Harold Zenick

The Use of Biomonitoring Data in Exposure and Human Health Risk Assessments

Biomonitoring uses analytic methods that permit the accurate measurement of low levels of environmental chemicals in human tissues. However, depending on the intended use, biomonitoring, like all exposure tools, may not be a stand-alone exposure assessment tool for some of its environmental public health uses. Although biomonitoring data demonstrate that many environmental chemicals are absorbed in human tissues, uncertainty exists regarding if and at what concentrations many of these chemicals cause adverse health outcomes. Moreover, without exposure pathway information, it is difficult to relate biomonitoring results to sources and routes of exposure and develop effective health risk management strategies. In September 2004, the Health and Environmental Sciences Institute, U.S. Environmental Protection Agency, Centers for Disease Control and Prevention, Agency for Toxic Substances and Disease Registry, and International Council of Chemical Associations co-sponsored the International Biomonitoring Workshop, which explored the processes and information needed for placing biomonitoring data into perspective for risk assessment purposes, with special emphasis on integrating biomarker measurements of exposure, internal dose, and potential health outcome. Scientists from international governments, academia, and industry recommended criteria for applying biomonitoring data for various uses. Six case studies, which are part of this mini-monograph, were examined: inorganic arsenic, methyl eugenol, organophosphorus pesticides, perfluorooctanesulfonate, phthalates, and polybrominated diphenyl ethers. Based on the workshop and follow-up discussions, this overview article summarizes lessons learned, identifies data gaps, outlines research needs, and offers guidance for designing and conducting biomonitoring studies, as well as interpreting biomonitoring data in the context of risk assessment and risk management.

Aging and the environment: a research framework.

The rapid growth in the number of older Americans has many implications for public health, including the need to better understand the risks posed to older adults by environmental exposures. Biologic capacity declines with normal aging; this may be exacerbated in individuals with pre-existing health conditions. This decline can result in compromised pharmacokinetic and pharmacodynamic responses to environmental exposures encountered in daily activities. In recognition of this issue, the U.S. Environmental Protection Agency (EPA) is developing a research agenda on the environment and older adults. The U.S. EPA proposes to apply an environmental public health paradigm to better understand the relationships between external pollution sources → human exposures → internal dose → early biologic effect → adverse health effects for older adults. The initial challenge will be using information about aging-related changes in exposure, pharmacokinetic, and pharmacodynamic factors to identify susceptible subgroups within the diverse population of older adults. These changes may interact with specific diseases of aging or medications used to treat these conditions. Constructs such as “frailty” may help to capture some of the diversity in the older adult population. Data are needed regarding a) behavior/activity patterns and exposure to the pollutants in the microenvironments of older adults; b) changes in absorption, distribution, metabolism, and excretion with aging; c) alterations in reserve capacity that alter the body’s ability to compensate for the effects of environmental exposures; and d) strategies for effective communication of risk and risk reduction methods to older individuals and communities. This article summarizes the U.S. EPA’s development of a framework to address and prioritize the exposure, health effects, and risk communications concerns for the U.S. EPA’s evolving research program on older adults as a susceptible subpopulation.

Dominant lethal effects of subchronic acrylamide administration in the male Long-Evans rat

Acrylamide, a widely used vinyl monomer, is well known as a neurotoxin but inactive as a mutagen in bacterial test systems. The experiments reported demonstrate that after subchronic oral dosing in the male rat, acrylamide induced significant elevations in both pre- and post-implantation loss following dominant lethal testing. These effects were seen at doses which failed to produce clinical or pathological evidence of neurotoxicity. In an accompanying cytogenetic study, no increase in chromosome aberrations was observed in spermatogonia or spermatocytes of treated animals. When spermatocytes from treated spermatogonial stem cells were analyzed, reciprocal translocations (4) were observed in the treated animals and not in the control, but the significance of this result still needs to be established.

Reproductive toxicity associated with acrylamide treatment in male and female rats

The present study was designed to evaluate the influence of acrylamide (ACR) on male and female reproductive function. Male rats received ACR in drinking water (50, 100, or 200 ppm) for up to 10 wk. Copulatory behavior, semen, and (for controls and 100 ppm only) fertility and fetal outcomes were evaluated. Females received ACR (25, 50, 100 ppm) for 2 wk prior to initiation of breeding and then throughout gestation and lactation. Hindlimb splaying was apparent in the 200-ppm males by wk 4; less severe splaying appeared in the 100-ppm group at wk 8. Disruptions in copulatory behavior preceded the appearance of this ataxia. These disruptions in mating performance interfered with ejaculatory processes and subsequent transport of sperm, since semen was found in the uterus of only 1 of the 15 females mated with the 100-ppm males at wk 9. Moreover, only 33% of the females mated (wk 10) to the 100-ppm males were pregnant. Postimplantation loss was also significantly increased in this group. Hindlimb splaying appeared in the females receiving 100 ppm ACR during wk 1-2 of pregnancy. Body weight and fluid intake were also depressed. Dams in the 50-ppm group showed depression in these parameters during the last 2 wk of lactation. ACR did not significantly affect mating performance of the females, pregnancy rates, litter size, or survival. However, ACR did significantly depress pup body weight at birth (100-ppm group) and weight gain during lactation through post-weaning, d 42 (50- and 100-ppm groups). Vaginal patency was delayed in the 100-ppm group only.

In vivo and in vitro evaluations of spermatotoxicity induced by 2-ethoxyethanol treatment.

2-Ethoxyethanol (EE), a member of the glycol ethers, has been shown to produce testicular atrophy in laboratory animals. The present study further identified the spectrum of effects on the male reproductive system in vivo and initiated in vitro studies on possible mechanisms of action. Adult, male rats were treated (po) with 0 or 936 mg EE/kg, 5 days/week for 6 weeks. Semen samples were collected on a weekly basis during the exposure period from ovariectomized, hormonally primed females immediately following mating and analyzed for sperm count, sperm morphology, and sperm motility. Sperm count and percent normal morphology were decreased at Weeks 5 and 6, and sperm motility was decreased at Week 6. These data, along with other studies, indicated that the pachytene spermatocyte was the most sensitive target for EE. In vitro studies monitored O2 consumption and ATP concentrations in isolated pachytene spermatocytes which were treated with 10 mM EE or 1 or 10 mM ethoxyacetic acid (EAA), the reported active metabolite of EE. An increase in respiratory ratio for the lactate rate/endogenous rate and a decrease in the 2,4-dinitrophenol rate/lactate rate were observed only for cells treated with 10 mM EAA. Additionally, a decrease in ATP concentration was seen only with 10 mM EAA. These results indicated that EAA interfered with energy metabolism in the pachytene spermatocyte. This effect may, in part, explain the testicular toxicity produced by this compound.

Evaluation of the reproductive toxicology of 2,4,6-trichlorophenol in male and female rats

The toxicity of chlorinated organic compounds which may be generated as a by-product of drinking water chlorination has been an issue of increasing concern. Relatively few data are available concerning their reproductive toxicity. The present study was designed to evaluate the reproductive effects of one of these compounds, 2,4,6-trichlorophenol (TCP), in male and female rats. Adult males were treated with either 0, 100, 500, or 1000 mg/kg of TCP (po) for 10 weeks, at which time semen evaluations were conducted on ejaculates recovered from the genital tract of receptive females. Fertility was assessed in the 0- and 1000-mg/kg groups. Females were treated with identical doses for 2 weeks prior to pregnancy then throughout gestation. Dams were allowed to litter and pup development was monitored until Day 42 postpartum. TCP had no effect on any sperm parameter or male fertility. Treatment of females with 1000 mg/kg of TCP produced gross maternal toxicity as reflected in increased lethality and decreased weight gains in the dams. However, no treatment-related differences were seen in litter sizes or pup survival. Male and female birth weights were significantly depressed in the 500- and 1000-mg/kg groups; these differences disappeared by Day 4 postpartum, suggesting that they were a reflection of maternal toxicity. To this extent, the reproductive processes of male and female rats do not appear to be a primary target for the effects of TCP.

An evaluation of the copulatory, endocrinologic, and spermatotoxic effects of carbon disulfide in the rat☆

The present study was undertaken to evaluate the endocrinologic and spermatogenic effects of carbon disulfide (CS2) exposure in the rat. Adult, male rats were exposed to either 600 ppm CS2 or filtered air for 6 hr/day for 5 days/week for 10 weeks. One week prior to exposure and then at Weeks 1, 4, 7, and 10, males were placed with ovariectomized, hormonally primed females, and copulatory behaviors were scored. Fifteen minutes postcopulation, the female was killed and the ejaculate was recovered from the excised uterine tract along with the semen plug. Sperm counts, sperm motility, and morphology were determined. A blood sample was obtained for analyses of testosterone, follicle-stimulating (FSH), and luteinizing hormone (LH). At the end of the 10th week, five animals in each group were challenged with either human chorionic gonadotropin (HCG, 50 IU/animal, iv) or gonadotropin-releasing hormone (GnRH, 100 ng/animal, iv), and the testosterone or gonadotropin responses were monitored over time. Animals were subsequently killed with one epididymis and testis processed for histology and a sperm count determined from the other epididymis. Analysis revealed that CS2 exposure produced significant alterations in copulatory behavior and a decrease in ejaculated sperm counts by the fourth and seventh weeks of exposure, respectively. No endocrinologic alterations were observed. Moreover, caudal epididymal sperm counts were not depressed and the testes appeared histologically normal. These data suggest that CS2 does not exert a direct effect on the testes, but rather may interfere with the processes regulating sperm transport and ejaculation.

Male reproductive toxicity and recovery associated with acute ethoxyethanol exposure in rats.

Effects of 2-ethoxyethanol (EE) on semen parameters in male rats were investigated employing an animal model that allowed assessment of toxicity and recovery in the same animal. Prior to exposure, 70-d-old Long-Evans hooded males were placed with ovariectomized, hormonally primed females on several occasions and their copulatory behaviors were monitored and scored. At 100 d of age, these males were mated with females that were sacrificed 15 min postejaculation. The semen sample was recovered from the female reproductive tract and scored for sperm motility, sperm count, and abnormal sperm morphology. Following this preexposure baseline assessment, the males were intubated with 0, 936, 1872, or 2808 mg EE/kg for 5 consecutive days. The males were mated weekly for the next 14 wk. Copulatory behaviors were monitored and ejaculated semen samples analyzed on wk 1, 4, 7, 10, and 14. The males were sacrificed at wk 16 and the testes and epididymides were processed for histological evaluation. Data analyses indicated that EE produced a rapid decline in sperm counts in the two highest groups, with most of the males becoming azoospermic by wk 7. The males in the low dose group also exhibited a significant decrease in sperm counts at this week. Additionally, there was a significant increase in abnormal sperm morphology at wk 7 in the low-dose males. Partial or complete recovery was apparent in the sperm parameters by wk 14, as evidenced by an increase in sperm counts and a decrease in abnormal morphology and further supported by epididymal and testicular histological assessment at wk 16. At sacrifice, there were no significant differences between groups on body weights, organ weights, or epididymal sperm counts, except for a significant depression of epididymal weight in the middle dose group. While high doses of EE produced a decline in sperm counts starting after the first week of exposure, the early spermatid-late spermatocyte stages, represented by mature spermatozoa in the wk 7 ejaculates, appeared to be particularly sensitive to this compound. Moreover, most of the males exhibited recovery following this acute dosing regimen.

Relationship between hematopoietic parameters and behavioral measures in lead-exposed rats

The effects of low level lead (Pb) exposure on learning tasks in developing rats were investigated and the results correlated with individual hematopoietic indices. Pups received exposure via the dams milk; dams were exposed to either 0-, 545-, or 1090-ppm Pb during the lactation period. At Day 30 of age, half of the high Pb group was placed on distilled water; the remaining groups continued on the same exposure regimens as their dams. On Days 20, 30, and 90, blood samples for all rats were obtained via cardiac puncture. Each sample was analyzed for Pb concentration, free erythrocyte protoporphyrin (FEPs), hematocrit, and hemoglobin. Beginning at Day 90, all rats were tested on a battery of tasks designed to investigate the following questions: (1) to what degree lead exposure interferes with reversal learning; (2) whether changing of task requirements adversely affects acquisition of a new task; (3) to what extent task difficulty contributes to lead-induced deficits; and (4) whether lead exposure affects the capacity to retain information over short or long periods of time. The actual testing paradigms included spatial discrimination with reversal, visual discrimination with reversal, and visual discrimination task with delay. No significant differences were observed among any of the groups on any of the tasks. Correlation of individual learning scores with individual measures of hematopoietic function also failed to reach significance. These findings indicate that at low exposure levels, lead has little appreciable effect on learning and memory function as measured by these tasks.

Statistical issues in risk assessment of reproductive outcomes with chemical mixtures.

Establishing the relationship between a given chemical exposure and human reproductive health risk is complicated by exposures or other concomitant factors that may vary from pregnancy to pregnancy. Moreover, when exposures are to complex mixtures of chemicals, varying with time in number of components, doses of individual components, and constancy of exposure, the picture becomes even more complicated. A pilot study of risk of adverse reproductive outcomes among male wastewater treatment workers and their wives is described here. The wives of 231 workers were interviewed to evaluate retrospectively the outcomes of spontaneous early fetal loss and infertility. In addition, 87 workers participated in a cross-sectional evaluation of sperm/semen parameters. Due to the ever-changing nature of the exposure and the lack of quantification of specific exposures, six dichotomous variables were used for each specific job description to give a surrogate measure of exposure. Hence, no quantitative exposure-response relationships could be modeled. These six variables were independently assigned by two environmental hygienists, and their interrater reliability was assessed. Results are presented and further innovations in statistical methodology are proposed for further applications.