Going Coastal

Mercury contamination can be a big problem in rivers, as it moves up the food chain accumulating in top predators. But what goes into the river largely stays in the river, or in creatures that feed in it — aquatic insects, fish and fish-eating birds.

In the South River in Virginia, however, the mercury has moved from the river to the shore, according to a study by Daniel A. Cristol and colleagues at the College of William and Mary. They report in Science that some nonaquatic bird species not feeding on fish but that breed within 50 yards of the river have high mercury levels in their blood.

The South, a Shenandoah tributary, was heavily contaminated with mercury sulfate from a DuPont factory from 1930 to 1950. Fish and aquatic birds on the river have long been known to be contaminated. But most of the 13 terrestrial birds tested had levels similar to or higher than the aquatic birds.

Researchers say the main culprit is spiders, which in some cases make up 30 percent of birds’ diets and have high levels of mercury. The spiders obtain mercury from their prey, either aquatic insects that are contaminated or terrestrial insects that develop in areas contaminated by flooding.

New York Times