Researchers find there could be more health effects lingering decades after a toxic contamination of Michigan’s food supply.
In 1973, a plant owned by Velsicol Chemical made a mistake and shipped a toxic flame retardant chemical to a livestock feed plant. It’s called polybrominated biphenyl, or PBB. It took about a year to discover the accident. Millions of Michiganders ate contaminated beef, chicken, pork, milk and eggs.
After the chemical mix-up in the 1970s, the state of Michigan enrolled about 6,000 people in a registry to track their health. A team at Emory University has been following those people and their children.
Melanie Jacobson is the lead author of the latest study from Emory. She and her team measured PBB levels (along with a related chemical, polychlorinated biphenyl, or PCB) as well as self-reported thyroid conditions and thyroid hormone levels in more than 700 participants.
“And we found that the prevalence of thyroid disease was greater than expected - up to 25% of women reported thyroid disease. And we also found that higher PBB levels were associated with an increased prevalence of thyroid disease. But this was only true among women, although estimates were somewhat imprecise.”
Jacobson says the implications of thyroid problems can be major, but she notes thyroid conditions are often easily treatable.
“Thyroid function is really important.” she explains, “It’s the major endocrine organ in the body. Thyroid function is also really important for other body systems - cardiovascular health, reproductive health - and so it’s just important for overall health and people may also want to get it screened.”
But this chemical exposure is associated with more than just thyroid problems. PBB can remain in the body for many years. Jacobson says Emory's previous studies have largely focused on reproductive health.
“PBB has been found to be associated in this cohort with changes to the menstrual cycle; altered timing of puberty for both girls and boys exposed to PBB in utero," she says. "We found that women who were exposed in utero, when they became adults they had a higher risk of miscarriage.”
Here are some of the team's findings noted on Emory's PBB research website:
60% of Michiganders recently tested have PBB levels above the U.S. population 95th percentile. In 2003-2004, as part of the National Health and Nutrition Examination Survey, the CDC tested blood samples for PBB 153, but have not tested for PBB in more recent surveys.
- Some women with high exposure to PBB had fewer days between menstrual periods, more days of bleeding, and lower estrogen levels. However, there was no evidence that these women had reduced fertility.
- There were a few more breast cancer cases among women with high exposure to PBB than expected.
- Chemical workers were more likely to have abnormal thyroid hormone levels.
- PBB was transferred to children in the womb and through breast milk. Children who were born after contaminated products were removed from farms had PBB detected in their blood, and those who were breastfed were much more likely to have PBB in their blood.
- On average, breastfed daughters of women with high PBB exposure started menstruating a year earlier than unexposed girls.
- Daughters of women with high exposure to PBB were more likely to experience a miscarriage.
- Sons of women with high exposure to PBB were more likely to report a genital or urinary condition.
Jacobson says the Emory team will continue to study other potential health effects, as well.
“One of the big priorities - and this was from community input - is looking at these multiple generation-type health effects, specifically when the father was exposed - in the family unit, can those types of health effects be passed down to future generations? And there is work looking into, is there something we can do about reducing PBB body burden in the people who were exposed to this 1970s contamination?” says Jacobson.