Wednesday, Jan. 14, 2009 | 5:03 p.m.
Fish caught in Lake Mead are safe to eat with mercury levels below both EPA and FDA guidelines, according to preliminary studies from UNLV.
The findings by UNLV graduate student Joanna Kramer were made public Wednesday at the Lake Mead Symposium held at UNLV. She conducted the study to help establish a contaminant monitoring protocol for the lake.
"There has been no formal study that has used EPA-approved methodology to determine the levels of mercury of fish in our lake," Kramer said.
The study measured levels in largemouth bass, striped bass, channel catfish and blue tilapia in four areas: the Gregg Basin, Virgin Basin, Boulder Basin and Overton Arm.
Mercury levels for all of the fish came in at 30 percent or less of what the EPA considers safe for human consumption: 0.5 parts per million. The Food and Drug Administration allows 1.0 parts per million.
The striped bass posted the highest average levels of mercury, at .155 parts per million, followed by channel catfish at .103 and largemouth bass at .090. Kramer said the tilapia returned levels below the limit of detection.
"The take home message is go ahead and eat your fish," Kramer said. "They're OK."
Methyl mercury can accumulate through the food chain after being introduced by coal-fired electrical plants and industrial activities, Kramer said. At high levels, the mercury can cause motor difficulties, mood problems and death, with pregnant women, fetuses and children most at risk.
"Six percent of women in the U.S. of child-bearing age have methyl mercury levels of concern," Kramer said.
Despite measurements indicating the fish were safe to eat, the striped bass posted significantly higher concentrations than the other fish, Kramer said, with two individual fish exceeding EPA standards. She hypothesized that this may occur because the striped bass are more competitive predators and are more abundant in the lake. On the other hand, the tilapia are primarily herbivores, so those fish accumulate less mercury.
The study also sought to illuminate any relationship between mercury levels and locations. Initially, Kramer believed the Boulder Basin might carry significantly higher concentrations because of its proximity to the Las Vegas Wash, which can carry industrial pollutants into the lake. However, the Boulder Basin had the lowest average concentration at .051 parts per million. The other locales carried levels with insignificant differences, Kramer said, with parts per million ranging from 0.092 to 0.105.
One reason may be a higher population of water-filtering quagga mussels, Kramer said, noting Boulder Basin was the first location where they were found in Lake Mead. Another factor could include the presence of a bacteria that consumes mercury.
Kramer plans to continue testing fish in the lake through 2010 as she finalizes her study.
Dave Clark can be reached at 990-2677 or firstname.lastname@example.org.