By now you’re probably well aware that environmental mercury has contaminated so much seafood that the US Food and Drug Administration (FDA) maintains an ongoing “do not eat” list for at-risk populations.
The mercury, which is a potent neurotoxin, among a plenitude of other adverse bodily effects, doesn’t stop at seafood, however. Mercury is extremely persistent once in the air, water, and soil; levels gradually increase over time, as it accumulates.
In addition to seafood, mercury is now found at alarming levels in many other species. It’s traveling up the food chain quickly and, even at sub-lethal doses, is threatening the future of songbirds, shorebirds, bats, and more.
Songbirds at Risk from Mercury Pollution
Biologists have been studying the effects of mercury exposure on fish-eating birds for decades, but it’s become apparent that even songbirds are at severe risk.
Forest birds may eat insects that come from rivers (such as mayflies) or insects that eat river insects (such as spiders). As a result, some songbirds, including Caroline wrens and red-eyed vireos, have higher levels of mercury than shorebirds like kingfishers.
Among songbirds living at the South River in Virginia, which was contaminated with mercury by DuPont from 1929 to 1950, the problem is particularly pronounced. Researchers from the College of William and Mary explained:
“They had 20 percent fewer babies… Their songs are sung at the wrong pitch. Their hormone levels are altered. Their immune systems are suppressed.”
In order to determine if it was, indeed, the mercury leading to these adverse effects (as opposed to another toxicant), the researchers measured the effects of sub-lethal doses of mercury on zebra finches… and found similarly devastating results.
The mercury-exposed birds had reduced reproductive success, with a 16 percent reduction in offspring produced in one year at the lowest dose of mercury (the equivalent of less than the amount found in a can of tuna).3 At higher doses, a 50 percent reduction in offspring occurred, and all the birds had a harder time remembering where food was located. The researchers concluded:
“Our results indicate that mercury levels in prey items at contaminated sites pose a significant threat to populations of songbirds through reduced reproductive success.”
Canadian Bird Eggs Contain Dangerous Levels of Mercury
The mercury threat exists across North America, where Alberta Health recently issued a health warning regarding the consumption of gull and tern eggs, which are sometimes eaten as part of the traditional diet.
The eggs, which were found downstream from oilsands (large deposits of crude oil), were found to contain dangerous levels of mercury, prompting health officials to warn pregnant women and children to limit their consumption.
According to Environment Canada data, levels of mercury in eggs from waterbirds downstream from oilsands have increased nearly 50 percent in the last 30 years, and some species shown increases of up to 139 percent from 2009 to 2012.
It’s unknown what levels of mercury exist in other traditional foods, such as moose, deer, or duck and goose eggs, which has officials calling for increased monitoring.
Shorebirds and Bats Are Also Being Poisoned by Mercury
At Onondaga Lake in Syracuse, New York, often referred to as the “most polluted lake” in the US due to 100 years of industrial dumping, the environmental toll of mercury pollution is also alarming. Mercury studies conducted by the Biodiversity Research Institute in Maine show that species both big and small – from spiders and beetles to bats and eagles – are teeming with mercury.
The birds and bats are exposed via their diet. As they eat insects, clams, fish, and other invertebrates, they accumulate increasing amounts of mercury. Some of the birds had mercury levels so high that 20 percent of their offspring would not survive, while more than half of bats tested had enough mercury to experience “adverse effects.” Results from the studies, which included testing of more than 400 birds and close to 300 bats, showed:6
More than half of the bats had mercury levels high enough to cause behavioral changes
Nearly half of tree-swallow eggs contained high levels of mercury
Some spotted sandpipers contained so much mercury that two out of every 10 chicks would not survive.
Part II highlights mercury in dental amalgams.