NJEHiS NewsMore Evidence of MercuryEffects in ChildrenIn research published last summer, scien-tists revealed that prenatal exposure tomethylmercury, an organic form of mer-cury that accumulates in animal tissues,may affect the blood pressure and abilityto respond to sensory stimuli in exposedchildren later in life. The team is now alsoconfirming findings of mercury-relatedneurodevelopmental effects among theFaroese subjects by studying a cohort ofMadeiran children.

The reports are the latest work ofl'hilippe Grandjean, an adjunct professor ofpublic health at Boston University inMassachusetts, and Pal Weihe, medicaldirector of the Faroese Hospital System inT6rshavn, who, with their colleagues, haveperformed extensive analysis of a longitudi-nal study on the effects of prenatalmethylmercury exposure among the inhabi-tants of the Faroe Islands. The Faroe Islandsstudy was funded by the NIEHS along withEuropean grant-making bodies includingthe European Commission EnvironmentResearch Programme and the DanishMedical Research Council. The Faroesewere chosen as study subjects because theirdiet is rich in pilot whale meat, a primesource of methylmercury. In the study of917 Faroese children, prenatal exposure tomethylmercury was assessed by analyzingmercury concentrations in cord blood andmaternal hair. At age 7, the children under-went extensive neurobehavioral testing aswell as a general health examination.

A whale of a meal. The meat and blubber of the long-finned pilot whale have been staples of theFaroese diet for centuries. People who eat a whale meal may be exposed to methylmercury, whichhas been found to cause neurodevelopmental and other effects in children exposed in utero.

A paper published in the July 1999 issueof Epidemiology describes mercury-relatedcardiovascular risk factors that were identi-fied among the Faroese children during thegeneral health exam. Because of earlier casereports and experimental findings of cardio-vascular effects of mercury, the children wereexamined for blood pressure, heart rate, andheart rate variability. As a whole, the chil-dren had normal blood pressure for their

age. But among children whose cord bloodmercury content had been measured at 1-10,ug/L, the scientists found that blood pres-sure was raised by an average of 14 points.The effect was magnified in children withlower birth weights, whose blood pressurewas raised by as much as 21 points. Noadditional increase was seen in childrenwhose cord blood mercury concentrationhad been higher than 10 Fig/L.

Implantation: Timing Is EverythingUnderstanding the many facets of human reproduction has longbeen considered a guessing game. According to Allen Wilcox,chief of the Epidemiology Branch at the NIEHS, until now,knowing exactly when implantation of an egg into the uterinewall occurs has been impossible because the eventhas never been observed in humans. However,Wilcox and his team have recently taken some ofthe guessing out of the process by shedding lighton how the timing of implantation may affect apregnancy's outcome. The results of their researchwere published in the 10 June 1999 issue of theNew EnglandJournal ofMedicine.

The NIEHS team collected urine samples forup to 100 days from 221 women who were tryingto conceive. The scientists pinpointed the time ofovulation by studying the ratio of estrogenmetabolites to progesterone metabolites. By study-ing levels of the hormone chorionic gonadotropin (hCG), theteam was able to detect when a fertilized egg was implanted intothe uterine lining.

Of the 189 women who yielded sufficient data for the team'sanalysis, 75% carried their pregnancies at least 6 weeks past theirlast menstrual cycle. The remaining 25% of pregnancies resulted in

When the time is right. A humanblastocyst is ready for implantation.

early loss that was strongly related to the time of implantation. Theinitial rise in hCG occurred 6-12 days after ovulation, with 84%occurring specifically 8-10 days after ovulation. On average, surviv-ing eggs were implanted 1 day earlier than nonsurviving eggs-9.1days versus 10.5 days from fertilization to implantation.

When implantation occurred by day 9, therewas only a 13% chance of embryonic loss. By day10, however, 26% of embryos had died. The per-centage of loss rose on day 11 to 52%, and to 82%beyond day 12. In the study, the three implanta-tions that occurred after day 12 ended in early loss.Not only does the receptivity of the mucous mem-brane lining the uterus decrease, but the body is lessresponsive to hCG by 1 1 or 12 days after ovulation.What this shows, according to Wilcox, is that "theuterus may be receptive to pregnancy only during alimited time-window, shutting out defectiveembryos that arrive too late. This would spare a

mother the physiologic burden of supporting a nonviable embryo."The study says that the data may provide implications for

efforts to manipulate receptivity of the uterus, offering new possi-bilities for infertile women. For example, fertility might beincreased by extending the window of time during whichimplantation could occur.

A 554 Volume 07, Number 11, November1999 Environmental Health Perspectives