Sperm count depression in pesticide applicators exposed to dibromochloropropane

Sperm concentration remains stable among fertile American men: a systematic review and meta-analysis

IMPORTANCE

Findings from several high profile meta-analyses have raised concerns about an ongoing global decline in sperm concentration and male fertility. However, these studies exhibit considerable heterogeneity in key variables including study population, methodology, fertility status, and geographic region.

OBJECTIVE

To perform a systematic review and meta-analysis exploring temporal trends in sperm concentration among fertile men and men unselected for fertility status in the United States.

DATA SOURCES

A literature search performed in Scopus and PubMed databases for studies published between 1970 and 2023. Additional studies were included from citations of prior global meta-analyses and reviews evaluating temporal trends in sperm count.

STUDY SELECTION AND SYNTHESIS

Studies were included if they presented original data on sperm concentration in US men without known infertility from 1970 to 2023. Aggregate data were assessed across all study populations, with additional subgroup analyses stratified by fertility status and US region.

MAIN OUTCOMES

Weighted generalized linear models were generated to evaluate the association between mean sperm concentration and sample collection year.

RESULTS

A total of 874 articles were screened, with 58 meeting the inclusion criteria. These represented 75 unique study populations totaling 11,787 men in the United States. Across all study populations, no change in sperm concentration was observed between 1970 and 2018 in unadjusted models (β = 0.14 million/mL per year). When adjusting for US region, no statistically significant decline in sperm concentration was seen. When adjusting for both region and fertility status, a modest annual decline was observed to meet statistical significance (β = -0.35 million/mL per year). Of the 49 study populations reporting adequate data to determine mean total sperm count, there was a significant increase in total sperm count of 2.9 million per year between 1970 and 2018. Subgroup analysis found no statistically significant change in mean sperm concentration among any US census region or fertility status cohort.

CONCLUSION AND RELEVANCE

In contrast to prior global studies, this analysis suggests no clinically significant decline in sperm concentration among confirmed fertile men and the general male US population without known infertility. Although these findings provide some reassurance against a widespread rapid decline, further studies are necessary to better understand this important topic.

Spatiotemporal trends in human semen quality

Over the past four decades, studies of various designs have reported spatial and temporal trends in human semen quality. Several standardized-methodology studies in homogeneous populations that compare specific cities within a country or a continent provide clear evidence of geographical differences in sperm production, even over short distances within the same country. Human sperm production is widely believed to be declining over time, but evidence from the scientific literature is less clear. Studies based on repeated cross-sectional data from a single centre have shown mixed results. Among the numerous retrospective studies conducted in a single centre, only some included homogeneous groups of men and appropriate methods, and most of them suggest a temporal decrease in human sperm production in the geographical areas considered. Conclusions reporting temporal trends in sperm production that came from existing retrospective multicentre studies based on individual semen data and those using means, medians or estimates of sperm production are questionable, owing to intrinsic limitations in the studies performed. Regardless of study design, studies on the percentage of motile or morphologically normal spermatozoa are still limited by the inherent variability in assessment. Overall, available data do not enable us to conclude that human semen quality is deteriorating worldwide or in the Western world, but that a trend is observed in some specific areas. To understand these trends and contrasts in sperm and semen quality, prospective studies should be encouraged and combined with assessment of the male exposome.

Several studies over the past few decades have suggested that sperm quality varies by geographical region and might be subject to a temporal decline worldwide. However, the data supporting these conclusions have come from studies of various methodologies and heterogeneous populations, making them unreliable. In this in-depth Review, Chevrier and colleagues discuss the data surrounding discussion of spatiotemporal trends in semen parameters and consider how these trends and the factors promoting them interact.

The vast literature on human semen quality trends is extremely heterogeneous in terms of the populations studied and study designs, and so these studies have been unable to draw firm conclusions.

Understanding the data around spatiotemporal semen trends requires a focus on the methodological choices and application of criteria to filter findings from the studies with optimal design.

Numerous appropriately designed studies suggest unambiguous geographical contrasts in human sperm production; however, evidence of a decline in sperm production is reliable only in specific populations and cities in which studies with a complete set of quality criteria have been conducted.

By contrast, suggestions of a worldwide drop in human semen quality on the basis of retrospective multicentre studies cannot be substantiated, owing to intrinsic limitations in the studies performed.

Many and varied factors of variation, in particular the diverse modalities of assessment, do not enable us to conclude that clear temporal trends of sperm motility and normal morphology are present.

Progress in our understanding of the highlighted trends and their causal factors requires prospective studies that minimize all known biases combined with the assessment of men’s exposome.

Metabolic diseases affect male reproduction and induce signatures in gametes that may compromise the offspring health

The most prevalent diseases worldwide are non-communicable such as obesity and type 2 diabetes. Noteworthy, the prevalence of obesity and type 2 diabetes is expected to steadily increase in the next decades, mostly fueled by bad feeding habits, stress, and sedentarism. The reproductive function of individuals is severely affected by abnormal metabolic environments, both at mechanical and biochemical levels. Along with mechanical dysfunctions, and decreased sperm quality (promoted both directly and indirectly by metabolic abnormalities), several studies have already reported the potentially harmful effects of metabolic disorders in the genetic and epigenetic cargo of spermatozoa, and the epigenetic inheritance of molecular signatures induced by metabolic profile (paternal diet, obesity, and diabetes). The inheritance of epigenetic factors towards the development of metabolic abnormalities means that more people in reproductive age can potentially suffer from these disorders and for longer periods. In its turn, these individuals can also transmit this (epi)genetic information to future generations, creating a vicious cycle. In this review, we collect the reported harmful effects related to acquired metabolic disorders and diet in sperm parameters and male reproductive potential. Besides, we will discuss the novel findings regarding paternal epigenetic inheritance, particularly the ones induced by paternal diet rich in fats, obesity, and type 2 diabetes. We analyze the data attained with in vitro and animal models as well as in long-term transgenerational population studies. Although the findings on this topic are very recent, epigenetic inheritance of metabolic disease has a huge societal impact, which may be crucial to tackle the 'fat epidemic' efficiently.

Gonadotoxic Effects of DBCP: A Historical Review and Current Concepts

Dibromo-chloro-propane (DBCP), a persistent liphophilic brominated organochlorine, has been produced for agricultural purposes as a nematocide since the 1950s. Widespread use due to its effectiveness as a pesticide continued until the late 1970s when early reports of its toxicity emerged from the laboratories, particularly its impact on spermatogenesis and other adverse reproductive health effects. Since then innumerable cases and studies have surfaced with clear impact after exposure to DBCP, however, the sustained effect of this exposure has yet to be completely understood. As a result of these studies, environmental agencies banned almost all agricultural uses of DBCP in the United States in the late 1970s. This review will try to balance the known toxicity of DBCP with a scientific assessment of published data and a summary of the legal issues that have resulted.

Environmental- and injury-related epidemic-assistance investigations, 1946-2005

This paper summarizes environmental investigations (n = 458) conducted during the first 60 years of the epidemic-assistance investigation program at the Centers for Disease Control and Prevention. These investigations were grouped into 10 categories: toxic chemicals (n = 102), indoor air quality and outdoor air toxics (n = 21), new or rare epidemic diseases and unexplained syndromes (n = 29), natural disasters (n = 81), terrorism and unintentional human-made disasters (n = 9), substance use and abuse (n = 13), environmental aspects of infectious disease (n = 132), those affecting neonates and infants (n = 11), violence and injuries (n = 51), and miscellaneous (n = 9). Among the most important or prominent were studies of lead and arsenic toxicity at smelters, mercury in paint and beauty creams, dioxin in waste oil in Missouri, polychlorinated biphenyls and multiple other toxic chemicals, global pesticide poisoning outbreaks, hepatic angiosarcoma among vinyl chloride workers, toxic oil syndrome in Spain, eosinophilia-myalgia syndrome from contaminated L-tryptophan, diethylene glycol poisoning in Haiti, aflatoxicosis in Kenya, Gulf War illness among veterans, impact and needs assessments during natural disasters (e.g., Hurricane Katrina (2005) and the Mount St. Helens volcano eruptions (1980)), risk factors for heat-related mortality, domestic and international terrorist attacks, Parkinsonism related to 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in California, and unintentional injury- and violence-related events.

Health effects classification and its role in the derivation of minimal risk levels: Reproductive and endocrine effects

The Agency for Toxic Substances and Disease Registry (ATSDR) derives health-based guidance values called minimal risk levels (MRLs) to assist with assessment of risks posed by exposures to hazardous chemicals. From the total of 326 MRLs currently posted on ATSDR's web site (www.atsdr.cdc.gov), 14 and 5 MRLs are based on reproductive and endocrine endpoints, respectively. The paper also describes the ranking of effects into less serious and serious categories according to ATSDR's Guidance for Developing Toxicological Profiles, endpoints used for the MRLs derivation, and the use of uncertainty factors.

Pesticides and children

Prevention and control of damage to health, crops, and property by insects, fungi, and noxious weeds are the major goals of pesticide applications. As with use of any biologically active agent, pesticides have unwanted side-effects. In this review, we will examine the thesis that adverse pesticide effects are more likely to occur in children who are at special developmental and behavioral risk. Children's exposures to pesticides in the rural and urban settings and differences in their exposure patterns are discussed. The relative frequency of pesticide poisoning in children is examined. In this connection, most reported acute pesticide poisonings occur in children younger than age 5. The possible epidemiological relationships between parental pesticide use or exposure and the risk of adverse reproductive outcomes and childhood cancer are discussed. The level of consensus among these studies is examined. Current concerns regarding neurobehavioral toxicity and endocrine disruption in juxtaposition to the relative paucity of toxicant mechanism-based studies of children are explored.

Human reproductive system disturbances and pesticide exposure in Brazil

The observation of reproductive disturbances in humans and in the wildlife has been reported in the last decade in different countries. Exposure to different chemicals possibly acting in the endocrine system or endocrine disruptors, including pesticides, has been a hypothesis raised to explain the observed changes. This paper aimed to present results of an epidemiological ecologic study carried out to explore population data on pesticides exposure in selected Brazilian states in the eighties and human reproductive outcomes in the nineties. Pearson correlation coefficients were ascertained between available data pesticides sales in eleven states in Brazil in 1985 and selected further reproductive outcomes or their surrogates. Moderate to high correlations were observed to infertility, testis, breast, prostate and ovarian cancer mortality. Despite the restrains of ecologic studies to establish cause-effect relationships, the observed results are in agreement with evidence supporting a possible association between pesticides exposure and the analyzed reproductive outcomes.

Reproductive toxicity of DDT in adult male rats

The reproductive toxicity of DDT was investigated in adult male rats exposed to 50 and 100 mg/kg body weight (b.wt) day(-1) for 10 successive days. Compared with control animals, administration of DDT led to a dose-dependent reduction of testicular weight and the number as well as the percentage of motile spermatozoa in the epididymis. Testicular histological observations revealed also a marked loss of gametes in the lumen of seminiferous tubules. In DDT-treated rats, the seminal vesicles weights dropped significantly, resulting from a decrease of testosterone production by testes, whereas serum LH and FSH increased after pesticide exposure. This increase of gonadotrophin levels may be related to an impairment of the negative feedback exerted by the steroid on the hypothalamic--pituitary axis. It is concluded that DDT induced adverse effects on male rat fertility by acting directly on the testes and altering the neuroendocrine function.

Azoospermia and oligospermia among a large cohort of DBCP applicators in 12 countries

Azoospermia and oligospermia have been well demonstrated among workers exposed to 1,2-dibromo-3-chloropropane (DBCP) in manufacturing and formulation of this pesticide. After DBCP was banned in the United States in the late 1970s, two American companies continued to export it to many less developed countries. In the early to mid-1990s, attorneys assembled a cohort of approximately 26,400 male plaintiffs who, as workers on banana and pineapple plantations in 12 of these countries, had been exposed to DBCP, primarily during its application. These attorneys, for the purpose of a lawsuit against the two American companies, developed from interrogatories a database on these men that included information about stated periods of occupational DBCP exposure. Seminal fluid analysis results were also entered into the database. Analyzing information in this database, the authors found that, after a median exposure to DBCP of three years, 64.3% of these men overall, and 90.1% of men studied from the Philippines, had azoospermia or oligospermia. The mean number of children reported by the men was 2.5 overall. The percentage of men with no children was 28.5% overall. This report represents the largest cohort of DBCP-exposed workers in which adverse reproductive health effects have been described, and the first report of the adverse effects on the reproductive health of workers exposed to DBCP primarily through its application in a cohort of this size. This serious and extensive occurrence of adverse reproductive health effects due to the export of a hazardous pesticide before and after its ban in the United States illustrates a number of needs for monitoring, research, education, and policy development.

Dibromochloropropane: epidemiological findings and current questions

Dibromochloropropane, DBCP, has had a seminal role in our current understanding of how to prevent chemical risks to health. Early toxicological studies showed its special impact on the testes, and detection of its mutagenic potency was soon followed by demonstration of its carcinogenicity to animals. Its commercial use as a useful nematocide ignored, at first, these warnings from the laboratory. When production workers, first in California and then in Israel, found they were sterile as a result of their exposure, this was convincing evidence that prevention had failed. The evidence, azospermia, oligospermia, and gonadotrophin response to testicular damage, were found first in production workers. In agricultural applicators in California who used the material, decreased sperm count and increased gonadotrophin levels were found. While production in California, Texas, and Israel was halted, studies continued and so, it seems, did use. Our first Israeli study was of workers on banana crops, and we found convincing evidence of increased spontaneous abortion in their family histories. Follow-up studies among production workers in Israel showed that some recovered testicular function, but among their offspring, otherwise in good health, there was a predominance of females. Those who did not recover from azospermia were those with high levels of follicle stimulating hormone. However data for production workers did not show increased spontaneous abortion. Nor have any studies so far shown increased birth defects or increased infant mortality. Unfavorable reproductive outcomes can be due to other agents, as shown by sprayers in Dutch orchards having hypofecundity (increased interpregnancy period) and sex ratio changes; but the agents responsible have not yet been identified. These experiences have lead to the general acceptance of some implications: (1) Paternal exposures can lead to a variety of unfavorable effects on reproductive outcome, including infertility, spontaneous abortion, and altered sex ratio. (2) Patterns of effects of potent agents in production workers and in applicators or users of chemicals may differ. (3) Although human carcinogenesis has not yet been confirmed, unfavorable reproductive outcomes are a reasonable early indicator of such risk. (4) Shifts in sex ratios of populations may be a subtle sign of more serious risks. (5) Continued use of an agent such as this under circumstances in which these UROs cannot be prevented is unconscionable.

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.

Time to pregnancy and occupational exposure to pesticides in fruit growers in The Netherlands

OBJECTIVES

Although pesticides are regularly used in agriculture, relatively little is known about possible adverse health effects, especially reproductive effects, due to occupational exposure. This explorative study investigates the relation between exposure of the fruit grower to pesticides and fecundability (probability of pregnancy) in a population of fruit growers.

METHODS

The analysis is based on self reported data and includes 91 pregnancies during 1978-1990 of 43 couples. Cox' proportional hazards model was used to analyse time to pregnancy after correction for gravidity and consultation with a physician for fertility problems.

RESULTS AND CONCLUSIONS

Application of pesticides solely by the owner was associated with a long time to pregnancy, resulting in a fecundability ratio of 0.46 (95% confidence interval (95% CI) 0.28-0.77). Similarly a low spraying velocity (< or = 1.5 hectares/h) resulted in a fecundability ratio of 0.47 (95% CI 0.29-0.76) and is associated with the use of older spraying techniques and tractors without a cabin. These factors were assumed to cause high exposure, which was confirmed by exposure measurements in the field. The effect of high exposure was mainly apparent if the couple had intended to become pregnant in the period from March-November (fecundability ratio 0.42, 95% CI 0.20-0.92). This is the period in which pesticides are applied. Out of the spraying season the effect of a high exposure was absent (fecundability ratio 0.82, 95% CI 0.33-2.02). In the high exposure group 28% of the pregnancies had been preceded by consulting a physician because of fertility problems, compared with 8% in the low exposure group. These findings indicate that an adverse effect of exposure to pesticides on fecundability is likely.

Environmental equity and pesticide exposure

Although people of color and low-income groups bear a disproportionate share of the health risks from exposure to pesticides, research attention has been meager, and data on acute and chronic health effects related to their toxic exposures are generally lacking. Increased resources are needed both to study this issue and to mitigate problems already identified. People of color should be a major research focus, with priority on long-term effects, particularly cancer, neurodevelopmental and neurobehavioral effects, long-term neurological dysfunction, and reproductive outcome. Suitable populations at high risk that have not been studied include noncertified pesticide applicators and seasonal and migrant farm workers, including children.

Male infertility: current concepts

The purpose of the article is to review the current concepts regarding the etiology and treatment of male-factor infertility. The following general conclusions can be drawn: (a) conventional parameters for sperm quality and male fertility are inadequate and any assessment should involve several different tests of sperm cell function to increase the fertility prognosis; (b) the causes of disturbed sperm quality are still poorly understood; (c) the role of the varicocele is still controversial but some of the discrepancies reported in the literature may be explained by the negative influence of other factors such as smoking, epididymal pathology or glandular infections operating either in conjunction or independent of the varicocele; (d) the role of chronic inflammatory processes in the reproductive organs, in particular the involvement of chronic chlamydial infections, has been underestimated, largely because it is often asymptomatic and difficult to demonstrate objectively; (e) partial androgen insensitivity may account for a significant number of cases of severe oligozoospermia; (f) no major advances have been made in the medical treatment of poor sperm quality; (g) assisted fertilization techniques such as IVF and GIFT offer encouraging possibilities for the treatment of male-factor infertility; and (h) recent advances in microsurgical techniques are increasing the treatment possibilities for certain forms of obstructive azoospermia and severe oligozoospermia.

The effects of 1,2-dibromo-3-chloropropane (DBCP) on general toxicity and gonadotoxicity in rats

This study was set to determine if there is a correlation between the general toxic effect and the gonadotoxic effect of DBCP on male rats. Groups of male rats were injected with a single dose of DBCP (50 mg kg-1) dissolved in dimethylsulfoxide (DMSO). Twenty four hours, one and four weeks post injection animals were sacrificed. Blood was collected for enzymes' and hormones' assays. Organs were weighed and testes were taken for histological examination and sperm counts. The results showed that DBCP at a dose of 50 mg kg-1 had a general toxic effect expressed by reduction in body and liver weights and reduced activities of serum glutamic oxaloacetic transaminase (SGOT) and serum glutamic pyruvic transaminase (SGPT). These changes show a tendency to revert to normal values with time. On the other hand, gonadotoxic effects increase in severity with time. The weight of testes and epididymides were reduced, sperm counts decreased and histological damage advanced, and FSH and LH blood levels increased 4 weeks post injection. It seems that in rats the gonadotoxic effect of DBCP is dissociated from the general toxic effects.

International Commission for Protection Against Environmental Mutagens and Carcinogens. ICPEMC publication No. 18. Review of the genotoxicity and carcinogenicity of antischistosomal drugs; is there a case for a study of mutation epidemiology? Report of a task group on mutagenic antischistosomals

One of the interests of ICPEMC is to identify situations in which the possible induction of inherited defects in man by mutagen exposure could actually be studied. The large-scale use of mutagenic drugs in field programmes against schistosomiasis, mainly during the 1970's, was considered a possible case. An ICPEMC task group approached the problem by (1) updating the genetic toxicology data base for antischistosomal drugs, and (2) reviewing possible study areas. Expertise was combined from genetic toxicology, mutation epidemiology and tropical medicine. It was considered that: (a) if any, hycanthone would be the most appropriate candidate drug for study; (b) it would be virtually impossible to meet the basic requirements of an appropriate mutation epidemiology study, in endemic countries; (c) as more defined genetic endpoints would be selected (e.g. sentinel phenotypes) the required large sample sizes would seem prohibitive, since documentation on past programmes is limited and local demography would render the reliable tracking of substantial numbers of offspring of treated persons an almost impossible task; (d) in most endemic countries proper diagnosis and registration of inherited defects is largely lacking; (e) the problems encountered in demonstrating inherited effects in humans after heavy or chronic exposure to established animal mutagens such as ionizing radiation and cancer chemotherapy, in combination with the ambiguous nature of the animal germ cell data with hycanthone, do not particularly warrant large expectations; (f) since non-mutagenic antischistosomal drugs are now in use, the problem is academic and of low priority in the endemic countries whose medical and research resources are often limited. Thus, studying offspring of hycanthone-treated people to demonstrate the mutagenic potential of the drug in man is not a viable enterprise.

Cytogenetic assays in genotoxic studies: somatic cell effects of benzene and germinal cell effects of dibromochloropropane

We have reviewed the results of our cytogenetic studies to evaluate the usefulness of these assays in genotoxic studies. In one study, we observed unusual dose-response in lymphocyte chromosome aberration frequencies after exposure of mice to low doses of a chemical mixture (benzene, chloroprene, epichlorohydrin, and xylene). The frequency in the high dose group is lower than those of the medium and low dose groups. This reduction of genotoxicity is correlated with a significant induction of a detoxifying enzyme, glutathione-S-transferase. The data also suggest that extrapolation of effects from high to low doses for risk assessment may be erroneous. Using benzene as a model clastogen, we found that the clastogenic effect persists for a long time after termination of exposure in mice. This phenomenon is probably due to a gradual release of benzene from absorption of the chemical in body fat. In an inhalation study, we observed that chromosome aberrations are induced in mice after exposure to benzene at below the occupational exposure limit of 1 ppm. Since benzene is a ubiquitous environmental contaminant, it may interact with other environmental agents to modify its genotoxic effects. We found that a nongenotoxic drug, praziquantel, and a free radical scavenger, DMSO, can enhance or reduce respectively the clastogenic activities of benzene in mice. Both modifying agents acted by altering the metabolic pathways of benzene. In a study with rats, we showed that carcinogenic doses of benzene can induce chromosome aberrations in lymphocytes of rats long before the expression of cancer. With dibromochloropropane, we observed that this chemical can induce dominant lethality in rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Genetic toxicology of 1,2-dibromo-3-chloropropane (DBCP)

1,2-Dibromo-3-chloropropane (DBCP) is a nematocide, which has been used extensively as a soil fumigant in agriculture. Since sterility was found among male workers involved in the manufacture of DBCP, great concern has been focused on the genetic hazards of DBCP. DBCP gave positive results in many tests such as microbial, in vitro cytogenetics, and Drosophila studies. In mammalian test systems, DBCP caused chromosomal aberrations in the bone marrow cells and dominant-lethal mutations in germ cells in rats. In mice, there were no signs of DBCP-induced heritable mutation in germ cells, although point mutations were detected in somatic cells. The occurrence of Y-chromosomal non-disjunction was indicated in DBCP-exposed male workers by an increased number of sperm containing 2 Y-chromosomes.

Chromosome aberrations in spermatogonia and sperm abnormalities in Curacron-treated mice

Curacron is an organophosphorus pesticide widely used in cotton fields. In order to assay its mutagenic potential in mammalian germ cells chromosomal aberrations in spermatogonial cells and sperm abnormalities were examined in mice after Curacron treatment. For studying chromosomal aberrations mice were treated both acutely (single treatment) and subacutely (for 5 consecutive days) with 3 dose levels of Curacron, 12, 36 and 72 mg/kg. Curacron was found to produce a significant increase in structural chromosomal aberrations after acute and subacute treatments. This increase was dose-dependent. A dose-dependent inhibition in mitotic activity in spermatogonia was also found. For studying sperm abnormalities mice were treated for 5 consecutive days with 20, 40 and 60 mg/kg. Morphological sperm abnormalities increased significantly after treatment with Curacron. The increase was dose-dependent. An inhibition of 40.2% in sperm count and of 74.5% in sperm motility occurred after treatment with 60 mg/kg Curacron. These results show that Curacron has a damaging effect on spermatogonial cells as well as on sperm morphology.

A genotoxic study of metal workers exposed to trichloroethylene. Sperm parameters and chromosome aberrations in lymphocytes

Metal workers exposed to trichloroethylene for the degreasing of metals were studied to evaluate the genotoxicity of this exposure. For 15 workers presently exposed to high doses of trichloroethylene there was no difference from unexposed persons with respect to sperm count and morphology, and a small increase of two fluorescent bodies (YFF%) in spermatozoa. In contrast, there was a highly significant increase in frequency of structural aberrations (breaks, gaps, translocation, deletions, inversions) and hyperdiploid cells in cultured lymphocytes from trichloroethylene degreasers. As control groups, physicians from chemically non-exposed surroundings and a concurrently sampled reference from cytogenetic investigations were used. This study indicates positive correlations between exposure to trichloroethylene and somatic chromosome aberrations, whereas no effect on male germ cells could be demonstrated.

Infertility, chemical exposure, and farming in Iowa: absence of an association

An increased incidence of infertility and abnormal semen analysis has been described in men and experimental animals exposed to agricultural chemicals. These reports led us to review the records of 382 consecutive new male patients who had semen analyses performed at the University of Iowa Hospitals and Clinics. No significant differences in the incidence of abnormalities in either the physical examination or the semen analysis were discovered with respect to occupation or possible exposure to chemical agents.

Phthalate esters and semen quality parameters

Analysis of reports in the world's literature suggests that average sperm densities for groups of unselected males were relatively constant at about 108 million cells per ml prior to 1950. Subsequent to that time mean sperm densities appear to have declined. Regression analysis indicates the existence of significant negative correlations between mean sperm densities and production of synthetic organic chemicals among other parameters. Phthalate esters are one class of large volume organic chemicals that are known to disturb testicular function in laboratory animals. These compounds are also the most abundant man-made chemicals in the environment. Plots of the concentration of dibutylphthalate in the cellular fraction of ejaculates against either the sperm density or the total number of sperm for the same ejaculates gave two clusters of points. These clusters suggest the existence of two or more populations vis à vis phthalate metabolism; both of which show a negative correlation between phthalate concentration and sperm production.

Twinning rates by residence in Denmark 1978 to 1982

It has been suggested in the literature that twinning rates are reduced by psychosocial stress associated with urban life. No support for this hypothesis was found in a study based upon the 5,762 twins and 280,158 singletons that were born in Denmark in the period 1978 to 1982.

Risk factors in male infertility: a case-control study

A case-control study was undertaken to evaluate environmental risk factors potentially involved in male infertility. One hundred twelve azoospermic or oligospermic subjects and 127 controls were interviewed, before sperm count results were available, about coffee and alcohol consumption, smoking habits, x-ray exposure, usual sitting posture, drug consumption, other nonoccupational risk factors, socioeconomic status, education level, and occupational history. An unmatched analysis was then conducted. None of the occupational risk factors appeared to be related to azoospermia or oligospermia. A high relative risk was associated with (1) occupation in the radioelectric industry, (2) nonsedentary clerical workers, (3) clerical work in the typographic industry, and (4) occupation in the textile industry, but none of these figures were statistically significant. Because of the population from which cases and controls were drawn, certain occupational risks could not be investigated in this study, e.g., exposure of agricultural workers to chemicals.

Spontaneous abortions among dental assistants, factory workers, painters, and gardening workers: a follow up study

This investigation was conducted to test the hypothesis that exposure of pregnant women to chemicals increases the risk of spontaneous abortion. The chemical risk factors under study to which dental assistants, factory workers, painters, and gardening workers were exposed were nitrous oxide, inorganic mercury, organic solvents, and pesticides. The study was carried out within the Danish county of Funen. It included all dental assistants employed in private or public dentistry. A comparable reference group was made up by employees less exposed to chemicals. Further study groups included all women painters within the county, women factory workers from selected factories, and about 50% of the women gardening workers within the county. Shop assistants and packers formed their control group. Information was obtained through a postal questionnaire study in May 1980 and from hospital records. Only among factory workers and painters was the odds ratio of spontaneous abortion found to be significantly increased. Neither among these women nor among dental assistants and gardening workers, however, was the reported exposure to any single chemical during pregnancy associated with a significantly increased odds ratio of spontaneous abortion.

Chronic disease in the workplace and the environment. Reproductive problems: fertility, teratogenesis, and mutagenesis

While information on the toxic attributes of specific compounds is voluminous, most of it is inconclusive regarding the risks of reproductive problems. Observations that seem to suggest freedom from risk are often insufficient to conclude they are not due to chance, and when clinically outstanding effects are apparent, the number of observations is often so small that it is probable that their importance has been overestimated. This presentation focuses on the process rather than specific agents on the persons at risk, the types of exposures, the possible nature of the hazards, the factors which impinge on this risk, and finally, the additional information required to make risk estimation more precise. It seeks to identify strategies which will improve the quality of information routinely collected, address the mensurational problems associated with the estimation of exposures, and permit earlier recognition of the especially vulnerable.

Reproductive outcomes in families of DBCP-exposed men

The families of 30 workers employed in a plant which, until 1977, had produced 1,2-dibromo-3-chloropropane (DBCP), have been monitored for 5 yr. Thirteen men who were azoospermic in 1977 had more than 100 hr of estimated exposure in production; of these, 4 have recovered spermatogenesis and 2 have fathered 4 female children. Eight men who were oligospermic in 1977 had been exposed for 34-95 hr; of 8 children subsequently born to their wives, 6 were female. Five men with exposure times estimated to be between 10 and 60 hr were normospermic in 1977, and of 5 children subsequently born to them, 4 were male and 1 was female. The outcome of the pregnancies among families of 4 non-exposed men and of exposed men prior to exposure resulted in 27 male and 24 female children. No increase in spontaneous abortion occurred in pregnancies fathered by exposed men. Four infant deaths and 5 congenital anomalies occurred among the babies born of unexposed pregnancies. No infant or fetal deaths and no congenital abnormalities occurred among children born to wives of men after the men were exposed. The birth of at least 10 females of 12 babies born to wives of exposed men with evidence of testicular toxicity would be expected according to binomial probabilities with a P = .015. The children born to families of exposed workers are in good health. A possible explanation for the observed female sex predominance might be Y chromosome non-disjunction, which was reported to be more frequent in sperm of DBCP workers by Kapp et al.

Lack of effect of dibromochloropropane on the mouse testis

A single intraperitoneal injection of (101 X C3Hf)F male mice with 110 mg/kg of 1,2-dibromo-3-chloropropane (DBCP) showed no effect on spermatogonial stem cells or on differentiating spermatogonia as measured by cell counts made 3, 5, and 8 days after injection.

Mortality experience of employees with occupational exposure to DBCP

Concern about the carcinogenic potential of 1,2-dibromo-3-chloropropane(DBCP) has arisen recently, focusing on six organ sites: stomach, liver, kidney, lung, testes, and skin. To examine the mortality experience of persons potentially exposed, a cohort of 550 employees involved in production and formulation from 1957 to 1976 was defined. A total of 35 deaths was observed through 1979 (39.2 expected). No statistically significant excess was observed for any cause of death. No cancer deaths were noted for five of the hypothesized sites. For the lung cancer category, five deaths were observed (2.7 expected, P greater than .135), two of which occurred in a subgroup directly exposed for at least 1 yr (0.5 expected, P greater than .077). Aside from arsenicals exposure, potential confounding resulting from smoking or multiple chemical exposures could not be evaluated.

The effect of testicular x-irradiation on spermatogenesis in man. A comparison with the mouse

Existing data concerning the effects of x-irradiation on spermatogenesis in man were analyzed and the results were compared to published data on the mouse. Testicular x-irradiation produced a transient, but substantial, suppression of sperm counts in man, with an ED50 near 11 rad. The length of time to recovery was proportional to the irradiation dose. The ED50 for suppression of type A spermatogonia following radiation exposure in man was similar (9.7 rad), although the response curves for spermatogonia and sperm count were matogonia in the mouse was parallel to that found in man, but with an ED 50 of 30.0 rad. These results suggest that, compared to the mouse, spermatogenesis in man is approximately 3.1 times more sensitive to ionizing irradiation.

Mutagenicity, carcinogenicity and reproductive effects of dibromochloropropane (DBCP)

Dibromochloropropane (DBCP), a brominated organochlorine nematocide, has been used since the mid-1950s. Its primary value was its effectiveness on perennial crops without damaging the plants. DBCP also had less acute toxicity than earlier soil fumigants such as ethylene dibromide. DBCP became widely used on citrus, grapes, peaches, pineapple, soybeans and tomatoes. In Central America and Israel, banana trees were treated with DBCP. By 1975, 25 million pounds were being produced in the U.S. per year. The majority of U.S. production was applied in the Pacific Coast states, particularly California's San Joaquin Valley, and the Southern Atlantic Coast states. Animal studies in the early 1960s revealed hepatic and renal effects and testicular atrophy in DBCP-treated rates. Testicular atrophy was noted at the lowest exposure level tested (5 ppm). In 1973, DBCP was found to cause gastric carcinoma in mice and rats, and mammary adenocarcinoma in rats. A later study linked DBCP to nasal cavity tumors in rats. DBCP is an in vitro mutagen after activation with microsomal enzymes. A dominant lethal effect has been observed in rats. DBCP also induces increases in sister-chromatid exchanges and chromosomal aberrations. Mean fetal weight and maternal weight gain is decreased in pregnant rats exposed to DBCP. In mid-1977, employees in a California pesticide formulation plant were discovered to be infertile. Further investigations documented azoospermia and oligospermia among many of the workers handling DBCP. These findings were duplicated in other DBCP production plants. In the United States, the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) rapidly restricted the use of DBCP. The application of DBCP to all but pineapples in Hawaii was banned by the EPA in 1979. In 1982, the EPA exempted the peach crop in the Southern Atlantic coast states from the ban on DBCP use. Prior to the 1977 events, no such agent in workplace concentrations had been shown to produce infertility and sterility in otherwise healthy men. Subsequently, the interest in DBCP had led to many other studies, and has contributed to a heightened awareness about workplace hazards to both the male and female reproductive systems. This article will review the current state of knowledge of the in vitro, animal, and human toxicology of DBCP.

Estimation of the increased risk of human infertility from alterations in semen characteristics

Although many toxicants lower sperm counts in exposed men, there is no means of estimating the resulting increase in infertility. A mathematical model was developed to provide such estimates, using sperm counts (i.e., concentration) as an indicator of fertility potential. Continuous functions were fit to published distributions of sperm counts of men from fertile and infertile couples. A distribution of sperm counts for the overall population was constructed from these two functions. Equations were derived for calculating the infertility risk for a man with a given sperm count and the incidence of infertility in an exposed population. The increase in infertility was calculated for a proportional reduction of all sperm counts within a population and for a group of workers exposed to dibromochloropropane.

An evaluation of human sperm as indicators of chemically induced alterations of spermatogenic function. A report of the U.S. Environmental Protection Agency Gene-Tox Program

To evaluate the utility of sperm tests as indicators of chemical effects on human spermatogenesis, the literature on 4 sperm tests used to assess chemically induced testicular dysfunction was reviewed. The tests surveyed included sperm count, motility, morphology (seminal cytology), and double Y-body (a fluorescence-based test thought to detect Y-chromosomal nondisjunction). There were 132 papers that provided sufficient data for evaluation. These reports encompassed 89 different chemical exposures: 53 were to single agents; 14 to complex mixtures; and 22 to combinations of 2 or more identified agents. Approximately 85% of the exposures were to experimental or therapeutic drugs, 10% were to occupational or environmental agents, and 5% were to drugs for personal use. The most common sperm parameter studied was sperm count (for 87 of the 89 exposures reviewed). Sperm motility was evaluated for 59 exposures, morphology for 44, and double Y-bodies for only 4. The 89 exposures reviewed were grouped into 4 classes: those which adversely effected spermatogenesis, as measured by one or more of the sperm tests (52); those suggestive of improving semen quality (11); those showing inconclusive evidence of adverse effects from exposure (14); and those showing no significant changes (12). Since the reviewed reports had a large variety of study designs, and since every attempt was made to include all reports with interpretable data, these classifications were based on reviewing committee decisions rather than on uniform statistical criteria. This review gives strong evidence that human sperm tests can be used to identify chemicals that affect sperm production, but because of our limited understanding of underlying mechanisms, the extent to which they can detect mutagens, carcinogens or agents that affect fertility remains uncertain. For the very few agents studied with both human and mouse sperm tests, similar test-responses were seen; thus sperm tests in mice and other laboratory mammals may have a potential role in hazard identification. An overall comparison of the 4 human sperm tests suggests that no one test is biologically more responsive than another; all of them may thus be needed when testing for chemically induced changes from agents of unknown activity. This review also gives evidence that sperm tests can be used to assess the extent and the potential reversibility of induced spermatogenic damage. The reviewing committee recommends further studies to determine (a) the dose-response characteristics of the human sperm tests, (b) details of the reversibility of induced changes with time after exposure, (c) the relative responses in the 4 sperm tests in exposed individuals, (d) the mechanism of action, (e) the biological and genetic implications of chemically induced effects, and (f) the comparison of responses among different species for risk assessment. The reviewing committee outlines specific considerations for planning new sperm studies on chemically exposed men.

Second survey of secular trends in twinning rates

A study has been made of twinning rates throughout the world over the last two decades. There has been a decline in age-specific dizygotic twinning rates in almost all of the developed countries during this period. Exceptions to this trend are provided by the United States, where the only decline in twinning rates in the last two decades was in births to older women in the 1960s, and by Czechoslovakia, Hungary and Bulgaria, where an initial decline in twinning during the 1960s was followed by stable twinning rates.

It is suggested that the cause may be some form of environmental pollutant, perhaps a pesticide, which has been the subject of restrictive legislation first in the United States and later in the three Communist countries. Possibly the cause of this decline may be identified by a study of such legislation.

This seems to be the first study of twinning rates in Central and South America. The low twinning rates in some of the countries there may indicate the genetic affiliations of their inhabitants with those (of Mongoloid origin) of countries in the Far East.

Dominant lethal studies in rats with 1,2-dibromo-3-chloropropane and its structurally related compounds

Dominant lethal studies were conducted in SD male rats with 5 halogenated 3-carbon compounds that are structurally similar to a known mutagen 1,2-dibromo-3-chloropropane (DBCP). 1,2,3-Tribromopropane induced dominant lethal mutation especially in the early spermatid stage. This finding was almost the same as that obtained after DBCP treatment. The estimated dominant lethal mutation index of a group treated with 1,2-dibromopropane was marginal at week 1 of testing. On the other hand, bromopropane, 1,2,3-trichloropropane and 1-chloropropane produced negative responses for induction of dominant lethals.

Testicular function among epichlorohydrin workers

Epichlorohydrin (1,2-epoxy-3-chloropropane) (ECH) is a colourless liquid used in the production of insecticides, agricultural chemicals, epoxy resins, and many other productions. It is highly reactive and an alkylating agent suspected of possessing carcinogenic properties in man. The results of a clinical-epidemiological investigation to ascertain whether exposure to ECH may be associated with sperm count suppression among ECH production workers at two chemical plants are presented. Medical histories and physical examinations with special emphasis on the genitourinary tract were completed on each participant. Blood samples and three semen specimens were also obtained. Since no internal control group were available, the data arising from this effort were analysed for each plant (plant A, 44 men; plant B, 84 men) using a control group of 90 chemical plants workers unexposed to any agents known to be toxic to the tests who were included in previous studies. This study provides no evidence that exposure to ECH at the concentrations existing at the two plants studied is responsible for sperm count suppression.

Dibromochloropropane (DBCP): a review

A highly persistent, lipophilic, brominated organochlorine which is effectively used against nematodes, dibromochloropropane (DBCP) has been produced for agriculture since 1955. In 1975, production of DBCP in the United States reached 25 million lbs. However, investigations with laboratory animals, some of which were published in the early 1960s, have shown that DBCP decreases sperm mobility and spermatogenesis, disturbs the estrous cycle, reduces phagocytosis by white blood cells, and induces malignant tumors. Later studies with procaryotic and eucaryotic cells, including human sperm, have demonstrated DBCP to be mutagenic and to effect the genome adversely. In 1977 many of the employees at the Occidental Chemical plant in Lathrop, California, who had handled DBCP, were found to be either azoospermic or oligospermic. Subsequent surveys of employees handling DBCP at other chemical plants confirmed these findings. In 1977 on edible crops and in 1979 DBCP per se was detected in well waters. As a result of these studies, the Occupational Safety and Health Administration (OSHA) and the Environmental Protection Agency (EPA) in 1977 promulgated regulations restricting the use and handling of DBCP. In 1979, the EPA banned almost all agricultural uses of DBCP.

Tris(dichloropropyl)phosphate, a mutagenic flame retardant: frequent cocurrence in human seminal plasma

Negative-chemical-ionization mass spectral screening of extracts of human seminal plasma has revealed a presence of a Cl7 ion cluster at a mass-to-charge ratio (m/z) of 463 in a significant number of the samples examined (34 out of 123). Experiments with different gases used to generate the negative-chemical-ionization plasma indicated that the ion at m/z 463 was a chloride adduca of a Cl6 molecule with a mass of 428 daltons. Negative-chemical-ionization mass measurement with ions from the iodoform mass spectrum used as reference peaks gave a mass of 427.882 daltons; C9H15PCl6 has a molecular weight of 427.883. Extraction of polyurethane foam with toluene produced an extract that consistently gave a negative-chemical-ionization spectrum containing an intense Cl7ion at m/z463. The component producing ion was isolated, and its proton nuclear magnetic resonance spectrum confirmed that it was tris (1,3-dichloro-2-propyl)phosphate, a mutagenic flame retardant. The negative-chemical-ionization screening evidence suggests that this flame retardant or its isomer tris(2,3-dichloro-l-propyl)phosphate, or both, are absorbved into the body from formulations in which they are used as flame retardants. Remedial action seems indicated to reduce human exposure to these compunds.

Secular changes in the twinning rate in Denmark 1931 to 1977

The present study examines secular changes in the rate of twinning in Denmark during the period of 1931-77. Total twinning (i.e., mono- and dizygotic twinning combined) declined from a crude rate of 15.0 twin births per 100 deliveries in 1931 to 9.6 twin births per 100 deliveries at the end of the period. After direct adjustment for maternal age and parity (between the years 1935 and 1965), a 22% decline in total twinning rates was noted. Estimates of the rates of dizygotic twinning over the same period, again adjusted for maternal age and parity, show a decline of 20%. Thus there is evidence of a real decline in twinning, independent of the effects of changing patterns of maternal age and parity. These findings are consistent with reports of a general decline in twinning rates from a number of other countries. The interpretation of such secular changes is a matter for speculation.