Monohaloacetic acid drinking water disinfection by-products inhibit follicle growth and steroidogenesis in mouse ovarian antral follicles in vitro

Urinary haloacetic acid concentrations in relation to sex and thyroid hormones among reproductive-aged men

Sex and thyroid hormones are critical for male reproductive health. However, the associations between haloacetic acid (HAA) exposure - a known endocrine disruptor - and sex and thyroid hormones in humans remains unclear. We thus recruited 502 male participants seeking fertility evaluation from a reproductive center. We measured concentrations of sex and thyroid hormones in a single blood sample and dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in repeated urine samples. Multivariable linear regression models were constructed to evaluate the associations between HAA concentrations and hormone measurements. After adjusting for potential confounders and urinary creatinine concentrations, urinary concentrations of TCAA were inversely associated with serum levels of sex hormone-binding globulin (SHBG), testosterone (T), T/luteinizing hormone ratio (T/LH), and thyroid stimulating hormone (TSH) (all P for trend < 0.10). Compared with participants in the lowest quartile of TCAA concentrations, those in the highest quartile had reduced serum levels of SHGB by 14.2 % (95% CI: -26.7, -3.0 %), T by 11.1 % (95% CI: -21.7, -1.3 %), T/LH by 21.0 % (95% CI: -36.7, -7.1 %), and TSH by 19.1 % (95% CI: -39.7, -1.5 %). Additionally, we observed inverse associations between continuous measurements of urinary HAAs and serum levels of free T, bioactive T, and estradiol. Our findings suggest that male HAA exposure may be associated with disrupted sex and thyroid function.

Advances in understanding the reproductive toxicity of endocrine-disrupting chemicals in women

Recently, there has been a noticeable increase in disorders of the female reproductive system, accompanied by a rise in adverse pregnancy outcomes. This trend is increasingly being linked to environmental pollution, particularly through the lens of Endocrine Disrupting Chemicals (EDCs). These external agents disrupt natural processes of hormones, including synthesis, metabolism, secretion, transport, binding, as well as elimination. These disruptions can significantly impair human reproductive functions. A wealth of animal studies and epidemiological research indicates that exposure to toxic environmental factors can interfere with the endocrine system's normal functioning, resulting in negative reproductive outcomes. However, the mechanisms of these adverse effects are largely unknown. This work reviews the reproductive toxicity of five major environmental EDCs-Bisphenol A (BPA), Phthalates (PAEs), Triclocarban Triclosan and Disinfection Byproducts (DBPs)-to lay a foundational theoretical basis for further toxicological study of EDCs. Additionally, it aims to spark advancements in the prevention and treatment of female reproductive toxicity caused by these chemicals.

Urinary biomarkers of drinking-water disinfection byproducts in relation to diminished ovarian reserve risk: A case-control study from the TREE cohort

BACKGROUND

Disinfection byproducts (DBPs) as ovarian toxicants have been documented in toxicological studies. However, no human studies have explored the effects of exposure to DBPs on diminished ovarian reserve (DOR).

OBJECTIVE

To assess whether urinary biomarkers of exposure to drinking-water DBPs were associated with DOR risk.

METHODS

A total of 311 women undergoing assisted reproductive technology were diagnosed with DOR in the Tongji Reproductive and Environmental (TREE) cohort from December 2018 to August 2021. The cases were matched to the controls with normal ovarian reserve function by age in a ratio of 1:1. Urinary trichloroacetic acid (TCAA) and dichloroacetic acid (DCAA) were quantified as biomarkers of drinking-water DBP exposures. The conditional logistic regression and restricted cubic spline (RCS) were used to explore urinary biomarkers of drinking-water DBP exposures in associations with the risk of DOR.

RESULTS

Elevated urinary DCAA levels were associated with higher DOR risk [adjusted odds ratio (OR) = 1.87; 95 % confidence interval (CI): 1.16, 3.03 for the highest vs. lowest quartiles; P for trend = 0.016]. The association was confirmed in the RCS model, with a linear dose-response curve (P for overall association = 0.029 and P for non-linear association = 0.708). The subgroup analysis by age and body mass index (BMI) showed that urinary DCAA in association with DOR risk was observed among women ≥35 years old and leaner women (BMI < 24 kg/m2), but the group differences were not statistically significant. Moreover, a U-shaped dose-response curve between urinary TCAA and DOR risk was estimated in the RCS model (P for overall association = 0.011 and P for non-linear association = 0.004).

CONCLUSIONS

Exposure to drinking-water DBPs may contribute to the risk of DOR among women undergoing assisted reproductive technology.

Associations between Urinary Concentrations of Disinfection Byproducts and in Vitro Fertilization Outcomes: A Prospective Cohort Study in China

BACKGROUND

Experimental studies show that disinfection byproducts (DBPs) can inhibit oocyte maturation, decrease fertilization capacity, and impair embryo development, but human evidence is lacking.

OBJECTIVES

We aimed to evaluate the associations between exposure to drinking water DBPs and in vitro fertilization (IVF) outcomes.

METHODS

The study included 1,048 women undergoing assisted reproductive technology (ART) treatment between December 2018 and January 2020 from a prospective cohort study, the Tongji Reproductive and Environmental study in Wuhan, China. Exposure to DBPs was assessed by dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) in up to four urine samples, which were collected on the day of both enrollment and oocyte retrieval. Multivariable generalized linear mixed models, accounting for multiple IVF cycles per woman, were applied to evaluate the associations between urinary biomarkers of DBP exposures and IVF outcomes. Stratified analyses were used to explore the potential effect modifiers.

RESULTS

The included 1,048 women underwent 1,136 IVF cycles, with 960 (91.6%), 84 (8.0%), and 4 (0.4%) women contributing one cycle, two cycles, and three cycles, respectively. We found that elevated quartiles of urinary DCAA and TCAA concentrations were associated with reduced numbers of total oocytes and metaphase II oocytes and that urinary DCAA concentrations with a lower proportion of best-quality embryos (all p for trends < 0.05 ). Moreover, elevated quartiles of urinary DCAA concentrations were associated with decreased proportions of successful implantation, clinical pregnancy, and live birth (14%, 15%, and 15% decreases in adjusted means comparing the extreme quartiles, respectively; all p for trends < 0.05 ). Stratification analyses showed that the inverse associations of urinary TCAA concentrations with multiple IVF outcomes were stronger among women ≥ 30 y of age (p for interactions < 0.05 ).

DISCUSSION

Exposure to drinking water DBPs was inversely associated with some IVF outcomes among women undergoing ART treatment. Further study is necessary to confirm our findings. https://doi.org/10.1289/EHP12447.

Genotoxicity and endocrine disruption potential of haloacetic acids in human placental and lung cells

Chlorination of water results in the formation of haloacetic acids (HAAs) as major disinfection byproducts (DBPs). Previous studies have reported some HAAs species to act as cytotoxic, genotoxic, and carcinogenic. This work aimed at further exploring the toxicity potential of the most investigated HAAs (chloroacetic (CAA), bromoacetic (BAA), iodoacetic (IAA) acid) and HAAs species with high content of bromine (tribromoacetic acid (TBAA)), and iodine in their structures (chloroiodoacetic (CIAA) and diiodoacetic acid (DIAA)) to human cells. Novel knowledge was generated regarding cytotoxicity, oxidative stress, endocrine disrupting potential, and genotoxicity of these HAAs by using human placental and lung cells as in vitro models, not previously used for DBP assessment. IAA showed the highest cytotoxicity (EC₅₀: 7.5 μM) and ability to generate ROS (up to 3-fold) in placental cells, followed by BAA (EC₅₀: 20-25 μM and 2.1-fold). TBAA, CAA, DIAA, and CIAA showed no significant cytotoxicity (EC₅₀ > 250 μM). All tested HAAs decreased the expression of the steroidogenic gene hsd17b1 up to 40 % in placental cells, and IAA and BAA (0.01-1 μM) slightly inhibited the aromatase activity. HAAs also induced the formation of micronuclei in A549 lung cells after 48 h of exposure. IAA and BAA showed a non-significant increase in micronuclei formation at low concentrations (1 μM), while BAA, CAA, CIAA and TBAA were genotoxic at exposure concentrations above 10 μM (100 μM in the case of DIAA). These results point to genotoxic and endocrine disruption effects associated with HAA exposure at low concentrations (0.01-1 μM), and the usefulness of the selected bioassays to provide fast and sensitive responses to HAA exposure, particularly in terms of genotoxicity and endocrine disruption effects. Further studies are needed to define thresholds that better protect public health.

Chloroacetonitrile reduces rat prenatal bone length and induces oxidative stress, apoptosis, and DNA damage in rat fetal liver

One of the disinfection byproducts of chlorinating drinking water is chloroacetonitrile (CAN). Thirty-six female rats were used and distributed equally into four groups. The low dose treated group received CAN at a dose of 5.5 mg/kg body weight/day (1/40 LD₅₀ ) orally from the 6th to 12th day of gestation. The high dose treated group received 11 mg/kg body weight/day (1/20 LD₅₀ ) of CAN orally for the same period, the vehicle control group received 1 mL of corn oil, and the water control group received 1 mL of distilled water orally for the same period. High dose exposure to CAN significantly reduced gravid uterine weight, fetal body weights, and length, and caused obvious skeletal deformities, weak mineralization. Fetal tibial growth plates displayed histopathologic changes. Induced oxidative stress and redox imbalance in fetal liver tissues was evidenced by significantly decreased in catalase and superoxide dismutase activity, and elevated malondialdehyde levels. Histopathological, glycogen content changes, and DNA damage were observed in the fetal liver of high dose treated group. Additionally, administration of high dose of CAN induced apoptosis, evidenced by increased caspase-3 concentration in fetal liver. Thus, extensive exposure to CAN induces poor pregnancy outcomes. CAN levels in water should be monitored regularly.

Potential Disrupting Effects of Wastewater-Derived Disinfection Byproducts on Chinese Rare Minnow (Gobiocypris rarus) Transthyretin: An In Vitro and In Silico Study

The available information about whether wastewater-derived disinfection byproducts (DBPs) could elicit potential endocrine-related detrimental effects on aquatic organisms was scarce. Herein, the potential disrupting effects and underlying binding mechanism of 14 wastewater-derived aliphatic and aromatic DBPs and 12 other substances on Chinese rare minnow (Gobiocypris rarus) transthyretin (CrmTTR) were tested and revealed by in vitro and in silico methods. The amino acid sequences of CrmTTR were determined, and the recombinant CrmTTR with a molecular mass of 66.3 kDa was expressed and purified. In vitro assay results indicated that eight selected aromatic DBPs exhibited detectable CrmTTR disrupting ability. Meanwhile, six aliphatic DBPs were not CrmTTR binders. Molecular modeling results implied that hydrophobic hydrogen bonds and/or ionic pair interactions were non-negligible. Four binary classification models with high classification performance were constructed. A significant positive linear relationship was observed for the binding affinity data from CrmTTR and human TTR (n = 18, r = 0.922, p < 0.0001). However, the binding affinity for 13 out of 18 tested compounds with CrmTTR was higher than that with human TTR. All the results highlighted that some wastewater-derived DBPs may be potential disruptors on the aquatic organism endocrine system, and interspecies variation should not be neglected in future determination of the potential endocrine disrupting effects of wastewater-derived DBPs.

Bromoacetic acid impairs mouse oocyte in vitro maturation through affecting cytoskeleton architecture and epigenetic modification

As a major public health achievement, disinfection of drinking water significantly decreases outbreaks of waterborne disease, but produces drinking water disinfection by-products (DBPs) unfortunately. The haloacetic acids (HAAs) including bromoacetic acid (BAA), the second major class of DBPs, are considered as a global public health concern. BAA has been identified as cytotoxic, genotoxic, mutagenic, carcinogenic, and teratogenic in somatic cells. However, the toxic effects of BAA on oocyte maturation remain obscure. Herein, we documented that exposure to BAA compromised mouse oocyte maturation in vitro, causing blocked polar body extrusion (PBE). Meiotic progression analysis demonstrated that exposure to BAA induced the activated spindle assembly checkpoint (SAC) mediated metaphase I (MI) arrest in oocytes. Further study revealed that exposure to BAA resulted in the hyperacetylation of α-tubulin, disrupting spindle assembly and chromosome alignment, which is responsible for the activation of SAC. Besides, the organization of actin, the other major component of cytoskeleton in oocytes, was disturbed after BAA exposure. In addition, exposure to BAA altered the status of histone H3 methylation and 5 mC, indicative of the damaged epigenetic modifications. Moreover, we found that exposure to BAA induced DNA damage in a dose-dependent manner in oocytes. Collectively, our study evidenced that exposure to BAA intervened mouse oocyte maturation via disrupting cytoskeletal dynamics, damaging epigenetic modifications and inducing accumulation of DNA damage.

Effect of iodoacetic acid on the reproductive system of male mice

Iodoacetic acid (IAA) is one of the most common water disinfection byproducts (DBPs). Humans and animals are widely and continuously exposed to it. Many species of water DBPs are harmful to the reproductive system of organisms. Nevertheless, the potential effects of IAA exposure on testosterone and spermatogenesis in vivo remain ambiguous. Spermatogenous cells are the site of spermatogenesis, Leydig cells are the site of testosterone synthesis, and Sertoli cells build the blood–testis barrier (BTB), providing a stable environment for the aforementioned important physiological functions in testicular tissue. Therefore, we observed the effects of IAA on spermatogenic cells, Leydig cells, and Sertoli cells in the testis. In this study, we found that oral administration of IAA (35 mg/kg body weight per day for 28 days) in male mice increased serum LH levels and reduced sperm motility, affecting average path velocity and straight line velocity of sperm. In addition, IAA promoted the expression of γH2AX, a marker for DNA double-strand breaks. Moreover, IAA downregulated the protein expression of the scavenger receptor class B type 1 (SRB1), and decreased lipid droplet transport into Leydig cells, which reduced the storage of testosterone synthesis raw materials and might cause a drop in testosterone production. Furthermore, IAA did not affect the function of BTB. Thus, our results indicated that IAA exposure affected spermatogenesis and testosterone synthesis by inducing DNA damage and reducing lipid droplet transport.

How well does XAD resin extraction recover halogenated disinfection byproducts for comprehensive identification and toxicity testing?

Halogenated disinfection byproducts (DBPs) are an unintended consequence of drinking water disinfection, and can have significant toxicity. XAD resins are commonly used to extract and enrich trace levels of DBPs for comprehensive, nontarget identification of DBPs and also for in vitro toxicity studies. However, XAD resin recoveries for complete classes of halogenated DBPs have not been evaluated, particularly for low, environmentally relevant levels (ng/L to low µg/L). Thus, it is not known whether levels of DBPs or the toxicity of drinking water might be underestimated. In this study, DAX-8/XAD-2 layered resins were evaluated, considering both adsorption and elution from the resins, for extracting 66 DBPs from water. Results demonstrate that among the 7 classes of DBPs investigated, trihalomethanes (THMs), including iodo-THMs, were the most efficiently adsorbed, with recovery of most THMs ranging from 50%-96%, followed by halonitromethanes (40%-90%). The adsorption ability of XAD resins for haloacetonitriles, haloacetamides, and haloacetaldehydes was highly dependent on the individual species. The adsorption capacity of XAD resins for haloacetic acids was lower (5%-48%), even after adjusting to pH 1 before extraction. Recovery efficiency for most DBPs was comparable with their adsorption, as most were eluted effectively from XAD resins by ethyl acetate. DBP polarity and molecular weight were the two most important factors that determine their recovery. Recovery of trichloromethane, iodoacetic acid, chloro- and iodo-acetonitrile, and chloroacetamide were among the lowest, which could lead to underestimation of toxicity, particularly for iodoacetic acid and iodo-acetonitrile, which are highly toxic.

Iodoacetic acid exposure alters the transcriptome in mouse ovarian antral follicles

Iodoacetic acid (IAA) is an unregulated water disinfection byproduct that is an ovarian toxicant. However, the mechanisms of action underlying IAA toxicity in ovarian follicles remain unclear. Thus, we determined whether IAA alters gene expression in ovarian follicles in mice. Adult female mice were dosed with water or IAA (10 or 500 mg/L) in the water for 35-40 days. Antral follicles were collected for RNA-sequencing analysis and sera were collected to measure estradiol. RNA-sequencing analysis identified 1063 differentially expressed genes (DEGs) in the 10 and 500 mg/L IAA groups (false discovery rate FDR < 0.1), respectively, compared to controls. Gene Ontology Enrichment analysis showed that DEGs were involved with RNA processing and regulation of angiogenesis (10 mg/L) and the cell cycle and cell division (500 mg/L). Pathway Enrichment analysis showed that DEGs were involved in the phosphatidylinositol 3-kinase and protein kinase B (PI3K-Akt), gonadotropin-releasing hormone (GnRH), estrogen, and insulin signaling pathways (10 mg/L). Pathway Enrichment analysis showed that DEGs were involved in the oocyte meiosis, GnRH, and oxytocin signaling pathways (500 mg/L). RNA-sequencing analysis identified 809 DEGs when comparing the 500 and 10 mg/L IAA groups (FDR < 0.1). DEGs were related to ribosome, translation, mRNA processing, oxidative phosphorylation, chromosome, cell cycle, cell division, protein folding, and the oxytocin signaling pathway. Moreover, IAA exposure significantly decreased estradiol levels (500 mg/L) compared to control. This study identified key candidate genes and pathways involved in IAA toxicity and can help to further understand the molecular mechanisms of IAA toxicity in ovarian follicles.

Effects of iodoacetic acid drinking water disinfection byproduct on the gut microbiota and its metabolism in rats

Iodoacetic acid (IAA) is an unregulated disinfection byproduct in drinking water and has been shown to exert cytotoxicity, genotoxicity, tumorigenicity, and reproductive and developmental toxicity. However, the effects of IAA on gut microbiota and its metabolism are still unknown, especially the association between gut microbiota and the metabolism and toxicity of IAA. In this study, female and male Sprague-Dawley rats were exposed to IAA at 0 and 16 mg/kg bw/day daily for 8 weeks by oral gavage. Results of 16S rRNA gene sequencing showed that IAA could alter the diversity, relative abundance and function of gut microbiota in female and male rats. IAA also increased the abundance of genes related to steroid hormone biosynthesis in the gut microbiota of male rats. Moreover, metabolomics profiling revealed that IAA could significantly disturb 6 and 13 metabolites in the feces of female and male rats, respectively. In female rats, the level of androstanediol increased in the IAA treatment group. These results were consistent with our previous findings, where IAA was identified as an androgen disruptor. Additionally, the perturbed gut microbiota and altered metabolites were correlated with each other. The results of this study indicated that IAA could disturb gut microbiota and its metabolism. These changes in gut microbiota and its metabolism were associated with the reproductive and developmental toxicity of IAA.

The antiestrogen-like activity and reproductive toxicity of 2,6-DCBQ on female zebrafish upon sub-chronic exposure

2,6-Dichloro-1,4-benzoquinone (2,6-DCBQ), an emerging water disinfection by-product, is widely detected in water resources. However, its potential effects on the reproductive system are largely unknown. Here, we investigated the long-term effects of 2,6-DCBQ on gonadal development by exposing zebrafish from 15 to 180 days postfertilization (dpf). Following exposure to 2,6-DCBQ (20 and 100 µg/L), female-specific effects including delayed puberty onset, retarded ovarian growth and breakdown of the zona radiata were observed, resulting in subfertility in adult females. Adverse effects in folliculogenesis disappeared two months after cessation of 2,6-DCBQ administration. In contrast, no adverse impacts were noted in male testes. The effects on females were associated with significant reduction in 17β-estradiol (E2) level, suggesting a role for 2,6-DCBQ in anti-estrogenic activity. E2 level change in blood was further supported by dysregulated expression of genes (cyp19a1a, fshb, kiss3, esr2b, vtg1, and vtg3) related to the hypothalamic-pituitary-gonad-liver (HPGL) axis. The present study demonstrates for the first time that 2,6-DCBQ induces reproductive impairments in female zebrafish through disrupting 17β-estradiol level.

Relationships between regulated DBPs and emerging DBPs of health concern in U.S. drinking water

A survey was conducted at eight U.S. drinking water plants, that spanned a wide range of water qualities and treatment/disinfection practices. Plants that treated heavily-wastewater-impacted source waters had lower trihalomethane to dihaloacetonitrile ratios due to the presence of more organic nitrogen and HAN precursors. As the bromide to total organic carbon ratio increased, there was more bromine incorporation into DBPs. This has been shown in other studies for THMs and selected emerging DBPs (HANs), whereas this study examined bromine incorporation for a wider group of emerging DBPs (haloacetaldehydes, halonitromethanes). Moreover, bromine incorporation into the emerging DBPs was, in general, similar to that of the THMs. Epidemiology studies that show an association between adverse health effects and brominated THMs may be due to the formation of brominated emerging DBPs of heath concern. Plants with higher free chlorine contact times before ammonia addition to form chloramines had less iodinated DBP formation in chloraminated distribution systems, where there was more oxidation of the iodide to iodate (a sink for the iodide) by the chlorine. This has been shown in many bench-scale studies (primarily for iodinated THMs), but seldom in full-scale studies (where this study also showed the impact on total organic iodine. Collectively, the THMs, haloacetic acids, and emerging DBPs accounted for a significant portion of the TOCl, TOBr, and TOI; however, ∼50% of the TOCl and TOBr is still unknown. The correlation of the sum of detected DBPs with the TOCl and TOBr suggests that they can be used as reliable surrogates.

Exposure to disinfection by-products and reproductive hormones among women: Results from the Tongji Reproductive and Environmental (TREE) study

BACKGROUND

Disinfection by-products (DBPs) have been shown to impair female reproductive function. However, epidemiological evidence on reproductive hormones is scarce.

OBJECTIVE

To investigate the associations between DBP exposures and reproductive hormones among women undergoing assisted reproductive technology.

METHODS

We included 725 women from the Tongji Reproductive and Environmental (TREE) Study, an ongoing cohort conducted in Wuhan, China during December 2018 and January 2020. Urine samples collected at recruitment were quantified for dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) as biomarkers of DBP exposures. At day 2-5 of menstruation, serum reproductive hormones including luteinizing hormone (LH), estradiol (E₂), total testosterone (T), progesterone (PRGE), and prolactin (PRL) were determined. Multivariate linear regression models were performed to assess the associations of urinary DCAA and TCAA concentrations with reproductive hormone levels. Dose-response relationships were investigated using natural cubic spline (NCS) and restricted cubic spline (RCS) models.

RESULTS

After adjusting for relevant confounders, we observed that higher urinary DCAA levels were associated with increased serum PRGE (9.2%; 95% CI: -0.55%, 19.8% for the highest vs. lowest tertile; P for trend = 0.06). Based on NCS models, we observed U-shaped associations of urinary DCAA with serum PRGE and PRL; each ln-unit increment in urinary DCAA concentrations above 3.61 μg/L and 6.30 μg/L was associated with 18.9% (95% CI: 4.8%, 34.7%) and 23.3% (95% CI: -0.92%, 53.5%) increase in serum PRGE and PRL, respectively. The U-shaped associations were further confirmed in RCS models (P for overall association ≤0.01 and P for non-linear associations ≤0.04). We did not observe evidence of associations between urinary TCAA and reproductive hormones.

CONCLUSION

Urinary DCAA but not TCAA was associated with altered serum PRGE and PRL levels among women undergoing assisted reproductive technology.

Drinking Water Disinfection Byproducts, Ingested Nitrate, and Risk of Endometrial Cancer in Postmenopausal Women

BACKGROUND

Disinfection byproducts (DBPs) and N-nitroso compounds (NOC), formed endogenously after nitrate ingestion, are suspected endometrial carcinogens, but epidemiological studies are limited.

OBJECTIVES

We investigated the relationship of these exposures with endometrial cancer risk in a large prospective cohort.

METHODS

Among postmenopausal women in the Iowa Women's Health Study cohort, we evaluated two major classes of DBPs, total trihalomethanes (TTHM) and five haloacetic acids (HAA5), and nitrate-nitrogen (NO3-N) in public water supplies (PWS) in relation to incident primary endometrial cancer (1986-2014). For women using their PWS >10y at enrollment (n=10,501; cases=261), we computed historical averages of annual concentrations; exposures were categorized into quantiles and when possible ≥95th percentile. We also computed years of PWS use above one-half the U.S. maximum contaminant level (>½ MCL; 40μg/L TTHM; 30μg/L HAA5; 5mg/L NO3-N). Dietary nitrate/nitrite intakes were estimated from a food frequency questionnaire. We estimated hazard ratios (HR) and 95% confidence intervals (CI) via Cox models adjusted for age, endometrial cancer risk factors [e.g., body mass index, hormone replacement therapy (HRT)], and mutually adjusted for DBPs or NO3-N. We evaluated associations for low-grade (cases=99) vs. high-grade (cases=114) type I tumors. We assessed interactions between exposures and endometrial cancer risk factors and dietary factors influencing NOC formation.

RESULTS

Higher average concentrations of DBPs (95th percentile: TTHM ≥93μg/L, HAA5 ≥49μg/L) were associated with endometrial cancer risk (TTHM: HR95vsQ1=2.19, 95% CI: 1.41, 3.40; HAA5: HR95vsQ1=1.84, 95% CI: 1.19, 2.83; ptrend<0.01). Associations were similarly observed for women greater than median years of PWS use with levels >½ MCL, in comparison with zero years (TTHM: HR36+vs0y=1.61, 95% CI: 1.18, 2.21; HAA5: HR38+vs0y=1.85, 95% CI: 1.31, 2.62). Associations with DBPs appeared stronger for low-grade tumors (TTHM: HRQ4vsQ1=2.12, 95% CI: 1.17, 3.83; p-trend=0.008) than for high-grade tumors (TTHM: HRQ4vsQ1=1.40, 95% CI: 0.80, 2.44; p-trend=0.339), but differences were not statistically significant (p-heterogeneity=0.43). Associations with TTHM were stronger among ever HRT users than non-HRT users (p-interaction<0.01). We observed no associations with NO3-N in drinking water or diet.

DISCUSSION

We report novel associations between the highest DBP levels and endometrial cancer for our Iowa cohort that warrant future evaluation. https://doi.org/10.1289/EHP10207.

Effects of prenatal and lactational exposure to iodoacetic acid on the F1 generation of mice†

Water disinfection can generate water disinfection byproducts (DBPs). Iodoacetic acid (IAA) is one DBP, and it has been shown to be an ovarian toxicant in vitro and in vivo. However, it is unknown if prenatal and lactational exposure to IAA affects reproductive outcomes in female offspring. This study tested the hypothesis that prenatal and lactational exposure to IAA adversely affects reproductive parameters in F1 female offspring. Adult female CD-1 mice were dosed with water (control) or IAA (10, 100, and 500 mg/L) in the drinking water for 35 days and then mated with unexposed males. IAA exposure continued throughout gestation. Dams delivered naturally, and pups were continuously exposed to IAA through lactation until postnatal day (PND) 21. Female pups were euthanized on PND 21 and subjected to measurements of anogenital distance, ovarian weight, and vaginal opening. Ovaries were subjected to histological analysis. In addition, sera were collected to measure reproductive hormone levels. IAA exposure decreased vaginal opening rate, increased the absolute weight of the ovaries, increased anogenital index, and decreased the percentage of atretic follicles in female pups compared to control. IAA exposure caused a borderline decrease in the levels of progesterone and follicle-stimulating hormone (FSH) and increased levels of testosterone in female pups compared to control. Collectively, these data show that prenatal and lactational exposure to IAA in drinking water affects vaginal opening, anogenital index, the weight of the ovaries, the percentage of atretic follicles, and hormone levels in the F1 generation in mice.

Associations between drinking water disinfection byproducts and menstrual cycle characteristics: A cross-sectional study among women attending an infertility clinic

Disinfection byproducts (DBPs) have been shown to alter ovarian steroidogenesis and cause estrous cyclicity disturbance and prolongation in experimental studies, however human studies are lacking. We aimed to evaluate the cross-sectional associations between drinking water DBPs and menstrual cycle characteristics. A total of 1078 women attending an infertility clinic in Wuhan, China were included between December 2018 and January 2020. Characteristics of menstrual cycle were collected by questionnaires. Concentrations of dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were measured in urine as biomarkers of drinking water DBPs. Multivariate logistic and linear regression models were used to evaluate the associations between urinary DCAA and TCAA concentrations and menstrual cycle characteristics. Higher urinary DCAA concentrations were associated with increased odds ratios (ORs) of irregular menstrual cycle (OR = 1.80; 95% CI: 0.97, 3.33 for the highest vs. lowest quartile; P for trend = 0.05) and long menstrual cycle (OR = 1.62; 95% CI: 0.97, 2.70 for the highest vs. lowest quartile; P for trend = 0.06), as well as prolonged variation in cycle length (β = 1.27 days; 95% CI: -0.11, 2.66 for the highest vs. lowest quartile; P for trend = 0.04). Higher urinary TCAA concentrations were associated with prolonged bleeding duration (β = 0.23 days; 95% CI: -0.06, 0.51 for the highest vs. lowest quartile; P for trend = 0.07). These results suggest that exposure to drinking water DBPs is associated with menstrual cycle disturbances. These findings are warranted to confirm in other studies.

Urinary biomarkers of exposure to drinking water disinfection byproducts and ovarian reserve: A cross-sectional study in China

Experimental studies have demonstrated that disinfection byproducts (DBPs) can cause ovarian toxicity including inhibition of antral follicle growth and disruption of steroidogenesis, but there is a paucity of human evidence. We aimed to investigate whether urinary biomarkers of exposure to drinking water DBPs were associated with ovarian reserve. The present study included 956 women attending an infertility clinic in Wuhan, China from December 2018 to January 2020. Antral follicle count (AFC), ovarian volume (OV), anti-Mullerian hormone (AMH), and follicle-stimulating hormone (FSH) were measured as indicators of ovarian reserve. Urinary dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA) were assessed as potential biomarkers of drinking water DBP exposures. Multivariate linear and Poisson regression models were applied to estimate the associations of urinary DCAA and TCAA concentrations with indicators of ovarian reserve. Elevated urinary DCAA and TCAA levels were monotonically associated with reduced total AFC (- 5.98%; 95% CI: - 10.30%, - 1.44% in DCAA and - 12.98%; 95% CI: - 17.00%, - 8.76% in TCAA comparing the extreme tertiles; both P for trends ≤ 0.01), and the former was only observed in right AFC but not in left AFC, whereas the latter was estimated for both right and left AFC. Moreover, elevated urinary TCAA levels were monotonically associated with decreased AMH (- 14.09%; 95% CI: - 24.79%, - 1.86% comparing the extreme tertiles; P for trend = 0.03). These negative associations were still observed for the exposure biomarkers modeled as continuous variables. Our findings suggest that exposure to drinking water DBPs may be associated with decreased ovarian reserve.

Drivers of Disinfection Byproduct Cytotoxicity in U.S. Drinking Water: Should Other DBPs Be Considered for Regulation?

This study reveals key disinfection byproduct (DBP) toxicity drivers in drinking water across the United States. DBPs, which are ubiquitous in drinking water, form by the reaction of disinfectants, organic matter, bromide, and iodide and are generally present at 100-1000× higher concentrations than other contaminants. DBPs are linked to bladder cancer, miscarriage, and birth defects in human epidemiologic studies, but it is not known as to which DBPs are responsible. We report the most comprehensive investigation of drinking water toxicity to date, with measurements of extracted whole-water mammalian cell chronic cytotoxicity, over 70 regulated and priority unregulated DBPs, and total organic chlorine, bromine, and iodine, revealing a more complete picture of toxicity drivers. A variety of impacted waters were investigated, including those impacted by wastewater, agriculture, and seawater. The results revealed that unregulated haloacetonitriles, particularly dihaloacetonitriles, are important toxicity drivers. In seawater-impacted water treated with chloramine, toxicity was driven by iodinated DBPs, particularly iodoacetic acids. In chlorinated waters, the combined total organic chlorine and bromine was highly and significantly correlated with toxicity (r = 0.94, P < 0.01); in chloraminated waters, total organic iodine was highly and significantly correlated with toxicity (r = 0.80, P < 0.001). These results indicate that haloacetonitriles and iodoacetic acids should be prioritized in future research for potential regulation consideration.

Iodoacetic Acid, a Water Disinfection Byproduct, Disrupts Hypothalamic, and Pituitary Reproductive Regulatory Factors and Induces Toxicity in the Female Pituitary

Iodoacetic acid (IAA) is a water disinfection byproduct (DBP) formed by reactions between oxidizing disinfectants and iodide. In vitro studies have indicated that IAA is one of the most cyto- and genotoxic DBPs. In humans, DBPs have been epidemiologically associated with reproductive dysfunction. In mouse ovarian culture, IAA exposure significantly inhibits antral follicle growth and reduces estradiol production. Despite this evidence, little is known about the effects of IAA on the other components of the reproductive axis: the hypothalamus and pituitary. We tested the hypothesis that IAA disrupts expression of key neuroendocrine factors and directly induces cell damage in the mouse pituitary. We exposed adult female mice to IAA in drinking water in vivo and found 0.5 and 10 mg/l IAA concentrations lead to significantly increased mRNA levels of kisspeptin (Kiss1) in the arcuate nucleus although not affecting Kiss1 in the anteroventral periventricular nucleus. Both 10 mg/l IAA exposure in vivo and 20 μM IAA in vitro reduced follicle stimulating hormone (FSHβ)-positive cell number and Fshb mRNA expression. IAA did not alter luteinizing hormone (LHβ) expression in vivo although exposure to 20 μM IAA decreased expression of Lhb and glycoprotein hormones, alpha subunit (Cga) mRNA in vitro. IAA also had toxic effects in the pituitary, inducing DNA damage and P21/Cdkn1a expression in vitro (20 μM IAA) and DNA damage and Cdkn1a expression in vivo (500 mg/l). These data implicate IAA as a hypothalamic-pituitary-gonadal axis toxicant and suggest the pituitary is directly affected by IAA exposure.

Iodoacetic acid affects Estrous Cyclicity, ovarian gene expression, and hormone levels in mice

Iodoacetic acid (IAA) is a water disinfection byproduct that is an ovarian toxicant in vitro. However, information on the effects of IAA on ovarian function in vivo was limited. Thus, we determined whether IAA exposure affects estrous cyclicity, steroidogenesis, and ovarian gene expression in mice. Adult CD-1 mice were dosed with water or IAA (0.5-500 mg/L) in the drinking water for 35-40 days during which estrous cyclicity was monitored for 14 days. Ovaries were analyzed for expression of apoptotic factors, cell cycle regulators, steroidogenic factors, estrogen receptors, oxidative stress markers, and a proliferation marker. Sera were collected to measure pregnenolone, androstenedione, testosterone, estradiol, inhibin B, and follicle-stimulating hormone (FSH) levels. IAA exposure decreased the time that the mice spent in proestrus compared to control. IAA exposure decreased expression of the pro-apoptotic factor Bok, the cell cycle regulator Ccnd2, and borderline decreased expression of the anti-apoptotic factor Bcl2l10, the pro-apoptotic factor Aimf1, and the steroidogenic factor Cyp19a1 compared to control. IAA exposure increased expression of the pro-apoptotic factors Bax and Aimf1, the anti-apoptotic factor Bcl2l10, the cell cycle regulators Ccna2, Ccnb1, Ccne1, and Cdk4, and estrogen receptor Esr1 compared to control. IAA exposure decreased expression of Cat and Sod1, and increased expression of Cat, Gpx, and Nrf2. IAA exposure did not affect expression of Star, Cyp11a1, Cyp17a1, Hsd17b1, Hsd3b1, Esr2 or Ki67 compared to control. IAA exposure decreased estradiol levels, but did not alter other hormone levels compared to control. In conclusion, IAA exposure alters estrous cyclicity, ovarian gene expression, and estradiol levels in mice.

Androgenic and Teratogenic Effects of Iodoacetic Acid Drinking Water Disinfection Byproduct in Vitro and in Vivo

Iodoacetic acid (IAA) is the most genotoxic iodinated disinfection byproduct known in drinking water. Previous studies have shown that IAA may be an endocrine disruptor. However, whether IAA has reproductive and developmental toxicity remains unclear. In this study, the reproductive and developmental toxicity of IAA was evaluated using a battery of in vitro and in vivo reproductive/developmental toxicity screening tests. The results of E-Screen, uterotrophic, and H295R steroidogenesis assays were negative. The Hershberger bioassay revealed that IAA could induce significant increases in absolute and relative weights of paired Cowper's glands. Moreover, there was an increasing trend in the relative weights of the ventral prostate. The micromass test showed that IAA could inhibit the differentiation of midbrain and limb bud cells. A reproductive/developmental toxicity screening test showed that IAA resulted in significantly increased relative weights of testis and seminal vesicles plus coagulating glands in parental male rats, with a dose-response relationship. IAA could not only induce head congestion in offspring but also decrease litter weight, viability index, and anogenital distance index of male pups on postnatal day 4. All these results indicated that IAA had reproductive and developmental toxicity.

Iodoacetic acid disrupts mouse oocyte maturation by inducing oxidative stress and spindle abnormalities

Disinfection by-products (DBPs) are compounds produced during the water disinfection process. Iodoacetic acid (IAA) is one of the unregulated DBPs in drinking water, with potent cytotoxicity and genotoxicity in animals. However, whether IAA has toxic effects on oocyte maturation remains unclear. Here, we show that IAA exposure resulted in metaphase I (MI) arrest and polar-body-extrusion failure in mouse oocytes, indicating that IAA had adverse effects on mouse oocyte maturation in vitro. Particularly, IAA treatment caused abnormal spindle assembly and chromosome misalignment. Previous studies reported that IAA is a known inducer of oxidative stress in non-germline cells. Correspondingly, we found that IAA exposure increased the reactive oxygen species (ROS) levels in oocytes in a dose-dependent manner, indicating IAA exposure could induce oxidative stress in oocytes. Simultaneously, DNA damage was also elevated in the nuclei of these IAA-exposed mouse oocytes, evidenced by increased γ-H2AX focus number. In addition, the un-arrested oocytes entered metaphase II (MII) with severe defects in spindle morphologies and chromosome alignment after 14-h IAA treatment. An antioxidant, N-acetyl-L-cysteine (NAC), reduced the elevated ROS level and restored the meiotic maturation in the IAA-exposed oocytes, which indicates that IAA-induced maturation failure in oocytes was mainly mediated by oxidative stress. Collectively, our results indicate that IAA exposure interfered with mouse oocyte maturation by elevating ROS levels, disrupting spindle assembly, inducing DNA damage, and causing MI arrest.

Endocrine Disruptors in Water and Their Effects on the Reproductive System

Anthropogenic contaminants in water can impose risks to reproductive health. Most of these compounds are known to be endocrine disrupting chemicals (EDCs). EDCs can impact the endocrine system and subsequently impair the development and fertility of non-human animals and humans. The source of chemical contamination in water is diverse, originating from byproducts formed during water disinfection processes, release from industry and livestock activity, or therapeutic drugs released into sewage. This review discusses the occurrence of EDCs in water such as disinfection byproducts, fluorinated compounds, bisphenol A, phthalates, pesticides, and estrogens, and it outlines their adverse reproductive effects in non-human animals and humans.

Iodoacetic acid inhibits follicle growth and alters expression of genes that regulate apoptosis, the cell cycle, estrogen receptors, and ovarian steroidogenesis in mouse ovarian follicles

The reaction between disinfectants and organic matter or inorganic matter in source water generates disinfection by-products (DBPs) such as iodoacetic acid (IAA). DBPs are associated with health effects such as bladder cancer and adverse reproductive outcomes, but the effects of IAA on the ovary are not well known. This study determined whether IAA exposure affects ovarian follicle growth, steroidogenesis, and expression of apoptotic factors, cell cycle regulators, estrogen receptors, and steroidogenic factors in vitro. IAA exposure significantly decreased follicle growth, expression of cell cycle stimulators, and the proliferation marker Ki67. In contrast, IAA increased expression of the cell cycle inhibitor Cdkn1a. Moreover, IAA exposure increased expression of pro-apoptotic factors, whereas it decreased expression of anti-apoptotic factors. IAA exposure also altered expression of steroidogenic factors and estrogen receptors, disrupting steroidogenesis. These data demonstrate that IAA exposure inhibits follicle growth, decreases cell proliferation, and alters steroidogenesis in mouse ovarian follicles in vitro.

Exposure Characterization of Haloacetic Acids in Humans for Exposure and Risk Assessment Applications: An Exploratory Study

Disinfected water is the major source of haloacetic acids (HAAs) in humans, but their inter- and intra-individual variability for exposure and risk assessment applications is under-researched. Thus, we measured HAAs in cross-sectional and longitudinal urine and water specimens from 17 individuals. Five regulated HAAs-mono, di, and trichloroacetic acid (MCAA, DCAA, and TCAA) and mono- and dibromoacetic acid (MBAA and DBAA)-and one unregulated HAA-bromochloroacetic acid (BCAA)-were measured. Urinary DCAA, MBAA, DBAA, and BCAA levels were always below the limits of detection (LOD). Measured levels and interindividual variability of urinary MCAA were higher than urinary TCAA. Longitudinal urinary specimens showed MCAA levels peaked in after-shower specimens, while TCAA levels remain unchanged. Correlation between urinary MCAA and TCAA was moderate but statistically significant. The prevalence of MCAA and TCAA in urine suggest they can be considered as biomarkers of HAA. Peak urinary MCAA in post-shower specimens suggest MCAA captures short-term exposure via dermal and/or inhalation, while urinary TCAA captures long-term exposure via ingestion. However, further research is warranted in a large pool of participants to test the reliability of MCAA as exposure biomarker.

Iodoacetic Acid Disrupting the Thyroid Endocrine System in Vitro and in Vivo

Exposure to drinking water disinfection byproducts (DBPs) is potentially associated with adverse developmental effects. Iodoacetic acid (IAA), an unregulated DBP, has been shown to be cytotoxic, mutagenic, genotoxic, and tumorigenic. However, its endocrine-disrupting effects remain unknown. This study evaluated the IAA-induced disruption of the thyroid endocrine system using in vitro and in vivo assays. Rat pituitary tumor GH3 cells were treated with IAA in the presence and absence of triiodothyronine (T3). IAA exposure significantly reduced T3-activated GH3 cell proliferation, indicating the antagonistic activity of IAA in vitro. Sprague-Dawley rats were also subjected to IAA treatment through oral gavage for 28 consecutive days. IAA exposure significantly down-regulated the mRNA expression levels of the thyrotropin receptor (TSHR), the sodium/iodide symporter (NIS), and type I deiodinase and simultaneously reduced the protein expression levels of TSHR and NIS. IAA exposure decreased T3 levels but increased the weights of hypothalamus and the levels of thyrotropin releasing hormone and thyrotropin. In addition, IAA induced the formation of smaller and more depleted follicles or even vacuolization in the thyroid. These results suggested that IAA potentially disrupts the thyroid endocrine system both in vitro and in vivo.

Formation of iodo-trihalomethanes, iodo-haloacetic acids, and haloacetaldehydes during chlorination and chloramination of iodine containing waters in laboratory controlled reactions

Iodine containing disinfection by-products (I-DBPs) and haloacetaldehydes (HALs) are emerging disinfection by-product (DBP) classes of concern. The former due to its increased potential toxicity and the latter because it was found to be the third most relevant DBP class in mass in a U.S. nationwide drinking water study. These DBP classes have been scarcely investigated, and this work was performed to further explore their formation in drinking water under chlorination and chloramination scenarios. In order to do this, iodo-trihalomethanes (I-THMs), iodo-haloacetic acids (I-HAAs) and selected HALs (mono-HALs and di-HALs species, including iodoacetaldehyde) were investigated in DBP mixtures generated after chlorination and chloramination of different water matrices containing different levels of bromide and iodide in laboratory controlled reactions. Results confirmed the enhancement of I-DBP formation in the presence of monochloramine. While I-THMs and I-HAAs contributed almost equally to total I-DBP concentrations in chlorinated water, I-THMs contributed the most to total I-DBP levels in the case of chloraminated water. The most abundant and common I-THM species generated were bromochloroiodomethane, dichloroiodomethane, and chlorodiiodomethane. Iodoacetic acid and chloroiodoacetic acid contributed the most to the total I-HAA concentrations measured in the investigated disinfected water. As for the studied HALs, dihalogenated species were the compounds that predominantly formed under both investigated treatments.