Researchers analyzing federal exposure and chemical-use databases found hundreds of substances with biological activity relevant to breast cancer across consumer products, food, pesticides, drinking water, medicines and building materials.
By yourNEWS Media Newsroom.
Hundreds of chemicals whose biological activity may be relevant to breast cancer are present across major sources of everyday exposure in the United States, according to a newly published analysis that examined federal records on chemical production, consumer uses, pollution, food, water and human exposure.
The study published Sept. 23 in Environmental Health Perspectives examined a previously developed list of 920 chemicals that researchers classified as breast cancer-relevant chemicals, or BC-Chems, because they caused mammary tumors in animal studies or demonstrated biological activity involving estrogen or progesterone pathways associated with breast cancer.
The research does not establish that exposure to each of the 920 chemicals causes breast cancer in humans. Rather, the authors used biological evidence to identify substances warranting further investigation and then examined where those chemicals are produced, used and encountered in the United States.
The analysis was conducted by Jennifer E. Kay, Rashmi Shakti, Jillian T. McEneaney, Claudia Polsky, Megan Schwarzman and Ruthann A. Rudel. Researchers affiliated with the Silent Spring Institute and the University of California examined more than a dozen government databases, including records maintained by the Environmental Protection Agency, Food and Drug Administration and federal biomonitoring programs.
“Exposure to these chemicals is ubiquitous,” the researchers wrote.
Their findings showed that exposure is not concentrated in a single category. Researchers identified 500 BC-Chems likely to be present in consumer products, 462 in dietary sources, 162 in drinking water, 485 in pesticide formulations, 142 in pharmaceuticals and 106 in construction materials.
Taken together, 652 of the chemicals were reported or predicted to occur in consumer products, food or drinking water. Of those, 277 were classified by the researchers as higher-confidence endocrine-disrupting chemicals, and 116 of that group also showed evidence of genotoxicity, meaning they can damage genetic material.
Consumer goods represented the largest single category examined, with 500 chemicals identified. Those included substances such as benzene, 1,3-butadiene, dichloromethane, bisphenol A, di(2-ethylhexyl) phthalate and methyl paraben, along with other chemicals that have received less attention in breast cancer research.
Pesticides also emerged as a significant potential exposure source. Of the 485 BC-Chems researchers associated with pesticide formulations, 145 were currently registered with the EPA as active pesticide ingredients, according to Silent Spring Institute. Other chemicals appeared as ingredients categorized as inactive or “inert.”
Lead author Kay said the results raise questions about how those additional ingredients are evaluated.
“Our findings highlight a regulatory blind spot around so-called inert ingredients,” Kay said. “When we think about pesticide safety, we tend to focus on the active ingredient. But people are exposed to the entire formulation, and our findings show that many of those other chemicals may also pose a risk.”
Researchers also examined the scale at which the chemicals move through the U.S. economy.
Federal Chemical Data Reporting records showed that 143 BC-Chems were manufactured or imported at volumes exceeding 1 million pounds in 2019. Ten mammary carcinogens identified by the researchers, along with bisphenol A, exceeded 5 billion pounds in production or import volume, according to the study. Many of the chemicals produced at the highest volumes were petrochemicals used in plastics manufacturing.
“Billions of pounds of BC-Chems were emitted to air in 2020. Tens of millions of pounds were released to the environment through industrial activities in 2024,” the study states.
National Emissions Inventory data placed the 2020 air releases at more than 2 billion pounds, according to Silent Spring Institute. Researchers also found more than 1 million pounds each of 11 different BC-Chems reported as industrial releases or off-site transfers through the Toxics Release Inventory in 2024.
The chemicals examined are not necessarily confined to one exposure route. A substance used in manufacturing, for example, may also occur in a consumer product, pesticide formulation, food source or environmental release, meaning people can encounter the same or biologically similar chemicals in several ways.
“When it comes to cancer, we need to think about the totality of our exposures,” Kay said. “People are exposed to hundreds of chemicals from multiple sources over the course of their lives, and these exposures add up. But regulators don’t consider these exposures together.”
Federal biomonitoring data supplied additional evidence that some of the chemicals or their metabolites are widespread in the population.
The study reported that metabolites associated with naphthols, 1,3-butadiene, styrene, several organophosphate and carbamate pesticides, multiple phthalates, methyl paraben and benzophenone-3 were detected in more than 95% of urine samples for the analytes examined. Researchers cautioned that some metabolites can originate from more than one parent chemical, making it impossible in certain cases to attribute the measured level entirely to a particular BC-Chem.
Several chemicals were also detected frequently in blood. The researchers noted that some measurements can reflect both environmental exposure and processes occurring naturally within the body, another limitation when interpreting biomonitoring results.
Older pesticides provided an example of how exposure can continue well after a chemical has been withdrawn from routine use. DDT and several other organochlorine pesticides remained detectable in population samples years after being banned, which researchers attributed to their persistence in the environment.
The researchers also examined predicted daily intake. For 84 BC-Chems, the high end of estimates for median daily intake in the U.S. population exceeded 0.1 milligram per kilogram of body weight per day. The authors said such information could help determine which substances deserve priority for additional toxicological research, exposure monitoring and regulation.
The analysis comes as researchers continue investigating why breast cancer incidence has increased, including among younger women. The paper states that changes in established reproductive risk factors cannot fully explain the increase across age groups and that rising incidence among women younger than 40 cannot be attributed to routine screening alone.
The researchers did not conclude that environmental chemical exposure by itself explains those trends. Instead, they said the findings provide a framework for determining which widely encountered chemicals and chemical mixtures warrant closer examination alongside established breast cancer risk factors.
The authors recommended considering measures aimed at reducing exposure, including tighter controls on drinking water contaminants, replacing higher-priority chemicals in commonly used products with safer alternatives and improving warnings for consumers and workers.
They also identified potential regulatory gaps. The study found mammary carcinogens and chemicals with endocrine and genotoxic activity that are not currently covered by some existing regulatory programs. Sixteen currently used mammary-carcinogenic pesticides identified in the analysis, for example, were not listed under California’s Proposition 65 at the time of the study.
The researchers said the database could also help scientists design future studies of workers and communities with unusually high exposures, including people exposed through industrial air pollution or pesticide drift.
“These findings provide quantitative evidence to guide systematic prioritization of chemicals and mixtures for studying health effects, monitoring exposures, assessing risks, and preventing harm through exposure reduction,” the researchers concluded.
The study was supported by the National Institute of Environmental Health Sciences, the California Breast Cancer Research Program and charitable donations to Silent Spring Institute’s Safer Chemicals Program. The authors reported no competing financial interest, and the published paper states that the funders had no role in the study design, data collection and interpretation, manuscript preparation or decision to submit the work for publication.
Comments