The Hidden Risk and Cost of Mercury Pollution

And the same rain that brings mer­cury pol­lu­tion down from the sky falls on us, too. So are these species a kind of canary in the coal mine for mercury’s effects on other ver­te­brates, includ­ing peo­ple? And will strict new fed­eral stan­dards lim­it­ing U.S. power plant pol­lu­tion be enough in a world where mer­cury pol­lu­tion is on the rise from China and other nations? I talked with two co-authors of “Hidden Risk” — BRI’s exec­u­tive direc­tor, Dave Evers, and Tim Tear, the Conservancy’s direc­tor of sci­ence for New York — to find out more. (Download the report here.)

Q. Some are going to be sur­prised that mer­cury pol­lu­tion is still a prob­lem — didn’t var­i­ous agen­cies and indus­tries take steps to reduce mer­cury emis­sions over the last decade in the United States? So why are high lev­els of mer­cury still a prob­lem in many wildlife species?

Dave Evers: Yes, a lot of mer­cury has been taken out of air pol­lu­tion over the past few decades — but our under­stand­ing is grow­ing of how just a lit­tle mer­cury can adversely affect wildlife, and how many species have been affected. More species are being impacted than we had thought, and the tox­i­c­ity of methylmer­cury to those species is at lower thresh­old lev­els than we ever realized.

Tim Tear: Many of these species and many of the places affected are in people’s back­yards. People used to think that mer­cury pol­lu­tion was a prob­lem iso­lated to remote areas of the Northeast. No more.

Q. So, would some­one see a bird or a bat act­ing strangely because of mer­cury pol­lu­tion? Or is this some­thing that data is telling you?

Evers: The effects are dif­fi­cult to see in the field for the aver­age observer. Mercury doesn’t cre­ate phys­i­cal muta­tions, and an indi­vid­ual ani­mal with mer­cury will prob­a­bly die from pre­da­tion first. But mer­cury is a neu­ro­toxin that does impact wildlife behav­ior, and that behav­ior impacts their sur­vival and repro­duc­tion. We focus on data to really quan­tify the impacts of mer­cury on the repro­duc­tive suc­cess of species.

For exam­ple, we quan­ti­fied mer­cury impacts on the com­mon loon. Common loons need to spend about 98 per­cent of their time on a nest incu­bat­ing their eggs to have those eggs suc­cess­fully hatch. We’ve quan­ti­fied with over 5,000 hours of obser­va­tion that loons with high mer­cury lev­els spend only 85 per­cent of their time incu­bat­ing those eggs. So they spend less time in an incu­ba­tion pos­ture, and because of that, eggs do not hatch, and because of that, the species’ repro­duc­tive suc­cess goes down.

Q. Where is the mer­cury pol­lu­tion still com­ing from? And what U.S. regions are of most concern?

Tear: Most of the research has really focused on the Northeast United States — an area that’s been really hard hit by acid rain, which makes mer­cury a big­ger prob­lem. But mer­cury pol­lu­tion is hap­pen­ing all over the world. It comes glob­ally from Asia, as well as nation­ally from power plants in the Midwest, to locally from waste incin­er­a­tors. We’re going to need to address all sources of mer­cury to be suc­cess­ful in stop­ping these impacts.

Q. And in dif­fer­ent habi­tats, right? Most peo­ple in the United States who know about mer­cury in nature know about it through warn­ings about the fish they eat.

Evers: Yes, there’s been a par­a­digm shift in new find­ings. In the past, most of the sci­en­tists assess­ing risk from mer­cury in an ecosys­tem would be look­ing at fish-eating birds and fish-eating mam­mals — because we knew methylmer­cury (the organic form of mer­cury) moved through the food web in aquatic organ­isms. But there’s been a miss­ing link in look­ing at mer­cury in ter­res­trial ecosys­tem food webs and look­ing at how species that eat insects and spi­ders — what we call “inverti­vores” — can be affected.

In the inverti­vore food web, the key pieces are no longer fish, but spi­ders. A bird that eats a spi­der that ate a spi­der that ate a fly — that’s four dif­fer­ent changes in the trophic food web. We’ve estab­lished that a lit­tle song­bird like a north­ern waterthrush or a spar­row that eats spi­ders can actu­ally be higher up in the food web than a bald eagle, which eats fish — and so that song­bird has more mer­cury in its body than does the eagle.

Tear: We’ve also dis­cov­ered that mer­cury is in many more food webs than we real­ized. It is not just in lakes and ponds. It’s in our forests, our estu­ar­ies; it’s in the low­lands and on the moun­tain­tops. It’s in the spi­ders in the Adirondacks, and it’s in back­yard birds in New York City.

Q. You men­tioned effects on repro­duc­tive suc­cess. What are some of the other impacts of mer­cury on ter­res­trial wildlife?

Evers: For exam­ple, bird song is affected. Two recent stud­ies show that birds with high mer­cury can’t hit the high notes, and their songs are sim­pli­fied. I also worry about long-distance migra­tion, because high mer­cury has been shown to affect the sym­me­try of devel­op­ment. If a bird’s left wing is 5 per­cent dif­fer­ent in shape than its right wing, that bird is going to fly in a crooked way to com­pen­sate for it, which requires more energy to make a flight of thou­sands of miles to its win­ter­ing area. Ultimately, that’s going to affect its survival.

Q. That’s sad. But ulti­mately, why should humans care?

Tear: First, if you care about the envi­ron­ment and you care about birds and bats and bugs, then you should care that many of these ani­mals are being heav­ily impacted.

But the sec­ond answer is that the neu­ro­toxic rain that con­tains mer­cury falls on humans as well as wildlife. We already know that mer­cury can be a big prob­lem in human health. This research estab­lishes that the effects of mer­cury are hap­pen­ing all over the planet, all over many habi­tat types, to ver­te­brate species other than our­selves. So peo­ple should be con­cerned about these effects, because there’s a link between human health and ecosys­tem health.

Q. Back to the sci­ence of this. How the heck do you mea­sure mer­cury in a bird pop­u­la­tion, anyway?

Evers: It’s actu­ally very sim­ple and straight­for­ward. There are nice and easy ways to cap­ture and/or take sam­ples from an indi­vid­ual bird that are quick and are non-harmful to the bird and do very lit­tle dis­rup­tion to its rou­tine, other than just hav­ing it in a net or hand for a half hour or so. We take a blood sam­ple — just a drop does the trick. We also can take a feather sam­ple, which gives us more of a long-term pic­ture of how much mer­cury has come into that indi­vid­ual over time.

Click here to read the rest of this arti­cle at Grist.org.