PCBs could harm babies' immune system.

Jusko, TA, D Sonneborn, L Palkovicova, A Kocan, B Drobna, T Trnovec and I Hertz-Picciotto. 2012. Pre- and postnatal polychlorinated biphenylconcentrations and longitudinal measures of thymus volume in infants. Environmental Health Perspectives http://dx.doi.org/10.1289/ehp.1104229.

PCBs may interfere with immune system development in infants exposed in the womb and early in life, report researchers from the United States and Slovakia.

Infants with higher PCB exposure during gestation and as newborns had smaller thymus organs at birth and at 6 months of age but not at 13 months. The results suggest the immune organ may be sensitive to PCBs as it develops during early infancy, although it is not known if the changes affect immune system function.

The thymus is an organ found above the heart. It is part of the immune system and is responsible for helping T-cells develop correctly. The immune system responds to infections using B- and T-cells. T-cells travel throughout body and scan for abnormal cells – such as cancerous cells – or cells infected with bacteria or viruses. They also remember what germs the body has seen in the past.

Experiments in animals show that PCB exposure can cause immune system dysfunction. But, few studies have examined the impact of these and other environmental chemicals on immune system development in humans. A prior study from the same researchers found that prenatal PCB exposure was associated with smaller thymus organs in newborns. This new study followed the infants into later life and found similar effects when infants were 6-months-old.

PCBs are now banned in the United States and other industrialized countries. The chemicals were widely used in many applications, including electrical equipment and hydraulic fluid. People continue to be exposed as PCBs have long half-lives and can persist in the body and the environment for decades.

This study – conducted between 2002 and 2004 – measured the concentrations of four types of PCBs in the blood of 1,134 women and infants from Slovakia during pregnancy and at six and 16 months after birth. The infants' thymus volume was measured using an ultrasound machine at birth, at six months old and at 16 months of age.

The mother's PCB levels were associated with decreased thymus volume at birth. PCB levels in the six-month-old infants were associated with decreased thymus volume at the same age. In contrast, PCB levels at 16 months of age were associated with larger thymus volume at the same time.

These associations were present even after adjusting for breastfeeding, the infant's weight and sex, and the mother's residence and ethnicity.

These results suggest that early life exposure to PCBs might impact the development of the immune system, but the effects seem to be limited to early infancy. The long-term implications of these changes remain to be determined.

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