Still skeptical about the pervasive existence of mercury in our environment? You probably won't be after reviewing this latest report, a seven-year study by U.S. Geological Survey (USGS) about the presence of mercury in more than 1,000 fish collected from 291 American freshwater streams.

The surprises were twofold for USGS researchers: All fish tested by the agency contained some mercury, and about 25 percent of them exceeded safety levels set by the EPA.

The highest concentrations of mercury were reported in remote blackwater streams located along the coasts of several Southeastern states (Florida, Louisiana, North Carolina, Georgia and South Carolina) and in Western states where streams may be contaminated by mining operations.

According to a 2000 USGA fact sheet, humans are exposed to the most toxic form of mercury -- methylmercury is a potent toxin for nerve cells -- almost entirely by eating fish and wildlife at the top of the aquatic food chains.

Even worse, a Duke University researcher recently discovered how organic matter and chemicals containing sulfur serve as catalysts that allow mercury to be converted into methylmercury at the nanoparticle level inside the microbe.

U.S. Geological Survey August 11, 2009

ABC News August 21, 2009

Time.com August 19, 2009

Science Daily August 19, 2009