How Mercury-Tainted Tuna Damages Fetal Brains

Sandra Steingraber

Last spring, I received a tan­ta­liz­ing invi­ta­tion from the edi­tor of Child­birth Forum: write a sto­ry on mer­cury in fish and the result­ing risks to preg­nant women. This was a top­ic dear to my heart. Dur­ing the four years I researched fetal tox­i­col­o­gy at Cor­nell Uni­ver­si­ty, I had become alarmed about the breach between what the sci­en­tif­ic com­mu­ni­ty knows about the effects of pre­na­tal mer­cury expo­sure (a lot) and what the gen­er­al pub­lic knows (very little). 

Preg­nant myself dur­ing some of this time, I expe­ri­enced this dis­con­nect direct­ly. I spent one Valentine’s Day por­ing through the data that inform the Food and Drug Administration’s ongo­ing rec­om­men­da­tion that preg­nant women avoid sword­fish. Then I joined my hus­band for a meal in a near­by restau­rant. I was hard­ly seat­ed when the wait­er sug­gest­ed to me — so preg­nant I couldn’t pull my chair up to the table — the sword­fish spe­cial. Behind the bar was a sign warn­ing preg­nant women that alco­hol can cause birth defects. No sign appeared in the menu warn­ing preg­nant women that mer­cury in cer­tain fish can cause fetal brain damage.

The book I even­tu­al­ly wrote on envi­ron­men­tal threats to preg­nan­cy devotes two chap­ters to mer­cury. It was this book, Hav­ing Faith: An Ecologist’s Jour­ney to Moth­er­hood, that prompt­ed Alice Berman, edi­tor of Child­birth Forum, to solic­it my article.

I said yes. Spon­sored by Pam­pers dia­pers, the mag­a­zine has a print run of 20,000, and most of its read­ers are nurs­es who work as child­birth edu­ca­tors, an audi­ence I had long wished to reach. So, with my own child­birth instruc­tor in mind, I traced the flow of mer­cury through the human food chain, start­ing with its intro­duc­tion into the atmos­phere and end­ing with its pres­ence in tuna fish sand­wich­es. I fin­ished my sto­ry before the dead­line. The edi­tor liked it. It went out for exter­nal review. The review­ers liked it. The sto­ry was accept­ed for publication.

At about the time I start­ed check­ing my mail­box for copies, I found out my arti­cle would not be pub­lished after all. In an apolo­getic e‑mail, Berman for­ward­ed me the fol­low­ing mes­sage, which she said she had received from the group that han­dles the publication’s pro­duc­tion: Although the fea­ture is rel­e­vant, well-researched, and well-writ­ten, it can­not be used for Child­birth Forum at this time based on a direc­tive from the newsletter’s spon­sor, Proc­ter & Gam­ble. … The infor­ma­tion about mer­cury and fish must be writ­ten about in a larg­er con­text of diet dur­ing preg­nan­cy, and is too con­tro­ver­sial’ to fea­ture as it is.”

I’m a biol­o­gist. I always thought that the food chain was our diet. But maybe I’m miss­ing some­thing. You tell me. Here is the sto­ry, Mer­cury in Preg­nan­cy: Eat Fish With Cau­tion,” that Proc­ter & Gam­ble doesn’t want the teach­ers of preg­nant women to read:

Fish is the last form of wildlife many Amer­i­cans still eat. Those who sel­dom dine on stewed squir­rel or veni­son may be very famil­iar with tuna salad.

And fish is good food. It is low in sat­u­rat­ed fat and high in pro­tein. It is also a lead­ing source of omega‑3 fat­ty acids, which reduce blood pres­sure. These same nutri­ents help build healthy brains in our chil­dren. Dur­ing the sec­ond half of preg­nan­cy, when the fetal brain under­goes a big growth spurt, omega‑3 fat­ty acids are required for the pro­lif­er­a­tion of fetal neu­rons and blood vessels.

But eat­ing fish is also the lead­ing route of expo­sure to methylmer­cury. Women who eat fish more than twice a week have blood mer­cury lev­els that are sev­en times high­er than women who eat no fish. And mer­cury, like lead, is a ter­ri­ble sabo­teur of fetal brain growth. The U.S. Envi­ron­men­tal Pro­tec­tion Agency (EPA) recent­ly esti­mat­ed that as many as 630,000 infants, or rough­ly one in every six U.S. babies, are born each year with unsafe lev­els of methylmer­cury in their blood. These rev­e­la­tions have ignit­ed a fiery debate both about fish con­sump­tion dur­ing preg­nan­cy and about how best to get mer­cury out of the envi­ron­ment in the first place. [Author’s update: The EPA has tak­en pains not to adopt the 630,000 fig­ure as its offi­cial posi­tion. Cal­cu­lat­ed by EPA sci­en­tist Kathryn Mahaf­fey, this esti­mate was pub­lished in Envi­ron­men­tal Health Per­spec­tives, April 2004.]

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The biggest known con­trib­u­tors to atmos­pher­ic mer­cury are coal-burn­ing pow­er plants, which put 50 tons of mer­cury into the air each year. Incin­er­a­tors and some chlor-alka­li facil­i­ties are also sig­nif­i­cant mer­cury pol­luters. Emis­sions from chlor-alka­li facil­i­ties are a dis­put­ed num­ber that is the sub­ject of an ongo­ing lawsuit.

As a vapor, mer­cury cir­cles the globe for up to a year, com­ing back down to earth with rain or snow. Once it lands, mer­cury is attached to car­bon atoms by bac­te­ria. This chem­i­cal trans­for­ma­tion turns ele­men­tal mer­cury into a high­ly potent neu­ro­tox­in called methylmer­cury, which is the form of mer­cury found in fish.

Fish are vul­ner­a­ble to methylmer­cury con­t­a­m­i­na­tion because watery envi­ron­ments enhance the abil­i­ty of this organ­ic met­al to bio­mag­ni­fy — mean­ing that it con­cen­trates as it is siphoned up the food chain.

In water, tox­ic sub­stances like methylmer­cury can reach high­er lev­els because food chains are longer than they are on land. Ter­res­tri­al food chains rarely have more than three links. Aquat­ic ecosys­tems can eas­i­ly sup­port food chains with six links, and some have as many as twelve. Thus, a top preda­to­ry fish, like a tuna, can eas­i­ly have sequestered in its flesh methylmer­cury lev­els that are a mil­lion times high­er than the water it swam in.

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The pla­cen­ta, which works well to bar pathogens from enter­ing the womb, does a ter­ri­ble job of keep­ing methylmer­cury out. In fact, the pla­cen­ta active­ly pumps mer­cury into the fetal cap­il­lar­ies as though it were a pre­cious mol­e­cule of cal­ci­um or iodine. This is why lev­els of mer­cury in the blood of a new­born typ­i­cal­ly exceed those of its moth­er by 70 per­cent. When con­front­ed with methylmer­cury, the pla­cen­ta func­tions more like a mag­ni­fy­ing glass than a barrier.

Once inside the fetal blood sup­ply, mer­cury is car­ried to the fetal brain, where it inter­feres with brain cell migra­tion. Just as a spi­der can low­er itself from the ceil­ing by reel­ing out a sin­gle strand of silk, a fetal brain cell moves from the cen­ter of the brain to the sur­face by rap­pelling along its own fiber. This process of brain cell migra­tion begins in earnest dur­ing month four of preg­nan­cy and con­tin­ues after birth at least through the age of two.

Methylmer­cury par­a­lyzes migrat­ing brain cells and thus inter­feres with their move­ment from cen­ter to sur­face. Methylmer­cury also halts cell divi­sion in the fetal brain by bind­ing direct­ly to neur­al chro­mo­somes. The cere­bel­lum — cen­ter of bal­ance and coor­di­na­tion — is a spe­cial tar­get of methylmer­cury. Pre­na­tal expo­sures to methylmer­cury have also been linked to deficits in mem­o­ry, learn­ing and atten­tion span that per­sist into ado­les­cence and appear irreversible.

In short, human fetus­es are more vul­ner­a­ble than adults to the brain-addling pow­ers of mer­cury for two immutable rea­sons: They receive a com­par­a­tive­ly big­ger expo­sure (because of the placenta’s con­cen­trat­ing pow­ers), and their brain cells need to move and multiply.

No fed­er­al laws present­ly require exist­ing pow­er plants to con­trol mer­cury emis­sions. In fall 2003, an EPA advi­so­ry com­mit­tee con­sid­ered reg­u­la­tions that would require cuts of 90 per­cent by 2008. But the Bush admin­is­tra­tion scrapped this approach and has sug­gest­ed far more mod­est cuts that would allow six times more mer­cury to enter the envi­ron­ment than the orig­i­nal, more strin­gent plan. [Author’s update: What con­tin­ues to anger crit­ics about the Bush plan is its depar­ture from max­i­mum achiev­able con­trol tech­nol­o­gy (MACT) stan­dards, to which the EPA had pre­vi­ous­ly com­mit­ted itself. If faith­ful­ly imple­ment­ed, many argue, MACT stan­dards would afford a 90 per­cent reduc­tion in mer­cury emissions.]

At this writ­ing, sev­er­al states’ attor­neys gen­er­al are expect­ed to sub­mit rebut­tals to the Bush plan. [Author’s update: These have been submitted.]

What­ev­er the out­come of this strug­gle, mer­cury in fish is not going away soon. There­fore, it is left to fed­er­al and state agen­cies to make rec­om­men­da­tions about fish con­sump­tion dur­ing preg­nan­cy. The Food and Drug Admin­is­tra­tion (FDA) now advis­es preg­nant moth­ers to eat no more than two six-ounce cans of light tuna a week (or no more than one can of alba­core tuna). Sword­fish, shark, tile­fish and king mack­er­el are to be avoid­ed com­plete­ly. Alto­geth­er, says the FDA, a preg­nant woman should lim­it her week­ly fish con­sump­tion to 12 ounces. Shrimp, pol­lock, salmon, or cat­fish are low-mer­cury fish and are there­fore good choic­es. [Author’s update: For the FDA’s cur­rent guide­lines, see]

Nev­er­the­less, many pub­lic health experts argue that these new guide­lines are still not suf­fi­cient­ly pro­tec­tive of fetal brain devel­op­ment. In Feb­ru­ary, lead­ing health, con­sumer and envi­ron­men­tal groups sent a let­ter to the FDA urg­ing stricter restric­tions on the fish con­sump­tion of preg­nant women. One of the FDA’s own com­mit­tee mem­bers resigned in March 2004 in protest over the new guide­lines which, he argues, are too lax. [Author’s update: The July 2004 issue of Con­sumer Reports advis­es women to eat no more than three ounces of alba­core tuna each week. This is half the FDA’s rec­om­mend­ed week­ly limit.]

Mean­while, because of ris­ing mer­cury lev­els, sport-caught fresh­wa­ter fish remain off lim­its to preg­nant women in most states. These advi­sories are pro­mul­gat­ed by state envi­ron­men­tal agen­cies and are under almost con­tin­u­al revi­sion. One con­tin­u­ous­ly updat­ed source for learn­ing about these var­i­ous guide­lines is the Web site of the non-prof­it insti­tute Mer­cury Pol­i­cy Project: www​.mer​cury​pol​i​cy​.org.

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My edi­tor said she received no spe­cif­ic expla­na­tion as to what made the above arti­cle objec­tion­able to Proc­ter & Gam­ble. The Nat­ur­al Resources Defense Coun­cil (NRDC), on the oth­er hand, did have some clues to offer. Accord­ing to the direc­tor of the Envi­ron­ment and Health pro­gram at the NRDC, Dr. Lin­da Greer, Proc­ter & Gam­ble has been active in oppos­ing mer­cury reg­u­la­tions. For exam­ple, Greer said, when the state of Maine was cre­at­ing leg­is­la­tion sev­er­al years ago that would autho­rize its hos­pi­tals to col­lect infor­ma­tion on mer­cury use, the com­pa­ny went straight to the governor’s office to complain.

The NRDC is involved in the ongo­ing law­suit that chal­lenges the EPA’s reg­u­la­tions for the chlor-alka­li indus­try (see para­graph 4 above). 

One prod­uct of that indus­try is caus­tic soda, which is used in the man­u­fac­ture of soap and deter­gent as well as in the pulp­ing of wood fibers for paper prod­ucts. Proc­ter & Gam­ble — whose oth­er brands include Tide, Cheer, Ivory Soap, Puffs and Boun­ty — is a big con­sumer of caus­tic soda. Does the com­pa­ny pur­chase its caus­tic soda from any of the many mer­cury chlor-alka­li plants here and around the world? Greer did not know. Chem­i­cal chains of cus­tody are care­ful­ly guard­ed indus­try secrets.

Cer­tain­ly Pam­pers is a major adver­tis­er in par­ent­ing and baby care mag­a­zines. Could the cud­dly dia­per ads in their pages have any­thing to do with the public’s lack of knowl­edge about mer­cury-con­t­a­m­i­nat­ed fish? Only Proc­ter & Gam­ble knows for sure.

The author ded­i­cates this essay to Mary Beth Doyle, MPH, who worked pas­sion­ate­ly to keep mer­cury and oth­er pol­lu­tants out of the diets of women and chil­dren. Mary Beth died on Novem­ber 13 in an auto­mo­bile acci­dent near her home in Ann Arbor, Michi­gan.

Biol­o­gist San­dra Ste­in­graber is a vis­it­ing dis­tin­guished schol­ar at Itha­ca Col­lege in Itha­ca, New York. Her most recent book is Hav­ing Faith: An Ecologist’s Jour­ney to Moth­er­hood.
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