This study documents lasting intellectual impairment in children
exposed to PCBs in the womb. For press coverage, see Banned
pollutant's legacy: lower IQs. Science News Online, Janet Raloff.
14 September 1996, and Food
for thought: Because we eat PCBs.
Science News Online, Janet Raloff. 14 September 1996.
the study, the Jacobsons gave a series of IQ and achievement tests
to 212 children, now age 11, whom the Jacobson's have followed since
birth. They then analyzed these indicators of intellectual development
and behavior in relation to the levels of PCBs found in the mother's
blood and milk at the time of the child's birth. Their results show
evidence of persistent, measurable intellectual impairment, which
has not been overcome by environment or education.
children in the study exposed to higher levels of PCBs showed deficits
in general intellectual ability, short-term and long-term memory,
and focused and sustained attention. The most highly exposed group
had a loss of 6.2 points in IQ. They were three times as likely
to have low average IQ scores and twice as likely to be at least
two years behind in reading comprehension.
the Jacobson's note, the levels of PCBs carried by these women were
similar to or slightly above the general population level in the
United States. They also stress that the implication of their findings
are not limited to children of women who eat fish from Lake Michigan.
Women who eat no fish may accumulate these compounds from other
food sources, including dairy products, such as cheese and butter,
and fatty meats, particularly beef and pork.
an interview by Janet
Raloff , Jacobson observes that most of the children are middle-class:
"I thought that once they reached a structured school environment,
whatever minor [PCB-induced] handicaps they had would be overcome.
So I was quite surprised to find that, if anything, the effects
were stronger and clearer at age 11 than they had been at age 4."
goes on to interview Dr. Bernard Weiss, a senior expert in neurotoxicology at the
University of Rochester: "Bernard Weiss of the University of Rochester
Medical Center is also impressed by the magnitude of this IQ change.
The population mean hovers around 100, with half scoring higher
and half lower. Ordinarily, for every 100 million people tested,
he says, 2.3 million lie above 130 on the IQ scale, and another
2.3 million score below 70--a level "at which most school districts
would consider [offering] remedial education."
a population the size of the United States, a
shift down the scale, he's calculated, "could move nearly 6
million children who had been above an IQ of 130 to below 130, and
push an equal number of children into the below-70 category."
when you look at populations, he says, even small reductions in
IQ come to represent "very substantial shifts." Moreover, he argues,
the financial consequences "could be stupendous."
have developed relationships that correlate IQ and earning power,
Weiss notes. "Over a 30-year working lifetime, each IQ point earns
[an individual] something like $5,500 (in 1990 dollars)." Multiplied
across a population, that differential would be large.