Effect of benzene, toluene, xylene on the semen quality and the function of accessory gonad of exposed workers

A metabolomic perspective on the mechanisms by which environmental pollutants and lifestyle lead to male infertility

The incidence of male infertility (MI) is rising annually. According to epidemiological studies, environmental pollution (e.g., organic, inorganic, and air pollutants), occupational exposure (e.g., high temperature, organic solvents, and pesticides), and poor lifestyle (e.g., diet, sleep, smoking, alcohol consumption, and exercise) are important non-genetic causative factors of MI. Due to multiple and complex causative factors, the dose-effect relationship, and the uncertainty of pathogenicity, the pathogenesis of MI is far from fully clarified. Recent data show that the pathogenesis of MI can be monitored by the metabolites in serum, seminal plasma, urine, testicular tissue, sperm, and other biological samples. It is considered that these metabolites are closely related to MI phenotypes and can directly reflect the individual pathological and physiological conditions. Therefore, qualitative and quantitative analysis of the metabolome, the related metabolic pathways, and the identification of biomarkers will help to explore the MI-related metabolic problems and provide valuable insights into its pathogenic mechanisms. Here, we summarized new findings in MI metabolomics biomarkers research and their abnormal metabolic pathways triggered by the presented non-genetic risk factors, providing a metabolic landscape of semen and seminal plasma in general MI patients. Then, we compared the similarities and differences in semen and seminal plasma biomarkers between MI patients exposed to environmental and poor lifestyle factors and MI patients in general, and summarized some common biomarkers. We provide a better understanding of the biological underpinnings of MI pathogenesis, which might offer novel diagnostic, prognostic, and precise treatment approaches to MI.

Studying full-shift inhalation exposures to volatile organic compounds (VOCs) among Latino workers in very small-sized beauty salons and auto repair shops

Background

One in every 200 US jobs is in a beauty salon or auto repair shop, where workers are regularly exposed to volatile organic compounds (VOCs) that may cause a range of short- and long-term health issues. In these shops, Latino workers are overrepresented and lack culturally and linguistically appropriate industrial hygiene resources. This leaves a gap in knowledge on inhalation exposures to VOCs in this hard-to-reach and ubiquitous worker population.

Objective

Our goal was to recruit hard-to-reach, predominantly Spanish-speaking workers in beauty salons and auto repair shops and monitor total VOC inhalation exposures for over entire work shifts, with minimal impact on workers, clients, and business.

Methods

We developed and refined measurement and exposure assessment methods for personal and area full-shift VOC inhalation exposures.

Results

With minimal participant loss, we measured over 500 h of real-time, personal VOC exposures and recorded activities and other exposure factors for 47 participants, while also documenting chemical inventories and quantifying indoor area concentrations of specific VOCs among 10 auto repair shops and 10 beauty salons.

Conclusion

Lessons learned from our study can assist future studies of inhalation exposures in other hard-to-reach occupational populations.

Comprehensive analysis between volatile organic compound (VOC) exposure and female sex hormones: a cross-sectional study from NHANES 2013-2016

There is growing evidence suggesting that exposure to volatile organic compounds (VOCs) can pose significant health risks, including interference with the function of the reproductive system. However, there has been a lack of research focused on the impact of common environmental VOCs on the levels of sex hormones in the general female population. In this study, we conducted a cross-sectional analysis utilizing the database of the National Health and Nutrition Examination Survey (NHANES, 2013-2016). A total of 2633 participants were included in this study. The Pearson correlation model revealed the potential of co-exposure or co-toxicity between benzene and 2,5-dimethylfuran. According to GLM models, we discovered a significant positive association between blood levels of 2,5-dimethylfuran and benzene with testosterone levels in women. Subgroup analysis further identified that the women with underweight and healthy weight might be the high-risk subgroup. Bayesian kernel machine regression (BKMR) was applied to further assess the univariate and bivariate exposure-response relationships between multiple VOCs. Our research systemically formulated the possible relationship between exposure to VOCs and female sex hormones, indicating the role of VOCs as a risk factor for endocrine disruption, especially benzene and 2,5-dimethylfuran. These findings have important implications for public health and call for further investigation.

Temporal trends in sperm count: a systematic review and meta-regression analysis of samples collected globally in the 20th and 21st centuries

BACKGROUND

Numerous studies have reported declines in semen quality and other markers of male reproductive health. Our previous meta-analysis reported a significant decrease in sperm concentration (SC) and total sperm count (TSC) among men from North America-Europe-Australia (NEA) based on studies published during 1981-2013. At that time, there were too few studies with data from South/Central America-Asia-Africa (SAA) to reliably estimate trends among men from these continents.

OBJECTIVE AND RATIONALE

The aim of this study was to examine trends in sperm count among men from all continents. The broader implications of a global decline in sperm count, the knowledge gaps left unfilled by our prior analysis and the controversies surrounding this issue warranted an up-to-date meta-analysis.

SEARCH METHODS

We searched PubMed/MEDLINE and EMBASE to identify studies of human SC and TSC published during 2014-2019. After review of 2936 abstracts and 868 full articles, 44 estimates of SC and TSC from 38 studies met the protocol criteria. Data were extracted on semen parameters (SC, TSC, semen volume), collection year and covariates. Combining these new data with data from our previous meta-analysis, the current meta-analysis includes results from 223 studies, yielding 288 estimates based on semen samples collected 1973-2018. Slopes of SC and TSC were estimated as functions of sample collection year using simple linear regression as well as weighted meta-regression. The latter models were adjusted for predetermined covariates and examined for modification by fertility status (unselected by fertility versus fertile), and by two groups of continents: NEA and SAA. These analyses were repeated for data collected post-2000. Multiple sensitivity analyses were conducted to examine assumptions, including linearity.

OUTCOMES

Overall, SC declined appreciably between 1973 and 2018 (slope in the simple linear model: -0.87 million/ml/year, 95% CI: -0.89 to -0.86; P < 0.001). In an adjusted meta-regression model, which included two interaction terms [time × fertility group (P = 0.012) and time × continents (P = 0.058)], declines were seen among unselected men from NEA (-1.27; -1.78 to -0.77; P < 0.001) and unselected men from SAA (-0.65; -1.29 to -0.01; P = 0.045) and fertile men from NEA (-0.50; -1.00 to -0.01; P = 0.046). Among unselected men from all continents, the mean SC declined by 51.6% between 1973 and 2018 (-1.17: -1.66 to -0.68; P < 0.001). The slope for SC among unselected men was steeper in a model restricted to post-2000 data (-1.73: -3.23 to -0.24; P = 0.024) and the percent decline per year doubled, increasing from 1.16% post-1972 to 2.64% post-2000. Results were similar for TSC, with a 62.3% overall decline among unselected men (-4.70 million/year; -6.56 to -2.83; P < 0.001) in the adjusted meta-regression model. All results changed only minimally in multiple sensitivity analyses.

WIDER IMPLICATIONS

This analysis is the first to report a decline in sperm count among unselected men from South/Central America-Asia-Africa, in contrast to our previous meta-analysis that was underpowered to examine those continents. Furthermore, data suggest that this world-wide decline is continuing in the 21st century at an accelerated pace. Research on the causes of this continuing decline and actions to prevent further disruption of male reproductive health are urgently needed.

Occupational Exposure to Physical and Chemical Risk Factors: A Systematic Review of Reproductive Pathophysiological Effects in Women and Men

The human reproductive system can be affected by occupational exposure to many physical and chemical risk factors. This study was carried out to review the studies conducted on the issue of the pathophysiological effects of occupational physical and chemical risk factors on the reproductive system of females and males. In this systematic review, the databases such as "Google Scholar," "Pub-Med," "Scopus," and "Web of Science" were used. Following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA 2020), the studies included in our study were published between 2000 and 2021. In order to extract the required data, all sections of the articles were reviewed. Out of 57 articles we reviewed, 34 articles were related to field studies and 23 articles to clinical studies. Among them, 43 studies dealt with the pathophysiological effects of chemical agents, six studies dealt with the pathophysiological effects of physical factors, and 8 studies dealt with the pathophysiological effects of physicochemical factors on the human reproductive system. Physical (noise, heat, and radiofrequency radiation) and chemical (such as carbamate and organophosphate pesticides, benzene, toluene, xylene, formaldehyde, NO₂, CS₂, manganese, lead, nickel, and n-hexane) risk factors had pathophysiological effects on the human reproductive system. The presence of these risk factors in the workplace caused damage to the human reproductive system. The rate of these negative pathophysiological effects can be reduced by performing appropriate managerial, technical, and engineering measures in work environments.

The Association Between Self-Reported Household Renovation and Semen Parameters Among Infertile Men: A Cross-Sectional Study

Previous studies have indicated that outdoor air pollution has a negative impact on semen quality; however, few studies have examined whether living in a recently renovated residence is one of the factors influencing semen parameters. We aimed to examine the association between household renovation and semen parameters among infertile men. Our study was conducted at the Reproductive Medicine Center, The First Hospital of Jilin University (Changchun, China) from July 2018 to April 2020. A total of 2267 participants were enrolled in the study. The participants completed the questionnaire and provided a semen sample. Univariate and multiple logistic regression models were used to estimate the association between household renovations and semen parameters. Of the participants, about one-fifth (n = 523, 23.1%) had undergone renovations in the last 24 months. The median progressive motility was 34.50%. There was a significant difference between participants whose residences had been renovated in the last 24 months and those whose residences had not been recently renovated (z = -2.114, p = .035). Compared with participants whose residences were not recently renovated, participants who moved into the residence within 3 months after renovation had a higher risk of abnormal progressive motility after adjusting for age and abstinence time (odds ratio [OR] = 1.537, 95% confidence interval [CI]: 1.088-2.172). Our findings indicated that progressive motility was significantly associated with household renovations.

Cancer-testis antigen lactate dehydrogenase C4 as a novel biomarker of male infertility and cancer

A unique lactate dehydrogenase (LDH) isoenzyme designated as lactate dehydrogenase C4 (LDH-C4) is found in mammalian mature testis and spermatozoa. Thus far, LDH-C4 has been well studied with regard to its gene and amino acid sequences, structure, biological properties, and peptide synthesis. Accumulating evidence has shown that LDH-C4 is closely related to spermatic energy metabolism and plays a critical role in sperm motility, capacitation, and fertilization. Defects in the catalytic activity of LDH-C4 are key to pathophysiological abnormalities underlying infertility. LDH-C4 was originally thought to be present only in mature testis and spermatozoa; however, recent studies have implicated LDH-C4 as a cancer-testis antigen (CTA), owing to its aberrant transcription in a broad spectrum of human neoplasms. This review highlights the recent findings on LDH-C4 with particular emphasis on its role in male infertility and tumors.

Occupational Exposures and Health Risks of Benzene, Toluene, and Xylenes (BTX) in Automobile Repair Industry in Beijing City, China

This study aimed to evaluate the occupational health risks of benzene, toluene, and xylenes (BTX) exposure in the automobile repair industry in Beijing city in China. The concentrations of BTX were monitored at 140 operating positions of 51 randomly selected automobile repair enterprises in 2018. Samples analysis showed that all monitoring concentrations were not higher than the occupational exposure limits. The long-term exposure concentration ranges of benzene, toluene, and xylenes were 0.1 to 0.3, 0.1 to 49.7, and 0.2 to 49.5 mg/m³, respectively. The short-term exposure concentration ranges of benzene, toluene, and xylenes were 0.1 to 0.3, 0.1 to 98.7, and 0.2 to 100.0 mg/m³, respectively. But assessment results revealed unneglectable occupational health risks, especially the combined health risks of BTX exposure. Thereafter, effective control and improvement measures were put forward, including strengthening the management of the production, sale, and use of vehicle paints and coatings; improving ventilation; and implementing hierarchical management measures for occupational health risks.

Indoor and outdoor air pollution and couple fecundability: a systematic review

BACKGROUND

Air pollution is both a sensory blight and a threat to human health. Inhaled environmental pollutants can be naturally occurring or human-made, and include traffic-related air pollution (TRAP), ozone, particulate matter (PM) and volatile organic compounds, among other substances, including those from secondhand smoking. Studies of air pollution on reproductive and endocrine systems have reported associations of TRAP, secondhand smoke (SHS), organic solvents and biomass fueled-cooking with adverse birth outcomes. While some evidence suggests that air pollution contributes to infertility, the extant literature is mixed, and varying effects of pollutants have been reported.

OBJECTIVE AND RATIONALE

Although some reviews have studied the association between common outdoor air pollutants and time to pregnancy (TTP), there are no comprehensive reviews that also include exposure to indoor inhaled pollutants, such as airborne occupational toxicants and SHS. The current systematic review summarizes the strength of evidence for associations of outdoor air pollution, SHS and indoor inhaled air pollution with couple fecundability and identifies gaps and limitations in the literature to inform policy decisions and future research.

SEARCH METHODS

We performed an electronic search of six databases for original research articles in English published since 1990 on TTP or fecundability and a number of chemicals in the context of air pollution, inhalation and aerosolization. Standardized forms for screening, data extraction and study quality were developed using DistillerSR software and completed in duplicate. We used the Newcastle-Ottawa Scale to assess risk of bias and devised additional quality metrics based on specific methodological features of both air pollution and fecundability studies.

OUTCOMES

The search returned 5200 articles, 4994 of which were excluded at the level of title and abstract screening. After full-text screening, 35 papers remained for data extraction and synthesis. An additional 3 papers were identified independently that fit criteria, and 5 papers involving multiple routes of exposure were removed, yielding 33 articles from 28 studies for analysis. There were 8 papers that examined outdoor air quality, while 6 papers examined SHS exposure and 19 papers examined indoor air quality. The results indicated an association between outdoor air pollution and reduced fecundability, including TRAP and specifically nitrogen oxides and PM with a diameter of ≤2.5 µm, as well as exposure to SHS and formaldehyde. However, exposure windows differed greatly between studies as did the method of exposure assessment. There was little evidence that exposure to volatile solvents is associated with reduced fecundability.

WIDER IMPLICATIONS

The evidence suggests that exposure to outdoor air pollutants, SHS and some occupational inhaled pollutants may reduce fecundability. Future studies of SHS should use indoor air monitors and biomarkers to improve exposure assessment. Air monitors that capture real-time exposure can provide valuable insight about the role of indoor air pollution and are helpful in assessing the short-term acute effects of pollutants on TTP.

Occupational health hazards and wide spectrum of genetic damage by the organic solvent fumes at the workplace: A critical appraisal

Long-term exposure to organic solvents is known to affect human health posing serious occupational hazards. Organic solvents are genotoxic, and they can cause genetic changes in the exposed employees' somatic or germ cells. Chemicals such as benzene, toluene, and gasoline induce an excessive amount of genotoxicity results either in genetic polymorphism or culminates in deleterious mutations when concentration crosses the threshold limits. The impact of genotoxicity is directly related to the time of exposure, types, and quantum of solvent. Genotoxicity affects almost all the physiological systems, but the most vulnerable ones are the nervous system, reproductive system, and blood circulatory system. Based on the available literature report, we propose to evaluate the outcomes of such chemicals on the exposed humans at the workplace. Attempts would be made to ascertain if the long-term exposure makes a person resistant to such chemicals. This may seem to be a far-fetched idea but has not been studied. The health prospect of this study is envisaged to complement the already existing data facilitating a deeper understanding of the genotoxicity across the population. This would also demonstrate if it correlates with the demographic profile of the population and contributes to comorbidity and epidemiology.

Environmental and occupational exposures associated with male infertility

The upsurge in male infertility over the last two decades, possibly due to environmental exposure, has raised significant interest, particularly boosted by reports from fertility clinics, which showed that chronic diseases and hereditary or other medical conditions might only partially explain current incidence of male infertility. Both environmental and occupational settings may have a significant role in exposure to complex mixtures of endocrine disruptors (ED), which play a major role in fertility disorders. The aim of this review is to give an insight into the current knowledge on exposure settings which may be associated with male infertility. Our study relied on a systematic search of PubMed, Scopus, and Web of Science for articles published between January 2000 and September 2020. It showed that some well documented factors associated with male infertility include smoking, and physiological disturbances or chronic diseases such as obesity and diabetes, which in turn, may also reflect lifestyle choices and environmental exposures, especially to EDs such as phthalates, bisphenols, pesticides, and flame retardants. However, the number of studies on the aetiology of male infertility is still too low in comparison with the size of affected population. Occupational health follow-ups and medical surveillance do not collect any data on male infertility, even though ED chemicals are part of many technological processes.

Evaluation of Exposure to Toluene and Xylene in Gasoline Station Workers

The main volatile organic compounds found at gasoline stations are benzene, toluene, ethylbenzene, and xylene isomers (BTEX). They cause several harmful effects on human health. Regulatory Norm 7 (1978) provides that, in Brazil, biological monitoring of toluene and xylene is carried out by measuring the urinary metabolites hippuric acid (HA) and methylhippuric acid (MHA), respectively. The objective of this study was to assess the exposure to toluene and xylene and to identify related signs and symptoms in gasoline station workers. A cross-sectional epidemiological study was conducted with workers occupationally exposed to fuels. These gasoline station workers were divided into two groups: 94 workers exposed mainly by inhalation (convenience store workers (CSWs)) and 181 workers exposed by inhalation and dermal route (filling station attendants (FSAs)). A comparison group was formed by 119 workers not occupationally exposed to fuels (office workers (OWs)). Workers exposed to fuels had higher average levels of these exposure biomarkers (HA and MHA), which were also higher in convenience store workers than in filling station attendants. In addition, individuals exposed to the solvents present in gasoline had altered mood/depression, cramps, dizziness, drowsiness, headaches, irritability/nervousness, weakness, weight loss, and other symptoms more frequently and had higher urinary levels of HA and MHA compared to the comparison group. Gasoline station workers showed high levels of HA and MHA, reflecting high occupational exposure to the solvents toluene and xylene present in gasoline, demonstrating that changes in the current legislation and in the work environment are necessary to ensure better health protection for these workers.

Proposing a social ecological approach to address disparities in occupational exposures and health for low-wage and minority workers employed in small businesses

Occupational disease and injuries are the 8th leading cause of death in the United States. Low-wage and minority workers are more likely to work in hazardous industries and are thus at greater risk. Within the small business sector, in particular, the health of low-wage and minority workers is threatened by a multitude of complex and interrelated factors that increase their risk for injuries, death, and even chronic disease. The COVID-19 pandemic has amplified these concerns, as many low-wage and minority workers are essential workers, and many small businesses are reopening with little to no guidance. The article describes work-related health risks and reviews current research on occupational and social ecological approaches to improving the health of minority and low-wage workers primarily employed by small businesses. We propose a conceptual framework that integrates the social ecological model with the hierarchy of controls to address work-related health among low-wage and minority workers specifically in the small business sector. Community-based strategies are recommended to engage small business owners and workers in efforts to address their immediate needs, while building towards sustainable policy change over time. These strategies are of particular importance as small businesses reopen in the ongoing pandemic.

Xylene delays the development of Leydig cells in pubertal rats by inducing reactive oxidative species

Xylene is a cyclic hydrocarbon, which is commonly used as a solvent in dyes, paints, polishes, and industrial solutions. It is a potential environmental pollutant. Here, we report the effect of xylene exposure on Leydig cell development in male rats during puberty. Xylene (0, 150, 750, and 1500 mg/kg) was gavaged to 35-day-old male Sprague Dawley rats for 21 days. Xylene significantly reduced serum testosterone levels at 750 and 1500 mg/kg without affecting serum luteinizing hormone and follicle-stimulating hormone levels. Xylene reduced the number of HSD11B1-positive Leydig cells at the advanced stage at 1500 mg/kg. At 750 and 1500 mg/kg, xylene also reduced the cell size and cytoplasm size. It down-regulated the expression of Leydig cell-specific genes (Lhcgr, Scarb1, Star, Cyp11a1, Hsd3b1, Cyp17a1, and Hsd11b1) and proteins. In addition, xylene significantly reduced the ratio of phosphorus-GSK-3β (pGSK-3β/GSK-3β), phosphorus-ERK1/2 (pERK)/ERK1/2, and phosphorus-AKT1 (pAKT1)/AKT1, and SIRT1 levels in the testes. In vitro Leydig cell culture showed that xylene induced oxidative stress by increasing the production of reactive oxygen species and lowing antioxidant (Sod2), and inhibited the production of testosterone, and down-regulated the expression of genes related to steroidogenesis, while vitamin E reversed the xylene-mediated effect as an antioxidant. In conclusion, xylene exposure may disrupt the development of pubertal Leydig cells by increasing reactive oxygen species production and reducing the expression of GSK-3β, ERK1/2, AKT1, and SIRT1.

DNA fragmentation of sperm in automobile painters

Reproductive health is a major concern for workers constantly exposed to chemicals at work, especially in developing countries. The problems mainly stemmed from chronic exposure to the chemicals contained in paint thinner, which is mainly toluene, used during automobile painting. Unfortunately, in Indonesia, there is no study on the reproductive health of male workers in automobile workshops, especially in relation to spermatogenesis. This study aimed to explore the possibility of reproductive problems, namely spermatozoa DNA fragmentation, among male workers in an automobile workshop in Malang. We recruited workers who have worked as automobile painters for years at an automobile workshop in Malang and have been chronically exposed to thinner. Semen samples were collected from 15 automobile workshop workers who were married and had children. Twelve office workers were used as the control group. The two groups of semen samples were tested with the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay combined with propidium iodide and analyzed by flow cytometry. The results showed a significant difference between DNA fragmentation of the control group and workshop workers at 14.9% and 47.66%, respectively. Risk factor analysis showed a significant increase in risk factors (p = 0.001). Taken together, chronic exposure to paint thinner in those engaged in painting at the automobile workshop increased the risk of DNA fragmentation in spermatozoa. Our study highlighted the importance of health education for the risked workers on minimization of exposure, which could be recommended to the health policy makers.

Investigating the Potential Toxicity of Hydraulic Fracturing Flowback and Produced Water Spills to Aquatic Animals in Freshwater Environments: A North American Perspective

Unconventional methods of oil and natural gas extraction have been a growing part of North America's energy sector for the past 20-30 years. Technologies such as horizontal hydraulic fracturing have facilitated the exploitation of geologic reserves that were previously resistant to standard drilling approaches. However, the environmental risks associated with hydraulic fracturing are relatively understudied. One such hazard is the wastewater by-product of hydraulic fracturing processes: flowback and produced water (FPW). During FPW production, transport, and storage, there are many potential pathways for environmental exposure. In the current review, toxicological hazards associated with FPW surface water contamination events and potential effects on freshwater biota are assessed. This review contains an extensive survey of chemicals commonly associated with FPW samples from shale formations across North America and median 50% lethal concentration values (LC₅₀) of corresponding chemicals for many freshwater organisms. We identify the characteristics of FPW which may have the greatest potential to be drivers of toxicity to freshwater organisms. Notably, components associated with salinity, the organic fraction, and metal species are reviewed. Additionally, we examine the current state of FPW production in North America and identify the most significant obstacles impeding proper risk assessment development when environmental contamination events of this wastewater occur. Findings within this study will serve to catalyze further work on areas currently lacking in FPW research, including expanded whole effluent testing, repeated and chronic FPW exposure studies, and toxicity identification evaluations.

Meta-Analysis Reveals the Association Between Male Occupational Exposure to Solvents and Impairment of Semen Parameters

OBJECTIVES

Solvent exposure is among the most common occupational exposures to chemical toxicants; data about the impact of such exposure on semen parameters are contradictory. We conducted the first meta-analysis to evaluate the risk of alteration in semen parameters related to occupational exposure to solvents.

METHODS

From the PubMed database, we selected studies analyzing the semen of subjects occupationally exposed to solvents, compared with unexposed controls. The meta-analysis was performed on the various semen parameters analyzed in both populations.

RESULTS

Seven studies were included in the study. The meta-analysis revealed a significant decrease in ejaculate volume [standardized mean difference (SMD) = -0.35 (-0.63 to -0.07)] and sperm concentration [SMD = -0.36 (-0.64 to -0.08)] in workers exposed to solvents compared with unexposed controls.

CONCLUSION

Our results highlight the importance of preventing reprotoxic risks to male fertility in the workplace.

Effects of environmental contaminants on fertility and reproductive health

Recent research indicates that the human infertility rate is increasing. Although various reasons have been hypothesized for the growing infertility rate, environmental contaminants are potentially important causal agents associated with this change. Chemical contaminants are widespread throughout our environment and human exposure is virtually unavoidable. The overall contribution of environmental exposure to infertility is unknown, but studies involving occupational exposure, together with results from animal experiments, suggest that environmental contaminants may adversely affect fertility. We reviewed the adverse effects of environmental exposure on fertility and related reproductive outcomes. Environmental contaminants covered in this review include heavy metals, organic solvents, pesticides and endocrine disrupting chemicals. It is hoped that this review will highlight the need for further research in this area.

Experimental exposure to gasohol impairs sperm quality with recognition of the classification pattern of exposure groups by machine learning algorithms

Contamination caused by leakage at gas stations leads to possible exposure of the general population when in contact with contaminated water and soil. The present study aimed to evaluate the reproductive effects of exposure of adult male rats to gasohol and evaluate the performance of machine learning (ML) algorithms for pattern recognition and classification of the exposure groups. Rats were orally exposed to 0 (control), 16 (EA), 160 (EB), or 800 mg kg^-1 bw day^-1 of gasohol (EC), for 30 consecutive days. Sperm quality of the groups exposed to two higher doses was reduced in comparison to the control group. The sperm parameters decreased were: daily sperm production, sperm number in the caput/corpus epididymis, progressive motility, mitochondrial activity, and acrosomal membrane integrity. Sperm transit time in the epididymis cauda and sperm isolated head were increased in EB and EC. Sertoli cells number was decreased in these groups, but their support capacity was maintained. ML methods were used to identify patterns between samples of control and exposure groups. The results obtained by ML methods were very promising, obtaining about 90% of accuracy. It was concluded that the exposure of rats to different doses of gasohol impair spermatogenesis and sperm quality, with a recognizable classification pattern of exposure groups at ML.

Association between BMI and semen quality: an observational study of 3966 sperm donors

STUDY QUESTION

What is the relationship between abnormal BMI and semen quality?

SUMMARY ANSWER

Underweight was significantly associated with lower sperm concentration, total sperm number and total motile sperm count, while overweight was significantly associated with lower semen volume, total sperm number and total motile sperm count.

WHAT IS KNOWN ALREADY

Abnormal BMI has been associated with lower semen quality, but the results remain somewhat controversial. In addition, most previous studies have focused on the influence of obesity or overweight on semen quality, and evidence on the association between underweight and semen quality is rare.

STUDY DESIGN, SIZE, DURATION

This research was an observational study investigating 3966 sperm donors from a large sperm bank in Wuhan city, China. These donors passed the screening for sperm donation and underwent 29 949 semen examinations between 1 January 2013 and 9 April 2018.

PARTICIPANTS/MATERIALS, SETTING, METHODS

BMI was categorized into four groups: underweight (<18.5 kg/m2), normal weight (18.5-24.9 kg/m2), overweight (25-29.9 kg/m2) and obese (≥30 kg/m2). Semen volume, sperm concentration, total sperm number, total motility, progressive motility and total motile sperm count were determined by trained clinical technicians. Linear mixed models were used to conduct dose-response analyses between BMI and semen quality parameters.

MAIN RESULTS AND THE ROLE OF CHANCE

Underweight was significantly associated with a 3.0% (95% CI: 0.1%, 5.8%), 6.7% (1.9%, 11.3%) and 7.4% (2.2%, 12.4%) reduction in sperm concentration, total sperm number and total motile sperm count, respectively. Overweight was significantly associated with a 4.2% (1.6%, 6.8%), 3.9% (0.9%, 6.9%) and 3.6% (0.2%, 6.9%) reduction in semen volume, total sperm number and total motile sperm count, respectively. Non-linear models including continuous BMI as a natural cubic spline function yielded similar results.

LIMITATIONS, REASONS FOR CAUTION

Our study subjects were sperm donors who are typically young and healthy, and therefore not representative of the general male population. Caution should be paid in generalizing our results to other populations. Furthermore, we did not measure the donors' weight repeatedly along with each semen donation; instead, we only measured it once during the screening, which may cause bias due to the variations of weight across time.

WIDER IMPLICATIONS OF THE FINDINGS

Our study provides evidence that underweight and overweight are associated with lower semen quality, and highlights the importance of maintaining a normal weight for men.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Health and Family Planning Commission of Hubei Province (Grant number WJ2015MA027), the Hubei Provincial Committee of the Communist Youth League of China, and Center for Global and Regional Environmental Research at the University of Iowa. The authors declare that there are no conflicts of interest.

TRIAL REGISTRATION NUMBER

N/A.

Temporal trends in sperm count: a systematic review and meta-regression analysis

BACKGROUND

Reported declines in sperm counts remain controversial today and recent trends are unknown. A definitive meta-analysis is critical given the predictive value of sperm count for fertility, morbidity and mortality.

OBJECTIVE AND RATIONALE

To provide a systematic review and meta-regression analysis of recent trends in sperm counts as measured by sperm concentration (SC) and total sperm count (TSC), and their modification by fertility and geographic group.

SEARCH METHODS

PubMed/MEDLINE and EMBASE were searched for English language studies of human SC published in 1981-2013. Following a predefined protocol 7518 abstracts were screened and 2510 full articles reporting primary data on SC were reviewed. A total of 244 estimates of SC and TSC from 185 studies of 42 935 men who provided semen samples in 1973-2011 were extracted for meta-regression analysis, as well as information on years of sample collection and covariates [fertility group ('Unselected by fertility' versus 'Fertile'), geographic group ('Western', including North America, Europe Australia and New Zealand versus 'Other', including South America, Asia and Africa), age, ejaculation abstinence time, semen collection method, method of measuring SC and semen volume, exclusion criteria and indicators of completeness of covariate data]. The slopes of SC and TSC were estimated as functions of sample collection year using both simple linear regression and weighted meta-regression models and the latter were adjusted for pre-determined covariates and modification by fertility and geographic group. Assumptions were examined using multiple sensitivity analyses and nonlinear models.

OUTCOMES

SC declined significantly between 1973 and 2011 (slope in unadjusted simple regression models -0.70 million/ml/year; 95% CI: -0.72 to -0.69; P < 0.001; slope in adjusted meta-regression models = -0.64; -1.06 to -0.22; P = 0.003). The slopes in the meta-regression model were modified by fertility (P for interaction = 0.064) and geographic group (P for interaction = 0.027). There was a significant decline in SC between 1973 and 2011 among Unselected Western (-1.38; -2.02 to -0.74; P < 0.001) and among Fertile Western (-0.68; -1.31 to -0.05; P = 0.033), while no significant trends were seen among Unselected Other and Fertile Other. Among Unselected Western studies, the mean SC declined, on average, 1.4% per year with an overall decline of 52.4% between 1973 and 2011. Trends for TSC and SC were similar, with a steep decline among Unselected Western (-5.33 million/year, -7.56 to -3.11; P < 0.001), corresponding to an average decline in mean TSC of 1.6% per year and overall decline of 59.3%. Results changed minimally in multiple sensitivity analyses, and there was no statistical support for the use of a nonlinear model. In a model restricted to data post-1995, the slope both for SC and TSC among Unselected Western was similar to that for the entire period (-2.06 million/ml, -3.38 to -0.74; P = 0.004 and -8.12 million, -13.73 to -2.51, P = 0.006, respectively).

WIDER IMPLICATIONS

This comprehensive meta-regression analysis reports a significant decline in sperm counts (as measured by SC and TSC) between 1973 and 2011, driven by a 50-60% decline among men unselected by fertility from North America, Europe, Australia and New Zealand. Because of the significant public health implications of these results, research on the causes of this continuing decline is urgently needed.

A review of environmental and occupational exposure to xylene and its health concerns

Xylene is a cyclic hydrocarbon, and an environmental pollutant. It is also used in dyes, paints, polishes, medical technology and different industries as a solvent. Xylene easily vaporizes and divides by sunlight into other harmless chemicals. The aim of the present review is to collect the evidence of the xylene toxicity, related to non-cancerous health hazards, as well as to provide possible effective measurement to minimize its risk ratio. For current study a bibliographic search of more than 250 peer-reviewed papers in scientific data including PubMed, and Google Scholar about xylene was done. But approximately 130 peer-reviewed papers relevant to xylene were included (Figure 1(Fig. 1)). All scientific data was reviewed with key words of "xylene toxicity", "xylene toxic health effects", "environmental volatile organic compounds", "human exposure to xylene", "xylene poisoning in laboratory workers", "effects of xylene along with other hydrocarbons", "neurotoxicity of selected hydrocarbons", and "toxic effects of particular xylene isomers in animals". According to these studies, xylene is released into the atmosphere as fugitive emissions from petrochemical industries, fire, cigarette, from different vehicles. Short term exposure to mixed xylene or their individual isomers result in irritation of the nose, eyes and throat subsequently leading toward neurological, gastrointestinal and reproductive harmful effects. In addition long term exposure to xylene may cause hazardous effects on respiratory system, central nervous system, cardiovascular system, and renal system. The health concerns of xylene are well documented in animals and human. It is important to improve health policies, launch xylene related health and toxicity awareness campaigns, to get rid of its dangerous outcomes. Chronic diseases have become a threat to human globally, with special prominence in regions, where xylene is used with other chemicals (benzene, toluene etc.) especially in petroleum and rubber industry. The mechanism of toxicity and interactions with endocrine system should be followed up which is the main threat to human health.

A review of environmental and occupational exposure to xylene and its health concerns

Xylene is a cyclic hydrocarbon, and an environmental pollutant. It is also used in dyes, paints, polishes, medical technology and different industries as a solvent. Xylene easily vaporizes and divides by sunlight into other harmless chemicals. The aim of the present review is to collect the evidence of the xylene toxicity, related to non-cancerous health hazards, as well as to provide possible effective measurement to minimize its risk ratio. For current study a bibliographic search of more than 250 peer-reviewed papers in scientific data including PubMed, and Google Scholar about xylene was done. But approximately 130 peer-reviewed papers relevant to xylene were included (Figure 1(Fig. 1)). All scientific data was reviewed with key words of "xylene toxicity", "xylene toxic health effects", "environmental volatile organic compounds", "human exposure to xylene", "xylene poisoning in laboratory workers", "effects of xylene along with other hydrocarbons", "neurotoxicity of selected hydrocarbons", and "toxic effects of particular xylene isomers in animals". According to these studies, xylene is released into the atmosphere as fugitive emissions from petrochemical industries, fire, cigarette, from different vehicles. Short term exposure to mixed xylene or their individual isomers result in irritation of the nose, eyes and throat subsequently leading toward neurological, gastrointestinal and reproductive harmful effects. In addition long term exposure to xylene may cause hazardous effects on respiratory system, central nervous system, cardiovascular system, and renal system. The health concerns of xylene are well documented in animals and human. It is important to improve health policies, launch xylene related health and toxicity awareness campaigns, to get rid of its dangerous outcomes. Chronic diseases have become a threat to human globally, with special prominence in regions, where xylene is used with other chemicals (benzene, toluene etc.) especially in petroleum and rubber industry. The mechanism of toxicity and interactions with endocrine system should be followed up which is the main threat to human health.

New Look at BTEX: Are Ambient Levels a Problem?

Benzene, toluene, ethylbenzene, and xylene (BTEX) are retrieved during fossil fuel extraction and used as solvents in consumer and industrial products, as gasoline additives, and as intermediates in the synthesis of organic compounds for many consumer products. Emissions from the combustion of gasoline and diesel fuels are the largest contributors to atmospheric BTEX concentrations. However, levels indoors (where people spend greater than 83% of their time) can be many times greater than outdoors. In this review we identified epidemiological studies assessing the noncancer health impacts of ambient level BTEX exposure (i.e., nonoccupational) and discussed how the health conditions may be hormonally mediated. Health effects significantly associated with ambient level exposure included sperm abnormalities, reduced fetal growth, cardiovascular disease, respiratory dysfunction, asthma, sensitization to common antigens, and more. Several hormones including estrogens, androgens, glucocorticoids, insulin, and serotonin may be involved in these health outcomes. This analysis suggests that all four chemicals may have endocrine disrupting properties at exposure levels below reference concentrations (i.e., safe levels) issued by the U.S. Environmental Protection Agency. These data should be considered when evaluating the use of BTEX in consumer and industrial products and indicates a need to change how chemicals present at low concentrations are assessed and regulated.

Relationship between self-reported residential indoor remodeling and semen quality: a case-control study

The present study examined the association between residential indoor remodeling and poor semen quality. Sperm donors aged 18–45 years old were recruited in Shanghai, China. Semen specimens were collected and analyzed. An in-person interview was conducted to obtain information on the history of indoor remodeling and potential confounders. A total of 70 participants with abnormal semen quality (case group) and 68 controls were examined. A total of 20 subjects reported indoor remodeling in the recent 24 months, and among them 17 subjects reported indoor remodeling in the recent 12 months. Compared with participants with no history of indoor remodeling, participants with a history of indoor remodeling in the recent 24 months were more than three times as likely to have poor sperm quality (adjusted odds ratio = 3.8, 95% confidence interval: 1.3–12.0) after controlling for potential confounders. The association was strengthened when the analysis was restricted to those who had indoor remodeling in the recent 12 months. Our findings provide preliminary evidence that indoor remodeling has an adverse effect on semen quality.

Hematological Evidence of Occupational Exposure to Chemicals and Other Factors among Auto-Repair Workers in Rawalpindi, Pakistan

Objectives

Occupational exposure to aromatic solvents causes many serious health hazards to workers, especially if an ambient environment increases the exposure during routine working hours. This study was conducted on two related groups, i.e., automobile mechanics (MCs) and automobile spray painters (PNs), with an effort to analyze effects of chemical exposure on hematological parameters, keeping a focus on environmental parameters and workers’ personal behavioral characteristics that could be held responsible for increasing exposure risk.

Methods

A preliminary survey of various chemicals used in these places was done, and 78 blood samples were collected from three groups (control, n = 24; mechanics, n = 25; painters, n = 29). Demographic features of workers were recorded through a short questionnaire.

Results

Results showed that mean red blood cell (RBC) count was lower both in MCs [t(51) = 2.38, p < 0.021, r = 0.32] and in PNs [t(47) = 2.12, p < 0.03, r = 0.29], whereas mean hemoglobin (Hb) was significantly lower in MCs [t(51) = 2.5, p = 0.017, r = 0.33]. Combined data for exposed groups for smokers (SMs) versus nonsmokers (NSs) showed that SMs had a significantly lower number (RBC count: t(52) = 2.28, p < 0.027, r = 0.25; Hb count: t(52) = 2.71, p < 0.009, r = 0.30] of these parameters than NSs, even compared to the control group. Moreover, logistic regression results showed that smoking is a significant predictor of reduction in RBC and Hb counts, besides occupational exposure and work experience to a little extent among exposed workers. Mean white blood cell count [t(47) = 2.63, p < 0.01, r=0.35], mean corpuscle volume [t(47)= –2.82, p = 0.007, r = 0.29], and packed cell volume [t(47)= –2.28, p = 0.027, r = 31] were higher exclusively in painters, which could be related to exposure to benzene in addition to isocyanate.

Conclusion

It appeared that workplace exposure may be complex due to interaction of multiple factors and PNs face much more exposure to isocyanate and aromatic solvents than MCs, which had significant effects on their hematopoiesis. Smoking enhances exposure risk manifolds, and among MCs it showed combined effects along with occupational exposure. There is a need to create awareness among these workers to adopt self-safety measures during routine tasks and also of a separate study to elucidate actual occupational exposure among them, eliminating confounding factors.

Effect of benzene exposure on fertility of male workers employed in bulk drug industries

AIMS AND OBJECTIVES

Industrial workers are constantly exposed to benzene, especially at the production unit. The present investigation explores any association of the outcome of various reproductive malfunctions in terms of infertility and other related factors as a result of benzene exposure.

METHODOLOGY

Blood and semen samples were collected from total 160 industrial workers exposed to benzene and 200 nonoccupationally exposed control subjects. We investigated macroscopic and microscopic semen parameters in the present study population. Body fluid benzene analysis was done by Head Space chromatography. The sperm DNA integrity was determined by modified alkaline single-cell gel electrophoresis or the comet assay method.

RESULTS

No significant changes were observed in macroscopic semen parameters. A duration-dependent decrement in total sperm count and the percentage of motility was observed among the benzene-exposed industrial workers (p<0.05). A duration-dependent increment of abnormal sperm morphology was observed among the benzene-exposed industrial workers (p<0.01). A significant increase in comet tail length was observed in the exposed groups (p<0.01) in comparison to the controls. In regression analysis, the data were observed to be significant at the level of p<0.05 for Group II industrial workers (t=2.301).

CONCLUSION

Sperm integrity is considered one of the major factors in male infertility. The sperm DNA damage is an important step from spermatogenesis to malfunctions such as infertility; therefore, the present study represents an important evaluation for correctly diagnosing the problem, precisely from the level of DNA itself.

A multi-biomarker analysis of DNA damage in automobile painters

The genotoxic effects associated with automobile painting were analyzed using a panel of biomarkers. Chromosomal aberrations (CAs), sister chromatid exchange (SCE), and micronuclei were evaluated in 25 car painters (12 smokers, 13 nonsmokers) working in different automobile paint-shops in Italy and in 37 control subjects. The controls were healthy blood donors (14 smokers, 23 non-smokers) that were matched with the experimental population for gender and age. Air samples were analyzed regularly at the work places, and elevated concentrations of benzene and toluene were detected consistently. The exposed group had higher frequencies of CAs (both chromosome- and chromatid-type), micronuclei, and SCE (P < 0.5 - P < 0.001). Furthermore, exposed and control subjects were also genotyped for GSTM1 and GSTT1 polymorphism. No significant associations were detected between the biomarker responses and either the GSTM1 or GSTT1 genotype of the subjects, but the small sample size does not allow definite conclusions on the relationship between the genetic polymorphism and the biomarkers. The results indicate that automobile painters have increased levels of clastogenic and possible aneugenic damage and that smoking may be a confounding factor for the responses.

The transport of chemicals in semen

Three mechanisms have been proposed for exposure of the conceptus to chemicals in semen: access of chemicals to the maternal circulation after absorption from the vagina, direct chemical exposure of the conceptus following transport from the vagina to the uterine cavity, and delivery to the egg and subsequent conceptus of chemical bound to the sperm cell. We review published data for each of these three mechanisms. Human seminal fluid chemical concentrations are typically similar to or lower than blood concentrations, although some antimicrobial agents achieve higher concentrations in semen than in blood. Vaginal absorption of medications has been shown to occur, although the vehicles in which these medications are delivered to the vagina may maintain contact with the vaginal epithelium to a greater extent than does semen. Assuming total absorption of a seminal dose of a chemical with a high semen:blood concentration ratio, distribution within the recipient woman would result in a blood concentration at least three orders of magnitude lower than that in the man. Direct delivery of seminal chemicals into the uterine cavity of humans has not been shown to occur, although it may occur in species such as the rat in which seminal fluid has access to the uterine cavity. Chemicals in or on human sperm cells have been demonstrated with respect to tetracycline and cocaine in vitro and aluminum, lead, and cadmium in vivo. The in vitro cocaine study offers sufficiently quantitative data with which to predict that oocyte concentrations would be five orders of magnitude lower than blood concentrations associated with cocaine abuse, assuming a maximally cocaine-bound sperm were capable of fertilizing. Thus, even using liberal assumptions about transmission of chemicals in semen or sperm, predicted exposure levels of a pregnant woman or of the conceptus are three or more orders of magnitude lower than blood concentrations in the man whose semen is the putative vehicle for chemical transport.

Paternal organic solvent exposure and adverse pregnancy outcomes: a meta-analysis

BACKGROUND

Organic solvents are widely used, but conflicting reports exist concerning paternal exposure and adverse pregnancy outcomes. We conducted a meta-analysis to assess the risks of spontaneous abortions (SAs) and major malformations (MMs) after paternal exposure to organic solvents.

METHODS

Medline, Toxline, Reprotox, and Embase from 1966 to 2003 were searched. Two independent reviewers searched for cohort and case-control studies in any language on adult human males exposed chronically to any organic solvent. Two non-blinded independent extractors used a standardized form for data extraction; disagreements were resolved through consensus discussion.

RESULTS

Forty-seven studies were identified; 32 exclusions left 14 useable studies. Overall random effects odds ratios and 95% confidence intervals (CI95%) were 1.30 (CI95%: 0.81-2.11, N=1,248) for SA, 1.47 (CI95%: 1.18-1.83, N=384,762) for MMs, 1.86 (CI95%: 1.40-2.46, N=180,242) for any neural tube defect, 2.18 (CI95%: 1.52-3.11, N=107,761) for anencephaly, and 1.59 (CI95%: 0.99-2.56, N=96,517; power=56.3%) for spina bifida.

CONCLUSIONS

Paternal exposure to organic solvents is associated with an increased risk for neural tube defects but not SAs.

A Population-Based Study on the Association Between Parental Occupations and Some Common Birth Defects in Singapore (1994???1998)

We sought to study the association between some common birth defects and parental occupations. The live births and congenital malformation born between January 1994 and December 1998 were obtained from the Singapore National Registry of Births and Deaths (the National Birth Defect Registry). The prevalence of overall birth defects among Singapore live births during the study period is 13.9 per 1,000 live births. The most frequent single coding defects were "bulbus cordis anomalies and anomalies of cardiac septal closure (BCA)," "congenital anomalies of urinary system (CUS)," "cleft palate and cleft lip (CPL)," and "certain congenital musculoskeletal deformities (CMD)." Using the "Legislators, Senior Officers & Managers" as reference and adjusting for possible confounders, there were significant associations for: (1) paternal "clerical workers" (adjusted RR 2.25) with the BCA; (2) maternal "professionals" with CUS (adjusted risk ratio [RR] 3.58); (3) paternal "production craftsmen and related workers" with both the BCA (adjusted RR 2.04), and the CMD (adjusted RR 2.83); (4) paternal "plant and machine operators and assemblers" with the BCA (adjusted RR 2.49), and the CUS (adjusted RR 5.19), and the CMD (adjusted RR 3.01). Paternal rather than maternal exposure might be more important in the causation of some common birth defects in Singapore.

Low birth weight in relation to parental occupations—a population-based registry in Singapore (1994–1998)

OBJECTIVES

To study the association between parental occupation and low birth weight (LBW) in infants born in Singapore between 1994 and 1998. Other factors that may be related to LBW were also investigated.

METHODS

A retrospective study. Information was obtained from the Singapore National Registry of Births and Deaths on parental occupations for live births between 1 January 1994 to 31 December 1998. Parental date of birth, ethnic group, and highest educational qualification were also obtained. The associations between these factors and the occurrence of LBW was assessed using descriptive statistics and logistic regression analysis.

RESULTS

A total 208,360 live births were studied. Analyses were restricted to singleton births > or =37th week gestation (total of 189,064). No significant differences in LBW risk were found for the different maternal occupational groups, compared with a referent group ("legislators, senior officers, and managers"). However, fathers who were "not working" (OR=2.04; 1.57-2.65), "not classifiable by occupation" (OR=1.34; 1.09-1.65), and "cleaners, laborers, and related workers" (OR=1.32; 1.12-1.55) had the highest risk of LBW infants when compared with "legislators, senior officers, and managers," after adjustment for maternal occupation, ethnic group, educational level and age, paternal educational level, infant gestational age, sex, and birth order.

CONCLUSION

Certain paternal occupational groups appear to be associated with a higher risk of having LBW infants. This may be linked to socioeconomic status and possible work-related factors. Future studies of pregnancy outcomes should not ignore the potential contributions of fathers.

The human spermatozoon--not waving but drowning

The poor quality of the human ejaculate sets man apart from all other mammalian species. Even in normal fertile men the ejaculate may contain up to 85% abnormal forms according to the World Heath Organization (1999). In the wake of this poor semen quality comes extremely poor fertility (Hull et al, 1985) and the highest rates of aneuploidy, pregnancy loss and birth defects in viviparous vertebrates. Thus, the poor quality of human spermatozoa is reflected in both their capacity for fertilization and their genetic integrity. The ultimate cause of defective sperm function is unknown. In certain patients a genetic basis for male infertility has been identified involving DNA deletions on the long arm of the Y chromosome. Such deletions might explain the impoverished semen quality seen in about 10-14% of men with severely impaired spermatogenesis, but fail to explain the infertility seen in most (>85%) cases of male infertility. One of the key attributes and probable causes of defective sperm function is oxidative stress created by excessive ROS generation by the spermatozoa and/or the disruption of antioxidant defence systems in the male reproductive tract. Excess free radical generation frequently involves an error in spermiogenesis resulting in the release of spermatozoa from the germinal epithelium exhibiting abnormally high levels of cytoplasmic retention. The excess cytoplasm contains enzymes that fuel the generation of ROS by the spermatozoa's plasma membrane redox systems. The consequences of such oxidative stress include a loss of motility and fertilizing potential and the induction of DNA damage in the sperm nucleus. The loss of sperm function is due to the peroxidation of unsaturated fatty acids in the sperm plasma membrane as a consequence of which the latter loses its fluidity and the cells lose their function. The causes and consequences of oxidative damage to the DNA in the sperm nucleus are still not known with certainty. The available evidence suggests that early pregnancy loss and morbidity in the offspring, including childhood cancer, are associated with such damage. Developing animal models with which to establish the validity of these relationships and identifying the environmental factors associated with the proposed 'testicular dysgenesis syndrome' will clearly be important tasks for the future.