Tag Archives: health

Mercury in Unexpected Products

by Hannah Horowitz

Written by Hannah Horowitz from Harvard University, this is the second in our series of Guest Scientist Blogs. Hannah is a graduate student in Earth and Planetary Sciences at Harvard University and a member of the Atmospheric Chemistry Modeling Group. Her research focuses on the environmental fate of mercury used in products and processes, and modeling the terrestrial mercury cycle.    Email: hmhorow@fas.harvard.edu        Website: http://people.fas.harvard.edu/~hmhorow/

When I first began my research on mercury used in products and processes, I was taken aback to learn that there were over 3000 known applications of the heavy metal [1]. What’s more interesting than the sheer number are some specific products containing mercury that are particularly surprising and unexpected. The vast variety of applications of mercury in the past and present are a result of its many unique chemical and physical properties. Its toxicity makes the disposal of mercury-containing products – some of which we may not realize are in our homes, schools, and businesses – challenging.

Some gym floors can release a lot of mercury.

Some gym floors can release a lot of mercury.

Polyurethane flooring used in school gymnasiums and indoor and outdoor tracks from the 1960s-1985 in the United States contain mercury used as a chemical catalyst [2]. One gym floor in Minnesota released mercury equivalent to breaking 280 compact fluorescent light bulbs per day, even 24 years after its installation [3]. However, measured concentrations and calculated total exposure in gyms tested in Ohio, Michigan, and Minnesota did not exceed levels that would result in health impacts [2, 4] from chronic (long-term) or acute (short-term) mercury exposure: 750 ng/m3 during 16 – 40 hours per week over a year, and 1800 ng/m3 for one hour, respectively [5]. Proper ventilation was key to reducing mercury levels [4]. However, average concentrations in Minnesota gyms were still around 200 times higher than typical outdoor background concentrations of 1.5 ng/m3 [6].

If a gym floor is believed to contain mercury, floor and air mercury concentrations should be measured, with help from the Agency for Toxic Substances and Disease Registry (ATSDR). If recommended exposures are exceeded, time spent in the gym should be limited, ventilation should be increased, and the floor may need to be removed (see [5]). Removal should be done carefully, as disturbing the floor may release more mercury than normal use [4]. Depending on its mercury content, the floor should be treated as hazardous waste or disposed in a lined landfill with leachate collection to prevent environmental releases [4].

Fishing lures

Fish lures can contain mercury.

Fish lures were once made using mercury.

Between the 1920s and the 1950s, fishing lures were made with visible liquid mercury inside to create motion and a shiny appearance to better attract fish [7]. Perhaps these mercury-containing fishing lures helped fishermen become exposed to methylmercury through the fish they successfully caught!

Now, care should be taken to avoid breakage and mercury release from the antique, fragile lures. For proper disposal, they should be brought to a hazardous waste collection program (varying state-by-state in the US) so the mercury can be removed and recycled [7].

Expected use in unexpected places

You can clearly see the mercury in this switch.

You can clearly see the mercury in this switch.

Some of the more typical uses of mercury – electrical switches and relays, lighting, and batteries – are widespread in many products that may be surprising. Mercury switches and relays help ovens and irons (pre-1990) shut off automatically [8, 9], thereby helping to prevent house fires. Similar switches and relays in cars brake with anti-lock brake systems (pre-2004) [10]  help prevent car crashes. However, these mercury-containing products may lead to environmental mercury contamination if their disposal is not handled properly. Electric lighting using mercury is ubiquitous – for example, LCD displays in cameras and sewing machines, UV lamps in printers, or fluorescent lamps in scanners and portable DVD players [8] to name a few. Button cell batteries present in children’s toys, calculators, and watches can also contain mercury [8, 11] and may be imported from other countries with less stringent mercury regulations [11].

The consumer should remove batteries from smaller products and contact their local municipality to find out about household hazardous waste collection services before throwing the object away [7, 12], so that they will not end up landfilled or incinerated along with general waste [13]. Electronics and larger appliances should also be collected if possible, and may be accepted by the original retailer depending on where you live (these services may or may not be free) [7, 12]. In the US, some automobile collection companies partner with End of Life Vehicle Solutions (or are mandated to do so by state law) to remove mercury-containing switches prior to turning the car into scrap metal, in order to prevent mercury emissions [10].

For more information, see the New England Waste Management Association’s mercury legacy products website.


  1. Nriagu, J. O. (1979), The biogeochemistry of mercury in the environment, Elsevier/North-Holland Biomedial Press, Amsterdam, the Netherlands.
  2. http://www.newmoa.org/prevention/mercury/projects/legacy/schools.cfm#gf
  3. http://www.newmoa.org/prevention/mercury/conferences/sciandpolicy/presentations/Herbrandson-Bush_Session3B.pdf
  4. http://www.atsdr.cdc.gov/HAC/pha/MercuryVaporReleaseAthleticPolymerFloors/MercuryVaporRelease-FloorsHC092806.pdf
  5. http://www.health.state.mn.us/divs/eh/hazardous/topics/mercury/hgflooringprofguide.pdf
  6. Slemr, F., E. G. Brunke, R. Ebinghaus, and J. Kuss (2011), Worldwide trend of atmospheric mercury since 1995, Atmospheric Chemistry and Physics, 11(10), 4779-4787.
  7. http://www.newmoa.org/prevention/mercury/projects/legacy/sport.cfm#fl
  8. https://imerc.newmoa.org/publicsearch/NEWMOA_IMERC.aspx#/CustomizedSearch
  9. http://www.newmoa.org/prevention/mercury/projects/legacy/appliances.cfm#ci
  10. http://www.newmoa.org/prevention/mercury/projects/legacy/automobiles.cfm#abs
  11. http://www.chem.unep.ch/mercury/GC-23-responses/GOV/Denmark-attachment-mercuryreport2004.pdf
  12. http://www.environment-agency.gov.uk/business/topics/waste/32096.aspx
  13. http://ec.europa.eu/environment/chemicals/mercury/pdf/study_report2008.pdf


ASGM and the Illicit Mercury Trade

By: Mark Staples

Artisanal and small-scale gold mining (ASGM) is a source of income for around 15 million miners in the developing world. Mercury is often used to separate and purify the gold from the soil and other sediments in the whole ore, and to pick up small amounts of gold.

Despite the environmental damage and health costs mercury causes, when it is boiled off from the gold-mercury amalgam, this practice is still widespread. Globally, over 700 tonnes of mercury are emitted to the atmosphere from ASGM each year, with over 800 tonnes released to land and water. These local releases can create significant health impacts in nearby communities.

In most developed nations, the use of mercury in industrial processes has tapered off as public awareness of its toxicity has grown. However, high gold prices continue to incentivize ASGM operations. As a result, mercury prices are correlated with gold prices.

This figure is taken from a study by Sippl & Selin, 2012.

This figure is taken from a study by Sippl & Selin, 2012.

Mercury mines are still open, primarily in China, and these sources provide a steady supply of mercury for ASGM operations in the developing world. In fact, a significant proportion of the mercury that is imported to ASGM countries and their neighbors is either mined in, or transported via, developed nations. This study provides some interesting insight into the global flows of primary mercury to ASGM practicing nations.

One of the greatest challenges for understanding the contribution of ASGM to anthropogenic releases of mercury to the environment is a lack of transparency and completeness of data. For example, the United Nations Commodity Trade Statistics Database (COMTRADE), used in a number of analyses of the global flow of commodities like mercury, is voluntary and incomplete. Further, mercury is almost never officially traded for the stated purpose of gold amalgamation, making it harder to track.

While many countries, including China, Brazil, French Guiana and Indonesia, have laws in place to monitor or limit the use of ASGM operations, large volumes of mercury are still imported for gold mining. Mercury is often imported for ostensibly legal use in dental amalgams, but is then made available to miners in chemical or dental shops once inside the country. The ease with which miners can obtain this neurotoxin is alarming.

At the negotiations, delegates focused heavily on ASGM on January 14 at INC5. The proposed text, Article 9, addresses ASGM; parties are debating whether continued use of mercury should be permitted or whether it should be phased out. Brazil, Mali and the Alliance for Responsible Mining (an industry group), all voiced support for the continued, legal international trade of mercury for ASGM. These delegations argued that ASGM is going to happen regardless of the outcome of these negotiations because it occurs in the informal sector. Banning mercury trade would only criminalize an important economic activity in developing nations. Instead of effectively discouraging the international trade of mercury, a phase out of the permissible import of mercury for ASGM might simply force the trade underground.

I’m not so näive as to believe that including a phase-out date for the legal trade of ASGM-destined mercury in the treaty would be entirely effective. In all likelihood, the illicit trade in mercury that already exists will simply grow to fill that gap. However, I do believe that better monitoring and reporting on ASGM-destined mercury, in preparation for a legally binding phase-out, could only aid in getting a handle on this harmful trade and on the extent of ASGM as an informal practice. It would also allow miners and developing nations to transition to alternative ASGM techniques, such as gravity concentration, sluice boxes or cyanidation.

There is clearly some cognitive dissonance in the way in which mercury is traded and used by importing and exporting nations. It seems to me that this is an issue that needs to be resolved to help stem the flow of mercury that is harmful to both human health and the environment. I’m excited to see the progress that will be made on this issue this week.

For more information about ASGM, you can check out the NGO Artisanal Gold Council’s site and the recent report from Human Rights Watch. Here is a short video which explains how ASGM with mercury works:

Daily Roundup for INC5 Day 3—Tuesday, January 16

by Alice Alpert

Day 3 began with snow falling, turning Geneva into a winter wonderland.


Everyone eagerly anticipated the first of the Swiss breaks, to be held in the evening. However, we are no longer “early” in the negotiations, so parties were eager make some progress before the Swiss break festivities began.

Here’s a recap of progress made on different topics.

Products and Processes

The technical articles contact group made progress on setting the mercury concentrations that different types of lightbulbs can contain, although the phase-out dates remain undecided. A breakout group, facilitated by one of the co-chairs, was started to address the controversial dental amalgam issue.

The group is in the midst of working through the annex regarding products and processes that will be exempt from regulation: antiques were removed because they are not being currently manufactured; there will be exceptions for some research and calibration standards (although there is no consensus yet exists on the details); thiomerisol will be allowed as a preservative in vaccines; polyurethane, vinyl chloride monomer, and sodium methylate are still under review. The group discussed the idea of discouraging distribution in commerce as a process provision rather than an outcome provision.

Emissions and Releases

In the morning, a technical group of about 30 attendees was tasked with discussing possible options for characterizing the nature of emissions and releases regulations. The group agreed that it would be useful to narrow the scope of the treaty to major sources, but there was no consensus around the several threshold types discussed (e.g., do you regulate based upon capacity, intensity, or aggregate emissions?).  In the afternoon and evening, the full emissions contact group reconvened and agreed to eliminate certain small-source categories. Into the evening, they were discussing releases, looking to start forming some draft text. Memorably, in response to one delegate’s suggestion that a ton of mercury was a small amount of emissions,  another party replied: “No single raindrop feels responsible for the flood.”

Institutions and Implementation

The treaty objective and definitions were discussed in morning plenary, focusing on whether a dedicated, stand-alone article on health impacts was required or even warranted. The plenary was divided on the issue: one side was of the opinion that a separate health article duplicates other sections of the text and/or impinges upon the effort of the World Health Organization, while the other side sees a stand-alone article as paramount to reaffirming the objective of the treaty. Many NGOs submitted interventions supporting the health article.

Also in plenary, parties showed no movement on how to ensure domestic implementation, with many developing nations saying that a uniform requirement for submitting a plan to meet treaty obligations did not take into account differing national socio-economic conditions. In the evening, a contact group on the implementation and health issues met. Gridlock continued, and a small group decided to work through the night to submit a suitable proposal in the morning.

Financial and Technical Assistance

Much of the work in this area occurred in a small contact group of “friends of the co-chairs”, which continues to discuss Articles 16 and 16bis regarding technical assistance and technology transfer. Article 17—which concerns whether to establish a committee for implementation or for compliance (or both)—was up for discussion in the afternoon plenary session. Several countries voiced the opinion that they would like the membership of and mechanism for decision-making by this group to be specified in the treaty,  rather than by the conference of parties. These specifics will be considered in a contact group set to convene on Day 4.

Supply and Trade, AGSM, and Waste

Work in this area began at 11pm in the technical articles contact group, with a discussion of Article 3 on supply and trade. One of the biggest struggles involved whether existing primary mining should be banned; this decision is still in a deadlock. The group didn’t break until after 1am, and we can expect more work on Day 4.

Highlight of the day

After the second plenary session, the loudspeakers came to life with the song “Under Pressure,” (featuring Freddie Mercury)—just to drive the point home. Then the Swiss break began, providing delicious food, wine, and opportunities for delegates to work out compromises in informal consultations.


The Swiss break also notably featured video footage of traditional Swiss culture, including whipcracking and running around in leaf costumes, in addition to skiing and yodeling. While the Swiss music was questionable, the event did not disappoint. We look forward to our second Swiss break this evening, and hope that the negotiations make significant progress in the meantime.

What to Expect from INC5 Day 4–Wednesday, January 16

It’s Day 4, and the negotiating sessions are, according to the current schedule, more than half over! What have the negotiators done with all the time so far? They’ve discovered key areas of disagreement, and forged some progress on text in various groups. The plenary sessions are plodding and/or breezing their way through various articles while contact, technical, and drafting groups untangle the details.

The schedule has become fluid, but we expect:

  • A sunny day, rather than yesterday’s snow.
  • “Under Pressure” on repeat in the plenary before we start the day.
  • A late start to the first plenary.
  • Updates on progress from the groups dealing with “Selected Technical Articles” (a.k.a. the “Mega-Contact Group”), Emissions and Releases (a.k.a. my personal favorite, led by witty UK delegate John Roberts), Health (a.k.a. “Guess WHO*?”),  Technical assistance (a.k.a. “Got Tech?”).
  • A polite and sincere urging from Chair Lugris for these groups to continue their “excellent work.”
  • The Mega-Contact Group chugging along continuously, tirelessly (and sleeplessly).
  • Optimistically: finalizing Article 3, 7, 8, Article 9 (ASGM) and maybe even some work on article 13 (storage and waste).
  • A drafting group to continue work on implementation plans.
  • A drafting group to tackle treaty text addressing releases to land and water.
  • A presentation by BRI-IPEN on mercury hotspots.
  • The legal group to continue their helpful work on reviewing some of the draft articles.
  • A small contact group called “Friends of Health” to discuss how to integrate wording on health into the treaty.
  • Another Swiss Break!

Stay tuned for Mark’s daily wrap-up blog, or follow us on twitter @MITmercury or at #MITmercury to catch all the action.

Interested in particular aspects of the treaty discussions?

An already-outdated snap of the day's schedule

An already-outdated snap of the day’s schedule – it’s a fast paced day!

Follow me, @BeckySaari, @NoelleSelin and @leahstokes for coverage on emissions and releases as the delegates try to tackle some text. Our friends are also tweeting away:

  • @alicealpert and (@jvanderhoop following technical and financial assistance.
  • @Bea_Edwards and @lncz will reflect on products and processes
  • @markdstaples and @DanyaRumore are tracking the hot issues of ASGM, supply, waste and trade.
  • @wolfeyp and @amandagiang tweeting on institutions and implementation!

*NOTE: WHO = World Health Organization

Benefit estimates and other health effects from mercury

By: Amanda Giang

When I’m not in glamorous Geneva, and instead in my much-less-glamorous cubicle in Cambridge, MA, I work on assessing the benefits of reducing mercury emissions. The bulk of these benefits are related to improved health—reviewed in our earlier post. Discussion on the health impacts of mercury normally focus on neurologic effects—and with good reason. These effects often have devastating impacts on the lives of victims, and heavy social and economic costs—even when we’re talking about subtle IQ loss from fetal exposure to methylmercury.

What’s more, we have a large body of scientific evidence that helps us understand these neurologic effects, and that can help guide policy decisions about preventing them. But, focusing on just neurologic effects may not tell the whole story. There may be other—though considerably more uncertain—health effects from mercury exposure that have serious policy implications. A large part of my research is about how to include these uncertain health effects in estimating benefits from reduced mercury emissions.

Of these uncertain effects, cardiovascular impacts may be the most important, and also the least uncertain. A growing body of evidence suggests that there may be a causal relationship between methylmercury and cardiovascular disease (coronary heart disease, heart attacks, increased blood pressure). Scientists still aren’t sure why mercury might promote heart attacks; one hypothesis is that it causes oxidative damage.

A committee convened by the US EPA recently decided that there was enough evidence, at least for heart attacks, to warrant including this health effect in future benefit assessments for mercury regulation.* Taking into account mercury-related heart attacks is important because the “cost” of a heart attack—personal, social, and economic—is very high; particularly if a heart attack leads to a fatality. In one of the first studies to include heart attacks in its calculations of costs and benefits, 80% of the benefits associated with reduced mercury exposure ($8.6 billion/year in the US) were due to reduced heart attacks.

If, through further research, it turns out there is a causal relationship between mercury and heart disease, then this week’s mercury treaty might be even more socially beneficial than countries initially thought. This was the case when the US regulated sulfur dioxide in the 1990s. Originally, the focus during the policy’s development was on environmental benefits from reduced acid rain. However, it later emerged that reducing sulfur dioxide has huge health benefits (an unexpected $70 billion/year!). As the science develops, we’ll see whether this will play out for mercury as well.

* NOTE: In the US, part of the regulation making process involves assessing the costs and benefits of regulation.

Mercury’s Health Effects

by Alice Alpert, Ellen Czaika, and Amanda Giang

Pathways to exposure

Although these negotiations are explicitly focused on creating an environmental treaty, mercury’s major significance is its toxicity to humans. When you think about mercury, you probably picture a mercury thermometer. In a thermometer, you can literally see the silvery mercury in its bulb – this is liquid, elemental mercury. If you are absent minded and accidentally drop that mercury thermometer on the bathroom floor, the mercury will spills and form into beads. Although it’s not a good idea to touch this mercury, it is also not easily absorbed by the digestive system in this form.

The more pernicious way for this mercury to enter your body is if it vaporizes, which happens to a small amount of the liquid mercury at room temperature. If you inhale the vapor it can easily pass from your lungs into your blood stream and damage tissues. In fact, vacuuming up the spilled mercury can increase its vaporization and therefore the danger.

In truth, most people will not be exposed to mercury in this form. Instead, people working in chlor-alkali production, mercury mining and refining, thermometer production, dentistry, and in the production of mercury-based chemicals are at increased risk. Although measures have been taken to limit occupational exposure to mercury, many workers may continue to be at risk. Similarly, artisanal or small-scale gold miners are routinely exposed to mercury vapor at very high levels, in the process of burning the mercury-gold amalgam used to extract gold from ore. Indeed, miners and their communities often exhibit clear signs of mercury poisoning.

Another important pathway for mercury exposure is through eating seafood. In fact, according to the World Health Organization (WHO) (Section 2.4, paragraph 128), for many people this is the main pathway for human exposure to methylmercury. Exposure happens through the process of bioaccumulation and biomagnification. In brief, mercury is methylated to methylmercury (CH3HgX) by bacteria in the ocean and then accumulates in fish and marine mammals. Long-lived predatory fish at the top of the food-chain, such as swordfish, tilefish, shark, and tuna, can accumulate dangerously high concentrations of mercury. The US EPA lists guidelines for safe consumption of fish. Women who are pregnant or who could become pregnant should be especially careful about eating mercury contaminated fish because the mercury can be harmful to the developing fetus.

In addition, exposure could happen through dental amalgams. Elemental mercury is used in dental amalgam, and it can be ingested or its vapors can be inhaled. This is a contentious issue in the negotiations. The American Dental Association and the US Environmental Protection Agency state that mercury in dental amalgam is safe, while a report by the WHO (p.11) states that dental amalgam is a significant source of mercury exposure in those who have mercury fillings. We encourage you to look into the reports if you are concerned about this issue. For a solid overview of all pathways, see the WHO report on mercury exposure.

How and why does mercury make us so sick?

The most serious effects of elemental mercury vapor concern the nervous system, including tremors, erethism (a neurological disorder characterized by irritability and shyness), insomnia, muscle weakness, and memory loss. At especially high concentrations, the kidneys, thyroid, and pulmonary system can be affected. Similarly to elemental mercury, mercury in its organic form, methylmercury, has serious neurological effects, including neurobehavioral deficits, neuronal loss, loss of muscle movement, hearing loss, paralysis, and death.

Why is mercury so toxic for the nervous system? There are two specific processes: first, elemental mercury and methylmercury can easily cross the blood-brain barrier and once in the brain, can be oxidized to the mercuric ion (Hg2+), which cannot cross back across the barrier. Instead, mercury is trapped in the brain, where the second process begins, neurotoxin by excitotoxicity. What? Okay, we’ll slow down and explain these multi-syllabic words: in studies of rats, Hg2+ inhibits glutamine and glutamate transport, causing receptors for these molecules to become overexcited. This causes a large influx of the calcium ion into the cell, which activates enzymes that can lead to the neuron’s death, and thus the serious neurological effects. This second process is the reason why mercury is so toxic.

Mercury crucially effects developing fetuses. In the same way that methylmercury can cross the blood-brain barrier, it can also pass through the placenta from a mother to her fetus and then to the developing fetus’ brain. As a neurotoxin, methylmercury can also damage its nervous system, and in fact mercury has lasting negative effects when fetuses are exposed to concentrations at levels that are only 10%-20% of toxic levels for adults.

Babies born to women who consumed significant amounts of methylmercury while pregnant display symptoms similar to cerebral palsy, including delayed walking and talking, altered muscle tone and reflexes. Tragically, these impairments are permanent and affected will suffer from these impairments for their entire life. In fact, recently published research estimates that IQ reductions due to chronic, low-level fetal mercury neurotoxicity costs the European Union alone € 8-9 billion euros per year. Clearly, there are significant social and economic impacts from mercury exposure, particularly for the young.

Measuring Our Mercury Exposure Through Hair Samples

By: Leah Stokes & Noelle Selin

Mercury is a toxin that harms human health. People become exposed to mercury primarily by eating fish. In some communities, where artisanal and small-scale gold mining (ASGM) occurs, exposure can be quite high. This is because people may breathe in mercury fumes from the process.

It is possible to tell how much mercury a person has been exposed to by testing their hair, blood and urine. Estimating mercury exposure through hair samples is primarily a measure of methylmercury — the most toxic form of mercury. But, it may also be influenced by the hair surface’s exposure to emissions. For example, if a person using mercury to capture gold stands over the amalgam (the mixture of mercury and gold) while they are burning off the mercury, it is likely that some of this mercury could end up on their hair.

At INC2, the second round of the mercury treaty negotiations in Chiba, Japan in early 2011, delegates and observers were able to measure the mercury concentration in their hair. We both sent in samples, and found out that Noelle had a concentration of 1.39 ppm while Leah had a concentration of 0.75 ppm. These values are close to, or below the WHO and the US EPA guidance values for mercury in hair: 1.8 ppm and 1.2 ppm respectively.* Many other delegates at the negotiations had mercury concentrations around 4.00 ppm, which is above these guidance values. For most people, mercury concentrations in hair reflect fish consumption, and Leah is mostly a vegetarian, while Noelle is from New England and loves fish.

Chart complied from Arnika data by Amanda Giang and Julie van der Hoop.

Chart complied by Amanda Giang and Julie van der Hoop using self-reported data on Arnika’s website.

Arnika, a Czech non-governmental organization (NGO), and a member of both International POPs Elimination Network (IPEN) and Zero Mercury Working Group (ZMWG), has posted a website where people around the world are reporting the mercury concentrations in their hair. These individuals then reflect on this information in light of the current negotiations, sending a message to delegates.

Amanda Giang and Julie van der Hoop compiled the self-reported data from Arnika’s website, to give you a sense of how mercury concentrations in hair can vary across countries.

* Note: The WHO and EPA actually give their recommendations in terms of daily oral intake of methylmercury. Amanda Giang converted these values to hair mercury concentrations using conversion factors developed by Rice et al. (2010), Stern (2005), and Allen et al. (2007).

Dinner…with a side of mercury?

by Julie van der Hoop

Worldwide, fish consumption is the main source of human exposure to methylmercury, a highly toxic form of mercury that biomagnifies up the food chain [1]. Accordingly, a fair amount of media attention has focused on mercury content in fish as a potential public health threat [2]. In an effort to protect consumers, US state and federal agencies have set guidelines for limiting consumption of fish that tend to be high in levels of methymercury (these guidelines are particularly important for pregnant women and women of childbearing age, as fetal exposure to methylmercury can create long-term developmental impacts). Additionally, health advisories are available online to help consumers avoid consuming types of fish that are particularly high in mercury and other toxins.

In light of these health concerns, it is no surprise that one of the aims of a global mercury treaty is to, through reducing mercury emissions, ultimately reduce the levels of toxic methylmercury in fish and shellfish.

Should we eat fish?

Fish are often touted for their great nutritional profile: they’re low in fat, with high-quality protein and an added dose of vitamins. The American Heart Association recommends at least two 3-ounce servings of fish per week to obtain beneficial omega-3 fatty acids. However, balancing the risks of mercury consumption and the benefits of fatty acids can be difficult for both consumers and those faced with the task of setting advisories.

Some studies are now urging consumers to weigh the risks and benefits of eating certain types of fish. In terms of what to avoid, shark and swordfish shouldn’t make it to your plate, not even for a single meal per month. The health benefits of fishes such as tilapia, pollack, flounder, shrimp, trout, herring, salmon, canned light tuna, and cod generally outweigh their potential mercury concentration cons [3]. That being said, other contaminants (e.g., persistent organochlorines in farmed salmon) and fishery sustainability (e.g., depletion of many cod stocks) are additional concerns worth considering when planning your meals.

Will fish mercury levels ever decrease?

It’s uncertain when—and whether—you’ll be able to enjoy all-you-can-eat sushi without thinking about how much mercury you’re consuming. However, recent research is helping us better understand how changes in mercury emissions could affect the future methylmercury content in fish.

In a new study, researchers added mercury to an experimental lake to learn how quickly it was incorporated into fish and to track what happened when mercury-addition stopped. Good news: concentrations of methylmercury in lake fish decreased much faster than previously thought. As reported by Susan Bence this week, researchers working on the project believe that reductions in mercury emissions could lead to a fairly rapid decrease in fish mercury levels in certain ecosystems. How fast these levels will decrease, however, will vary depending on where the fish are caught.

Still, mercury cycles through the environment very slowly, and even if we can restrict future emissions to current level, this will not reduce the global mercury burden. A major cut in mercury emissions is needed to reduce methylmercury concentrations in marine fish: as a recent report by Chen et al. shows, cutting mercury emissions by about 40% could lead to a 16% decline in mercury concentrations in fish in the North Atlantic Ocean.

What should you do in the meantime?

To help guide you in your fish dining decisions, check out the EPA’s online guidelines for eating and selecting fish and shellfish, as well as the consumer guides and apps available from groups such as NRDC and the Sierra Club. Still, what might matter most in is not the species of fish, but where it was caught [4]. Informing ourselves as consumers is increasingly important – whether it be for concerns over sustainability or mercury consumption.