Mercury Poisoning in a Young Saltmarsh Sparrow

Saltmarsh Sparrow / Photo by Wolfgang Wander

Most of us are familiar with the hazards posed by mercury. In the compound known as methylmercury, it becomes a potent neurotoxin, for both humans and wildlife. When infants are exposed in utero, methylmercury causes a variety of developmental problems. Environmental mercury comes primarily from industrial sources, such as waste incineration and the burning of fossil fuels for energy. Burning coal for electricity is a particularly strong contributor. Mercury is aerosolized by these processes and then enters waterways via precipitation. Aquatic invertebrates and fish consume mercury through their diets. It is for this reason that pregnant women are advised to avoid fish, some of which store significant levels of methylmercury in their tissues.

Methylmercury has already been documented in multiple bird species, with particularly high concentrations in Wood Thrushes. Some birds such as raptors and kingfishers have fish as a mainstay of their diets. Songbirds consume mercury by eating invertebrates that spend the early stages of their life in the water (such as mosquitoes, dragonflies, and caddisflies) or by eating spiders that prey on those aquatic invertebrates. Mercury is associated with behavioral changes in songbirds and may skew sex ratios. Like in humans, mercury affects learning and memory in songbirds. It also hampers birds' ability to learn and sing songs.

A new study by Sheila Scoville and Oksana Lane adds to the evidence for mercury's harmful effects in songbirds. When a fledgling Saltmarsh Sparrow (Ammodramus caudacutus) was accidentally killed at a study site on Long Island, it was collected and analyzed for mercury poisoning. Feathers were collected and sent to the Biodiversity Research Institute to test for mercury exposure, and the sparrow's brain was analyzed at the Eastern Virginia Medical School. The fledgling showed some exposure to mercury, though not at the levels measured in adults at that study site (which overall were very high).

Based on feather samples taken from adult birds at the study site, it can be inferred that this fledgling's mother had high exposure to mercury at the time that she laid her eggs. This is analogous to in utero exposure in humans. In humans, in utero exposure can lead to brain abnormalities like Minamata Disease. This fledgling Saltmarsh Sparrow showed abnormalities in its cerebellum that would have similar effects on motor control and coordination. Birds with these sorts of defects would have trouble recognizing and escaping danger, thus making them more susceptible to predation and accidental deaths.

While this fledgling Saltmarsh Sparrow is only one data point, the findings have disturbing implications. Since mercury levels among adult birds were so high, many other young Saltmarsh Sparrows are presumably exposed to mercury at the time of egg formation. We cannot know how many of them have brain abnormalities like the one documented in this study, but it seems safe to assume that the problem is widespread.

Even without human interference, Saltmarsh Sparrows lead a precarious existence. At any time during the breeding season, their nests may be flooded by particularly high tides or destroyed by violent storms. Their breeding range is restricted to a narrow strip of saltmarshes along the Atlantic Coast of the United States. Their habitat is constantly under pressure from human encroachment, as more and more coastal areas are developed as beach resorts. Oil and chemical spills further degrade their remaining habitat. There is an additional threat from sea level rise due to climate change and subsidence. For these reasons, BirdLife rates the Saltmarsh Sparrow as a vulnerable species. Now we know that in addition to all these other problems, the species also faces a threat from ingestion of mercury.

The harm caused by mercury is not something conservationists can easily remedy. Shifting away from coal as a source of electricity would at least reduce the amount of mercury entering our waterways. What we can and should do is protect and maintain as much remaining saltmarsh as possible so that the sparrows that survive to adulthood will have enough habitat for breeding.

Thanks to Peter Doherty for alerting me to this study.

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Scoville, S., & Lane, O. (2013). Cerebellar Abnormalities Typical of Methylmercury Poisoning in a Fledged Saltmarsh Sparrow, Ammodramus caudacutus Bulletin of Environmental Contamination and Toxicology, 90 (5), 616-620 DOI: 10.1007/s00128-013-0974-y

New Greenhouse Gas Regulations

This week the EPA proposed its first-ever regulation of carbon dioxide as a greenhouse gas.

The proposed rule — years in the making and approved by the White House after months of review — will require any new power plant to emit no more than 1,000 pounds of carbon dioxide per megawatt of electricity produced. The average U.S. natural-gas plant emits 800 to 850 pounds of CO2 per megawatt; coal plants emit an average of 1,768 pounds of carbon dioxide per megawatt.

Industry officials and environmentalists said in interviews that the rule, which comes on the heels of tough new requirements that the Obama administration imposed on mercury emissions and cross-state pollution from utilities within the past year, dooms any proposal to build a new coal-fired plant that does not have costly carbon controls....

The rule provides an exception for coal plants that are already permitted and beginning construction within a year. There are about 20 coal plants now pursuing permits; two of them are federally subsidized and would meet the new standard with advanced pollution controls.

Based on the coverage I read, it looks like the coal industry and its political patrons are trying to paint this as a sign of the EPA having a radical agenda. The EPA only came to this point reluctantly, however. The EPA was bound by a Supreme Court decision in 2007 to determine whether carbon dioxide was a harmful pollutant as defined by the Clean Air Act. Once the EPA determined that carbon dioxide emissions are causing harm in 2009, it was bound by the Clean Air Act to issue regulations. Even so, the Obama administration waited three years after the initial determination to do something about it because they wanted Congress to pass a new climate change bill.

A potential downside of the new regulation is that it only applies to new power plants and not existing ones. So this will not lead to an immediate decrease in greenhouse gas emissions. That will only happen once older coal plants come offline and get replaced with cleaner power sources. However, David Roberts argues that regulations of existing plants are bound to come at some point.

Here’s the story: Once something is deemed a pollutant under the Clean Air Act (which, in the case of CO2, was settled by the Mass v. EPA Supreme Court case), then it must be regulated under Section 111 of the act, the New Source Performance Standards program.

Section 111b governs new sources. That’s what was issued today. But when EPA regulates under 111b, that triggers a legal obligation for it also to regulate existing sources under 111d.
Which is a nerdy way of saying: EPA is legally obligated to regulate existing power-plant sources of CO2.

All that remains is to determine the timing. A bunch of green groups sued EPA over their delay on CO2 several years back. The settlement that was reached obligated EPA to issue CO2 regs by last September. Obviously that didn’t happen. Green groups then agreed to a few extensions. They have taken the issuance of the rule today as a sign of good faith from EPA that it’s on track.

Regulation of existing sources under 111d is a much trickier, more difficult matter than regulation of new sources. There are genuinely novel questions of law and technology involved. EPA has been grappling with these questions, but it’s not easy and there are a great many interested stakeholders, to say the least. Even if it wanted to, EPA probably couldn’t get that rule done and issued before the election.

On the whole, I think this is a step in the right direction, though perhaps not one that will bear immediate fruit. If Obama is reelected, it would not surprise me to see some regulation of existing sources during his second term. Of course, if he loses, the new regulation could be watered down or rescinded entirely, though the latter would be in defiance of the Supreme Court.

Mercury Poisoning Is Harming Songbirds

Wood Thrush / USFWS Photo

A new study by scientists at the Biodiversity Research Institute confirms that songbirds suffer harmful effects from ingesting methylmercury, one of the toxic chemicals produced by burning coal for energy. Despite some moves towards cleaner energy sources, coal is still the principal fuel for producing electricity through much of the Midwest and Northeast. The emissions from power plants include methylmercury in addition to carbon dioxide and other chemicals; the methylmercury is absorbed by tree leaves or falls to the ground in rainstorms and subsequently enters the food web.

The new study found dangerously high levels of mercury in several Northeastern bird species, including rusty blackbirds, saltmarsh sparrows and wood thrushes. Previous studies have shown mercury’s effects on loons and other fish-eating waterfowl, as well as bald eagles, panthers and otters. In one study, zebra finches lost the ability to hit high notes in mating songs when mercury levels rose, affecting reproduction.

“We’re seeing many other species in a much larger landscape of harm from mercury,” said the principal author, David C. Evers, who is the institute’s executive director. He called the Environmental Protection Agency’s new mercury standards, adopted last month and scheduled to take effect over the next four years, “an excellent step forward in reducing and minimizing the impact on ecosystems and improving ecological health, and therefore our own health.”

And the results of mercury poisoning were quite severe, even at fairly low levels of contamination.

Songbirds with blood mercury levels of just 0.7 parts per million generally showed a 10 percent reduction in the rate at which eggs successfully hatched. As mercury increases, reproduction decreases. At mercury levels of greater than 1.7 parts per million, the ability of eggs to hatch is reduced by more than 30 percent, according to the study.

Over all, birds in contaminated sites were found to be three times as likely to abandon their nests or exhibit abnormal incubation or feeding behavior. In some nests, the chicks seemed to have been affected most; they vocalized less and did not beg as aggressively to be fed.

Such consequences mimic the effects of mercury on humans whose primary contact with the toxin is through the consumption of fish. The contamination can be passed to children in the womb or while they are nursing, damaging their nervous systems and impairing their ability to learn.

The authors found similar effects in bats that they tested. Perhaps the new mercury regulations will reduce some of these problems over the next decade or two.