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Scientists Begin to Explore Impact of Chemical Combinations on Human Health

Five trillion plastic bags, that’s 160,000 bags every second, will be used this year.

Photo by Pixabay

The statistics on the amount of plastic people use every year are so large that it’s difficult to wrap your head around them. Five trillion plastic bags, that’s 160,000 bags every second, will be used this year. In 2021, 583 billion plastic bottles were produced. To put that in perspective, there are 100 billion stars in the Milky Way. That means humans produced almost six times as many plastic bottles in one year as there are stars in our galaxy. 

Those are just bags and bottles. Now add to that a half billion plastic straws, 50 billion plastic-coated coffee cups, and all the takeout containers that caused single-use plastic use to triple during the pandemic. Why are we telling you this? Because the chemicals used to manufacture all those plastics aren’t as well-regulated as you might expect and hope. A recent study reveals why addressing that regulation gap is more important than ever. 

Manufacturers don’t have to prove a specific chemical is safe for human exposure before they use it if they can show it’s similar enough to another chemical already being used. That means scientists and regulators are always playing catch-up to learn about the impact of different manufacturing chemicals on human health. By the time they find a possible health risk, companies are already able to move on to a very similar chemical that is just different enough to be legally used but probably not different enough to be safe for human health. 

Consider, for example, how companies responded to research that bisphenol-A (BPA) can harm health. Companies replaced BPA with an extremely similar chemical called BPS and slapped millions of “BPA-free” labels on their products, never mentioning that the chemical they used to replace the BPA could have the same effects. A 2019 study found that of the 906 chemicals likely associated with plastic manufacturing, 63 rank highest for human health hazards.

Most of the research into chemicals used in manufacturing has focused on individual compounds. What we don’t know is how all those chemicals interact with each other and affect human health when together. A study published earlier this year did look at the aggregate impact of one group of chemicals on human health: the endocrine-disrupting chemicals (EDCs). These chemicals interfere with the human endocrine system, including hormones and metabolism. 

The new study found that children exposed to a wide range of EDCs during gestation appear to have a greater risk of neurodevelopmental delays. This study is different from previous studies as it’s emphasis is on the potential effects of exposure from mixtures of different EDCs as opposed to a single EDC, like BPA. This study focused on 15 chemicals belonging to three groups: phthalates, alkyl phenols, and perfluoroalkyl substances (PFAS).

The study involved 1,874 pregnant women enrolled in a long-term Swedish population study between November 2007 to March 2010. At 10 weeks gestation, urine tests were used to estimate exposures to the chemicals being studied and the women answered questionnaires about food and environmental exposures. The women’s children’s language delay was assessed at 2.5 years old (30 months) using standardized, validated tests. About 10% of children in the population had language delay, which was defined as having fewer than 50 vocabulary words by 30 months old.

The researchers also conducted a series of experiments using fetal brain tissue (not related to the study population), tadpoles, and zebrafish to better understand effects of EDCs on the tissue and molecular pathways involved in the brain. To conduct these experiments, they tested six different concentrations of the EDC mixture seen in the study population: 0.01, 0.1, 1, 10, 100, and 1000 times the levels measured in the women. 

Combining the experimental evidence and the epidemiology exposure evidence from the Swedish study, the researchers’ findings suggested that EDCs are linked to language delay and they identified the ways in which that kind of effect could happen. Their calculations suggested that about 54% of the children in the study had been prenatally exposed to concentrations of EDC mixtures that could have biological effects, including language development delays. 

In an accompanying commentary about the study, Zeyan Liew and Pengfei Guo, both environmental health scientists at Yale, noted that “humans are exposed to multiple classes of EDCs through their encounters with polluted air, water, food, and consumer products.” They note that PFAS are particularly persistent in the human body with a halflife of 4 to 8 years. While phthalates and phenols are less persistent, “humans are repeatedly and constantly exposed to them, for example, from personal care products.”

We still don’t fully understand the potential long-term developmental consequences that can be caused by widespread use of EDCs. Liew and Guo note that “the biological mechanisms of how EDCs influence human fetal brain development are difficult to study, partly because the tools to effectively monitor brain development in utero are lacking.” The difficulty in understanding exposures and effects is compounded by the wide range of EDCs that exist and their varying use. 

”The traditional risk assessment approach depends on testing single chemicals across dosage concentrations in animal models, but uncertainty remains about directly applying these toxicological outputs to guide policy,” the Yale researchers wrote. 

It’s hard to know which combinations of chemicals to test and in what concentrations, but studies like this are a step in the right direction to learning more. At the same time, this study only looked at three classes of EDCs and only a small number of chemicals within those groups. It’s estimated that more than 4,000 PFAS alone have been used in commercial products, and currently, “no human studies can accurately detect and quantify the concentrations for all possible PFAS,” the Yale researchers wrote.

It will take pressure on legislators and regulators, as well as advocacy and awareness about the possible and confirmed health harms of EDCs, to lead to adequate research and meaningful regulations to protect people’s health. 

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