How One Banned Chemical Continues to Cause Harm to Infants
Polychlorinated biphenyls (PCBs) are part of a class of chemicals called polycyclic chlorinated hydrocarbons. Over 200 types of PCB cogeners exist, and are marked by different degrees of chlorination and different positions of the chlorine atom within the molecule’s structure. The manufacture of PCBs was banned in the U.S. in 1979. Prior to the ban, PCBs were widely used in a variety of industrial processes including paints, fabric treatments, adhesives and insulation fluids. The compound continues to persist in air, soil and water, and can be detected in the biologic tissue of most residents in industrialized countries.
PCBs are extremely stable compounds that do not decompose readily in the environment. They have long half-lives of 8 to 10 years, are not prone to natural oxidation, and are insoluble in water. PCBs are also lipophilic, which means they are attracted to the fatty tissue of organisms and can be stored there. This property allows PCBs to bioaccumulate in organisms, and the concentration increases as it works its way up the food chain. Since the 1970s, researchers have been documenting the toxic effects of PCBs on adults and children. However, not much effort has been put into developing technologies to remove PCBs from contaminated environments.
The first evidence of PCBs’ toxic effects on infants were seen in pregnant women in Japan and Taiwan, where rice oil was accidentally contaminated with high concentrations of PCBs. Around 14,000 people in Japan were affected, and the symptoms were termed Yusho disease. Common symptoms in adults included dermal and ocular lesions, lowered immune response, headache, fatigue and cough.
Most pregnant women exposed to the rice oil in Japan gave birth to underweight babies that suffered permanent neurological damage. The average IQ of children born to PCB-exposed women was around 70, whereas the normal average is 100. Many of the children also suffered long-term growth abnormalities, including shorter height, lower weight and deformed fingers. Over 400,000 birds died in Japan in 1968 after the contaminated oil was sold to poultry farmers as a feed supplement. In 1979, over 2000 Taiwanese people ingested rice oil contaminated with PCBs. They developed similar symptoms to the Japanese outbreak, and it was termed Yu-Cheng, or “oil disease.”
In the U.S., the main source of PCB exposure is through consumption of sportfish from contaminated waters. Lake Michigan has high PCB levels because of the large surface area and depth of the lake, slow sedimentation rate and close proximity to industrial facilities. Symptoms of PCB exposure in adults have not been as severe in the U.S. as it was in Japan or Taiwan, because chronic PCB exposure through ingestion of contaminated food and drinking water is at much lower concentrations. However, researchers have observed severe toxic effects in children born to mothers who have eaten contaminated fish from Lake Michigan and Lake Ontario.
Consumption of PCB-contaminated fish from Lake Michigan has been shown to predict PCB concentrations in maternal serum and milk. Maternal serum values can then predict cord serum PCB levels. Much larger concentrations of PCBs are transferred postnatally through maternal milk due to its high lipid content, which is favored by the lipophilic PCB molecules. Researchers have documented that in utero exposure can have more toxic effects at lower quantities, versus higher concentrations postnatally through maternal milk. The developing fetus lacks the capacity for drug detoxification that is present postnatally, and the incomplete development of the blood-brain barrier increases the chances for permanent central nervous system damage. Prenatal exposure is associated with impaired immunity, resulting in a higher childhood frequency of respiratory infections. Immune deficits as infants may result in issues later in life such as allergies, immune suppression or autoimmunity.
Newborns of mothers that had a history of eating contaminated fish from Lake Ontario exhibited a greater number of abnormal reflexes, less mature autonomic responses and less attention to visual and auditory stimuli.
At first, I assumed everything pointed to exposed mothers breastfeeding and that presented an easy solution—don’t breastfeed if you’ve eaten fish from contaminated waters. Unfortunately, it turns out it’s not that simple. Despite much larger concentrations of PCBs transferred postnatally through lactation, intellectual impairment only occurred in relation to transplacental exposure. This means that the bioaccumulation in the mothers had a greater effect on the development of the infant than exposure during pregnancy. This suggests that women should not only limit fish consumption from contaminated sources during pregnancy, but also before pregnancy, to reduce the accumulation of toxins that are transferred in utero. As for breastfeeding, researchers have documented intellectual and behavioral improvements in breastfed infants who were exposed in utero, compared to PCB-exposed infants who were not breastfed.
For information on fish advisories in your area, visit the EPA’s Fish Consumption Advisories website.