A group of researchers found large concentrations of mercury and other toxic chemicals in the fish, insects, and plants of Colorado River in the Grand Canyon. Study authors said that the concentrations often exceeded the safe limits for wildlife and even humans in some areas.
According to the U.S. Geological Survey, Colorado River is no longer shielded from polluters by its relatively remote location. High concentrations of selenium and mercury were found in the Grand Canyon as well.
Both chemicals hinder wildlife’s reproduction, stunt growth, and sicken the aquatic and land species. The research team acknowledged that selenium may occur naturally in the region, but air pollutants including mercury can travel half the globe and taint the ecosystem.
Researchers took samples from six locations along the river and found that mercury levels were dangerously high in the fish and other small animals dwelling in the canyon. Moreover, in some fish species mercury levels were so high that they even threatened the life of humans.
Fortunately, the rainbow trout, a fish very popular with local fishermen, did not contain hazardous concentrations of the toxic chemical. Ted Kennedy,, one of the researchers involved in the study explained that both the trout in Glen Canyon and the trout downstream was safe to eat under EPA standards.
The recent study is unique because it is the first that tries to assess mercury pollution in the Grand Canyon. USGS researchers analyzed the trout there but five other species were also taken into consideration including carp and the rare speckled dace. Trout is of particular concern because humans usually prefer it.
The team admitted that they need to study more to learn whether eating fish from the Glen Canyon and Grand Canyon is hazardous to health for humans.
During the study they made some surprising findings. They learned that small rainbow trout was more likely to carry high concentrations of mercury than bigger trout. This finding is at odds with a widespread theory in biology called biomagnification, which states that polluter concentrations are higher in the upper areas of the food chain.
Kennedy explained that the oddity may be caused by Grand Canyon ecosystem’s particularities. For instance, in the Grand Canyon insects are scarce along the river due to temperatures and other circumstances. So, small fish can survive by eating only insects, while larger trout needs something else to supplement its calorie needs. As a result large trout eat algae, while smaller trout eat bugs, which are laden with mercury and other toxic chemicals.
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