Fertility rates among lead workers and professional bus drivers: a comparative study

Derivation of benchmark doses for male reproductive toxicity in a subacute low-level Pb exposure model in rats

The objectives of the study were to simulate low-level Pb exposure scenario in an animal model and to examine reproductive adverse effects. Based on obtained data, we have performed Benchmark dose (BMD)-response modelling. Male Wistar rats were randomized in seven groups (n = 6): one control and six treated with: 0.1, 0.5, 1, 3, 7, and 15 mg Pb/kg body weight, daily for 28 days by oral gavage. The rats were sacrificed and the blood and testes were used for further analysis of testosterone levels in serum, testicular essential metal levels and histological analysis. The Pb treatment led to a dose-dependent decrease of serum testosterone levels with a negative trend (BMDI 0.17-6.13 mg Pb/kg). Increase of Zn (dose-dependent, BMDI 0.004-19.7 mg Pb/kg) and Cu and a decrease of Mn testicular levels were also detected with unscathed histology of the testes. The presented results might be used in further evaluation of the point of departure in human health risk assessment for Pb.

The Impact of the Flint Water Crisis on Fertility

Flint switched its public water source in April 2014, increasing exposure to lead and other contaminants. We compare the change in the fertility rate and in health at birth in Flint before and after the water switch to the changes in other cities in Michigan. We find that Flint fertility rates decreased by 12 % and that overall health at birth decreased. This effect on health at birth is a function of two countervailing mechanisms: (1) negative selection of less healthy embryos and fetuses not surviving (raising the average health of survivors), and (2) those who survived being scarred (decreasing average health). We untangle this to find a net of selection scarring effect of 5.4 % decrease in birth weight. Because of long-term effects of in utero exposure, these effects are likely lower bounds on the overall effects of this exposure.

Impaired hypothalamic-pituitary-testicular axis activity, spermatogenesis, and sperm function promote infertility in males with lead poisoning

Lead poisoning is a stealthy threat to human physiological systems as chronic exposure can remain asymptomatic for long periods of time before symptoms manifest. We presently review the biophysical mechanisms of lead poisoning that contribute to male infertility. Environmental and occupational exposure of lead may adversely affect the hypothalamic-pituitary-testicular axis, impairing the induction of spermatogenesis. Dysfunction at the reproductive axis, namely testosterone suppression, is most susceptible and irreversible during pubertal development. Lead poisoning also appears to directly impair the process of spermatogenesis itself as well as sperm function. Spermatogenesis issues may manifest as low sperm count and stem from reproductive axis dysfunction or testicular degeneration. Generation of excessive reactive oxygen species due to lead-associated oxidative stress can potentially affect sperm viability, motility, DNA fragmentation, membrane lipid peroxidation, capacitation, hyperactivation, acrosome reaction, and chemotaxis for sperm-oocyte fusion, all of which can contribute to deter fertilization. Reproductive toxicity has been tested through cross-sectional analysis studies in humans as well as in vivo and in vitro studies in animals.

Associated factors with male infertility: a case control study

OBJECTIVE

Sperm analysis is an important step to evaluate and diagnose male's infertility. The present study aimed to determine associated factors with males' infertility by using semen analysis.

MATERIALS AND METHODS

In this study 96 men were evaluated who attended to the infertility clinics of Ilam province, western Iran between May 2010 to May 2011. Semen analysis was done using the Weili Dynamic Sperm Analysis software adapted to the WHO classification. Based on movement and speed characters, sperms were classified to either A, B, C or D classes. Participants were stratified into two groups that called "Oligospermia (OS)" with sperm counts of less than 20 million in mL (n=48) and "Non-Oligospermia (NOS)" with values more than determined cutoff point (n=48).

RESULTS

The Mean age ±SD for OS and NOS group were 29.9 ±5.1 y and 31.17 ±5.24 y, respectively (p>0.05). Overall, 62.5% of OS and 31.2% of NOS were clinically infertile (OR=3.6, CI, 1.5-8.5, p=0.01). A significant difference was found between job and live ratio(A+B+C) in NOS group (F=2.8, p<0.05).

CONCLUSION

Prevalence of infertility was higher in the OS men compared to the NOS group. The main risk factors in the OS group were History of Varicocele surgery and residence site of patients that are totally similar to the NOS men. Further case-control studies and clinical trials are recommended to recognize infertility causes in men.

The role of MAPK and FAS death receptor pathways in testicular germ cell apoptosis induced by lead

The aim of the present study is to investigate gene expression involved in the signal pathway of MAPK and death signal receptor pathway of FAS in lead-induced apoptosis of testicular germ cells. First, cell viabilities were determined by MTT assay. Second, using single cell gel-electrophoresis test (comet assay) and TUNEL staining technique, apoptotic rate and cell apoptosis localization of testicular germ cells were measured in mice treated with 0.15%, 0.3%, and 0.6% lead, respectively. Third, the immunolocalization of K-ras, c-fos, Fas, and active caspase-3 proteins was determined by immunohistochemistry. Finally, changes in the translational levels of K-ras, c-fos, Fas, and active caspase-3 were further detected by western blot analysis. Our results showed that lead could significantly induce testicular germ cell apoptosis in a dose-dependent manner (P<0.01). The mechanisms were closely related to the increased expressions of K-ras, c-fos, Fas, and active caspase-3 in apoptotic germ cells. In conclusion, K-ras/c-fos and Fas/caspase-3 death signaling receptor pathways were involved in the lead-induced apoptosis of the testicular germ cells in mice.

Lead toxicity and chelation therapy

PURPOSE

Common sources of lead exposure, the primary clinical effects of lead toxicity, and current recommendations for managing lead toxicity, including chelation therapy, are reviewed.

SUMMARY

Common sources of lead exposure in children and adults include industrial and mining activities, paint, dust, soil, water, air, the workplace, food, trinkets, ethnic folk remedies, and cosmetics. The absorption and biological fate of lead are affected by a variety of factors, including an individual's nutritional status, health, and age. Children with a blood lead concentration of >10 microg/dL and adults with a blood lead concentration of > or = 45 mug/dL should undergo further evaluation. Symptoms and time to onset of symptoms postexposure may vary, and it can be difficult to identify the early, subtle neurologic effects of lead toxicity. The classic symptoms of lead toxicity generally correlate with blood lead concentrations of 25-50 microg/dL in children and 40-60 microg/dL in adults. Management of lead toxicity requires extensive risk assessment and caregiver education. Chelation is generally not indicated for adults with blood lead concentrations of < 45 microg/dL because of the potential risk of adverse drug events and concerns about remobilized lead, and chelation for children with blood lead concentrations of < 45 microg/dL remains controversial. Dimercaprol, edetate calcium disodium, and succimer are the three agents primarily used for chelation.

CONCLUSION

Lead toxicity remains a significant public health concern. Elimination of elevated blood lead levels in children can be accomplished by educating appropriate health care providers and caregivers, recognizing potential lead sources, and adopting aggressive prevention and case management measures.

Teratogen update: lead and pregnancy

This review focuses on the impacts of lead exposure on reproductive health and outcomes. High levels of paternal lead exposure (>40 microg/dl or >25 microg/dl for a period of years) appear to reduce fertility and to increase the risks of spontaneous abortion and reduced fetal growth (preterm delivery, low birth weight). Maternal blood lead levels of approximately 10 microg/dl have been linked to increased risks of pregnancy hypertension, spontaneous abortion, and reduced offspring neurobehavioral development. Somewhat higher maternal lead levels have been linked to reduced fetal growth. Some studies suggest a link between increased parental lead exposure and congenital malformations, although considerable uncertainty remains regarding the specific malformations and the dose-response relationships. Common methodological weaknesses of studies include potential exposure misclassifications due to the frequent unavailability of exposure biomarker measurements at biologically appropriate times and uncertainty regarding the best exposure biomarker(s) for the various outcomes. A special concern with regard to the pregnant woman is the possibility that a fetus might be exposed to lead mobilized from bone stores as a result of pregnancy-related metabolic changes, making fetal lead exposure the result of exposure to exogenous lead during pregnancy and exposure to endogenous lead accumulated by the woman prior to pregnancy. By reducing bone resorption, increased calcium intake during the second half of pregnancy might reduce the mobilization of lead from bone compartments, even at low blood lead levels. Subgroups of women who incurred substantial exposures to lead prior to pregnancy should be considered to be at increased risk.

Decreased fecundity among male lead workers

AIMS

To investigate time to pregnancy (TTP) in male lead workers in order to determine the dose-response relation between blood lead and decreased fecundity.

METHODS

A total of 163 currently employed married male lead battery workers were classified into five categories of exposure based on questionnaire information and annual individual blood lead measurement. Information pertaining to the TTP was collected using personal interviews with 133 men and their spouses, with 280 valid pregnancies. The fecundability ratios (FRs) were calculated with the Cox discrete proportional hazard regression technique to evaluate the effects of lead exposure.

RESULTS

After other factors associated with TTP were controlled for, there was a dose-response relation between blood lead level and TTP. The measured FRs were 0.90 (95% CI 0.61 to 1.34), 0.72 (0.46 to 1.11), 0.52 (0.35 to 0.77), and 0.40 (0.27 to 0.59) for concurrent blood lead levels of <20, 20-29, 30-39, and > or =40 microg/dl, respectively. Paired self comparison was also performed for 41 couples that had pregnancies prior to lead exposure and pregnancies with male occupational lead exposure. The TTP was prolonged for 0.15 cycles by a 1 microg/dl increase in blood lead.

CONCLUSIONS

These results corroborate the hypothesis that a raised blood lead level affects fecundity. A blood lead level of less than 40 microg/dl may still significantly prolong TTP.

Parental lead exposure and total anomalous pulmonary venous return

BACKGROUND

Investigators from the Baltimore-Washington Infant Study (BWIS) reported an association between self-reported maternal lead exposure and total anomalous pulmonary venous return (TAPVR) in their offspring. This association was further evaluated in the BWIS population using a more sensitive exposure estimate.

METHODS

Cases included 54 live-born infants with TAPVR; controls were a stratified random sample of 522 live-born infants from the BWIS control group. Parental lead exposure was based on three assessment methods, including: an industrial hygiene assessment, an a priori job exposure matrix, and self-reported exposures. A parent was classified as exposed to lead if he/she was classified as exposed by any one of the assessment methods.

RESULTS

Approximately 17% of case mothers and 11% of control mothers were classified as exposed to lead during the three months prior to conception through the first trimester (odds ratio [OR], 1.57; 95% confidence interval [CI], 0.64-3.47). Among fathers, 61% of case fathers and 46% of control fathers were classified as exposed to lead during the six months prior to conception (paternal critical period) (OR, 1.83; 95% CI, 1.00-3.42). During the paternal critical period, when only the father was exposed compared to neither parent exposed, the OR for any lead exposure and TAPVR was 1.65 (95% CI, 0.84-3.25).

CONCLUSIONS

This study supports a possible association between paternal lead exposure and TAPVR. Further studies are warranted using validated assessment methods for occupational and nonoccupational lead exposures to corroborate this association and to elucidate the possible biological mechanism. Birth Defects Research (Part A), 2004.

Time To Pregnancy and occupational lead exposure

BACKGROUND

Lead exposure is known to be harmful to the male reproductive system, including impairment of fertility. However, it is unclear whether currently existing low levels of exposure have this effect.

AIMS

To study retrospectively current workers in lead using industries (battery manufacture, smelting, etc), and in non-lead using control industries, in four European countries, with Time To Pregnancy as the outcome variable, as part of the EU funded Asclepios Project.

METHODS

Exposure assessment was mainly by blood lead values, which were available from the late 1970s, supplemented by imputed values where necessary. Three exposure models were studied: (1) short term (recent) exposure; (2) total duration of work in a lead using industry; and (3) cumulative exposure. A Cox proportional hazards model with discrete ties was used for the statistical analysis, with covariates for both partners.

RESULTS

A total of 1104 subjects took part, of whom 638 were occupationally exposed to lead at the relevant time. Blood lead levels were mainly less than 50 microg/dl. No consistent association of Time To Pregnancy with lead exposure was found in any of the exposure models, although reduced fertility was observed in one category each in models (2) and (3).

CONCLUSIONS

This basically negative result is unlikely to be due to the misclassification of key variables, to insufficient statistical power, or to bias, for example, response bias. If any impairment of male reproductive function exists at the levels of occupational lead exposure now current, it does not appear to reduce biological fertility.

Lead reduces messenger RNA and protein levels of cytochrome p450 aromatase and estrogen receptor beta in human ovarian granulosa cells

Exposure to lead causes decreased fertility in women. In the present study, we examined the in vitro effects of lead on cytochrome p450 aromatase (p450 arom) and on estrogen receptor beta (ERbeta), two key proteins for the human ovary. Aromatase is required for the bioconversion of androgen to estradiol; ERbeta mediates estrogen effects in granulosa cells. Granulosa cells were collected from women undergoing in vitro fertilization and then cultured with 10 microM lead acetate. Using atomic absorption spectrometry, we showed that lead accumulated in cells. Aromatase activity as measured by a tritiated water production assay was significantly reduced. Using semiquantitative reverse transcription-polymerase chain reaction and Western blotting procedures, we showed that p450 arom and ERbeta mRNA and protein content were both significantly reduced. Adding 10 microg/ml of cycloheximide, a protein inhibitor, did not eliminate the effects of lead. The present results support the hypothesis that the action of lead on fertility in women may result, in part, from the down-regulation of p450 arom and ERbeta gene transcription in ovarian granulosa.

Paternal exposure to lead and infertility

To assess whether paternal exposure to lead is associated with infertility, we performed a register-based study among married men biologically monitored for exposure to inorganic lead. We obtained information about the marriages and the wives of the men from the Finnish Central Population Register. Data on pregnancies were obtained from medical records. Paternal exposure to lead was assessed on the basis of blood lead measurements. We estimated the risk of infertility, defined as nonoccurrence of a marital pregnancy, by applying binomial regression. For the blood lead categories of 0.5-0.9, 1.0-1.4, 1.5-1.9, 2.0-2.4, and > or =2.5 micromol/L the relative risk of infertility, compared with the risk in the lowest exposure category (<0.5 micromol/L), was 1.27 (95% confidence interval 1.08-1.51), 1.35 (1.12-1.63), 1.37 (1.08-1.72), 1.50 (1.08-2.02), and 1.90 (1.30-2.59), respectively. The findings support the hypothesis that paternal exposure to lead increases the risk of infertility at low occupational exposure levels. We applied proportional hazards regression to the analysis of pregnancy delay. A delay was observed among the wives of men exposed to lead. Exposure to lead was not clearly associated with delayed pregnancy, however, when the analysis was restricted to couples with at least one pregnancy. This finding suggests that the restriction of the study on time to pregnancy to fertile couples may introduce a bias toward no association.

Time to pregnancy among the wives of men occupationally exposed to lead

We conducted a retrospective study on time to pregnancy among the wives of men biologically monitored for lead to assess whether paternal occupational exposure to inorganic lead is associated with decreased fertility. After three mailings, 554 (72.2%) wives of the monitored men participated. The final study population consisted of 502 couples who did not use contraception at the beginning of the pregnancy. We assessed lead exposure from blood lead measurements and from questionnaires completed by the men. We calculated the relative fecundability density ratios with discrete proportional hazards regression. The fecundability density ratios, adjusted for potential confounders, were 0.92 [95% confidence interval (95% CI) = 0.73-1.16], 0.89 (95% CI = 0.66-1.20), 0.58 (95% CI = 0.33-0.96), and 0.83 (95% CI = 0.50-1.32) for blood lead categories 0.5-0.9, 1.0-1.4, 1.5-1.8, and > or =1.9 micromol/L, respectively, as compared with <0.5 micromol/L. The findings provide limited support for the hypothesis that paternal exposure to lead is associated with decreased fertility.

Clinical evaluation and management of lead-exposed construction workers

An estimated one million construction workers are currently occupationally exposed to lead. Until 1993, construction workers were not offered the protections of OSHA's 1978 standard for lead exposure in industrial activities. Preventing exposure to lead in the construction setting presents many challenges, given the rapidly and frequently changing work environment. This article reviews the adverse effects of lead on human health and presents an approach to the diagnosis, management, and prevention of lead-related illness. The medical aspects of the 1993 OSHA standard for lead in construction are described.