Winged Mercury

  • Mercury - Not just for fish anymore
    Mercury - Not just for fish anymore
    Big juicy spiders are a favored food for songbirds, but researchers have found that arachnids sometimes come with a side order of methylated mercury.
    Photo by Dan Cristol

If you like to fish, you may or may not know that there are hundreds - no, thousands - of lakes and rivers in the U.S. holding fish that are too contaminated to eat safely.

Often, the contamination is caused by mercury pollution. Mercury has gotten into the water, sometimes decades ago, and then the bacteria start to work on it. The bacteria convert, or methylate, the mercury into a deadlier form, taking the stuff from the bottom of the stream and into the food chain. Scientists, by the way, usually say "trophic web," rather than "food chain."

The bacteria are eaten by other animals, methylated mercury and all. Whatever eats the bacteria is dinner for something larger and so on. The mercury, through a phenomenon called biomagnification, concentrates in larger and larger amounts as it goes up the food chain, until you have smallmouth bass and fish-eating herons with levels of mercury in them.

All of this is bad news, of course, but it's old science. Until 2008, everyone thought that the good news was that aquatic mercury concerns were confined to the aquatic trophic web. If an animal doesn’t eat food from the contaminated river, there should be no problem, right?

Wrong.

A team of researchers from William and Mary — all students except for a single professor — has shown that songbirds near a polluted river in Virginia are getting alarmingly high levels of mercury in their bodies even though they don’t eat food from the river. Birds along unpolluted streams were mercury-free.

Where are the birds getting the mercury?

"The birds eat a lot of spiders," explained ornithologist Dan Cristol of William and Mary's biology department. Spiders are like little tiny wolves, basically, and they’ll bioaccumulate lots of contaminants in the environment. The spiders have a lot of mercury in them and are delivering the mercury to these songbirds."

He was lead author on a groundbreaking article in the journal Science showing that the mercury was getting out of the river and into the terrestrial trophic web. His co-authors were all William and Mary students. The editors of Science thought having a bunch of student co-authors was pretty cool. So do we, but it's not unusual here.

So. Next question: How are the spiders getting their mercury?

Cristol and his team of student researchers will be working on that one next.