Reproductive effects of sodium borates on male employees: birth rate assessment

Extended exposure to tetrabromobisphenol A-bis(2,3-dibromopropyl ether) leads to subfertility in male mice at the late reproductive age

Tetrabromobisphenol A-bis(2,3-dibromopropyl ether) (TBBPA-BDBPE), a commonly used brominated flame retardant as a decabromodiphenyl ether substitute, has been detected in various environmental compartments, but its health hazards remain largely unknown. Our recent study showed that low-dose exposure of male mice to TBBPA-BDBPE from postnatal day (PND) 0 to 56 caused remarkable damage to the microtubule skeleton in Sertoli cells and the blood-testis barrier (BTB) but exerted little effect on conventional reproductive endpoints in adulthood. To investigate whether TBBPA-BDBPE may cause severe reproductive impairments at late reproductive age, here, we extended exposure of historically administrated male mice to 8-month age and allowed them to mate with non-treated females for the evaluation of fertility, followed by a general examination for the reproductive system. As expected, we found that 8-month exposure to 50 μg/kg/d as well as 1000 μg/kg/d TBBPA-BDBPE caused severe damage to the reproductive system, including reduced sperm counts, increased sperm abnormality, histological alterations of testes. Moreover, microtubule damage and BTB-related impairment were still observed following 8-month exposure. Noticeably, high-dose TBBPA-BDBPE-treated mice had fewer offspring with a female-biased sex ratio. All results show that long-term exposure to TBBPA-BDBPE caused severe reproductive impairment, including poor fertility at late reproductive age. It is therefore concluded that slight testicular injuries in early life can contribute to reproductive impairment at late reproductive age, highlighting that alterations in certain non-conventional endpoints should be noticed as well as conventional endpoints in future reproductive toxicity studies.

Effects of Boron-Containing Compounds on Liposoluble Hormone Functions

Boron-containing compounds (BCC), particularly boronic acids and derivatives, are being increasingly tested as diagnostic and therapeutic agents. Some effects of BCC involve phenomena linked to the action of steroid or thyroid hormones; among these, are the effects on muscle mass or basal metabolism. Additionally, some toxicology reports on mammals, including humans, sound an alert concerning damage to several systems, among which are the negative effects on the induction of male infertility. Systemic and local mechanisms to explain changes in metabolism and impaired fertility were collected and presented. Then, we presented the putative pharmacodynamic and pharmacokinetic mechanisms involved and demonstrated in these events. In addition, it is proposed that there are adducts of some oxygenated BCC with cis-diols in fructose, an essential source of energy for sperm–cell motility, an uncoupling of sex hormone-binding globulin (SHBG) and its ligands, and the modulation of the DNA synthetic rate. These effects share the reactivity of boron-containing compounds on the cis-diols of key molecules. Moreover, data reporting no DNA damage after BCC administration are included. Further studies are required to support the clear role of BCC through these events to disrupt metabolism or fertility in mammals. If such phenomena are confirmed and elucidated, an advance could be useful to design strategies for avoiding BCC toxicity after BCC administration, and possibly for designing metabolism regulators and contraceptive drugs, among other purposes. Boronic derivatives and carboranes have been proposed and studied in this field.

Learning to Value Girls: Balanced Infant Sex Ratios at Higher Parental Education in the United States, 1969-2018

Infant sex ratios that differ from the biological norm provide a measure of gender status inequality that is not susceptible to social desirability bias. Ratios may become less biased with educational expansion through reduced preference for male children. Alternatively, bias could increase with education through more access to sex-selective medical technologies. Using National Vital Statistics data on the population of live births in the United States for 1969-2018, we examine trends in infant sex ratios by parental race/ethnicity, education, and birth parity over five decades. We find son-biased infant sex ratios among Chinese and Asian Indian births that have persisted in recent years, and regressions suggest son-biased ratios among births to Filipino and Japanese mothers with less than a high school education. Infant sex ratios are more balanced at higher levels of maternal education, particularly when both parents are college educated. Results suggest greater equality of gender status with higher education in the United States.

Boric Acid Is Reproductively Toxic to Adult Xenopus laevis, but Not Endocrine Active

The potential reproductive and endocrine toxicity of boric acid (BA) in the African clawed frog, Xenopus laevis, was evaluated using a 30-day exposure of adult frogs. Adult female and male frogs established as breeders were exposed to a culture water control and 4 target (nominal) test concentrations [5.0, 7.5, 10.0, and 15 mg boron (B)/L, equivalent to 28.5, 42.8, 57.0, and 85.5 mg BA/L] using flow-through diluter exposure system. The primary endpoints measured were adult survival, growth (weight and snout-vent length [SVL]), necropsy data, reproductive fecundity, and development of progeny (F1) from the exposed frogs. Necropsy endpoints included gonad weight, gonado-somatic index (GSI), ovary profile (oocyte normalcy and stage distribution), sperm count, and dysmorphology. Endocrine endpoints included plasma estradiol (E2), testosterone (T), dihydrotestosteone (DHT), gonadal CYP 19 (aromatase), and gonadal 5α-reductase (5-AR). BA exposure to adult female X. laevis increased the proportion of immature oocytes (< stage II) in the ovaries of females, reduced sperm counts and increased sperm cell dysmorphology frequency in male frogs exposed to 15 mg B/L. No effects on the other general, developmental (F1), or endocrine endpoints were observed. Based on the results of the present study, the no observed adverse effects concentration (NOAEC) for the reproductive endpoints was 10 mg B/L; and 15 mg B/L for reproductive fecundity, F1 embryo larval development, and endocrine function. These results confirmed that although BA is capable of inducing reproductive toxicity at high concentrations, it is not an endocrine disrupting agent.

Metals and female reproductive toxicity

Research into occupational exposure of metals and consequences of reproductive systems has made imperative scientific offerings in the preceding few decades. Early research works focused on possible effects on the reproductive functions rather than the complete reproductive health of the woman. Later, it was realized that metals, as reproductive toxins, may also induce hormonal changes affecting other facets of reproductive health such as the menstrual cycle, ovulation, and fertility. Concern is now shifting from considerations for the pregnant woman to the entire spectrum of occupational health threats and thus reproductive health among women.

Reproductive toxicity of metals in men

A combination of genetic, environmental and lifestyle factors contributes to adverse effects on the reproductive health in men. Metals are pervasive in food, water, air, tobacco smoke, and alcoholic beverages. Experimental studies suggest that many metals have adverse effects on the male reproductive function. However, information about reproductive effects of human exposure to metals is scarce and/or inconsistent. This review summarises the information from epidemiological studies of the effects of metal exposure on reproductive function in men. Factors capable of affecting these relationships were identified and discussed. A particular attention is given to the studies considering influence of concomitant exposure to various metals. These studies have generally confirmed that even moderate- to low-level exposure to lead affects certain reproductive parameters, and that exposure to cadmium affects the prostate function and serum testosterone levels. Adverse effects of mercury, manganese, chromium and arsenic on semen quality and altered serum hormone are less well documented. There is no clear evidence that boron exposure may impair reproductive health in men. Only a few studies have investigated reproductive effects of concomitant exposure to several metals and controlled for potential confounders. Future studies should consider the contribution of combined exposure to various metals and/or other factors that may influence individual susceptibility to reproductive health impairment in men.

Effects of chronic boron exposure on semen profile

The possible changes in semen quality were studied in men living in a boron mining area. The subjects in the boron group had exposure to boron at an average level of 6.5 mg/day, as determined by urinary analysis. The results obtained by the boron group were compared to those obtained for the control group whose subjects were living in the same geographical area but away from the boron region; average exposure level was 1.4 mg/day for this group. The semen samples were analyzed according to the recommendations of the World Health Organization. Boron levels were established in the water samples obtained from various locations in the study region. In the boron mining fields where the subjects in the boron group live, water samples contained boron in the range of 1.4-6.5 mg/L, while the values were <0.01 mg/L for the water samples obtained from the region where the subjects of the control group reside. No negative effects were found in the sperm samples obtained from the subjects of the boron group.

Health impact evaluation of boron in drinking water: a geographical risk assessment in Northern France

OBJECTIVE

To evaluate health impact of boron in drinking water.

METHODS

A regional scale geographical study in Northern France was conducted. Assessment of boron blood levels in a group of 180 healthy individuals and correlation with boron content in drinking water were followed by an assessment of health indicators such as birth rates, mortality rates, and sex ratios in zones of different boron content in drinking water.

RESULTS

After necessary adjustments, men living in municipalities with more than 0.30 mg/L of boron in drinking water had elevated but not significant boron blood levels compared with those living in municipalities with boron water levels of less than 0.30 mg/L (159.1 versus 123.0 ng/g; p > 0.05). The standardized birth ratio adjusted for the reference geographic zone and calendar time period was 1.07 and 1.28 in the low and high (>0.3 mg/L) boron content municipalities, respectively. The birth rate in municipalities with high boron content in drinking water was higher than that of the reference geographic zone and of the French general population (p < 10(-4)). The standardized mortality ratio adjusted for the reference geographic zone and calendar time period was 0.94 and 0.92 in the low and high boron content municipalities, respectively. The mortality rate in municipalities with high boron content in drinking water was less than that of the reference geographic zone and of the French general population (p < 10(-3)). No statistical difference was noted in the male-female sex ratios between the different municipality zones (p = 0.45).

CONCLUSIONS

The results of this study do not support the idea of a deleterious effect of boron on human health, at the boron water level contents found in this specific region. In fact, there is a tendency toward a beneficial effect with low-dose environmental exposure (less than 1 mg/L of boron) in drinking water.

Hexachlorobenzene exposure and the proportion of male births in Turkey 1935-1990

Hexachlorobenzene (C(6)Cl(6), HCB) is a chemical that has been associated with significant immediate and long term adverse health effects in humans. It has been associated with both porphyria cutanea tarda and spontaneous abortions among survivors of widespread exposure in the 1950s in southeastern Turkey. HCB binds to the Ah receptor, albeit with lower affinity than dioxin. Dioxin exposure has been reported to lower human secondary sex ratio, putatively through a male mediated effect. We therefore wished to evaluate the impact of the HCB environmental event on the sex ratio of the progeny of the survivors. We undertook an assessment of 1) the effects of HCB exposure on the proportion of male births of individual subjects who had survived, 2) variables that significantly predicted the proportion of males among these individuals, and 3) the trend of the population sex ratio born in Turkey from 1935 to 1990. Women known to have been exposed to HCB in the 1950s did not have offspring with a significantly different sex ratio when compared to control populations. However, subjects reporting exposure at the peak of the episode (1955-57) had a significantly lower lifetime proportion of males than those exposed at a later date. The lifetime reported spontaneous abortion rate of these women also significantly predicted the percent males per subject. The available national data demonstrated a significant reduction in the calculated proportion of males from 1935 to 1970 that stabilized from 1970 to 1990. These data indicate that HCB exposure that was sufficient to induce clinical porphyria cutanea tarda may also have reduced the proportion of males in subjects over their reproductive life-span. The HCB episode does not explain the pattern of the national trend from a population perspective.

Declining trends of male proportion at birth in Europe

Declining trends in male proportion at birth observed in several Western countries might reflect widespread exposure to pollutants capable of interfering with human reproduction. In this study, the authors describe male live birth proportion trends in 23 European countries from 1950 to 1996 (total of 305 million live births). Overall, there was a significant linearly decreasing trend of 10 fewer males per 100,000 births each year, resulting in a loss of 73,462 boys during a 47-yr period. The proportion of male births during the first 3 yr of the study period was higher than in the last 3 yr in 18 countries (i.e., 78%). Decreasing trends, which varied in slope and shape, were observed in 11 countries; no significant trend was found in 8 countries, and male birth proportion increased in 4 countries. The results of this study confirmed that the proportion of male births is declining in Europe, and differences exist by region and country. Social and cultural aggregations of countries with decreasing trends suggest that sociodemographic characteristics might be more likely to explain trends than environmental exposures to chemicals. Investigators should evaluate this hypothesis to assess the usefulness of male birth proportion as a sentinel event.

Male reproductive effects of solvent and fuel exposure during aircraft maintenance

Few studies have addressed the effects of mixed, low-level exposures to complex mixtures on a man's reproductive potential. In this prospective study, each subject was evaluated before first exposure and at 15 and 30 weeks after exposures had begun. A total of 50 men working on aircraft maintenance at an Air Force installation were included in the study. In addition, eight unexposed men were concurrently sampled. Industrial hygiene (IH) sampling and expired breath samples were collected for jet fuel as measured by total napthas, benzene--a component of jet fuel, 1,1,1-trichloroethane, methyl ethyl ketone, xylenes, toluene, and methylene chloride. Sperm production, structure, and function (sperm concentration, sperm motion, viability, morphology, morphometrics, and stability of sperm chromatin) were evaluated. Exposures were low. All mean IH measures were below 6 ppm, which is less than 10% of the Occupational Safety and Health Administration standard for all chemicals except benzene. Sheet metal workers had the highest mean breath levels for both total solvents (24 ppb) and fuels (28.3 ppb). For most sperm measures, mean values remained in the normal range throughout the 30 weeks of exposure. When jobs were analyzed by exposure groups, some adverse changes were observed. The paint shop group had a significant decline in motility of 19.5% at 30 weeks. Internal dose measures, however, did not show a significant association with spermatogenic changes.

An assessment of fertility in boron-exposed Turkish subpopulations

Relationships between elevated boron intake and fertility were sought by comparing reproduction in the residents of two Turkish villages with high levels of boron in their drinking water (one with 8.5 to 29 mg B/L and the other with 2.05 to 2.5 mg B/L), with three nearby villages with more typical low boron levels (0.03 to 0.40 mg B/L). The two high boron villages were designated as Region I, and the three villages with low boron in the drinking water were designated Region II. In addition to exposure to elevated boron in drinking water, 28.3% of the probands in Region I were employed in borate mining or processing, whereas in Region II, 11.7% were so employed. An observational study was carried out in which the authors compared the reproductive history of families living in Region I with families living in Region II by identifying married adults (referred to as probands) who were able to provide information about their and their spouses' family pedigrees covering three generations. Probands were identified by home visits and, if ever married, accepted for ascertainment. Evidence of fertility was birth of a living child, and data were obtained about the fertility of the proband generation, their parents' and also their childrens' generations. In high-boron villages (Region I), 159 three-generation kindreds containing 1068 families were ascertained and, in low-boron villages (Region II), 154 three-generation kindreds containing 610 families were ascertained. In Region 1, 96% of marriages produced at least one child, with primary infertility estimated at 2.34% compared with 96% and 2.62%, respectively, for Region II. There was no significant difference in fertility either between Region I and Region II or between the villages within the Regions. The fertility figures are not different from similar measures of fertility in other parts of Turkey. In Region I, the gender ratio (M:F) of offspring was 0.89, whereas in the Region II villages the gender ratio was 1.04 (NS, chi2 = 1.335, P > 0.05). It is concluded that at the elevated boron drinking water levels studied, a boron-related effect on reproduction was not found.

General, reproductive, developmental, and endocrine toxicity of boronated compounds

Boric acid and inorganic borates are abundant in nature. They are widely used in industrial, agricultural, cosmetic, and numerous smaller applications. These compounds are toxic to all species tested at high doses, but they are not carcinogenic or mutagenic. The major toxicities are reproductive and developmental. Testicular effects occurred at approximately 26 mg boron equivalents/kg body weight (bw)/d (26 mg boron equivalent (BE)/kg bw/d). New data on endocrine toxicity includes altered follicle stimulating hormone and testosterone within 14 d of treatment. Because these hormonal changes may be secondary effects of testicular toxicity, borates are not suspect as endocrine disrupters. The most sensitive of all the endpoints are prenatal growth and morphologic development in the rat; these changes occurred at a dose of 12.9 mg BE/kg bw/d. The no observed adverse effect level for rat fetal development was 9.6 mg/kg BE. Considering the estimated human exposure levels and a safety factor of 30, humans are not at significant risk of reproductive failure due to borates from environmental sources. The margin of exposure is estimated at 72 for males and 129 for females. Thus, the likelihood of human toxicity caused by boric acid and inorganic borates from exposure during normal activities is remote.

Comparison of infertility rates in communities from boron-rich and boron-poor territories

As a part of a large-scale work aimed at studying the health effects of boron (B) in residents of a country with the world's largest supply, developmental effects of B are presented. Spontaneous abortions, stillbirths, and congenital malformations in addition to early infant mortality were questioned in the field by home visits. Although the number of families so far ascertained is rather small, the rates related to spontaneous abortions and stillbirths from high B exposure vs low B exposure subpopulations revealed no differences of significance, providing no evidence that B affects human development adversely.

Comparative toxicology of borates

Inorganic borates, including boric acid, Na, ammonium, K, and Zn borates generally display low acute toxicity orally, dermally, and by inhalation. They are either not irritant or mild skin and eye irritants. Exceptions owing to physiochemical properties do occur. Longer-term toxicological studies have been reported mainly on boric acid or borax where the properties are generally similar on an equivalent boron (B) basis. The critical effects in several species are male reproductive toxicity and developmental toxicity. The doses that cause these effects are far higher than any levels to which the human population could be exposed. Humans would need to consume daily some 3.3 g of boric acid (or 5.0 g borax) to ingest the same dose level as the lowest animal NOAEL. No effects on fertility were seen in a population of workers exposed to borates or to a population exposed to high environmental borate levels. There is remarkable similarity in the toxicological effects of boric acid and borax across different species. Other inorganic borates that simply dissociate to boric acid are expected to display similar toxicity, whereas those that do not dissociate simply to boric acid may display a different toxicological profile.

An assessment of fertility in boron-exposed Turkish subpopulations: 2. Evidence that boron has no effect on human reproduction

In order to assess the effects of boron and its compounds on human health in a country with the world's largest deposits, investigations were carried out on fertility and reproduction in the most highly exposed populations. The 927 probands, 697 male and 230 female, interviewed in the field were selected from six different areas of Turkey, in the provinces of Balikesir, Eskisehir, and Kutahya, with the highest boron deposits. These people are exposed to boron environmentally or occupationally or both. The drinking waters of high-boron soils contain 0.7-29 mg B/L compared with 0.05-0.45 mg B/L of low-boron soils. By the so-called pedigree technique 5,934 marriages were ascertained over three generations from all study areas. Childless families among 911 probands were 29 in number and 3.17% in frequency with minor variations from one area to the next, and 3.0% averaged over the generations. Infertility rates in a boron-free community near Ankara with 625 families studied over three generations was 4.48%, and in a larger population of 49,856 families randomly investigated by us throughout the country was 3.84%. No significant differences were observed in terms of marital status and childbearing between 222 and 399 occupationally boron-unrelated and boron-related men, respectively. Nor was there any difference with respect to other aspects studied. It was concluded that, within the limitations of this study, there was no evidence that boron interferes with human fertility and reproduction.

Hazard assessment of boric acid in toys

Boric acid (H3BO3) has been used in a wide variety of applications--medication, pesticides, and household products. Reports of child poisoning by H3BO3 were common in the clinical literature before 1975. However, a decline in its use as a bacteriostatic agent coupled with increased regulatory control has almost eliminated poisonings by accidental ingestion. Schedule I (Part I, Item 8) of the Hazardous Products Act of Canada, proclaimed in the late 1960s, followed in the wake of concerns about accidental poisoning and prohibits its use in toys. Since that time, scientific knowledge has increased and has led to a reevaluation of the hazard associated with H3BO3. A maximum tolerated dose (MTD) was sought for children in the most susceptible age range, with a view to determine a maximum acceptable concentration (MAC) in toys. The effects of H3BO3 in a variety of exposure scenarios were evaluated. Precedence was given to clinical data in humans, particularly children, since there is no suitable animal model of boric acid intoxication. An extensive search of the pediatric literature was conducted to find a no-observed-adverse-effect level (NOAEL) or a lowest-observed-adverse-effect level (LOAEL). An analysis of the pivotal study to the present assessment resulted in the application of an uncertainty factor of 100 to account for variations in sensitivity among children and for the use of a LOAEL. Based on a pediatric LOAEL of 300 mg/kg body wt, we derived a MTD of 3 mg H3BO3/ kg body wt and a MAC of 9.1 mg H3BO3/g of toy. These results compared favorably with calculations from other human and animal NOAELs/LOAELs.

An assessment of boric acid and borax using the IEHR Evaluative Process for Assessing Human Developmental and Reproductive Toxicity of Agents. Expert Scientific Committee

BACKGROUND

Boron is a ubiquitous element widely distributed in nature in the form of borates at low concentrations in soils and rocks. Boron is released from these minerals by the natural weathering processes in the form of boric acid, which is water soluble and biologically available. High levels of boric acid are naturally found in sea water. Boric acid and borax are used in the greatest quantities and represent the major boron chemical exposures to humans and the environment. The principal use of boric acid and borax is in the manufacture of various types of glass products that do not result in exposure to the consumer. Boric acid and borax are also found in an array of consumer goods including fireproofing for fabrics and wood, insecticides, and in many cosmetics and personal care products as well. Boron may be an essential element for higher animals including humans.

HUMAN EXPOSURE

Boric acid and borax are considered to be completely absorbed by the oral route of exposure. Absorption through intact skin is considered negligible, although absorption can occur through denuded or irritated skin. Boron levels in the body do not persist upon cessation of exposure. People may be exposed to boron through three primary sources: 1) consumption of private, municipal, or commercial (bottled) sources of drinking water; 2) dietary consumption of crops and other foodstuffs (including dietary supplements for body building); and 3) inhalation of boron compounds during their mining, manufacturing, and other industrial processing. While boron has been detected in 81.8% of the municipal water systems, it is a minor source of boron in most parts of the U.S. The mean boron concentration is reported as 0.2 mg B/L. However, residents of California and other western states with boron-rich geologic deposits may be regularly exposed to higher levels in drinking water. Individuals who drink bottled mineral water may also increase their exposure to boron. An EPA health advisory, recommends boron concentrations in drinking water not exceed 0.6 mg B/L [0.06 mM B] over a lifetime of exposure. Dietary exposure to boron for an adult typically ranges from ranges from 0.25 to 3.1 mg B/d with an average of 1.5 mg B/d. The high end of the exposure range, 3.1 mg B/d, was selected by the Expert Committee as best estimate of exposure. It should be noted that a diet high in fruits, vegetables, grains, legumes, and other food stuffs with high boron contents may lead to daily exposures as high as 10 mg B/d from diet alone. Some body building supplements contain boron at levels ranging from 1.5 to 10 mg B, with a median of 4 mg B. Use of the supplements containing the median concentration of boron could equal the daily intake an individual receives from diet and drinking water combined. Adults in the U.S. at the high end of the food exposure range may typically ingest up to 3.5 mg B/d, or a daily dose of 0.005 mmol B/kg b.wt., through exposure from diet (3.1 mg B/d) and drinking water (0.4 mg B/d). Individuals who also use body-building supplements may have a total daily boron intake of 7.5 mg B resulting in a daily dose of 0.01 mmol B/kg b.wt./d. Occupational exposure to boron is mainly through inhalation of borate containing dust during mining and manufacturing processes. Current occupational exposures to boron are reported to result in a daily dose of < 0.0001 to 0.2 mmol B/kg b.wt./d. Current U.S. OSHA permissible exposure limit (PEL) for sodium tetraborates is 10 mg/m3, and the California Occupational Safety and Health Administration PEL is 5 mg/m3. An exposure of 5 mg B/m3 translates to approximately 0.01 mmol B/kg b.wt./d that, coincidentally, is the same as exposure levels associated with combined municipal drinking water, diet, and body building supplement consumption. Infants may receive exposures to boric acid when it is used as a household insecticide for cockroach control. Exposure from boric acid-containing cosmetic and personal care products applie

Occupational hazards for the male reproductive system

The etiology of male infertilities is largely undetermined, and our knowledge of exogenous factors affecting the male reproductive system is still limited. In particular, the role of specific environmental and occupational factors is incompletely elucidated. Various occupational (physical and chemical) agents have been shown to affect male reproductive functions in animals, but large differences in reproductive function and/or xenobiotic handling between species limit extrapolation to humans. When available, human data are often conflicting and, except in a few instances, usually refer to broad and heterogenous occupational categories or to groups of agents (e.g., solvents). It is often difficult to elucidate the role of a single agent because occupational exposure conditions are often complex and various confounding factors related to lifestyle (smoking, alcohol, and diet) or socioeconomic state may also affect sperm quality, fertility, or pregnancy outcomes. The objective of this work is to summarize the main epidemiological and, where relevant, experimental findings pertaining to agents (physical and chemical) encountered in the occupational environment that might affect the male reproductive system (sperm count, motility and morphology, libido, and fertility) and/or related pregnancy outcomes (spontaneous abortion, stillbirth, low birth weight, and birth defects and childhood malignancy in offspring). Some methodological issues related to research on the reproductive effects of toxicants are also discussed briefly.