Study links PCBs to lower IQs

Intelligence

 

Another piece has been added to the puzzle of how great is the threat from organochlorines.

They stand accused of disrupting the way hormones work. Of being responsible for the increase in the incidence of breast cancer from one in twenty women to one in eight, for the fourfold increase in testicular cancer, for the 50 per cent drop in sperm counts, and for genital deformation in newborn babies.

In its defence, the chlorine industry has argued that there is no proof that chlorine is the culprit. All there is to support the accusations are experiments with  animals.

The new piece in the puzzle is a scientific paper published by Joseph and Sandra Jacobson in the September 12 issue of The New England Journal of Medicine. Their finding is that schoolchildren who were exposed in the womb to « polychlorinated biphenyls (PCBs) and related contaminants’’ exhibit « poorer intellectual function.’’

PCBs are one of the worst of the organochlorine families. There are 209 of them and they have extremely long lifespans. Production in most countries in banned but, as the Jacobsons point out, « the amount in use in older electrical equipment and in landfills exceeds the total quantity that has escaped into the environment to date.’’

The related contaminants referred to in the Jacobsons’ paper are mainly dioxins, a family with 75 members, and furans, a family with 135 members. Wherever there are PCBs in the environment, they are usually accompanied by dioxins and furans, Joseph Jacobson said in a telephone interview from the laboratory he and his wife Sandra run in the psychology department at Wayne State University in Detroit.

They have been following the development of children born in 1980 and 1981 whose mothers had eaten at least 11.8 kilograms of lake trout or salmon from Lake Michigan during the six years prior to giving birth. At that time, the fish were known to be heavily contaminated with PCBs, dioxin, and furans.

The Jacobsons began testing the children shortly after they were born. They found the children had not grown as much as normal children during their fetal and postnatal periods and, as infants and again as four-year-olds, they had poorer short-term memories.

The scientific paper just published deals with tests given to the children when they were 11 years old. Those children who had the greatest exposure (as had been measured by the level of PCBs in their mothers’ milk) were found to be more than three times as likely to have lower IQs, to perform poorly in verbal comprehension and to be less able to concentrate.

They also were twice as likely to be at least two years behind in word comprehension and reading.

On average, their general IQs were 6.2 points lower than they should have been and that, say the Jacobsons, is similar to IQs reported in children who have experienced low-level exposure to lead.

The Jacobsons are acutely aware of the debate concerning organochlorines and refuse to attribute their findings to hormone disruption. In our telephone conversation, Joseph Jacobson said they simply didn’t know if hormone disruption — endocrine disruption, he called it — had occurred.

Experiments have pinpointed 51 synthetic chemicals that can disrupt the endocrine systems of animals, and chief among them are organochlorines such as PCBs, dioxins, furans, DDT, hexachlorobenzene, dieldrin, toxaphene, and mirex.

Sometimes they mimic estrogen, the main female hormone; sometimes they block testosterone, the main male hormone; sometimes they compete more vigorously than natural hormones to deliver messages; sometimes they simply scramble messages; and often they escape an animal’s inbuilt control system by going unrecognized by proteins in the blood that destroy excess hormones.

Since development in the fetus and during infancy depends on hormones to relay messages that tell an animal’s body what to develop and when, anything that disrupts those messages can produce dreadful results.

The issue is whether humans are similarly vulnerable. To wait for unassailable proof may be to wait for endless tragedies to happen. So instead of arguing over proof, we should be assessing risk and taking precautions.

The Jacobson’s paper gives a measure of what’s at stake.

 

NEXT: A precaution proposed

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