By Peter Montague
A study published on September 12 in the New England Journal of Medicine confirms that children exposed to low levels of PCBs in the womb grow up with low IQs, poor reading comprehension, difficulty paying attention and memory problems. PCBs are a family of toxic industrial chemicals commercialised in 1929 by Monsanto, and now found in nearly all humans on earth.
This latest study describes a group of 11-year-old children whose mothers ate fish from Lake Michigan. The greatest mental deficits occurred in the 11% of the children whose mothers ate the most fish.
Since 1980, Joseph and Sandra Jacobson, psychologists at Wayne State University in Detroit, Michigan, have studied 242 children whose mothers had eaten salmon and lake trout from Lake Michigan an average of two to three times each month for many years. Those children have been compared to a control group of 71 babies whose mothers had not eaten any Lake Michigan fish. Large fish in Lake Michigan, such as lake trout and salmon, are typically contaminated with PCBs, mercury and a host of other chlorinated organic chemicals.
The Jacobsons analysed PCB levels in the blood of the babies' umbilical cords, thus providing a reliable measure of pre-natal exposure. At birth, a mother's overall fish consumption and the PCB level in her baby's blood both correlated with the baby's birth size. Eating more fish was linked to babies with reduced head size, diminished girth in the chest and shorter gestation.
On standardised tests for infant development, higher fish consumption was correlated with abnormally weak reflexes, less responsiveness to stimulation, more jerky, unbalanced movement and more startles in the babies. At birth, the babies whose mothers had eaten the most PCB-contaminated fish were clearly different from normal children.
At age seven months, 123 of the original 242 infants were tested for "visual recognition memory." The Jacobsons concluded that the high-PCB babies had memory problems. Lower scores on this test (known as the Fagan Test of Visual Recognition or the Fagan Test of Infant Intelligence) have been shown to correlate with lower intelligence later in life.
Two hundred and thirty-six of the original 242 children were tested again at the age of four. Two effects became apparent. First, 17 of the children whose mothers had the highest levels of PCBs in their breast milk refused to complete the tests; they were balky and uncooperative. Secondly, the remainder of the children were given a series of tests to measure memory and general mental capabilities; again, the children whose mothers had eaten the most fish had the poorest memories.
The balky, uncooperative behaviour is of some interest by itself. Helen Daly, of the Center for Behavioral Effects of Environmental Toxins at the State University of New York at Oswego, has been studying humans and laboratory animals exposed to PCBs and other chlorinated hydrocarbons. She reports that when rats were fed contaminated salmon from Lake Ontario, they overreacted to negative events. Significantly, the offspring of those rats showed the same pattern of altered responses to stress, even though the offspring themselves were not fed contaminated fish. Helen Daly wonders whether rats and children don't develop similar overreactions to stress after being exposed to PCBs while in the womb.
In the New England Journal of Medicine, the Jacobsons reported their most recent examination of 212 of the original children. At age 11, maternal exposure to PCBs was correlated with lower overall IQ and lower verbal IQ score. The 11% of the children whose mothers had the highest exposures now have IQs 6.2 points lower than average.
In these 11-year-olds, prenatal exposure to PCBs was linked to poor word comprehension and poor reading ability. The highest-exposed children were twice as likely to be at least two years behind their peers in word comprehension.
The Jacobsons summarise: "Our IQ results indicate deficits in general intellectual ability, short-term and long-term memory, and focused and sustained attention." They speculate that the mechanism of harm is PCB interference with thyroid hormones, which are essential for development of the brain.
It is especially noteworthy that the children's intellectual deficits correlate most closely with the mother's overall fish consumption. The data indicate that these children were harmed most by PCBs passed to them by their mothers prior to birth. It was not the mother's fish-eating habits during pregnancy that were important —it was the mothers' cumulative lifetime exposure to PCBs that lowered their children's IQs. In other words, exposure of females to PCBs at any time in their lives before they bear children may eventually translate into mental deficits for their offspring.
The children studied by the Jacobsons had PCB exposures which, though on the high side, are still considered to be within normal background exposure levels. Many other possible causes, such as exposure to lead or pesticides, or the mother's use of tobacco or alcohol, were ruled out. (Unfortunately, maternal exposure to methyl mercury was not assessed by the Jacobsons, weakening their study.)
Four previous studies of children had reported similar problems from PCB exposures, ranging from small size at birth to developmental disorders.
Importantly, the Jacobsons' latest findings have been mirrored in several animal studies,and in studies of Taiwanese children accidentally exposed to high levels of PCBs.
And the PCB problem is not going away soon. Between 1929 and 1989, total world production of PCBs (excluding the Soviet Union) was 1.5 billion kilograms, or about 25.8 million kilograms per year. Even after the US banned PCBs in 1976, world production continued at 16.3 million kilograms per year from 1980 to 1984 and 10 million kilograms per year, 1984-1989. The end of PCB production is not in sight.
The whereabouts of 30% of all PCBs remains unknown. Another 30% reside in land fills, in storage or in the sediments of lakes, rivers and estuaries. Some 30% to 70% remain in use.
The characteristics of PCBs (their stability and their solubility in fat) tend to move them into the oceans as time passes. Nevertheless, it is estimated that only 1% of all PCBs have, so far, reached the oceans.Without major efforts to locate, capture and destroy the PCBs that are "out there", future generations will continue to be poisoned by PCBs, at great social (and individual) cost.
We hear much of late about the good intentions of the Monsanto Corporation. Some of our friends tell us this corporation has turned over a new leaf, and is committed to behaving responsibly. If this is so, Monsanto could demonstrate its awakening by leading an effort to locate and destroy PCBs. Monsanto created (or licensed the creation of) all the PCBs in the world. This corporation could demonstrate its commitment to environmental sustainability by cleansing the planet of this brain-damaging substance, to the extent possible.
An obvious first step would be to undertake a comprehensive inventory of the problem, assessing the damage done so far and cleanup-costs, as a demonstration of good faith and serious intentions.
[From Rachel's Environment & Health Weekly.]