Prenatal exposure to a particular category of polychlorinated biphenyls is associated with the strongest detrimental effects on foetal neurodevelopment, according to a new study from scientists in California.
The study, by researchers at UC Davis M.I.N.D. Institute and published in Neurotoxicology, looked at more than 200 PCBs to examine their effects on neurodevelopment.
Field work took place in Slovakia's Michalovce district where PCBs were dumped by a local factory into a river and on land between 1959 and 1984.
While most previous studies looked at PCBs as a single block, the researchers looked at non-dioxin-like PCBs, dioxin-like PCBs and anti-oestrogenic PCBs and measured babies' mental development and motor skills at 16 months.
Mothers were interviewed about other factors like education levels, health status and cigarette and alcohol use and a control group from a town called Svidnik with lower contamination levels was also studied.
The study found that only the two dioxin-like PCBs, #118 and #156, were associated with deficits in neurodevelopment, but non-dioxin-like PCBs had no effect on mental function although they adversely affected motor functions.
"We found that the prenatal dioxin-like PCBs were associated with reduced mental and motor-development scores," said study lead author Hye-Youn Park.
The study does not identify a specific mechanism by which PCBs affect neurodevelopment but the researchers theorized that hormonal activity and interactions with certain receptors may be important.
Senior study author Irva Hertz-Picciotto said some Americans have been exposed to PCB levels comparable to those in Slovakia and pointed out that a plant in Anniston, Alabama, had produced 10 times as many PCBs over the years as the one in Michalovce.
Separate work at UC Davis earlier this year suggested PCBs harm the developing brain by binding to ryanodine receptors which are calcium channels on brain cells' surface.
"Though these chemicals persist for years and even decades, it takes a while for the epidemiology and the toxicology research to catch up and find out what these chemicals are capable of doing to humans," said Prof Hertz-Picciotto.
