Click here for Lao version/ຄລິກບ່ອນນີ້ເພື່ອອ່ານພາສາລາວ
A new study in the United
States found widespread contamination of toxic mercury in fish from streams
that appear to be pristine. It's the
latest indication of how widespread mercury pollution is.
Mercury is poisonous to the nervous system, and it's especially harmful
to young children. Exposure to a form of Mercury called methylmercury can
damage children's memory, attention, language skills, and other mental
abilities as they develop.
In the new report,
researchers from the U.S. Geological Survey, or U-S-G-S, studied nearly 300
freshwater streams across the United States from 1998 to 2005. They examined
mercury levels in fish at the top of the food chain -- the kind that fishermen
prize, such as bass and trout. The study found that one-quarter of them had
mercury levels above what are considered safe.
Geochemist Mark Brigham, one of the authors of the study, says some of the
highest levels of contamination were in fish from relatively undisturbed
streams that are surrounded by forests and wetlands. He thinks the only mercury
they're getting is from atmospheric deposition or in other words, mercury
falling from the sky. Brigham says it gets into the atmosphere from a variety
of natural and industrial sources. The single largest man-made contributor to
that pollution is burning coal for energy.
That mercury may also be coming from far outside the United States. So, any
emission of mercury from one continent can affect the other continents. So, if
you say there are emissions from Asia, for example, it can affect North
America. Or the other way around, [emissions] from North America can also
That makes mercury pollution a global issue. The U.S. is the number-three
mercury emitter, behind India, and well behind China. Gina Solomon with the
Natural Resources Defense Council, says the U.S. needs to take the lead in
reducing its mercury emissions before asking the same of developing countries
There is a compelling need,
for health reasons, for all the countries of the world to reduce their mercury
pollution. And this certainly applies to Asia, where the power industry is a
major source of global mercury pollution.
Asia is also a major fish consumer. Not a lot of good research has been done in
this area, but the U-N's Desiree Narvaez says spot checks have turned up some
high levels of mercury in Asian fish.
Study author Mark Brigham says mercury accumulates up the food chain from algae
to small fish to big. So the biggest fish tend to have the most mercury.
Smaller fish and those lower in the food chain tend to be safer -- for example,
catfish, shrimp, and pollock. Brigham notes that most of the fish his group
sampled were safe to eat. And health experts recommend eating fish as part of a
healthy diet -- as long as it's not contaminated with too much mercury.