what I didn't know about mercury- fyi

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What I Didn't Know About Mercury -- NRDC's This Green Life 9/06

September 2006

WHAT I DIDN'T KNOW ABOUT MERCURY

Until I decided to write the present piece, I thought I knew as much as I

needed about the risk I faced from eating mercury-laden fish. I knew, for

instance, that mercury -- which passes easily from mother to child in utero

and through breast milk -- is a neurotoxin that can damage the developing

brain. I also thought I knew that I, personally, had nothing to worry about,

as I eat very little fish that's high in mercury and don't plan to have more

kids.

I have been chastened.

Surprise #1: My mercury exposure has been above the level considered safe by

the Environmental Protection Agency for three of the past four weeks,

according to NRDC's mercury calculator. (This is just an estimate based on

averages, not a measurement of my actual exposure, which would require that

I be tested.)

It wasn't that I overindulged. There was only one week when I ate fish more

than once (ironically, my " safe " week), and my portions were all moderate in

size.

The problem is with the fish I chose to eat -- in particular, shark and

swordfish. As large, predatory species, they contain much higher levels of

mercury than small fish, such as anchovies and sardines, because of the way

mercury moves up the food chain. I knew this but didn't realize that a

single 6-ounce portion in a week would be enough to put me over the top --

by a factor of four.

(In passing, I should note that shark was a bad choice from a sustainability

standpoint, as well, as shark populations are dangerously low.)

Even the single portion of smoked bluefish I had one week was borderline.

And bluefish has the added problem of contamination with PCBs.

Surprise #2: The danger from mercury is not just to developing brains. A

growing body of evidence suggests an association between mercury exposure

and heart disease. So even middle-aged people, like my husband and myself,

should take care what they eat.

These two surprises were enough to make me shun the fish stand at the

greenmarket last Saturday. But that was foolish: eating fish low in mercury

is good for the heart, and low-mercury choices abound.

So, which fish are good choices? There's a longish list, including some

popular fish, such as sole, tilapia, clams and oysters. When it comes to

canned tuna, chunk light is much better than white albacore, as it typically

has about a third of the mercury (though Consumer Reports recently found

that some cans of chunk light can contain as much mercury as most albacore).

Just be careful how much canned tuna you consume, as quantity matters --

even more for kids than adults because they weigh so little.

And what's bad? Well, swordfish and shark top the list, along with king

mackerel, marlin, orange roughy and tilefish. Steer clear of them altogether

if you are trying to become pregnant, are already pregnant or are nursing,

and obviously, don't feed them to young children. Even if you aren't

planning on children, if you are a woman of reproductive age, it would be

wise to limit your intake in case you change your plans or become pregnant

without planning -- as it takes months to shed your body of mercury.

There are many other fish besides the ones I've listed here, including many

with moderate levels of mercury that are safe to eat in limited quantities.

So, do yourself a favor and consult NRDC's guide to mercury in fish.

Knowledge is power -- and a key to good health.

-Sheryl Eisenberg

Where does mercury come from?

Mercury is a natural substance, one of the basic elements (Hg), and is bound

up in the earth's crust where it does no harm. It becomes a problem when it

is released into the atmosphere and settles in bodies of water. It can then

be converted by microorganisms to a more dangerous form (methyl mercury) and

ingested by fish, which are consumed by fish-eating animals, including

humans.

The release of mercury occurs through natural processes, such as volcanic

eruptions and forest fires. However, human activities since the beginning of

the Industrial Age have tripled the amount of mercury in the atmosphere,

according to the U.S. Geological Survey.

There are a number of human sources of mercury emissions, from old chlorine

plants to gold mining, but the single largest one is coal-fired power

plants. This is just one reason why coal is such a bad source of

electricity. Global warming is another.

(requires Adobe Acrobat)

Sheryl Eisenberg, a long-time advisor to NRDC, posts a new This Green Life

every month. Sheryl makes her home in Tribeca (NYC), where-along with her

children, Sophie and Gabby, and husband, -she tries to put her

environmental principles into practice. No fooling.

Mercury (at left). If a mercury thermometer breaks, the mercury will bead

like this and release toxic vapors. Learn how to protect yourself.

ONLINE RESOURCES

NRDC

Mercury Contamination in Fish

GREENFACTS

Scientific Facts on Mercury

SAN FRANCISCO CHRONICLE

Mercury In Fish Poses Heart Risk For Middle-Aged Men

UNIVERSITY OF CALGARY

How Mercury Causes Brain Neuron Degeneration (video)

MARKETPLACE

New Test Promises Safe Fish Faster

AMERICAN HEART ASSOCIATION

Fish and Omega-3 Fatty Acids

MONTEREY BAY AQUARIUM

Seafood Watch

Risk to children in the United States. One in 17 women of childbearing age

has more mercury in her blood than the safety level set by the government of

5.8 micrograms per liter of blood, according to a 2005 report from the

Centers for Disease Control and Prevention. Recent science suggests that

even 3.4 micrograms might pose a risk to the fetus because mercury

concentrates in the umbilical cord. Nearly one in 10 women of reproductive

age in the United States has that level or higher.

Don't give up on fish. The American Heart Association recommends that you

eat fish at least two times a week because fish-especially fatty

varieties-are high in omega-3 fatty acids, which can help prevent heart

attacks. Fatty fish that are low in mercury include mackerel (but not king

mackerel), herring, sardines and salmon.

Suspect your mercury is high? You can get a self-testing kit from Greenpeace

for $25. Your lab results will be kept confidential but used in a study,

anonymously, to determine if mercury exposure levels in the United States

exceed standards set to protect public health. If you have serious reason

for concern, consult your doctor. In general, you should be able to bring

your mercury down to safe levels in 6 months if you alter your diet to avoid

mercury.

Consult local advisories. If you fish for sport and eat your catch, consult

local fish advisories for mercury contamination warnings. This is also a

good idea if you buy fish caught in local waters.

Coal plants are the biggest human source of mercury emissions in the world.

To have This Green Life sent to you each month by email, subscribe to our

mailing list.

---------------------------------

Sheryl Eisenberg is a web developer and writer. With her firm, Mixit

Productions (http://www.mixitproductions.com), she brought NRDC online in

1996, designed NRDC's first websites, and continues to develop special web

features for NRDC. She created and, for several years, wrote the Union of

Concerned Scientists' green living column, Greentips, and has designed and

contributed content to many nonprofit sites.

© 2006 Natural Resources Defense Council

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