Consumer products, food, drinking water, pesticides, medicines and construction materials all contained chemicals that the researchers had previously identified as having biological activities relevant to breast cancer. When the researchers combined those hazard data with U.S. production, emissions, exposure and biomonitoring databases, they found that people are encountering a large and diverse set of these chemicals, although the analysis does not establish that the exposures themselves cause breast cancer in humans.
The analysis began with a list of 920 chemicals that had previously been identified as potentially relevant to breast cancer. The chemicals were selected because they either caused mammary tumors in at least one rodent study or showed activity in laboratory tests involving estrogen or progesterone production or estrogen-receptor signaling. The researchers also classified the chemicals according to evidence of genotoxicity.
That distinction is important. The new analysis was not an experiment in which people were exposed to these chemicals and then followed for breast cancer. Instead, it asked a different question: Where are these chemicals found, how much of them enters commerce or the environment, what evidence exists that people are exposed to them, and how are they regulated?
To answer that question, the researchers assembled information from U.S. government databases covering chemical production, consumer and industrial uses, food, drinking water, pesticides, pharmaceuticals, environmental releases, human biomonitoring and modeled population intake. They used the most recent available release of each dataset at the time of the analysis.
The result is a broad exposure map rather than a single exposure measurement. It brings together information collected for different purposes and from different years, allowing the researchers to see where the chemicals occur and where information about them remains missing.
The researchers refer to these substances as breast cancer-relevant chemicals, or BC-Chems. Within the group are mammary carcinogens, chemicals with stronger evidence of endocrine-disrupting activity, chemicals with weaker or equivocal endocrine evidence, and chemicals for which relevant biological activity has not been fully tested.
The underlying biological evidence also varies. A chemical classified as an MC caused mammary tumors in at least one rodent study. An EDC+ chemical showed higher-confidence activity in estrogen or progesterone steroidogenesis or estrogen-receptor assays. Genotoxicity was classified separately. The categories therefore describe different kinds of evidence rather than a single measure of human breast-cancer risk.
Large quantities are already moving through commerce
Production data provided one indication of how extensively some of these chemicals are used.
The researchers matched their BC-Chem list against the U.S. Environmental Protection Agency’s Chemical Data Reporting data. For 240 BC-Chems, including 45 mammary carcinogens, they obtained reported production or importation volumes for 2019. One hundred forty-three were produced in quantities greater than 1 million pounds that year, including 33 mammary carcinogens.
At the highest end, 10 mammary carcinogens and bisphenol A were each produced in quantities exceeding 5 billion pounds in 2019. The researchers noted that the highest-volume BC-Chems were mostly genotoxic mammary carcinogens that lacked testing for steroidogenesis or estrogen-receptor activity. Many of those chemicals may have been too volatile for the relevant laboratory testing.
The largest production volumes were dominated by petrochemicals used in plastic manufacturing. The researchers therefore found that some of the chemicals with evidence relevant to breast cancer are not obscure substances confined to specialized laboratories. They are produced at very large scales.
Production volume, however, is not the same thing as human exposure. The authors use it as an indication of how heavily a chemical is used in manufacturing and commerce, and they note that production volume is particularly relevant when considering potential workplace exposure.
The production data also have limits. Manufacturers report under the Chemical Data Reporting rule only when applicable reporting thresholds are exceeded, so chemicals produced or released in smaller quantities from many different sources may not appear in the same way in these records.
The chemicals occur in products, food and water
The researchers next looked for specific routes by which people could encounter the BC-Chems.
Across U.S. EPA and Food and Drug Administration databases, they identified 500 BC-Chems known or predicted to occur in consumer products, 462 in dietary sources, 162 in drinking water, 106 in construction materials, 485 in pesticide formulations, and 142 in pharmaceuticals. The categories were not mutually exclusive, so one chemical could occur in several of them.
The researchers found that most BC-Chems in each of those exposure categories were either mammary carcinogens or had higher-confidence endocrine-disrupting activity.
Taken together, 652 BC-Chems were reported or predicted to occur in consumer products, food or drinking water. Of those, 144 were mammary carcinogens, while 277 had higher-confidence endocrine-disrupting activity. One hundred sixteen were both mammary carcinogens and genotoxic.
Consumer products accounted for the largest number of individual chemicals in the analysis. The researchers identified 500 BC-Chems in this category, including 191 with higher-confidence endocrine activity. Eighty-eight of those 191 were also genotoxic.
The consumer-product group included chemicals already familiar from environmental-health research, such as benzene, 1,3-butadiene, dichloromethane, bisphenol A, di(2-ethylhexyl) phthalate and methyl paraben. It also included chemicals the authors say have received less attention in environmental-health research, including 2,4-dimethylphenol, p-cresol and 4-chloroaniline.
The researchers also found that 129 consumer-product BC-Chems had been produced at least 1 million pounds in 2019, including 29 mammary carcinogens and 41 chemicals classified as EDC+.
The dietary category contained a mixture of substances identified through different databases. Eighty-three of the 462 dietary BC-Chems were on the FDA’s list of substances added to food. Among those 83 were 13 mammary carcinogens or 28 EDC+ chemicals. Another 266 BC-Chems were identified in dietary sources through the EPA’s Chemical and Products Database even though they were not currently FDA-approved substances added to food.
The researchers emphasize that these database classifications do not mean every person is exposed to every chemical. The Chemical and Products Database, for example, relies partly on voluntary reporting and public data sources, and the authors note that it is not a comprehensive record of all chemical uses or product ingredients. Some entries may also be outdated.
Drinking water contains another set of exposures
The drinking-water analysis identified pesticides, pharmaceuticals and disinfection byproducts among the BC-Chems reported in public water supplies.
The researchers identified 143 BC-Chems in drinking water through the Chemical and Products Database, including 51 mammary carcinogens. Fifty of the chemicals were pesticides with current registrations, 37 were canceled pesticides and 15 were FDA-approved active drug ingredients.
They also identified 27 BC-Chems as drinking-water disinfection byproducts. Eleven were mammary carcinogens, seven had higher-confidence endocrine activity and 19 were genotoxic.
Some chemicals were not directly listed as drinking-water contaminants but could contribute constituent chemicals after breaking apart. The researchers give ammonium perfluorooctanoate as an example because it can dissociate to produce perfluorooctanoic acid, which they note contaminates many drinking-water supplies.
The pesticide analysis revealed another extensive overlap. The EPA’s pesticide database listed 245 BC-Chems as active pesticide ingredients, including 52 mammary carcinogens. Of these, 145 were currently registered, including 31 mammary carcinogens.
Among the 1,060 currently registered active pesticide ingredients in the database, 99 were either mammary carcinogens or EDC+ chemicals. Twenty-three current-use EDC+ active ingredients were also genotoxic.
The researchers identified 202 BC-relevant active pesticide ingredients in dietary sources or drinking water. EPA had canceled registrations for 73 of them. The authors suggest that detection of pesticides such as DDT, dieldrin and chlordane, whose registrations were canceled long ago, may reflect persistent contamination because those chemicals degrade slowly.
Among the 129 current-use BC-relevant active pesticide ingredients detected in food or drinking water, 71 were EDC+ and 51 were genotoxic. Twenty-three had both characteristics.
Medicines appear on the list for a different reason
Pharmaceuticals form a distinct part of the exposure picture because some BC-Chems are deliberately used as active or inactive ingredients in medicines.
The researchers identified 142 BC-Chems in U.S. drug products, including 48 mammary carcinogens. Sixty-nine were listed as active ingredients in the 2025 FDA Orange Book, and 50 of those were being used in prescription drugs. Another 40 BC-Chems were listed as active ingredients in over-the-counter drugs, while 34 appeared in the FDA Inactive Ingredients Database.
The researchers found that 19 BC-Chem active drug ingredients were among the 200 most-prescribed active drug ingredients in 2023. The examples included spironolactone, ketoconazole, triamcinolone, simvastatin, metronidazole, nitrofurantoin and hormones.
The presence of a BC-Chem in a medicine does not by itself mean that the medication causes breast cancer. The analysis identifies chemicals according to the biological criteria used to construct the BC-Chem list and then documents where those chemicals occur. The authors explicitly frame pharmaceutical exposure as something that needs to be considered alongside the therapeutic benefits and risks of the products in which the chemicals are used.
Industrial releases add another route
The researchers also examined chemicals entering the environment from industrial facilities.
For 2024, the EPA’s Toxics Release Inventory contained reported releases for 141 BC-Chems, including 70 mammary carcinogens. Together, those facilities reported nearly 82 million pounds of BC-Chems released on-site or off-site.
Five mammary carcinogens — styrene, acetaldehyde, benzene, dichloromethane and 1,3-butadiene — accounted for more than 90% of the BC-Chem air emissions reported through the TRI. More than half of the total BC-Chem release volume came from genotoxic mammary carcinogens that had not been tested for steroidogenesis or estrogen-receptor activity. The authors suggest that volatility may help explain why some of these chemicals lacked those tests.
Several individual chemicals had reported on-site releases exceeding 1 million pounds in 2024. They included styrene, acetaldehyde, acrylonitrile, benzene, acrylamide, sodium nitrite, dichloromethane and 1,3-butadiene. Sixty-nine percent of the emissions from those chemicals were released to air.
The researchers also identified more than 1 million pounds each of styrene, benzene, sodium nitrite and bisphenol A transported off-site for disposal in 2024.
Those figures represent a particular reporting system rather than every chemical release in the country. TRI covers facilities and chemicals that meet reporting requirements, and the researchers note that environmental releases can vary substantially from year to year because of accidents, equipment problems, wildfires and other events.
More than 2 billion pounds were estimated in air emissions
A separate EPA dataset produced a much larger number.
The 2020 National Emissions Inventory estimated that more than 2 billion pounds of BC-Chems were emitted to air that year. The inventory covered 81 BC-Chems, including 53 mammary carcinogens and 28 other BC-Chems.
The largest-volume emissions came from the genotoxic mammary carcinogens acetaldehyde, benzene, 1,3-butadiene and styrene. More than 66% of all BC-Chem emissions in the 2020 inventory came from nonpoint emissions of acetaldehyde, with vegetation, wildfires and fossil-fuel extraction and combustion identified as major sources.
Another 18% came from nonpoint emissions of benzene, 1,3-butadiene and styrene. The researchers identified wildfires, oil and gas production, prescribed fires, residential wood burning, commercial and consumer solvent use and other sources within those categories.
The emissions data therefore encompass far more than manufacturing plants. The National Emissions Inventory includes large stationary sources such as industrial facilities and power plants, smaller stationary sources, commercial and residential combustion, paving, solvent use and on-road and nonroad transportation.
The authors note that the predominance of combustion-related BC-Chems in the air-emissions data may help explain previously reported epidemiological associations between air pollution and breast cancer. That is presented as a possible explanation, not as a demonstration that these emissions caused those associations.
Chemical traces are detectable in people
The most direct evidence of human exposure came from biomonitoring data from the National Health and Nutrition Examination Survey, or NHANES.
The researchers identified parent chemicals or metabolites corresponding to 103 BC-Chems in NHANES. Urine measurements covered 84 BC-Chems, including 25 mammary carcinogens.
Many urine analytes associated with BC-Chems were detected in more than 95% of samples. They included metabolites associated with naphthols, 1,3-butadiene, styrene, organophosphate and carbamate pesticides, several phthalates, methyl paraben, benzophenone-3 and several phytoestrogens.
Those frequently detected analytes mapped to 43 possible BC-Chem exposures, including 28 chemicals classified as EDC+ and 31 classified as genotoxic. Some of the metabolites associated with 1,3-butadiene, styrene and pyrene were also among those with the highest median or 95th-percentile detection levels.
The researchers caution that a biomonitoring result does not always identify one specific parent chemical. A urinary metabolite associated with styrene, for example, can also arise from ethylbenzene exposure, while metabolites associated with 1,3-butadiene can come from other unsaturated olefins.
Organophosphate pesticides provided one particularly broad exposure pattern. Dialkyl phosphate metabolites measured in NHANES mapped to 20 different parent BC-Chems. Their high detection frequencies and measured levels, combined with information showing use of these pesticides in homes, buildings, lawns and food production and their presence on produce and in drinking water, led the researchers to describe exposure to these pesticides as widespread. Eleven of the 20 increased synthesis of both estrogen and progesterone in the H295R laboratory assay used to classify endocrine activity.
Blood measurements provided another view of exposure.
Of 27 BC-Chems measured in blood, six were detected in more than 90% of the population: nitromethane, p,p′-DDE and heptanal, along with acrylamide, glycidamide and ethylene oxide measured as hemoglobin adducts. The authors note that only p,p′-DDE among these can be attributed entirely to outside exposure. The others can also arise through endogenous processes.
Several older pesticides remained detectable even though their use had been banned decades earlier. Dieldrin, DDT, beta-hexachlorocyclohexane and mirex had detection frequencies above 40% in the NHANES cycles in which they were measured, most recently in 2003–2004. The authors point to their persistence and continued detection in food as a possible source of ongoing exposure.
Other BC-Chem blood analytes included styrene, detected in 38% of the population in the relevant NHANES cycle, and benzene, detected in 36%. Tetrachloroethylene was detected in 8%, 1,2-dichloroethane in 3%, trichloroethylene in 0.7%, perfluorooctanesulfonamide in 0.6% and 1,2-dichlorobenzene in 0.01%.
The measurements vary in age because NHANES does not measure every chemical during every survey cycle. The authors therefore do not treat the absence of a recent measurement as evidence that exposure does not occur.
Modeling fills some of the gaps, but with major uncertainty
Because most BC-Chems are not measured in NHANES, the researchers also examined EPA’s ExpoCast estimates.
The SEEM3 consensus model provided predicted median daily intakes for 872 BC-Chems, including 252 mammary carcinogens. For the general U.S. population, seven chemicals had predicted median intakes of at least 1 microgram per kilogram of body weight per day, while 425 fell between 1 and 1,000 nanograms per kilogram per day and 440 were below 1 nanogram per kilogram per day.
Among the 432 chemicals with predicted intakes of at least 1 nanogram per kilogram per day, 169 were EDC+. Twenty-eight of those had production volumes of at least 1 million pounds in 2019.
But these numbers are modeled estimates, not direct measurements of people’s exposure.
The authors emphasize that SEEM predictions depend on limited information, including production volumes, physical and chemical properties, and assumptions about how chemicals enter the economy through consumer products, food, pesticides and other pathways. They therefore regard biomonitoring and direct exposure measurements as more reliable descriptions of actual human exposure.
The model also estimates the median population intake and does not attempt to capture people at the highest end of exposure. The researchers note that chemical exposure distributions can have long tails, with the 95th and 99th percentiles sometimes several orders of magnitude above the median.
To show some of the uncertainty around the modeled estimates, the researchers examined the upper bound of the model’s 95% credible interval. That upper value can differ from the predicted median by as much as six orders of magnitude. Using that measure, 29 BC-Chems had high-end median predictions of at least 1 milligram per kilogram per day, including five mammary carcinogens. Another 365 had high-end median predictions between 1 and 1,000 micrograms per kilogram per day.
The researchers explicitly caution that even this upper-bound measure does not fully capture the highest exposures within the population. It is therefore not appropriate to interpret the modeled values as precise measurements of what individuals are actually receiving.
The researchers also compared modeled exposure among demographic groups using an earlier ExpoCast model. Predicted median intake was higher for females than males for 484 of 735 BC-Chems, or 66%. Reproductive-age females had higher predicted intakes than females overall for 430 of 735 chemicals, or 59%.
These subgroup comparisons came from the earlier SEEM2 model rather than the newer SEEM3 model because SEEM3 had not generated predictions for those subgroups. The researchers therefore do not directly compare the SEEM2 and SEEM3 estimates.
The exposure record is incomplete
One of the clearest findings from the analysis is not a chemical concentration but a gap in measurement.
NHANES currently measures analytes corresponding to only 103 of the BC-Chems. For most chemicals on the list, there is no comparable population biomonitoring measurement. In some cases, methods capable of reliably measuring human exposure have not yet been developed.
The authors identified 17 NHANES analytes corresponding to 21 genotoxic EDC+ BC-Chems that were detected in at least 90% of biomonitoring samples. Those chemicals included organophosphate and carbamate pesticides, phthalates, industrial chemicals and phytoestrogens.
At the same time, chemicals with potentially substantial exposure can be difficult to detect with existing biomonitoring methods. The researchers highlight several halogenated solvents that had relatively high predicted population intakes and had been detected in drinking water, while only two of them were detected through NHANES measurements. The authors suggest that poor analytical sensitivity may contribute to those low detection frequencies.
That distinction matters because a chemical that is not frequently detected in a biomonitoring program is not necessarily absent from the population. The study’s authors argue that expanding biomonitoring could help distinguish genuinely uncommon exposure from exposure that current methods simply fail to capture reliably.
The researchers also emphasize that people can experience very different levels of exposure depending on where they live, where they work, how close they are to emission sources and what products they use. Their database analysis cannot reconstruct that full distribution of exposure.
Regulation covers only part of the chemical landscape
The researchers compared the BC-Chem list with several U.S. regulatory programs, including the Toxic Substances Control Act, Toxics Release Inventory, Clean Air Act, Safe Drinking Water Act and California’s Proposition 65.
The 2025 TSCA inventory contained more than 70,000 nonconfidential chemicals used in U.S. commerce outside areas covered by other statutes. Within that inventory, the researchers identified 485 TSCA-active BC-Chems, including 116 mammary carcinogens. Another 21 were classified as TSCA-inactive, including three mammary carcinogens.
Among the TSCA-active BC-Chems, 187 were EDC+, including 98 that were both EDC+ and genotoxic.
The researchers then compared those chemicals with the 2024 TRI list. They found 205 BC-Chems on the TRI list, including 96 mammary carcinogens. But 341 BC-Chems that were active in commerce under TSCA were not included in TRI, including 37 mammary carcinogens.
Among those TSCA-active but TRI-unlisted chemicals were 136 EDC+ chemicals, 50 of which were also genotoxic. Eighty-eight had production or importation volumes above 1 million pounds in 2019. The researchers also identified chemicals in this group with relatively high modeled intake estimates. Based on their combined biological, production and exposure information, they suggest that many could be candidates for emissions monitoring, although they are not currently tracked through TRI.
Air regulation covers another subset. The researchers found 67 BC-Chems designated as hazardous air pollutants under the Clean Air Act, including 47 mammary carcinogens. None of the BC-Chems was itself designated as a criteria air pollutant, although the authors note that particulate matter can contain polycyclic aromatic hydrocarbons that are BC-Chems and hazardous air pollutants.
Drinking-water regulation also covered only part of the chemicals identified in the study. As of 2025, EPA had National Primary Drinking Water Standards for 25 BC-Chems, including 18 mammary carcinogens. The researchers identified another 123 BC-Chems detected in drinking water that were not regulated under the Safe Drinking Water Act, including 34 mammary carcinogens.
They also identified 20 additional drinking-water disinfection byproducts relevant to their BC-Chem list that were not among the 11 groups of disinfection byproducts currently regulated under the Safe Drinking Water Act. Seven of those 20 were mammary carcinogens.
California’s list captures some but not all
The researchers also compared the chemicals with California’s Proposition 65 list of carcinogens and developmental or reproductive toxicants.
They found 262 BC-Chems on the Proposition 65 list, including 164 mammary carcinogens. Of those chemicals, 225 were recognized by California as carcinogens, 37 as reproductive toxicants and 65 as developmental toxicants, with some appearing in more than one category.
The researchers identified 149 Proposition 65-listed BC-Chems in consumer products and 105 in dietary sources. Some were also EDC+ chemicals or pesticides with current registrations.
At the same time, 122 mammary carcinogens on the researchers’ list were not listed as carcinogens under Proposition 65. One example was 1,4-benzenediamine, also known as p-phenylenediamine, which the researchers classified as both genotoxic and EDC+. They identified it as a high-production-volume chemical used in hair dyes and other products.
The authors also identified 16 currently used mammary-carcinogen pesticides that were not on Proposition 65, along with 42 genotoxic EDC+ BC-Chems that lacked a carcinogenicity bioassay. The authors say some of the latter could potentially be considered likely breast carcinogens, but this is a proposed interpretation based on their biological activity rather than a demonstrated result from a carcinogenicity study.
The researchers used several filters to identify priorities
The study did not treat all 920 BC-Chems as equally informative or equally exposed.
One prioritization combined three characteristics: evidence of mammary carcinogenicity or higher-confidence endocrine activity, production above 1 million pounds in 2019, and predicted general-population median intake above 0.5 nanograms per kilogram per day. That produced a set of 39 BC-Chems for further research and possible policy intervention.
The researchers emphasize that the high-end modeled intake values for these chemicals varied enormously, from 10 micrograms per kilogram per day to 26.5 grams per kilogram per day, illustrating the large uncertainty around some of the model estimates.
A different prioritization focused on genotoxic EDC+ chemicals found in consumer products, dietary sources or drinking water. The researchers identified 116 such chemicals, including 10 with high-end median intake predictions of at least 0.1 milligrams per kilogram per day. They propose that some of these chemicals warrant more intensive study of health effects, biomonitoring and cumulative exposure.
The authors also identified five chemicals — 2,4,6-tribromophenol, 2-methoxy-5-methylaniline, C.I. azoic diazo component 12, methyl 3-methylorsellinate and nitrilotriacetic acid — as strong candidates for biomonitoring, cumulative risk assessments and epidemiological studies, in addition to chemicals shown in their broader priority list.
Those priorities are not claims that the chemicals have been demonstrated to cause breast cancer in exposed people. They are the researchers’ selections based on combinations of biological activity and exposure-related information.
Workplace exposure is another unresolved piece
The production data also drew attention to people who work directly with chemicals.
The researchers identified 143 BC-Chems produced at more than 1 million pounds in 2019, including 33 mammary carcinogens. Ten mammary carcinogens and bisphenol A were each produced above 5 billion pounds. The authors argue that such high production volumes make workplace exposure a particular area for investigation, while noting that occupational epidemiology has historically included many studies of predominantly male workers.
The paper points to several occupations in which workers could encounter BC-Chems through commonly used products. The authors describe potential exposures to chemicals in antimicrobial products, solvents, fragrances, personal-care products and other workplace materials among health care workers, janitors, cleaners and salon workers. They also cite previous biomonitoring research reporting elevated levels of several BC-Chems among blue-collar workers.
Industrial-emission records could provide another way to identify potentially exposed workers and communities near facilities. But the researchers note that the 2024 TRI covered only 205 BC-Chems, leaving hundreds of TSCA-listed chemicals outside that reporting system.
The evidence does not establish a single breast cancer pathway
The researchers’ BC-Chem classification deliberately combines several types of biological evidence.
Some chemicals have actually caused mammary tumors in rodents. Others have not been shown to cause such tumors but have demonstrated endocrine activity in laboratory systems. Some are genotoxic. Some have more than one of these characteristics.
The earlier work underlying the BC-Chem list found that mammary carcinogens were more likely than other tested chemicals to show estrogen or progesterone steroidogenesis, estrogen-receptor agonism and genotoxicity. Stronger activity in those endocrine assays was associated with a greater likelihood of mammary carcinogenicity in the compiled data.
That relationship was used to identify chemicals that may warrant further investigation, but it does not convert an in-vitro endocrine signal into proof of human breast-cancer causation.
The authors likewise discuss the possibility that chemicals with estrogenic activity could affect breast-cancer development, recurrence or prognosis, particularly because estrogen signaling is relevant to hormone-receptor-positive disease. They present this as a biological rationale for further exposure research rather than as a result demonstrated by the current database analysis.
The same caution applies to mixtures. The study identifies many chemicals with overlapping exposure sources and biological characteristics, and the authors argue that the combined information can help researchers design studies of chemical mixtures. The database analysis itself does not measure the health effects of those mixtures.
Important chemicals are missing from the list
The researchers acknowledge that their 920-chemical list is not a complete catalog of every chemical that could influence breast cancer.
The list was built from mammary-tumor evidence and specific ToxCast endocrine assays. It therefore does not automatically include chemicals that have been associated with breast cancer in epidemiological studies unless they also met the criteria used to construct the BC-Chem list. The authors specifically mention metals, polychlorinated biphenyls, PFAS and some personal-care-product ingredients among chemicals that can be missed by their criteria.
The researchers also note that chemicals not tested by ToxCast, including some emerging contaminants and substances whose physical properties make them difficult to test in vitro, may be absent unless rodent mammary-tumor evidence exists.
Potency is another unresolved issue. The researchers ranked endocrine-disrupting chemicals according to the magnitude of their effects in the steroidogenesis and estrogen-receptor assays, but they did not have comparable potency information for mammary carcinogenicity or genotoxicity. They say future work should examine chemical potency together with biomonitored and predicted exposure levels.
The exposure databases themselves also have blind spots. Production and release reporting can miss lower-volume chemicals, while the Chemical and Products Database depends heavily on voluntary reporting and compilation of public data. The authors acknowledge that some chemical uses may not have been captured and that errors in database curation can lead to misclassification.
Finally, the underlying datasets come from different years. Production data were based on 2019, the National Emissions Inventory on 2020, NHANES measurements on the most recent cycle available for each analyte, and TRI releases on 2024. Chemical production, emissions and exposure can change over time, so the researchers caution that these snapshots should not be treated as a single simultaneous picture of U.S. exposure.
The study’s central result is therefore not that 920 chemicals have been proven to cause breast cancer in humans. Rather, it shows that a large set of chemicals already identified through mammary-cancer evidence or breast-cancer-relevant biological activity occurs across multiple parts of the U.S. chemical economy and exposure environment, while direct measurements of human exposure remain available for only a fraction of them.
The authors conclude that bringing production, exposure, biomonitoring, environmental-release and regulatory information together can help identify chemicals and combinations of chemicals for additional study and exposure assessment. They emphasize the need for better measurement of human exposure, particularly for chemicals that are currently poorly represented in biomonitoring programs.
The study was published in Environmental Health Perspectives.
