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Biomedical subjects

A S Rowland

Publications and source records attributed to A S Rowland.

17 recordsLinked to original sources
PubMed2001

Mercury vapor and female reproductive toxicity.

Epidemiological studies finding menstrual cycle abnormalities among women occupationally exposed to Hg degrees prompted us to investigate the mechanisms of reproductive toxicity of Hg degrees in the female rat. Nose-only Hg degrees vapor inhalation exposures were conducted on regularly cycling rats 80-90 days of age in dose-response and acute time-course studies, which have previously proven useful as a model to identify ovarian toxicants. Vaginal smears were evaluated daily and serum hormone levels were correlated with cycle and with ovarian morphology at necropsy. Exposure concentration-related effects of Hg degrees were evaluated by exposing rats to 0, 1, 2, or 4 mg/m3 Hg degrees vapor 2 h/day for 11 consecutive days. Tissue Hg levels correlated with exposure concentration and duration. Exposure of rats to 4 mg/m3 (but not 1 or 2 mg/m3) Hg vapor for 11 days resulted in significant decreases in body weights relative to controls. Estrous cycles were slightly prolonged in the 2 and 4 mg/m3 dose groups, and serum estradiol and progesterone levels were significantly different in the 4 mg/m3 group compared to controls. The alterations in cycle and hormones at the 4 mg/m3 exposure concentration were attributed to body weight loss and generalized toxicity. In the time-course study, rats were exposed to 2 mg/m3 Hg degrees or air beginning in metestrus and evaluated daily for 8 days. A lengthening of the cycle was detected and morphological changes were observed in the corpora lutea (CL) after exposure for 6 days. To determine if changes in the CL and cyclicity correlated with a functional defect, rats were exposed to Hg degrees vapor and evaluated for pregnancy outcome. There were no significant effects on pregnancy rate or numbers of implantation sites when rats were exposed to 1 or 2 mg/m3 Hg degrees for 8 days prior to breeding, or when exposed for 8 days after breeding. These studies indicate that exposure to Hg degrees vapor altered estrous cyclicity, but had no significant effect on ovulation, implantation, or maintenance of first pregnancy during exposure of short duration in female rats.

Administration, Inhalation↗
PubMed2001

Studying the epidemiology of attention-deficit hyperactivity disorder: screening method and pilot results.

OBJECTIVE: As part of a larger epidemiologic study of risk factors for attention-deficit hyperactivity disorder (ADHD), this pilot study combined parent and teacher information to estimate ADHD prevalence among elementary school children in a North Carolina county. The methods developed for this study and the pitfalls we encountered illustrate the challenges involved in conducting population-based studies of ADHD. METHODS: We employed 2-stage screening using DSM-IV criteria. Teachers completed behaviour-rating scales for all children. We then administered a structured telephone interview to parents of potential cases. We screened 362 of 424 (85%) children in grades 1 to 5 in 4 schools. RESULTS: According to parent reports, 43 children (12%) had previously been diagnosed with ADHD by a health professional. Thirty-four children (9%) were taking ADHD medication. Forty-six children (12.7%) met study case criteria for ADHD, based on combined teacher and parent reports. Of the 46 cases, 18 (39%) had not been previously identified. Eight previously diagnosed children, however, did not meet case criteria. After we adjusted for nonresponse, the estimated prevalence was 16% (95%CI, 12% to 20%). CONCLUSIONS: These data suggest that the DSM-IV prevalence of ADHD has been substantially underestimated, although the true prevalence in this population may be less than the 16% estimated here. Population-based studies of ADHD are feasible and may provide important information about practice and treatment patterns in community settings, as well as a broader understanding of the etiology and life course of this common disorder.

Attention Deficit Disorder with Hyperactivity↗
PubMed2001

Recruiting a community sample in collaboration with farmworkers.

Few studies have examined health effects of pesticides in farmworkers, possibly because researchers perceive this population to be relatively inaccessible. We conducted an epidemiologic study of health effects among farmworkers in two towns in central Florida--Apopka and Pierson. Apopka is a suburb of Orlando with a diffuse farmworker community working in many crops, whereas Pierson is a small rural town with a tightly knit farmworker community working mainly in ferns. We collaborated with the Farmworker Association of Florida, a grassroots organization representing 6,700 farmworker families. We identified potential participants using membership lists of the Community Trust Federal Credit Union. Members of the Farmworker Association served as recruiters for the study, locating randomly selected Credit Union members and administering a screening interview to determine eligibility. In Apopka 90% of contacted workers were screened, and 79% of eligible workers participated in the study; corresponding proportions in Pierson were 94 and 85%. Farmworkers who had worked for 6-15 years and those who worked in a defined type of agriculture (nursery, citrus, or ferns) were more likely to enroll than others. Thus, while the response rate was good for a multistage recruiting process, study participants had a slightly different work history from those who chose not to enroll. We conclude that it is possible to conduct a study of health outcomes in farmworkers with a defined population and good response rates. Collaboration with the community is essential to the success of such a project, and community characteristics can affect response rates.

Adult↗
PubMed2000

Retinal degeneration in licensed pesticide applicators.

BACKGROUND: Retinal degeneration is the leading cause of visual impairment in older adults, but little is known about its relationship to neurotoxic exposures. METHODS: The Agricultural Health Study is a cohort study of licensed pesticide applicators from Iowa and North Carolina. We used cross-sectional data from self-administered questionnaires given at enrollment in 1994-1996 to compare pesticide use in 154 applicators who reported retinal degeneration and 17,804 controls. RESULTS: Retinal degeneration was associated with fungicide use (odds ratio = 1.8, 95% confidence interval = 1.3-2.6). This relationship was seen in subgroups defined by state, demographic characteristics, or medical history, as well as in the entire group. Risk increased with cumulative days of fungicide use (P for trend = 0.011) and was greater when application methods involving greater personal exposure were used. Retinal degeneration was also related to use of organochlorine or carbamate insecticides, but these associations were less consistent. Since nearly all applicators used organophosphate insecticides and herbicides, these exposures could not be effectively evaluated. CONCLUSIONS: These results suggest that exposure to some fungicides and insecticides may increase risk of retinal degeneration.

Adolescent↗
PubMed1999

Characteristics of persons who self-reported a high pesticide exposure event in the Agricultural Health Study.

Characteristics of persons who report high pesticide exposure events (HPEE) were studied in a large cohort of licensed pesticide applicators from Iowa and North Carolina who enrolled in the Agricultural Health Study between December 1993 and December 1995. Fourteen percent reported having "an incident or experience while using any pesticide which caused an unusually high personal exposure. " After taking into account total number of applications made and education, females (OR=0.76), applicators from NC (OR=0.65), and privately licensed applicators (OR=0.65) were less likely to have reported an HPEE. Work practices more common among both private and commercial applicators with an HPEE included delay in changing clothing or washing after pesticide application, mixing pesticide application clothing with the family wash, washing up inside the house after application, applying pesticides within 50 yards of their well, and storing pesticides in the home. Job characteristics more common among those with an HPEE included self-repair of application equipment and first pesticide use more than 10 years in the past. These job characteristics explained much of the difference in reported HPEE between males and females, but not between IA and NC subjects or between commercial or private applicators.

Adult↗
PubMed1998

Exposure opportunities of families of farmer pesticide applicators.

BACKGROUND: Families of farmer pesticide applicators have unusual opportunities for exposure, directly or indirectly, to pesticides. These exposures are not well characterized. METHODS: Subjects were 26,793 licensed private pesticide applicators enrolled in the Agricultural Health Study, a cohort study being conducted in Iowa and North Carolina. Questionnaires were completed by the applicators and their spouses. RESULTS: Many indirect exposure opportunities exist; for example, 21% of homes are within 50 yards of pesticide mixing areas, 27% of applicators store pesticides in their homes, and 94% of clothing worn for pesticide work is washed in the same machine as other laundry. Direct exposure opportunities also occur; for example, 51% of wives of applicators worked in the fields in the last growing season, 40% of wives have ever mixed or applied pesticides, and over half of children aged 11 or more do farm chores. DISCUSSION/CONCLUSIONS: The extent of the opportunities for exposure of family members of farmer pesticide applicators makes studies of their health important.

Adult↗
PubMed1996

Ethylene oxide exposure may increase the risk of spontaneous abortion, preterm birth, and postterm birth.

Ethylene oxide is a gas used in some dental offices to sterilize equipment. In pregnant laboratory animals, ethylene oxide increases malformations and feral loss. Increased gestation length has also been reported. In humans, two studies have reported increased spontaneous abortions among ethylene oxide-exposed women, but few other data exist. We sent questionnaires to 7,000 dental assistants, age 18-39 years, registered in California in 1987; 4,856 responded (69%). We based our analysis on 1,320 women whose most recent pregnancy was conceived while working full-time. Thirty-two women reported exposure to ethylene oxide; unexposed dental assistants comprised the comparison group. We estimated relative risks of spontaneous abortion and preterm birth using a person-week model. We estimated relative risks of postterm birth (> or = 42 weeks) and a combined adverse outcomes model using logistic regression. Among exposed women, the age-adjusted relative risk of spontaneous abortion was 2.5 [95% confidence interval (CI) = 1.0-6.3], for preterm birth 2.7 (95% CI = 0.8-8.8), and for postterm birth 2.1 (95% CI = 0.7-5.9). The estimated relative risk of any of these adverse outcomes among exposed women was 2.5 (95% CI = 1.0-6.1) after adjusting for age, nitrous oxide, and number of mercury amalgams prepared. These data further implicate ethylene oxide as a possible reproductive toxicant in humans.

Abortion, Spontaneous↗
PubMed1995

Nitrous oxide and spontaneous abortion in female dental assistants.

The relation between anesthetic gas exposure and spontaneous abortion remains unresolved. We examined the effect of nitrous oxide on spontaneous abortion among female dental assistants. Questionnaires were sent to 7,000 dental assistants aged 18-39 years who were registered in California in 1987; 4,856 (69%) responded. Analysis was based on 1,465 respondents whose most recent pregnancy was conceived while working full time. Women were asked how many hours a week they worked with nitrous oxide during this pregnancy and whether the excess gas was scavenged (vented). Relative risk of spontaneous abortion (through week 20) was calculated using a person-week model. This allowed women with current pregnancies (13%) or induced abortions (10%) to be included for appropriate time periods of risk. A total of 101 pregnancies (7%) ended as spontaneous abortions. An elevation in risk of spontaneous abortion was seen among women who worked with nitrous oxide for 3 or more hours per week in offices not using scavenging equipment (relative risk = 2.6, 95% confidence interval 1.3-5.0, adjusted for age, smoking, and number of amalgams prepared per week), but not among those using nitrous oxide in offices with scavenging equipment. This relation changed little when analyses were restricted to confirmed pregnancies or examined for several types of potential bias. Scavenging equipment appears to be important in protecting the reproductive health of women working with nitrous oxide.

Abortion, Spontaneous↗
PubMed1994

The effect of occupational exposure to mercury vapour on the fertility of female dental assistants.

Exposure to mercury vapour or inorganic mercury compounds can impair fertility in laboratory animals. To study the effects of mercury vapour on fertility in women, eligibility questionnaires were sent to 7000 registered dental assistants in California. The final eligible sample of 418 women, who had become pregnant during the previous four years, were interviewed by telephone. Detailed information was collected on mercury handling practices and the number of menstrual cycles without contraception it had taken them to become pregnant. Dental assistants not working with amalgam served as unexposed controls. Women with high occupational exposure to mercury were less fertile than unexposed controls. The fecundability (probability of conception each menstrual cycle) of women who prepared 30 or more amalgams per week and who had five or more poor mercury hygiene factors was only 63% of that for unexposed women (95% CI 42%-96%) after controlling for covariates. Women with low exposure were more fertile, however, than unexposed controls. Possible explanations for the U shaped dose response and limitations of the exposure measure are discussed. Further investigation is needed that uses biological measures of mercury exposure.

Adolescent↗
PubMed1993

Pitfalls inherent in retrospective time-to-event studies: the example of time to pregnancy.

Retrospective studies of time from initiation of risk (for example, transfusion of HIV-infected blood) to the occurrence of an endpoint of interest are useful in epidemiology. One example is studies of time to pregnancy, which have evaluated exposures that may affect human fertility. One can reconstruct the non-contracepting interval required for each woman's most recent pregnancy and then treat the data as if the couples had been studied prospectively. As we illustrate, however, failure-time models can be dangerously misleading when there have been trends over calendar time in exposures under study. We propose an ad hoc method for evaluating possible effects on fertility despite this bias, by making use of external data on trends in the exposure over time. This approach applies a prospective model and generates an empirical p-value, based on comparing the data-based estimated exposure coefficient with its null distribution estimated by simulation. A second method maximizes a conditional likelihood, and we show that this is equivalent to logistically modelling the relative odds for the subject's exposure as related to the reported time she required to achieve pregnancy.

Bias↗
PubMed1992

Reduced fertility among women employed as dental assistants exposed to high levels of nitrous oxide.

BACKGROUND: Fertility is reduced in female rats exposed to levels of nitrous oxide similar to those found in some dental offices. Epidemiologic studies have suggested an association between exposure to mixed anesthetic gases and impaired fertility. We investigated the effects of occupational exposure to nitrous oxide on the fertility of female dental assistants. METHODS: Screening questionnaires were mailed to 7000 female dental assistants, ages 18 to 39, registered by the California Department of Consumer Affairs. Sixty-nine percent responded. Four hundred fifty-nine women were determined to be eligible, having become pregnant during the previous four years for reasons unrelated to the failure of birth control, and 91 percent of these women completed telephone interviews. Detailed information was collected on exposure to nitrous oxide and fertility (measured by the number of menstrual cycles without contraception that the women required to become pregnant). RESULTS: After controlling for covariates, we found that women exposed to high levels of nitrous oxide were significantly less fertile than women who were unexposed or exposed to lower levels of nitrous oxide. The effect was evident only in the 19 women with five or more hours of exposure per week. These women were only 41 percent (95 percent confidence interval, 23 to 74 percent; P less than 0.003) as likely as unexposed women to conceive during each menstrual cycle. CONCLUSIONS: Occupational exposure to high levels of nitrous oxide may adversely affect women's ability to become pregnant.

Adolescent↗
PubMed1991

Reporting errors in time-to-pregnancy data collected with a short questionnaire. Impact on power and estimation of fecundability ratios.

Few tools exist in reproductive epidemiology for studying adverse effects on fertility. Data on time to pregnancy (the number of menstrual cycles required to conceive) can be used to estimate fecundability ratios, a sensitive endpoint for identifying factors associated with reduced fertility. Time-to-pregnancy data can be collected in detailed interviews. The accuracy of data collected on brief, self-administered questionnaires is not known. In a study of occupational exposures to dental assistants conducted in 1987-1988, 523 women provided time-to-pregnancy data both on a short, mailed questionnaire and in a detailed telephone interview. The correlation between the two measures was 0.82. Assuming that the detailed data were accurate, reporting errors in data from the short form were distributed nondifferentially with respect to most covariates of interest in fecundability analyses. Simulation studies were conducted to estimate bias and loss of power from the misclassification. Bias was toward the null. Substantial power was lost in detecting weak exposures. However, exposures that reduce fecundability by 50 percent (equivalent to adding about three cycles to the median time to pregnancy) could still be detected with 80 percent power in samples of about 100 women (half of them exposed to a possible toxin). The authors conclude that time-to-pregnancy data collected with a few self-administered questions can be useful in a variety of epidemiologic studies, including occupational and environmental surveillance programs.

Bias↗
PubMed1990

Maternal employment and reproductive risk factors.

Studies of reproductive hazards in the workplace must address potential biases related to selection for employment. The National Natality Survey, a probability sample of live births to married women in 1980, was used to examine the relation between female employment during pregnancy and factors that might affect reproductive outcome by analyzing the 5,927 women with complete occupational data. Demographic and behavioral attributes as well as reproductive history were compared for the 3,712 women employed and the 2,215 women not employed during pregnancy. Employed mothers were of more optimal reproductive age, were more highly educated, had higher incomes, began prenatal care earlier, had greater weight gain during pregnancy, and were slightly less likely to be heavy smokers. Employed women had markedly fewer previous births and less favorable reproductive histories (more stillbirths, miscarriages, and induced abortions) than unemployed women, controlling for gravidity. Full- and part-time workers were similar with regard to demographic and behavioral characteristics, but part-time workers had higher parity. Differences were noted by employment sector: professional women had especially favorable demographic and behavioral traits, and women employed as operatives and service workers were less advantaged. These results indicate that substantial differences in pregnancy-related risk factors exist in relation to employment, with working women generally having more favorable demographic and behavioral characteristics and less favorable reproductive histories. This pattern could produce selection bias in studies of work and reproductive health, and it encourages the restriction of comparison groups to other employed women, with a need to consider heterogeneity among working women as well.

Adult↗
PubMedDate not supplied

Attention deficit/hyperactivity disorder: characteristics, interventions and models.

An epidemiological study of Attention Deficit/Hyperactivity Disorder (ADHD) suggests that the prevalence may be two to three times higher than the figure of 3-5% often cited. In addition, the data suggest that both underdiagnosis and overdiagnosis occur frequently. Rodent animal models of ADHD, like the Spontaneously Hypertensive Rat (SHR) and other rat models such as those with chemical and radiation-induced brain lesions and cerebellar stunting, and the Coloboma mouse model exhibit clear similarities with several aspects of the human disorder and should prove useful in studying specific traits. Operant behavioral tasks that model learning, short-term memory and simple discriminations are sensitive to ADHD and methylphenidate has been shown to normalize ADHD performance in a short-term memory task. Recent findings challenge not only the current postulate that response inhibition is a unique deficit in ADHD, but also the concepts of ADHD and its treatment, which presume intact perceptual abilities. Time perception deficits may account, in part, for the excessive variability in motor response times on speeded reaction time tasks, motor control problems and motor clumsiness associated with ADHD. The Multimodality Treatment Study of ADHD (MTA) provided data suggesting that pharmacological interventions that included systematic and frequent follow-up with parents and teachers, with or without psychosocial interventions, are superior to psychosocial interventions or standard community care alone. Additionally, the MTA was one of the first studies to demonstrate benefits of multimodal and pharmacological interventions lasting longer than 1 year. Imaging studies have demonstrated differences in brain areas in children with ADHD: anterior corpus callosum, right anterior white matter, and cerebellar volumes are all decreased in children with ADHD and there is less brain asymmetry in ADHD subjects. Additionally, functional imaging studies, coupled with pharmacological manipulations, suggest decreased blood flow and energy utilization in prefrontal cortex and striatum and the dysregulation of catecholamine systems in persons with ADHD.

Animals↗