Relationship of drinking water disinfectants to plasma cholesterol and thyroid hormone levels in experimental studies

Urinary haloacetic acid concentrations and thyroid function among women: Results from the TREE study

BACKGROUND

Disinfection byproducts (DBPs) have been shown to impair thyroid function in experimental models. However, epidemiological evidence is scarce.

METHODS

This study included 1190 women undergoing assisted reproductive technology (ART) treatment from the Tongji Reproductive and Environmental (TREE) cohort from December 2018 to August 2021. Serum thyrotropin (TSH), free triiodothyronine (FT3), and free thyroxine (FT4) were measured as indicators of thyroid function. FT4/FT3 and TSH/FT4 ratios were calculated as markers of thyroid hormone homeostasis. Dichloroacetic acid (DCAA) and trichloroacetic acid (TCAA), the two most abundant HAAs, in urine were detected to assess individual DBP exposures.

RESULTS

After adjusting for relevant covariates, positive associations were observed between urinary TCAA concentrations and serum TSH and TSH/FT4 levels (e.g., percent change = 5.82 %, 95 % CI: 0.70 %, 11.21 % for TSH), whereas inverse associations were found for serum FT3 and FT4 (e.g., percent change = -1.29 %, 95 % CI: -2.49 %, -0.07 % for FT3). There also was a negative association between urinary DCAA concentration and serum FT4/FT3 (percent change = -2.49 %, 95 % CI: -4.71 %, -0.23 %). These associations were further confirmed in the restricted cubic spline and generalized additive models with linear or U-shaped dose-response relationships.

CONCLUSION

Urinary HAAs were associated with altered thyroid hormone homeostasis among women undergoing ART treatment.

Risk of chlorine dioxide as emerging contaminant during SARS-CoV-2 pandemic: enzyme, cardiac, and behavior effects on amphibian tadpoles

Objective

The use of chlorine dioxide (ClO₂) increased in the last year to prevent SARS-CoV-2 infection due to its use as disinfectant and therapeutic human treatments against viral infections. The absence of toxicological studies and sanitary regulation of this contaminant represents a serious threat to human and environmental health worldwide. The aim of this study was to evaluate the acute toxicity and sublethal effects of ClO₂ on tadpoles of Trachycephalus typhonius, which is a common bioindicator species of contamination from aquatic ecosystems.

Materials and methods

Median lethal concentration (LC50), the lowest-observed effect concentration (LOEC), and the no-observed effect concentration (NOEC) were performed. Acetylcholinesterase (AChE) and glutathione-S-transferase (GST) activities, swimming behavior parameters, and cardiac rhythm were estimated on tadpoles of concentrations ≤ LOEC exposed at 24 and 96 h. ANOVA and Dunnett’s post-hoc comparisons were performed to define treatments significance (p ≤ 0.05).

Results

The LC50 of ClO₂ was 4.17 mg L⁻¹ (confidence limits: 3.73–4.66). In addition, NOEC and LOEC values were 1.56 and 3.12 mg L⁻¹ ClO₂, respectively, at 48 h. AChE and GST activities, swimming parameters, and heart rates increased in sublethal exposure of ClO₂ (0.78–1.56 mg L⁻¹) at 24 h. However, both enzyme activities and swimming parameters decreased, whereas heart rates increased at 96 h.

Conclusion

Overall, this study determined that sublethal concentrations of ClO₂ produced alterations on antioxidant systems, neurotoxicity reflected on swimming performances, and variations in cardiac rhythm on treated tadpoles. Thus, our findings highlighted the need for urgent monitoring of this chemical in the aquatic ecosystems.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s13530-021-00116-3.

Occupational exposure to pesticides and other biocides and risk of thyroid cancer

OBJECTIVES

To assess the associations between occupational exposure to biocides and pesticides and risk of thyroid cancer.

METHODS

Using data from a population-based case-control study involving 462 incident thyroid cancer cases and 498 controls in Connecticut collected in 2010-2011, we examined the association with occupational exposure to biocides and pesticides through a job-exposure matrix. We used unconditional logistic regression models to estimate OR and 95% CI, adjusting for potential confounders.

RESULTS

Individuals who were occupationally ever exposed to biocides had an increased risk of thyroid cancer (OR=1.65, 95% CI 1.16 to 2.35), and the highest risk was observed for the high cumulative probability of exposure (OR=2.18, 95% CI 1.28 to 3.73). The observed associations were similar when we restricted to papillary thyroid cancer and well-differentiated thyroid cancer. Stronger associations were observed for thyroid microcarcinomas (tumour size ≤1 cm). No significant association was observed for occupational exposure to pesticides.

CONCLUSIONS

Our study provides the first evidence linking occupational exposure to biocides and risk of thyroid cancer. The results warrant further investigation.

Pesticide use in the U.S. and policy implications: A focus on herbicides

This article examines herbicide use in the United States, providing estimates of poundage, land surface covered, distribution, and recent trends based on federal and state figures. Herbicides are by far the most widely used class of pesticide in the US, where 556 million lbs of herbicide active ingredients (AIs) were applied in 1995. Agriculture accounts for the majority of herbicide use, totaling 461 million lbs of AIs in 1995. Over 60% of the poundage of all agricultural herbicides consist of those that are capable of disrupting the endocrine and/or reproductive systems of animals. In addition, at least 17 types of `inert ingredients,' which can equal 90% or more of a pesticide product, have been identified as having potential endocrine-disrupting effects. Atrazine is the predominant herbicide used according to poundage, with 68-73 million lbs of AIs applied in 1995. However, 2,4-D is the most widespread herbicide, covering 78 million acres for agricultural uses alone. Both of these herbicides are reported endocrine disruptors. Acetolactate synthase (ALS) inhibitors, namely the sulfonylureas and imidazolinones, are one of the fastest growing classes of herbicides. Many of these herbicides are 100 times more toxic to select plant species than their predecessors, so they can be applied at rates approximately 100 times lower. Consequently, they can affect plant species at concentration levels so low that no standard chemical protocol can detect them. Due in part to these more potent herbicides, the poundage of herbicides used in the US has decreased since the mid-1980s; however, the available data suggest that the number of treated acres has not significantly declined. A thorough assessment of potential exposure to herbicides by wildlife and humans is limited due to the inaccessibility of production and usage data.

Thyroid function of newborns and exposure to chlorine dioxide by-products

In this study, the authors compared thyroid function of newborns from 11 municipalities where drinking water was disinfected by chlorine dioxide (ClO2) with that of newborns from 15 municipalities using chlorine disinfection. They estimated the mean neonatal blood thyroid stimulating hormone (TSH) levels and proportion of congenital hypothyroidism cases using the results of the Quebec neonatal screening for congenital hypothyroidism for 32,978 newborns over the period 1993-1999. There was no significant increase in the TSH level and no excess of congenital hypothyroidism when all newborns exposed to ClO2 were considered. However, for newborns with low birth weight, mean TSH level was significantly higher among those exposed to ClO2 than for those in the reference group.

Effects of environmental synthetic chemicals on thyroid function

Synthetic chemicals are released into the environment by design (pesticides) or as a result of industrial activity. It is well known that natural environmental chemicals can cause goiter or thyroid imbalance. However, the effects of synthetic chemicals on thyroid function have received little attention, and there is much controversy over their potential clinical impact, because few studies have been conducted in humans. This article reviews the literature on possible thyroid disruption in wildlife, humans, and experimental animals and focuses on the most studied chemicals: the pesticides DDT, amitrole, and the thiocarbamate family, including ethylenethiourea, and the industrial chemicals polyhalogenated hydrocarbons, phenol derivatives, and phthalates. Wildlife observations in polluted areas clearly demonstrate a significant incidence of goiter and/or thyroid imbalance in several species. Experimental evidence in rodents, fish, and primates confirms the potentiality for thyroid disruption of several chemicals and illustrates the mechanisms involved. In adult humans, however, exposure to background levels of chemicals does not seem to have a significant negative effect on thyroid function, while exposure at higher levels, occupational or accidental, may produce mild thyroid changes. The impact of transgenerational, background exposure in utero on fetal neurodevelopment and later childhood cognitive function is now under scrutiny. There are several studies linking a lack of optimal neurological function in infants and children with high background levels of exposure to polychlorinated biphenyls (PCBs), dioxins, and/or co-contaminants, but it is unclear if the effects are caused by thyroid disruption in utero or direct neurotoxicity.

Effects of subchronic exposure of monochloramine in drinking water on male rats

A subchronic rat study with paired-water control was conducted to resolve the question of whether monochloramine at 200 ppm in drinking water can cause reduced body weight gain and other changes observed in earlier investigations. Male Sprague-Dawley rats (93 +/- 5 g) were divided into three groups of 10 rats each: the treatment group was fed drinking water containing 200 ppm monochloramine, the control group was fed bicarbonate-buffered water ad libitum, and the paired-water control rats were given a daily volume of bicarbonate-buffered water equal to that consumed by the monochloramine treatment group. Compared to the control group, rats in the treatment group consumed an average of 42% less fluid and 16% less food over the 13-week treatment period and had 15-20% lower final body weight gain. Similar degrees of reduction in food consumption and body weight gain were observed in the paired-water rats. A decreased liver to body weight ratio occurred in the treatment and paired-water groups. Increased inorganic phosphate, albumin, total protein, and urea nitrogen were detected in sera from both the treatment group and the paired-water groups. The paired-water animals had lower levels of white blood cells and lymphocytes, while the paired-water and monochloramine-treated groups had reduced monocyte counts. Except for a slightly increased response to Con A observed in splenic lymphocytes of the monochloramine-treated rats (versus the paired-water), no significant changes were found in mitogen responsiveness to T cell, B cell, and B plus T cell mitogens or in splenic natural killer (NK) cell activities. There were no significant changes in serum levels of IgG, IgA, and IgM. The following biochemical parameters showed no significant variations among the three groups: serum thyroxin, liver phase I (PROD, EROD, and MROD) and phase II (UDPGT and GST) drug-metabolizing enzyme activities; serum and liver thiobarbituric acid-reactive substances (TBARS); bronchoalveolar lavage fluid protein and N-acetylgluosaminidase (NAGA) activity; and urinary ascorbic acid, protein, and NAGA activity. Histopathological examination revealed minimal to mild adaptive changes in the liver of the paired-water and monochloramine-treated rats and in the thyroid of the monochloramine-treated animals. No treatment-related cytological changes were found in red cells and bone marrow. The results indicate that the reduced body weight gain and the minor biochemical, hematological, immunological, and histopathological changes associated with subchronic exposure to 200 ppm monochloramine in drinking water (equivalent to an intake of 21.6 mg/kg/day) were largely related to the reduced water intake and food consumption and not caused by monochloramine.

Water chlorination and lipo- and apolipoproteins: the relationship in elderly white women of western Pennsylvania

The relationship between consumption of chlorinated drinking water in the home water supply and serum lipids was examined in 2070 elderly White women. Private springs, cisterns, and wells were considered nonchlorinated and public water sources, chlorinated. Mean serum lipids and lipoproteins were similar in the chlorinated and nonchlorinated groups. Stratification by years of exposure revealed little difference in lipid concentrations. Lifestyle factors--for example, smoking and alcohol consumption--differed by years of exposure. Hence, previous reports of an association between chlorinated drinking water and serum cholesterol levels may reflect inadequate control of other factors differentially distributed across chlorinated exposure groups.

Lack of effect of drinking water chlorine on lipid and thyroid metabolism in healthy humans

Animal studies and a single human epidemiological study have suggested that chlorine in drinking water may raise the level of blood cholesterol. The purpose of this study was to determine whether a 4-week exposure to drinking water chlorine (1.5 L per day) at a concentration of 20 ppm (ppm = mg/L) under controlled conditions would alter circulating parameters of lipid metabolism in healthy humans. Thirty men and thirty women each completed an 8-week protocol during which diet (600 mg cholesterol per day, 40% calories as fat) and other factors known to affect lipid metabolism were controlled. For the first 4 weeks of the protocol, all subjects consumed distilled water. For the second 4 weeks, half of the subjects were assigned randomly to drink 1.5 L per day of chlorinated water (20 ppm), while the others continued drinking distilled water. Four blood samples were collected from each subject at the end of each 4-week study period. Compared to the control group, those subjects given chlorine showed no significant changes in total plasma cholesterol, triglycerides, HDL-cholesterol, LDL-cholesterol, or apolipoproteins A1, A2, or B. There was a trend toward low serum thyroxine and triiodothyronine levels in men given chlorine, though thyroid-stimulating hormone levels were unchanged. This trend, if real, was not clinically significant. Thus, short-term exposure to chlorinated drinking water at 20 ppm appears to have no significant impact on parameters of lipid or thyroid metabolism in healthy humans.

Effects of drinking water monochloramine on lipid and thyroid metabolism in healthy men

The purpose of this study was to determine whether a 4-week consumption of 1.5L per day of drinking water containing monochloramine at a concentration of 2 ppm (ppm = mg/L) or 15 ppm under controlled conditions would alter parameters of lipid or thyroid metabolism in healthy men. Forty-eight men completed an 8-week protocol during which diet (600 mg cholesterol per day, 40% calories as fat) and other factors known to affect lipid metabolism were controlled. During the first 4 weeks of the protocol, all subjects consumed distilled water. During the second 4 weeks, one-third of the subjects were assigned randomly to drink 1.5 L per day of water containing 2 ppm of monochloramine, to drink 1.5 L per day of water containing 15 ppm monochloramine, or to continue drinking distilled water. Four blood samples were collected from each subject at the end of each 4-week study period. Subjects drinking monochloramine at a concentration of 2 ppm showed no significant changes in total cholesterol, triglycerides, HDL cholesterol, LDL cholesterol, apolipoproteins A1, A2, or B when compared to the distilled water group. Parameters of thyroid function also were unchanged by exposure to monochloramine at this concentration. However, subjects drinking monochloramine at a concentration of 15 ppm experienced an increase in the level of apolipoprotein B. Other parameters of lipid and thyroid metabolism did not change. We conclude that consumption of drinking water containing 2 ppm of monochloramine does not alter parameters of lipid and thyroid metabolism in healthy men. Consumption of water containing 15 ppm monochloramine may be associated with increased levels of plasma apolipoprotein B.