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Catfish from Patagonia Lake have elevated mercury levels, Az officials warn
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Catfish from Patagonia Lake have elevated mercury levels, Az officials warn

  • Alan Schmierer/Flickr

Anglers should limit their consumption of catfish from Patagonia Lake because of elevated levels of mercury, state officials announced Wednesday.

Recent analyses of fish tissue showed high levels of the chemical, prompting an advisory about Flathead Catfish caught in the lake in Santa Cruz County from Arizona Department of Environmental Quality and the Arizona Game and Fish Department.

"To protect the health of everyone who enjoys eating fish caught in Arizona waters, ADEQ tests filets of sampled fish for mercury and other pollutants of concern to recommend healthy amounts of fish species to catch and eat," officials said in a news release.

Adults should limit the amount of Flathead Catfish hauled in from Patagonia Lake to 2.5 ounces per week, ADEQ said. Children under 12 shouldn't eat more than 2 ounces per month. 

Native to the lower Great Lakes and Mississippi River Basin, the Flathead Catfish was introduced to Arizona in the 1940s. The catfish is dark-brown or yellow-brow and has a yellowish-white belly, according to Game and Fish.

Patagonia Lake is a man-made reservoir about 50 miles southwest of Tucson, and is part of the state park system.

State officials said mercury can come from "various sources." Mercury is a common element in nature, and naturally occurs in rock, soil and water, said ADEQ. Additionally, abandoned mines, established before the development of modern mining practices "can be major contributors to mercury in the environment." 

Some industrial and manufacturing processes, including some mining activities can put mercury into the atmosphere, ADEQ said. The element can also be released into the air by fossil fuel burning, as well as when municipal solid waste or medical waste is incinerated, ADEQ said.

"Mercury in lakes is common throughout the United States and can be deposited in bodies of water far from the source through atmospheric deposition, meaning tiny particles of mercury settle out of the air and into the water or are deposited through rain- and snowfall," said ADEQ.

Mercury accumulates in fish because it "binds to muscle or fat with levels building up in the tissue over time" in a process known as bioaccumulation, and larger fish can accumulate elevated levels of mercury by eating smaller fish and insects, ADEQ said.

"Generally, contaminant levels found in water are significantly lower than those found in fish tissue," said ADEQ.

In 2001, the Environmental Protection Agency released a nationwide advisory for freshwater fish, warning women who are pregnant, or may become pregnant, as well as nursing mothers and young children to limit eating fish. The EPA said "sensitive adults" should eat just 6 ounces of cooked fish, or 8 ounces uncooked, of fish per week. And, young children should eat no more than 2 ounces of cooked fish, or 3 ounces uncooked, per week.

State officials said there are two "Green Light" fish at the lake that have been tested and do not show the same levels of mercury as the lake's catfish.

The Redear Sunfish and the Bluegill can be eaten may be eaten without limits under standard dietary guidelines.

State officials said despite the warning fishing, bird watching and "other recreational activities" at Patagonia Lake "are not affected by this advisory and are encouraged for enjoying the great outdoors."

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