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2025
Environ Health
This case-control study of 942 Brazilian women (471 with breast cancer and 471 matched controls) found that higher blood levels of certain per- and polyfluoroalkyl substances (PFAS)—persistent environmental chemicals found in products like non-stick cookware and food packaging—were significantly associated with increased breast cancer risk. Specifically, elevated concentrations of n-perfluoroheptane sulfonate (n-PFHpS) doubled the breast cancer risk, and this association was particularly strong for hormone receptor-positive breast cancers and varied by ethnicity. The study emphasizes the importance of analyzing specific PFAS chemical variants (isomers) rather than treating all PFAS as identical, as different forms showed different associations with breast cancer risk across ethnic groups. These findings add to growing evidence that PFAS exposure may be a modifiable environmental risk factor for breast cancer, though the researchers note that previous studies have shown mixed results.
2024
Environ Res
A decade-long study of 135 breast cancer cases and 540 controls found that exposure to PFAS (perfluoroalkyl substances) was strongly associated with increased breast cancer risk, with mixed PFAS exposure showing more than double the odds of developing the disease. Several specific PFAS compounds—including PFBA, PFOS, PFHxS, and PFDA—were identified as particularly significant risk factors, with some associations appearing exclusively in premenopausal women. The findings suggest that premenopausal women should be especially cautious about PFAS exposure, as these persistent “forever chemicals” may pose a substantial breast cancer risk.
2024
Am J Epidemiol
This systematic review of 18 epidemiological studies evaluated whether exposure to PFAS—measured in blood or plasma—is associated with breast cancer risk. Across 11 of the studies included in the meta-analysis, higher concentrations of common PFAS such as PFOA and PFOS were not associated with increased breast cancer risk (per-log-unit RR for PFOA = 0.95, 95% CI: 0.77–1.18; PFOS = 0.98, 95% CI: 0.87–1.11). When analyses were restricted to studies where PFAS levels were measured before diagnosis, risk estimates were slightly higher (for PFOA: RR = 1.16, 95% CI: 0.96–1.40), but still not statistically significant. Overall, the evidence suggests that current PFAS exposures measured do not show a consistent link to breast cancer, though the authors note substantial study variability and the need for better prospective data.
2024
Sci Total Environ
A Chinese study of 226 breast cancer cases and 990 controls found that exposure to certain perfluoroalkyl substances (PFAS), particularly perfluorononanoic acid (PFNA) and perfluoroheptanoic acid (PFHpA), was associated with increased mitochondrial DNA copy number (mtDNAcn) in blood, which in turn was linked to breast cancer risk. Women with the highest mtDNAcn levels had a 234% increased risk of breast cancer and a 271% increased risk of postmenopausal breast cancer compared to those with the lowest levels. The study found that mtDNAcn mediated about 15% of the relationship between PFHpA exposure and breast cancer, suggesting that PFAS may increase breast cancer risk partly by affecting mitochondrial function. These findings provide new insights into how PFAS chemicals may contribute to breast cancer development through effects on cellular energy production and mitochondrial health.
2024
Environ Health Perspect
A nationwide study using CDC biomonitoring data found that California’s Proposition 65, which requires warnings about chemicals that cause cancer or reproductive harm, led to reduced exposures to listed chemicals across the entire United States, not just California. While blood and urine concentrations of 37 monitored chemicals generally declined over time, the researchers found evidence of problematic chemical substitution—for example, after bisphenol A (BPA) was listed, its concentrations dropped 15% but levels of the unlisted substitute bisphenol S (BPS) increased 20%. Californians generally had lower levels of harmful chemicals in their bodies compared to residents of other states, suggesting the law had additional protective effects. The findings indicate that transparency laws like Prop 65 can drive manufacturers to reformulate products nationwide, but regulations need to address entire chemical classes rather than individual substances to prevent companies from simply switching to similar but unlisted toxic chemicals.
2023
Int J Cancer
This study of over 1,200 postmenopausal women found that higher blood levels of PFOS (a common “forever chemical” found in items like stain-resistant fabrics and food packaging) were associated with 59-134% increased risk of hormone receptor-positive breast cancers, while PFOA (another widespread PFAS chemical) showed modest associations with hormone receptor-negative tumors. PFAS are called “forever chemicals” because they persist indefinitely in the environment and human body, and these findings suggest they may contribute to breast cancer through hormone disruption. These results add to growing concerns about PFAS exposure from contaminated water, food packaging, and consumer products, though the different associations for PFOS and PFOA by tumor subtype require further investigation to fully understand how these chemicals affect breast cancer development.
2023
Environ Sci Poll Res
This meta-analysis pooled data from 17 epidemiological studies to examine whether exposure to the dioxin compound 2,3,7,8-TCDD or to per- and polyfluoroalkyl substances (PFAS) is associated with breast cancer risk. The authors found evidence of a modest but statistically significant increased breast cancer risk associated with TCDD levels in the body,
2022
Environ Pollut
This Chinese prospective study of over 1,200 women found that higher baseline plasma concentrations of PFOA and PFHpA (a shorter-chain PFAS) were associated with 35% and 20% increased risk of developing breast cancer, respectively, with similar or stronger associations seen in postmenopausal women. When researchers examined the combined effect of all perfluorinated carboxylic acids together, they found a 19% increased breast cancer risk for each quartile increase in exposure, with PFOA accounting for more than half of this effect. Importantly, this is the first study to identify PFHpA—a shorter-chain PFAS increasingly used as a replacement for longer-chain compounds—as a breast cancer risk factor, raising concerns that newer “replacement” PFAS chemicals may not be safer alternatives. These prospective findings strengthen the evidence that PFAS exposure is a modifiable risk factor for breast cancer and support the need to regulate PFAS as an entire chemical class rather than individual compounds.
2022
Toxics
A meta-analysis of eight studies examining the relationship between PFAS chemicals and breast cancer found that two specific PFAS compounds—PFOA and PFHxS—were associated with significantly increased breast cancer risk, showing 32% and 79% elevated risk respectively. Surprisingly, PFNA showed a protective association with 24% reduced risk, while PFOS showed no association with breast cancer risk, though all findings had substantial statistical heterogeneity between studies. The researchers concluded that certain PFAS compounds may be potential breast cancer risk factors, with concerning evidence that even low-level exposures could have harmful impacts on human health, highlighting the need for further research to clarify the varied effects of different PFAS chemicals on breast cancer development.
2022
Chemosphere
Researchers measured 41 endocrine-disrupting chemicals (EDCs) in women living in the Greater Manila Area, Philippines, comparing those with and without breast cancer. They found that certain perfluoroalkyl substances (PFAS) were significantly associated with breast cancer, with some chemicals showing dramatically increased risk: PFDoA was associated with a 1,263% increased risk, PFDA with an 826% increased risk, and PFHxA with a 166% increased risk. Long-chain PFAS levels were higher in women from heavily industrialized areas compared to the National Capital Region. This study provides the first baseline data on EDC exposure levels in Filipino women, filling a critical gap in knowledge about chemical exposures in Southeast Asian populations and suggesting that industrial pollution may be contributing to elevated PFAS levels and breast cancer risk.
2022
Environ Health
This large Chinese case-control study of 373 breast cancer patients and 657 controls found that higher plasma levels of PFOA and PFDA were positively associated with breast cancer risk, with PFOA showing particularly strong associations with hormone receptor-positive and HER2-positive breast cancers (47%, 36%, and 62% increased odds, respectively). Interestingly, the study found that PFTrDA (a longer-chain PFAS) was inversely associated with breast cancer risk, though the reasons for this protective effect are unclear. The findings add to growing international evidence linking PFAS exposure to breast cancer, demonstrating that these “forever chemicals” pose breast cancer risks not just in Europe and America but also in Asian populations. These results are concerning because PFOS was found at the highest concentrations in blood samples from both cases and controls, indicating widespread population exposure to these persistent environmental contaminants in Chin
2022
Crit Rev Food Sci Nutr
A systematic review of 131 epidemiological studies examining endocrine-disrupting chemicals (EDCs) and breast cancer risk found evidence that exposure to various EDCs—including pesticides (DDT/DDE, atrazine, dioxin), synthetic chemicals (BPA, phthalates, PFAS, PCBs, PBDEs), and other compounds found in everyday products—may elevate breast cancer risk, particularly when exposure occurs during early life. The review identified food as a major route of EDC exposure and emphasized that because most EDCs persist in the environment and accumulate in the body over time, long-term multi-generational health impacts need to be assessed. The authors call for improved exposure assessments of EDCs in food and food packaging, along with careful evaluation of their links to breast cancer development to inform policy-making and regulations aimed at protecting public health.
2021
Sci Total Environ
This Japanese case-control study of 405 matched pairs of women found that higher serum concentrations of PFAS chemicals were generally associated with reduced breast cancer risk rather than increased risk, with women in the highest exposure quartile showing 79-85% lower odds of breast cancer for linear isomers of PFOS and PFOA. However, the study revealed important differences between chemical structures: among postmenopausal women, while the linear form of one PFAS (PFTrDA) was protective, the branched form showed a marginally increased risk (74% higher odds approaching significance at medium exposure levels). These unexpected inverse associations contrast with several other studies showing increased breast cancer risk from PFAS exposure, highlighting the complexity of PFAS research and the importance of distinguishing between different chemical structures (branched vs. linear isomers) that may have opposite health effects, though the reasons for these protective associations remain unclear and warrant further investigation.
2021
Environ Res
This large U.S. study using NHANES data found that multiple PFAS chemicals were associated with increased odds of both breast and ovarian cancer, with dose-response relationships showing dramatically higher risks at the highest exposure levels—women in the highest quartile of exposure had 130% increased odds for breast cancer (up to 607% for PFHxS) and 77-125% increased odds for ovarian cancer compared to those in the lowest quartile. Different PFAS chemicals showed stronger correlations with different cancers: PFOA was most strongly correlated with breast cancer while PFHxS was most strongly correlated with ovarian cancer, suggesting these endocrine-disrupting chemicals may affect different hormone-sensitive tissues through distinct mechanisms. No associations were found with prostate or uterine cancers. These findings are particularly concerning because PFAS are ubiquitous environmental contaminants found in everyday products and the water supply, and the strong dose-response relationships suggest that reducing PFAS exposure could potentially lower the risk of these estrogen-related cancers in women.
2020
Environ Int
This Taiwanese study of 239 women found that higher plasma levels of PFOS (a “forever chemical”) were associated with 134% increased breast cancer risk in women aged 50 and younger, with each natural log unit increase in exposure more than doubling the odds of developing the disease. Both PFOS and PFHxS (another PFAS chemical) showed positive associations specifically with estrogen receptor-positive breast tumors in younger women, suggesting these endocrine-disrupting chemicals may particularly affect hormone-sensitive breast cancers during reproductive years. These findings are concerning because PFAS are ubiquitous environmental contaminants found in water, food packaging, and consumer products, and the study adds to growing evidence that these persistent chemicals may contribute to rising breast cancer rates among younger women. The results highlight the potential health consequences of widespread PFAS contamination, particularly for women of reproductive age who may face elevated risk of hormone-driven breast cancers.
2020
Int J Cancer
his French study of 388 women found that higher blood levels of PFOS (a “forever chemical”) were associated with 122-133% increased breast cancer risk for estrogen receptor-positive tumors and 147-176% increased risk for progesterone receptor-positive tumors, with a clear dose-response relationship showing increasing risk at higher exposure levels. Interestingly, the study found different patterns for hormone receptor-negative tumors, where only low-to-moderate levels of PFOS and PFOA were associated with dramatically increased risk (up to 1,440% for estrogen receptor-negative tumors at moderate PFOS levels). These findings suggest that PFAS chemicals—which are widespread in human blood worldwide due to contamination from products like stain-resistant fabrics, non-stick cookware, and food packaging—may contribute to breast cancer through different mechanisms depending on tumor type, highlighting the complexity of how these persistent environmental chemicals affect breast cancer risk.
2025
J Exp Sci Environ Epidemiol
A nationwide US study analyzing drinking water contamination and cancer incidence (2016-2021) found that PFAS (“forever chemicals”) in public water systems were associated with increased rates of multiple cancers, with incidence rate increases ranging from 2% to 33% across different cancer types. The strongest association was a 33% increased rate of oral cavity and pharyngeal cancers linked to PFBS exposure, with other significant associations found for digestive, respiratory, endocrine, thyroid, urinary, brain, and soft tissue cancers, showing notable sex-based differences in cancer patterns. Researchers estimate that PFAS contamination in US drinking water may contribute to approximately 4,600-6,900 new cancer cases annually, underscoring the urgent public health need for stricter water quality standards and expanded monitoring of these persistent environmental pollutants.
2024
Crit Rev Toxicol
A meta-analysis of 13 observational studies through May 2022 examined the dose-response relationship between per- and polyfluoroalkyl substances (PFAS) exposure—including PFOS, PFOA, PFNA, PFDA, and PFHxS—and risk of breast, prostate, colorectal, and ovarian cancers. The highest versus lowest exposure analysis found no significant associations between any PFAS compound and breast cancer (ORs ranging from 0.88-1.29), ovarian cancer (OR = 1.43), prostate cancer (OR = 1.05), or colorectal cancer (OR = 0.77). However, linear dose-response analysis revealed unexpected inverse associations, with each 1 ng/ml increase in PFNA and 2 ng/ml increase in PFOA associated with significant decreases in breast cancer risk (RR = 0.67 and 0.94, respectively), though non-linear analysis found no significant changes. The findings provide no evidence that PFAS exposure increases cancer risk for these sites, and the unexpected inverse associations observed in linear dose-response analyses—suggesting potential protective effects—are unexplained and may reflect study artifacts, reverse causation, or confounding factors rather than true biological protection, warranting further investigation to clarify these paradoxical relationships and determine whether they reflect real phenomena or methodological limitations.
2024
J Hazard Mater
A study analyzing 162 non-alcoholic beverages found that 63 endocrine-disrupting chemicals (EDCs) were present in 144 products, with concentrations highest in metal-canned beverages and significantly lower or absent in glass, plastic, and carton packaging. Bisphenol A (BPA) levels were notably elevated in canned drinks compared to identical products from the same manufacturers packaged in glass or plastic, and researchers identified two previously unknown BPA structural isomers in beverages for the first time. The calculated daily BPA exposure from average beverage consumption (364 mL/day) exceeded the European Food Safety Authority’s revised safety guideline by up to 2,000-fold, suggesting that regular consumption of canned non-alcoholic beverages—particularly by young children—poses a potential health hazard due to EDC exposure from packaging materials.
2023
Environ Health Perspect
A case-cohort study within the prospective Cancer Prevention Study II (CPS-II) LifeLink cohort examined associations between serum per- and polyfluoroalkyl substances (PFAS) concentrations and cancer risk by analyzing blood samples collected 1998-2001 from 999 randomly selected participants and 3,762 cancer cases (breast, bladder, kidney, pancreas, prostate, and hematologic cancers), with particular attention to histologic subtypes. The study found that higher serum PFOA concentrations were positively associated with renal cell carcinoma in women (HR per PFOA doubling: 1.54; 95% CI: 1.05-2.26) but not men, while higher PFHxS concentrations were associated with chronic lymphocytic leukemia/small lymphocytic lymphoma (CLL/SLL) in men (HR per PFHxS doubling: 1.34; 95% CI: 1.02-1.75), with some variation in associations observed across histologic subtypes within cancer sites. These findings in a general population cohort support previous observations linking PFOA to kidney cancer in women and identify a new association between PFHxS and CLL/SLL in men, highlighting the importance of considering both sex differences and specific histologic cancer subtypes when evaluating PFAS-cancer relationships. The study demonstrates that PFAS exposure at levels found in the general U.S. population may be associated with increased risk of certain cancers, extending concerns beyond highly exposed occupational or community populations.
2023
Frontiers
This meta-analysis aimed to evaluate the association between exposure to endocrine-disrupting chemicals (EDCs), including phthalates and other common environmental pollutants, and breast cancer risk. The study found that certain EDCs—such as p,p′-DDT, chlordane, HCH, and specific PCBs—were positively associated with increased breast cancer risk, while a few compounds like BBP and PFDoDA showed a negative association.
2023
Endocrinol Metab Clin North Am
Multiple social and structural determinants of health undoubtedly contribute to the marked racial/ethnic-, gender-, and socioeconomic-based disparities in endocrine health; however, the contribution of environmental injustice is vastly underappreciated. Indeed, those groups disproportionately burdened by endocrine disorders are often exposed to higher levels of various EDCs, including PCBs, phthalates, bisphenols, OC pesticides, air pollutants, PFASs, toxic metals/metalloids, and BFRs. These chemicals threaten our reproductive and metabolic health, contributing to diabetes prevalences, obesity, and disorders related to hormonal regulation. This review increases awareness of these disparities and encouraged equitable healthcare for those who are disadvantaged.
2022
Endocrinology
A review examining PFAS (found in nonstick cookware, food packaging, and stain-resistant fabrics) and parabens (used in personal care products) found that exposure to these endocrine-disrupting chemicals is linked to breast cancer development, with marginalized and socially disadvantaged communities facing disproportionately higher exposures due to structural racism and inequitable environmental conditions. These disparities in chemical exposure may contribute to poorer breast cancer outcomes in these populations, yet breast cancer research continues to underrepresent these communities, limiting our ability to address treatment disparities and improve survival rates. The authors emphasize the urgent need to both reduce EDC exposures in vulnerable communities and increase research inclusion of diverse populations to understand how environmental injustices intersect with breast cancer risk and develop interventions that address these health inequities.
2022
Crit Rev Food Sci Nutr
This systematic review of 131 epidemiological studies evaluated the association between various endocrine-disrupting chemicals, including phthalates and hormonal exposures like contraceptive pills, and the risk of breast cancer. It found that several EDCs, particularly phthalates and oral contraceptive use, were consistently associated with increased breast cancer risk across multiple studies.
2021
Water Res
A study of 101 bottled water products sold in the US found that PFAS chemicals were detected in 39% of tested products at concentrations ranging from 0.17 to 18.87 ng/L (median 0.98 ng/L), with 97% of samples below 5 ng/L, though some products approached levels of regulatory concern. Spring water products contained significantly higher PFAS levels than purified water, with reverse osmosis (RO) treatment—used in 71% of purified waters but only 2% of spring waters—effectively removing PFAS contamination across all chain lengths. Notably, perfluoropropanoic acid (PFPrA), an ultrashort-chain PFAS measured for the first time in bottled water, accounted for 42% of detected PFAS mass and was found almost exclusively in spring water products, raising concerns given the lack of enforceable PFAS regulations for bottled water in the US despite these “forever chemicals” being linked to multiple health concerns including potential breast cancer risk, and highlighting the need for mandatory PFAS monitoring and disclosure requirements for bottled water manufacturers.
2020
Repro Toxicol
A 54-year follow-up study of 102 breast cancer cases and 310 matched controls among 9,300 daughters born 1959-1967 in the Child Health and Development Studies cohort found that high maternal perinatal levels of N-ethyl-perfluorooctane sulfonamido acetic acid (EtFOSAA, a precursor to PFOS) combined with high maternal cholesterol predicted a 3.6-fold increased breast cancer risk in daughters by age 52 (95% CI: 1.1-11.6), while maternal PFOS alone was paradoxically associated with decreased risk. These robust findings—consistent across alternative modeling approaches and independent of other maternal factors—demonstrate that prenatal exposure to specific PFAS compounds during critical developmental windows can influence breast cancer risk decades later, revealing multigenerational health consequences of persistent environmental chemicals. The results emphasize the critical importance of studying internal PFAS doses and chemical mixture exposures during vulnerable early-life periods for breast cancer prevention, particularly as current and future generations face continued ubiquitous exposure to these persistent compounds, though experimental validation and replication in additional epidemiological cohorts are needed to confirm causality and inform prevention strategies.
2020
Environ Res
A systematic review of 100 publications across 56 epidemiologic studies found that research enriched with women at higher baseline breast cancer risk—through family history, early-onset disease, or genetic susceptibility—consistently showed stronger and more frequent associations between environmental chemical exposures and breast cancer compared to average-risk populations. Specifically, 80% of studies enriched with family history or early-onset cases showed significant associations with exposures including PAHs, air pollution, DDT, PCBs, PFAS, metals, personal care products, and occupational chemicals, while 74% of studies examining genetic susceptibility found significant gene-environment interactions for various pollutants in women with variants affecting carcinogen metabolism, DNA repair, and oxidative stress. These findings suggest that the inconsistent evidence for environmental chemicals and breast cancer in the literature may partly stem from studying predominantly average-risk populations who may be less susceptible to environmental carcinogens, highlighting the critical need for future research to focus on high-risk populations and measure exposures during key windows of susceptibility (puberty, pregnancy, menopause) to more accurately capture the role of environmental chemicals in breast cancer development.
2018
Eur J Public Health
A 34-year study in Italy’s Veneto Region, where drinking water was contaminated with PFAS chemicals from a manufacturing plant operating since 1964, found significantly higher mortality rates in contaminated communities compared to uncontaminated areas for multiple diseases including diabetes, heart disease, stroke, Alzheimer’s, and breast cancer in women. Women in PFAS-contaminated areas showed elevated mortality from kidney cancer, breast cancer, and Parkinson’s disease, while both men and women had increased deaths from cardiovascular and metabolic diseases. These population-level findings suggest PFAS exposure—from widespread “forever chemicals” used in nonstick cookware, food packaging, stain-resistant fabrics, and firefighting foam—may increase risks for multiple serious diseases including breast cancer, though individual-level studies are needed to confirm causal relationships and understand the mechanisms behind these health impacts.
2018
Environ Health
A nested case-control study within the California Teachers Study examined 902 women with invasive breast cancer and 858 controls who provided blood samples an average of 35 months after case diagnosis to assess whether serum concentrations of six per- and poly-fluoroalkyl substances (PFASs)—PFOA, PFNA, PFUnDA, PFHxS, PFOS, and MeFOSAA—were associated with breast cancer risk. For all invasive breast cancers combined, none of the adjusted odds ratios were statistically significant, though marginally significant inverse associations were observed for PFUnDA and PFHxS; statistically significant inverse associations for these two compounds were found only among the 107 women with hormone receptor-negative tumors, not among the 743 with hormone-positive tumors. The authors conclude that the study provides no evidence that post-diagnosis serum PFAS levels are related to breast cancer risk, and suggest that the few inverse associations observed may be due to chance or study design artifacts, particularly because measurements were taken after diagnosis rather than before. Future research should include pre-diagnosis PFAS measurements, genetic susceptibility factors, and endogenous estrogen levels to better assess whether these widely used synthetic chemicals—some of which are known mammary toxicants and endocrine disruptors—influence breast cancer development.
2018
Environ Res
A systematic review of 158 studies examining environmental chemicals and breast cancer found the strongest evidence for increased risk from exposures during critical developmental periods (in utero, adolescence, pregnancy) to DDT, dioxins, PFOSA, air pollution, and occupational solvents, with risk estimates ranging from 1.4 to 5 times higher. A landmark 50-year study that captured DDT exposure during windows of breast development showed particularly elevated risks, while research on genetic variations found that women with certain DNA repair gene variants had higher breast cancer risk from PAH (polycyclic aromatic hydrocarbon) exposure. However, most studies failed to assess exposure timing during biologically relevant windows of susceptibility, and many current-use chemicals in consumer products remain inadequately studied, with major challenges including reconstructing decades-old exposures and measuring rapidly metabolized chemicals in complex real-world mixtures.
2024
Environ Sci Technol
Trifluoroacetic acid (TFA)—a persistent and mobile chemical produced when many PFAS, fluorinated gases, pesticides, and pharmaceuticals break down—is accumulating irreversibly in rain, soil, drinking water, human blood, and food at concentrations orders of magnitude higher than other PFAS. TFA exhibits reproductive and liver toxicity in mammals and bioaccumulates readily in plants, yet ecotoxicity data remain limited, particularly for terrestrial ecosystems. Due to its extreme persistence, ongoing emissions from multiple sources, and irreversibly increasing concentrations, TFA may represent a “planetary boundary threat”—a substance reaching global-scale exposure levels that could trigger irreversible disruptions to vital Earth systems. The authors call for binding regulatory actions to reduce emissions of TFA and the many precursor chemicals that transform into TFA in the environment.
2024
Water Res
A pilot study collected tapwater samples from low-income California communities in five regions (Gold Country, San Francisco Bay Area, Central Valley, and southeast Los Angeles) with suspected water quality challenges and elevated breast cancer rates, analyzing 251 organic chemicals and 32 inorganic constituents. The five most frequently detected contaminants were barium (100% of samples), disinfection byproducts including total trihalomethanes (90%), bromodichloromethane (86.7%), and chloroform (85%), and copper (95%), with mixtures of regulated and unregulated contaminants varying by region, water source, and public water system size. Multiple exceedances of health-based Maximum Contaminant Level Goals (MCLGs) were observed—including 54 samples exceeding zero tolerance for total trihalomethanes, 52 for bromodichloromethane, 11 for lead, and 10 each for PFOA and PFOS—along with enforceable Maximum Contaminant Level (MCL) exceedances for total trihalomethanes (3 samples) and PFAS compounds (9-10 samples for PFOA/PFOS). The findings underscore critical water quality concerns in socially disadvantaged communities and provide a foundation for future studies examining potential linkages between tapwater contaminant mixtures and breast cancer rates in vulnerable California populations facing compounded environmental stressors.