A new analysis of federal databases found more than 2 billion pounds of chemicals with biological characteristics relevant to breast cancer were emitted into U.S. air in 2020, while hundreds also appeared in consumer products, food, pesticides, drinking water and other everyday exposure sources.
By yourNEWS Media Newsroom.
Hundreds of chemicals with biological activity that researchers say warrants closer examination for possible breast cancer risk are circulating through the U.S. economy, environment and consumer marketplace, according to a new analysis that combined more than a dozen federal databases to identify where Americans may encounter them.
The study, published Sept. 23 in Environmental Health Perspectives, examined 920 chemicals previously identified because they caused mammary tumors in laboratory animals or displayed biological activity involving estrogen or progesterone pathways associated with breast cancer development. The researchers refer to them as breast cancer-relevant chemicals, or BC-Chems.
The designation does not mean all 920 chemicals have been demonstrated to cause breast cancer in humans. Rather, the list was developed as a screening and research tool based on toxicological and endocrine evidence that researchers believe can help identify chemicals deserving further study, exposure monitoring and possible regulatory attention.
Using government information on manufacturing, product ingredients, pesticides, pharmaceuticals, air emissions, industrial releases, drinking water and human biomonitoring, researchers found evidence of potential exposure across nearly every major part of daily life.
The peer-reviewed analysis identified 500 of the chemicals as known or predicted ingredients in consumer products, 462 in food or other dietary sources, 485 in pesticide formulations, 162 associated with drinking water, 142 in pharmaceuticals and 106 in construction materials. The categories overlap, meaning the same chemical can occur in more than one source.
Researchers also found that 143 of the chemicals were manufactured or imported in quantities of at least 1 million pounds during 2019, the production year examined through the Environmental Protection Agency’s Chemical Data Reporting system.
The scale of air emissions was still larger.
EPA National Emissions Inventory data indicated that more than 2 billion pounds of BC-Chems were emitted into U.S. air in 2020. The study said most of that volume came from combustion-related sources.
That figure encompasses emissions captured by the National Emissions Inventory and should not be interpreted as 2 billion pounds released solely by factories.
A separate EPA program, the Toxics Release Inventory, showed nearly 82 million pounds of BC-Chems were reported as releases or off-site transfers from covered industrial facilities during 2024. TRI reporting included 141 BC-Chems, 15 of which had no reported releases that year.
Among the mammary carcinogens tracked through the industrial database, styrene, acetaldehyde, acrylonitrile, benzene, acrylamide, sodium nitrite, dichloromethane and 1,3-butadiene each had more than 1 million pounds of reported on-site releases in 2024, according to the study. Approximately 69% of releases of those chemicals went into the air.
The researchers said the findings illustrate why chemical exposure may deserve greater attention as scientists investigate changes in breast cancer incidence.
Breast cancer rates have been increasing among U.S. women across age groups, with particularly rapid growth among younger women.
Between 2010 and 2019, breast cancer incidence among females ages 15 to 29 increased an average of 1.85% annually, more than twice the annual percentage increase recorded in any older age category analyzed by the researchers. Because women in that age group generally are below the age for routine mammography screening, the authors said increased screening cannot account for that trend.
Established factors including inherited genetics, obesity, smoking and reproductive patterns also do not fully account for changing breast cancer incidence, according to the researchers.
In its summary of the findings, StudyFinds described the researchers’ concern this way:
“the researchers note that between 2010 and 2019 the annual increase in breast cancer rates among females aged 15 to 29 was more than double that of any older age group. That rise can’t be explained by genetics, obesity, smoking, or fertility patterns, and it isn’t simply due to more frequent mammograms, since the increase is happening in women below the typical screening age. Something else appears to be going on, and the study’s authors argue that everyday chemical exposure deserves a much closer look.”
The study does not establish that chemical exposure is responsible for the increase in breast cancer among younger women. Its purpose was to map possible sources and magnitudes of exposure so that researchers can determine which chemicals and mixtures deserve priority in future epidemiological and toxicological studies.
The chemical list includes substances that are already familiar in public debates over environmental and consumer exposures.
Among the 500 BC-Chems identified in consumer products were bisphenol A, commonly known as BPA; di(2-ethylhexyl) phthalate and other phthalates used in plastics; benzene; 1,3-butadiene; dichloromethane; methyl paraben; and chemicals used in dyes and other commercial applications.
Of the 500 consumer-product chemicals, 191 showed stronger evidence of endocrine-disrupting activity under the researchers’ criteria, and 88 of those were also classified as genotoxic.
Researchers identified 129 consumer-product BC-Chems that were manufactured or imported at volumes of at least 1 million pounds during 2019.
Pesticides represented another major exposure category.
The analysis identified 485 BC-Chems in pesticide formulations. Of those, 145 were currently registered by EPA as active pesticide ingredients. Another group consisted of ingredients categorized as “inert,” a regulatory term that does not necessarily mean biologically inactive or harmless.
“Our findings highlight a regulatory blind spot around so-called inert ingredients,” lead author Jennifer Kay, a research scientist at Silent Spring Institute, 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.”
The researchers identified 99 currently registered pesticide active ingredients that were either mammary carcinogens in animal studies or had stronger endocrine-disrupting activity under the team’s classification system.
Food was another major category, with 462 BC-Chems classified as known or predicted dietary exposures.
That category was broader than chemicals intentionally added to food. It could include food additives, substances associated with food-contact materials, pesticide residues and other compounds capable of reaching food or beverages.
Eighty-three of the chemicals appeared on an FDA list of substances added to food at the time of the analysis. Other dietary-source chemicals identified through EPA databases were not necessarily approved food additives.
Drinking water presented a similar distinction.
The researchers categorized 162 BC-Chems as drinking-water exposures overall, while a more detailed analysis identified 143 on EPA databases as having been detected in public drinking-water supplies. The group included pesticides, pharmaceuticals and disinfection byproducts.
Federal drinking-water standards covered only 25 BC-Chems as of 2025, including 18 chemicals the researchers classified as mammary carcinogens.
The study identified 123 additional BC-Chems that had been detected in drinking water but lacked National Primary Drinking Water Standards under the Safe Drinking Water Act. It also identified 20 breast cancer-relevant disinfection byproducts that were not federally regulated through those standards.
That regulatory gap does not by itself demonstrate that the unregulated chemicals occur at concentrations that present a breast cancer risk. Federal drinking-water regulation considers occurrence, toxicity, analytical feasibility and other factors, while the new analysis was intended to identify potential priorities for further assessment.
Air regulation showed another gap between the researchers’ list and existing federal classifications.
Only 67 of the 920 BC-Chems were designated hazardous air pollutants under the Clean Air Act. None were independently classified as criteria pollutants, although particulate matter can contain polycyclic aromatic hydrocarbons and other compounds included on the BC-Chem list.
The study also examined whether federal biomonitoring programs were finding the chemicals or their metabolites in Americans.
Researchers mapped National Health and Nutrition Examination Survey urine measurements to 84 BC-Chems. Among the most frequently detected urinary analytes were metabolites associated with phthalates, 1,3-butadiene, styrene, organophosphate and carbamate pesticides, methyl paraben and benzophenone-3. Some were detected in more than 95% of tested samples.
Seventeen NHANES analytes corresponding to 21 BC-Chems that were both genotoxic and classified as stronger endocrine disruptors were detected in at least 90% of biomonitoring samples, according to the researchers.
Blood measurements showed similarly widespread exposure to several substances.
Of 27 BC-Chems measured in blood, six were detected in more than 90% of the population tested: nitromethane, p,p’-DDE, heptanal and biomarkers involving acrylamide, glycidamide and ethylene oxide. Researchers cautioned that several of those compounds can arise from biological processes inside the body as well as from outside exposures, meaning detection cannot always be attributed exclusively to environmental contact.
Persistent pesticides provided a striking example of how long some environmental contaminants can remain detectable after their use ends.
DDT was banned for most U.S. uses in 1972, yet DDT and several other organochlorine pesticide-related BC-Chems were still found in more than 40% of NHANES samples when they were last measured in the 2003-2004 survey cycle.
The DDT metabolite p,p’-DDE has persisted even longer. The researchers cited a Detroit epidemiological study conducted from 2010 through 2012 in which DDT was detected in half of participants and p,p’-DDE was found in all participants tested.
The authors said existing biomonitoring likely understates the true scope of exposure because most of the 920 chemicals are not routinely measured in the general U.S. population.
“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.”
The study’s authors developed the 920-chemical list through earlier research that combined multiple types of biological evidence.
Chemicals qualified if they caused mammary tumors in rodents, increased production of estrogen or progesterone in laboratory screening, activated estrogen-receptor pathways or displayed combinations of those biological characteristics. Researchers also evaluated genotoxicity, meaning the ability to damage genetic material.
That framework is intended to identify hazards before decades of human epidemiological evidence accumulate, but it also means the chemicals on the list vary substantially in the strength and type of evidence linking them to breast cancer biology.
Some are well-studied mammary carcinogens in laboratory animals. Others were included because of endocrine activity observed in cell-based assays rather than evidence that they produce breast tumors in people.
The authors therefore did not conclude that exposure to every chemical on the list causes breast cancer.
Instead, they said combining biological hazard data with information about production volume, environmental emissions and likely human exposure can help scientists identify chemicals that should receive the highest priority for additional testing.
The researchers ultimately highlighted 39 chemicals for potential research and policy attention using a combination of biological activity, production of more than 1 million pounds in 2019 and predicted population intake.
They also identified compounds that could be priorities for expanded biomonitoring, cumulative risk assessments and epidemiological studies designed to examine breast cancer incidence and progression.
The authors said reducing unnecessary exposure may provide one avenue for breast cancer prevention while scientists continue examining how chemical mixtures affect disease development.
“Transparency about how and where people are exposed to BC-Chems will support public health research, exposure reduction, and health protective regulation,” the researchers wrote.
The study was led by scientists at Silent Spring Institute and supported by the National Institute of Environmental Health Sciences, the California Breast Cancer Research Program and charitable donations to Silent Spring’s Safer Chemicals Program. The authors reported no competing financial interest.
The findings provide a national map of where potentially breast cancer-relevant chemicals occur and how extensively some are produced or released, but they do not quantify how much breast cancer in the United States is caused by those exposures.
Establishing that connection will require further research linking specific chemical doses and mixtures to long-term human health outcomes. The study instead supplies researchers with a prioritized starting point: hundreds of chemicals with breast cancer-relevant biological activity are in commerce, the environment and common sources of human exposure, while comparatively few are routinely monitored in people or specifically regulated based on those characteristics.
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