By Leah Burrows, SEAS Communications
Add another item to the ever-growing list of the dangerous impacts of global climate change: Warming oceans are leading to an increase in the harmful neurotoxicant methylmercury in popular seafood, including cod, Atlantic bluefin tuna and swordfish, according to research led by the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and the Harvard T. H. Chan School of Public Health (HSPH).
Researchers developed a first-of-its-kind, comprehensive model that simulates how environmental factors, including increasing sea temperatures and overfishing, impact levels of methylmercury in fish. The researchers found that while the regulation of mercury emissions have successfully reduced methylmercury levels in fish, spiking temperatures are driving those levels back up and will play a major role in the methylmercury levels of marine life in the future.82% of U.S. population-wide exposure to methylmercury comes from the consumption of marine seafood
The research is published in Nature.
“This research is a major advance in understanding how and why ocean predators, such as tuna and swordfish, are accumulating mercury,” said Elsie Sunderland, the Gordon McKay Professor of Environmental Chemistry at SEAS and HSPH, and senior author of the paper.
“Being able to predict the future of mercury levels in fish is the holy grail of mercury research,” said Amina Schartup, former research associate at SEAS and HSPH and first author of the paper. “That question has been so difficult to answer because, until now, we didn’t have a good understanding of why methylmercury levels were so high in big fish.”
It’s been long understood that methylmercury, a type of organic mercury, bioaccumulates in food webs, meaning organisms at the top of the food chain have higher levels of methylmercury than those at the bottom. But to understand all the factors that influence the process, you have to understand how fish live.
If you’ve ever owned a goldfish, you know that fish do pretty much two things: eat and swim. What they eat, how much they eat, and how much they swim all affect how much methylmercury fish will accumulate in the wild.
Let’s start with what fish eat.
The researchers analyzed 30 years of ecosystem data from the Gulf of Maine, including an extensive analysis of the stomach contents of two marine predators, Atlantic cod and spiny dogfish from the 1970s to 2000s.
The researchers modeled methylmercury levels in cod based on their diet and results indicated levels were 6 to 20 percent lower in 1970 than they were in 2000. Modeled concentrations of methylmercury in spiny dogfish, however, were 33 to 61 percent higher in 1970 compared to 2000 despite living in the same ecosystem and occupying a similar place in the food web. What accounts for these differences?
In the 1970s, the Gulf of Maine was experiencing a dramatic loss in herring population due to overfishing. Both cod and spiny dogfish eat herring. Without it, each turned to a different substitute. Cod ate other small fish such as shads and sardines (small herring), which are low in methylmercury. Spiny dogfish however, substituted herring with higher in methylmercury food such as squid and other cephalopods.
When the herring population bounced back in 2000, cod reverted to a diet higher in methylmercury while spiny dogfish reverted to a diet lower in methylmercury.
There’s another factor that impacts what fish eat: mouth size.
Unlike humans, fish can’t chew – so most fish can only eat what fits in their mouth whole. However, there are a few exceptions. Swordfish, for example, use their titular bills to knock down large prey so they can eat it without resistance. Cephalopods catch prey with their tentacles and use their sharp beaks to rip off mouthfuls.40% of U.S. population-wide exposure to methylmercury comes from fresh and canned tuna
“There’s always been a problem modeling methylmercury levels in organisms like cephalopods and swordfish because they don’t follow typical bioaccumulation patterns based on their size,” said Sunderland. “Their unique feeding patterns means they can eat bigger prey, which means they’re eating things that have bioaccumulated more methylmercury. We were able to represent that in our model.”
But what fish eat isn’t the only thing that impacts their methylmercury levels.
When Schartup was developing the model, she was having trouble accounting for the methylmercury levels in tuna, which are among the highest of all marine fish. Its place on the top of the food web accounts for part of this but doesn’t fully explain just how high its levels are. Schartup solved that mystery with inspiration from an unlikely source: swimmer Michael Phelps.
“I was watching the Olympics and the TV commentators were talking about how Michael Phelps consumes 12,000 calories a day during the competition,” Schartup remembered. “I thought, that’s six times more calories than I consume. If we were fish, he would be exposed to six times more methylmercury than me.”
As it turns out, high-speed hunters and migratory fish use a lot more energy than scavengers and other fish, which requires they consume more calories.
“These Michael Phelps-style fish eat a lot more for their size but, because they swim so much, they don’t have compensatory growth that dilutes their body burden. So, you can model that as a function,” said Schartup.
Another factor that comes into play is water temperature; as waters get warmer, fish use more energy to swim, which requires more calories.
The Gulf of Maine is one of the fastest warming bodies of water in the world. The researchers found that between 2012 and 2017, methylmercury levels in Atlantic bluefin tuna increased by 3.5 percent per year despite decreasing emissions of mercury.
Based on their model, the researchers predict that an increase of 1 degree Celsius in seawater temperature relative to the year 2000 would lead to a 32 percent increase in methylmercury levels in cod and a 70-percent increase in spiny dogfish.
The model allows the researchers to simulate different scenarios at once. For example:
“This model allows us to look at all these different parameters at the same time, just as it happens in the real world,” said Schartup.
“We have shown that the benefits of reducing mercury emissions holds, irrespective of what else is happening in the ecosystem. But if we want to continue the trend of reducing methylmercury exposure in the future, we need a two-pronged approach,” said Sunderland. “Climate change is going to exacerbate human exposure to methylmercury through seafood, so to protect ecosystems and human health, we need to regulate both mercury emissions and greenhouse gases. It is important also to remember that fish are a very healthy food overall and when people switch away from fish in their diet they generally pick less healthy alternatives. We can all agree less methylmercury in these fish in the future would be a good thing.”
This study was co-authored by Colin P. Thackray and Clifton Dassuncao, of SEAS and HSPH; Asif Qureshi, of the Department of Civil Engineering, Indian Institute of Technology Hyderabad, Kandi, India; and Kyle Gillespie and Alex Hanke of Fisheries and Oceans Canada. This research was supported in part by the US Environmental Protection Agency, the US National Science Foundation and the Nereus Program sponsored by the Nippon Foundation.
Nate Herpich, Harvard Correspondent
If a tree could talk, what might it say?
Would it plead for rain in a drought? Fawn over a neighbor’s foliage? Crack jokes about how fast another tree loses its leaves in fall?
It seems unlikely anyone will ever come across a loquacious linden. But for the arbor-curious, a red oak at the Harvard Forest in Petersham has been tweeting as @awitnesstree since July 17. Outfitted with sensors and cameras, and programmed with code that allows it to string together posts with prewritten bits of text, the Harvard Forest Witness Tree has been sharing on-the-ground insights into its own environmental life and that of its forest.
Already renowned in certain circles as the subject of the popular climate-change book “Witness Tree” by Lynda Mapes, the century-old oak’s social-media debut was the brainchild of Harvard Forest postdoctoral fellow Tim Rademacher and is now a team effort with Clarisse Hart, who heads outreach and education for the forest. Its online presence is modeled after similar “twittering” trees that chronicle their life experiences as part of a tree-water and carbon-monitoring network based in Europe called TreeWatch.net.
“We’ve done the work as a team to equip the tree with a voice, which we decided made the most sense in the first person, and even with a personality, in order to make it relatable to a larger audience,” said Rademacher. “But most importantly, our Witness Tree is an objectively data-driven account, which I expect will amplify messages of climate change. But we don’t decide what gets posted, the tree does.”
By Samuel Myers
Image: Narendra Shrestha/EPA-EFE/REX/Shutterstock
Samuel Myers is a principal research scientist at the Harvard Chan School of Public Health and director of the Planetary Health Alliance.
Feeding a planet inhabited by 10 billion people by mid-century — already a daunting task — is getting harder due to a little-known impact of global warming: the decline of essential nutrients in the world’s staple foods that exist in almost every single person’s diet around the world.
The mechanism by which rising carbon dioxide saps nutrients from our food crops remains somewhat unclear, but the effect is consistent across most plant types from trees to grasses to edible crops: It is reducing the availability of zinc, iron, protein and key vitamins in wheat, rice and several other fundamental grains and legumes.
The implications are huge: By 2050, hundreds of millions of people could slip below the minimum thresholds of these nutrients needed for good health, and more than 2 billion already deficient could see their conditions worsen. And it extends well beyond human nutrition as every animal in the biosphere depends, directly or indirectly, on plant consumption for nutrients.
These findings, which will appear this week as part of the most comprehensive review ever compiled on the two-way relationship between global warming and land use, highlight the urgent need to slash the greenhouse gas emissions that drive climate change. Human activity has increased atmospheric carbon more than 40 percent since the mid-19th century, enough to unleash a deadly onslaught of extreme weather made more destructive by rising seas. Without a drastic drop in emissions, those levels will climb even more quickly over the coming decades.
Scientists from the United Nations' Intergovernmental Panel on Climate Change are meeting in Geneva this week to validate a 30-page summary for policymakers of a 1,000-page underlying report. Food security is high on the agenda.
Nutritional deficiencies continue to take a heavy toll. Zinc deficiency affects the immune system and increases vulnerability to malaria, lung infections and deadly diarrheal diseases, claiming the lives of some 30,000 children younger than 5 each year. Protein deficiency causes stunting and increases infant mortality. Iron deficiency is linked to nearly 60,000 deaths and 34 million “life years” lost to disability or premature death every year, and can also result in decreased work capacity, reduced IQ and anemia.
Humans are deeply vulnerable to reductions in the nutrient content of staple food crops. We get 60 percent of dietary protein, 80 percent of iron and 70 percent of zinc requirements from plants, most of which are losing these nutrients in response to rising carbon dioxide levels.
Research I have co-written indicates that as a result of these emissions, nearly 2 percent of the global population — an extra 175 million people — could become zinc-deficient, and 122 million would no longer get enough protein. Some 1.4 billion women and children younger than 5 would find their iron intake reduced by 4 percent or more. Half a billion in this group risk developing iron-deficiency-related disease.
By 2050, the vitamin B content of rice is expected to drop 17 to 30 percent, upping the risk of deficiencies in folate (B9), thiamine (B1) and riboflavin (B2) for tens of millions of people, especially in regions dependent on rice. All these vitamins are crucial for normal and healthy development.
The reason for this is still a bit of a mystery. There are theories, such as that more carbon dioxide causes plants to produce more starch, which could have a diluting effect whereby plants become carbohydrate-rich and nutrient-poor. But that’s not the case for all nutrients; the science has a long way to go before we have sound answers.
We do know, however, that when the carbon dioxide effect is combined with the impact of climate change on crop yields, we see even larger reductions in the availability of nutrients in the global diet. Compared with a world without these effects, we anticipate a 14 to 20 percentreduction in the global availability of iron, zinc and protein by 2050, which would threaten large segments of the global population with nutrient deficiencies.
Supplements and vitamins could temporarily alleviate some of the health consequences, but these options have existed for decades and have not protected the billions of people who already suffer from nutrient deficiencies, in part because they are difficult to distribute and do not address the underlying cause of malnutrition.
The countries hit hardest are primarily those that have contributed the least to global carbon emissions, particularly nations in South Asia, the Middle East, sub-Saharan Africa and North Africa, and the former Soviet Union. India would also be hit especially hard, and there would be dramatic increases in zinc and protein deficiencies in China, Indonesia, Bangladesh, Brazil, Kenya and other emerging economies.
The bottom line is frighteningly clear: Unless governments dramatically step up their emissions-reduction efforts, nutritional deficiencies and their associated burdens are set to become even more severe and widespread. We cannot wait to act any longer.
By Leah Burrows, SEAS Communications
After years of making progress on an organic aqueous flow battery, Harvard University researchers ran into a problem: the organic anthraquinone molecules that powered their ground-breaking battery were slowly decomposing over time, reducing the long-term usefulness of the battery.
Now, the researchers — led by Michael Aziz, the Gene and Tracy Sykes Professor of Materials and Energy Technologies at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Roy Gordon, the Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science — have figured out not only how the molecules decompose, but also how to mitigate and even reverse the decomposition.
The death-defying molecule, named DHAQ in their paper but dubbed the “zombie quinone” in the lab, is among the cheapest to produce at large scale. The team’s rejuvenation method cuts the capacity fade rate of the battery at least a factor of 40, while enabling the battery to be composed entirely of low-cost chemicals.
The research was published in the Journal of the American Chemical Society.
“Low mass-production cost is really important if organic flow batteries are going to gain wide market penetration," said Aziz. “So, if we can use these techniques to extend the DHAQ lifetime to decades, then we have a winning chemistry.”
“This is a major step forward in enabling us to replace fossil fuels with intermittent renewable electricity,” said Gordon.
Since 2014, Aziz, Gordon and their team have been pioneering the development of safe and cost-effective organic aqueous flow batteries for storing electricity from intermittent renewable sources like wind and solar and delivering it when the wind isn’t blowing and the sun isn’t shining. Their batteries use molecules known as anthraquinones, which are composed of naturally abundant elements such as carbon, hydrogen, and oxygen, to store and release energy.
At first, the researchers thought that the lifetime of the molecules depended on how many times the battery was charged and discharged, like in solid-electrode batteries such as lithium ion. However, in reconciling inconsistent results, the researchers discovered that these anthraquinones are decomposing slowly over the course of time, regardless of how many times the battery has been used. They found that the amount of decomposition was based on the calendar age of the molecules, not how often they’ve been charged and discharged.
That discovery led the researchers to study the mechanisms by which the molecules were decomposing.
“We found that these anthraquinone molecules, which have two oxygen atoms built into a carbon ring, have a slight tendency to lose one of their oxygen atoms when they’re charged up, becoming a different molecule,” said Gordon. “Once that happens, it starts of a chain reaction of events that leads to irreversible loss of energy storage material.”
The researchers found two techniques to avoid that chain reaction. The first: expose the molecule to oxygen. The team found that if the molecule is exposed to air at just the right part of its charge-discharge cycle, it grabs the oxygen from the air and turns back into the original anthraquinone molecule — as if returning from the dead. A single experiment recovered 70 percent of the lost capacity this way.
Second, the team found that overcharging the battery creates conditions that accelerate decomposition. Avoiding overcharging extends the lifetime by a factor of 40.
“In future work, we need to determine just how much the combination of these approaches can extend the lifetime of the battery if we engineer them right,” said Aziz.
“The decomposition and rebirth mechanisms are likely to be relevant for all anthraquinones, and anthraquinones have been the best-recognized and most promising organic molecules for flow batteries,” said Gordon.
“This important work represents a significant advance toward low-cost, long-life flow batteries,” said Imre Gyuk, Director of the Department of Energy’s Office of Electricity Storage program. “Such devices are needed to allow the electric grid to absorb increasing amounts of green but variable renewable generation.”
This research was co-authored by Marc-Antoni Goulet, Liuchuan Tong, Daniel A. Pollack, Daniel P. Tabor, and Eugene E. Kwan, all from Harvard; and Susan A. Odom of the University of Kentucky; and Alán Aspuru-Guzik of the University of Toronto.
The research was supported by the Energy Storage program of the U.S. Department of Energy, the Advanced Research Projects Agency – Energy, the Innovation Fund Denmark, the Massachusetts Clean Energy Technology Center, and Harvard SEAS.
With assistance from Harvard’s Office of Technology Development (OTD), the researchers are seeking commercial partners to scale up the technology for industrial applications. Harvard OTD has filed a portfolio of pending patents on innovations in flow battery technology.