scientists who do research on different aspects on mercury cycle and they all seemed to agree with many recently presented and published peer-reviewed studies (see a selected list below): Climate change can significantly worsen mercury pollution. Even if global anthropogenic emission rate of mercury was to somehow be made constant, climate change can make fish-eating more dangerous because of the following:

Enhanced inorganic mercury release into waters — A combination of the following climate-related factors can lead to the release of higher amounts of mercury into waters:

  • Climate change (i.e., increased local precipitation under warmer conditions) will cause more local direct deposition of the emitted inorganic mercury on our lakes and ocean as compared to deposition under colder and dryer conditions.
  • Run-off (i.e., flow of mercury over land in a watershed that drains into one water body) an indirect but primary means by which mercury enters our local waters, will also increase under warmer and wetter conditions.
  • Extreme events (storms, hurricanes, forest-fires, tornadoes and alternating wetting-drying cycles) will cause erosive mobilization of inorganic mercury and organic matter in soils and release it into coastal and open waters where it can get methylated.
  • Thawing of the enormous areas of northern frozen peatlands may release globally significant amounts of long-stored mercury and organic matter into lakes (including those in the Arctic), rivers and ocean.

Enhanced Methylmercury production from inorganic mercury: In addition to increased release on inorganic mercury into the waters, the inorganic mercury might also have higher chances of getting converted to methylmercury.

  • In the open ocean, methylmercury is produced in regions known as “oxygen minimum zones”. Increased carbon dioxide concentrations in the atmosphere will cause higher primary productivity  which will widen the existing ocean’s oxygen deficient zones leading to enhanced production of methylmercury.
  • Continued melting of permafrost will release organic matter which naturally contains high concentration of aromatic structures (structures similar to benzene rings). These kinds of organic matter have been shown to enhance the production rate of methylmercury.

Enhanced methylmercury bioaccumulation in the fish:

  • For a given amount of methylmercury in the water, there are various factors that control the concentration and bioaccumulation of methylmercury in the food chain. In a given water body, bigger fishaccumulate more methylmercury than smaller fish. Because of climate change, oceanic temperatures will be higher and higher temperatures have been shown to increase the metabolic growth rate and size of fish. Therefore, for a given amount of inorganic mercury emitted in the atmosphere or water, more methylmercury will accumulate in the fish (consequently, increase human exposure to methylmercury) as climate change becomes more severe.

These research results combined with the recent reports on higher genetic susceptibility of some people to mercury poisoning suggest that in order to protect human and wildlife health from negative effects of methylmercury exposure it is essential to swiftly enact and implement stringent laws to reduce both global mercury and greenhouse emissions from all major sources including coal power plants.

Governments across the globe now recognize that mercury is an extremely toxic metal that harms health of millions of children and adults every year and have moved forward with an international treaty to address this toxic pollution, called the Minamata convention. The Minamata convention was recently opened for signatures after 4 years of negotiations. The treaty will come into effect as soon as the 50th nation ratifies it. It has already been signed by 93 nation-states. I am happy to note that United States has been the first nation to ratify the treaty. We await , however, ratification from 49 more countries before the treaty can go into effect.

As an organization, EDF has been educating consumers and seafood businesses about mercury in seafood via our EDF Seafood Selector by doing quantitative Synthesis of Mercury in Commercial Seafood for many years. We also have expertise on the scientific, legal, and stakeholder processes that laid the groundwork for implementation of Mercury and Air Toxics Standards in the U.S; the health and economic implications of these emission standards; and the current state of technology available to reduce emissions from power plants in the U.S.

Thanks to your strong support, the U.S. has taken action to reduce mercury from power plants, the largest domestic source of mercury pollution. While many power plant companies are moving forward with investments to reduce mercury pollution, we need you to continue making your voices heard because the mercury standards (MATS) are still being challenged in the court from time to time.


  1. Kathryn R. Mahaffey, Robert P. Clickner, and Rebecca A. Jeffries (2009) Adult Women’s Blood Mercury Concentrations Vary Regionally in the United States: Association with Patterns of Fish Consumption (NHANES 1999–2004) Environ Health Perspect. 117(1): 47–53.
  2. Goacher, W. James and Brian Branfireun (2013). Evidence of millennial trends in mercury deposition in pristine peat geochronologies. Presented at the 11th International Conference on Mercury as a Global Pollutant; Edinburgh, Scotland.
  3. Dijkstra JA, Buckman KL, Ward D, Evans DW, Dionne M, et al. (2013) Experimental and Natural Warming Elevates Mercury Concentrations in Estuarine Fish. PLoS ONE 8(3): e58401. doi:10.1371/journal.pone.0058401
  4. Webster, Jackson P. et al. (2013) The Effect of Historical and Recent Wildfires on Soil-Mercury Distribution and Mobilization at Mesa Verde National Park, Colorado, USA. Presented at the 11th International Conference on Mercury as a Global Pollutant; Edinburgh, Scotland.
  5. Blum et al (2013) Methylmercury production below the mixed layer in the North Pacific Ocean Nature Geoscience 6, 879–884
  6. Stramma, Lothar (2010) “Ocean oxygen minima expansions and their biological impacts,” Deep Sea Research Part I: Oceanographic Research Papers. 57: 587–595
  7. Bjorn, Erik et al. (2013) Impact of Nutrient and Humic Matter Loadings on Methylmercury Formation and Bioaccumulation in Estuarine Ecosystems. Presented at the 11th International Conference on Mercury as a Global Pollutant; Edinburgh, Scotland.
  8. Bedowski, Jacek et al. (2013) Mercury in the coastal zone of Southern Baltic Sea as a function of changing climate: preliminary results. Presented at the 11th International Conference on Mercury as a Global Pollutant; Edinburgh, Scotland.
  9. Grandjean, Philippe, et al. (2013) Genetic vulnerability to MeHg. Presented at the 11th International Conference on Mercury as a Global Pollutant; Edinburgh, Scotland.
  10. Qureshi et al (2013): Impacts of Ecosystem Change on Mercury Bioaccumulation in a Coastal-Marine Food Web presented at the 11th International Conference on Mercury as a Global Pollutant; Edinburgh, Scotland.

This entry was posted in Health, Policy, Science. Bookmark the permalink. Both comments and trackbacks are currently closed.
  • About this blog

    Expert to expert commentary on the science, law and economics of climate change.

  • Get blog posts by email

    Subscribe via RSS

  • Categories

  • Meet The Bloggers