Changes in persistent organic pollutant levels from adolescence to young adulthood

Elimination rates and their corresponding half-lives are conceptually important and intuitively accessible pharmacokinetic measures of toxicant elimination, but regression-based estimates are biased proportional to the degree of continuing (background) exposure. We propose an alternative estimator, the censored normal regression model, which uses all observations, but treats individuals whose initial level failed to exceed their follow-up level as censored observations to weight the regression estimates from those that declined between blood draws. In this manner, we derive the intrinsic elimination rate, the elimination rate free from ongoing exposure, as a parameter in a regression with an unobserved, latent dependent variable. We utilize sequential measurements of persistent organic pollutants (POPs) levels from adolescence to adulthood, a period of intense change in size and body composition, to quantify individual-level change within a community exposed to significant quantities of contaminants over an extended period of time. Although much research has been conducted on effects of POPs, far less attention has been given to vectors of intake and changes in toxicant levels during the life course. We apply exploratory factor analysis (EFA) to types and timing of consumption, along with physical behavioral characteristics, to identify a structure of seven underlying factors. Although several variables show factorial complexity, the latent constructs included an age/maturation and period-related factor, a nutritional composite, consumption prior to pregnancy, fish and fowl consumed during pregnancy, factors distinguishing body mass and weight from height, and bottom-feeding fish consumption. Unadjusted and adjusted half-lives using the censored normal regression estimator, as well as estimated half-lives from conventional log concentration regressions, are reported for PCB groupings, specific congeners, p,p'-DDE, and HCB.

Relationships of polychlorinated biphenyls and dichlorodiphenyldichloroethylene (p,p'-DDE) with testosterone levels in adolescent males

BACKGROUND

Concern persists over endocrine-disrupting effects of persistent organic pollutants (POPs) on human growth and sexual maturation. Potential effects of toxicant exposures on testosterone levels during puberty are not well characterized.

OBJECTIVES

In this study we evaluated the relationship between toxicants [polychlorinated biphenyls (PCBs), dichlorodiphenyldichloroethylene (p,p´-DDE), hexachlorobenzene (HCB), and lead] and testosterone levels among 127 Akwesasne Mohawk males 10 to < 17 years of age with documented toxicant exposures.

METHODS

Data were collected between February 1996 and January 2000. Fasting blood specimens were collected before breakfast by trained Akwesasne Mohawk staff. Multivariable regression models were used to estimates associations between toxicants and serum testosterone, adjusted for other toxicants, Tanner stage, and potential confounders.

RESULTS

The sum of 16 PCB congeners (Σ16PCBs) that were detected in ≥ 50% of the population was significantly and negatively associated with serum testosterone levels, such that a 10% change in exposure was associated with a 5.6% decrease in testosterone (95% CI: -10.8, -0.5%). Of the 16 congeners, the more persistent ones (Σ8PerPCBs) were related to testosterone, whereas the less persistent ones, possibly reflecting more recent exposure, were not. When PCB congeners were subgrouped, the association was significant for the sum of eight more persistent PCBs (5.7% decrease; 95% CI: -11, -0.4%), and stronger than the sum of six less persistent congeners (3.1% decrease; 95% CI: -7.2, 0.9%). p,p´-DDE was positively but not significantly associated with serum testosterone (5.2% increase with a 10% increase in exposure; 95% CI: -0.5, 10.9%). Neither lead nor HCB was significantly associated with testosterone levels.

CONCLUSIONS

Exposure to PCBs, particularly the more highly persistent congeners, may negatively influence testosterone levels among adolescent males. The positive relationship between p,p´-DDE and testosterone indicates that not all POPs act similarly.

CITATION

Schell LM, Gallo MV, Deane GD, Nelder KR, DeCaprio AP, Jacobs A; Akwesasne Task Force on the Environment. 2014. Relationships of polychlorinated biphenyls and dichlorodiphenyldichloroethylene (p,p´-DDE) with testosterone levels in adolescent males. Environ Health Perspect 122:304-309; http://dx.doi.org/10.1289/ehp.1205984.

Land Transitions in the American Plains: Multilevel Modeling of Drivers of Grassland Conversion (1950 to 2000)

This paper examines drivers of land-cover change in the U.S. Great Plains in the last half of the twentieth century. Its central aim is to evaluate the dynamics of grassland preservation and conversion, across the region, and to identify areas of grassland that were never plowed during the period. The research compares land-cover data from 400 sample areas, selected from and nested within 50 counties, to aggregate data from the agricultural and population censuses. The spatially explicit land-cover data were interpreted from aerial photographs taken at three time points (1950s, 1970s and 2000s). Sample areas were chosen using a stratified random design based on the Public Land Survey grid with in the target counties, in several clusters across the region. We modeled the sequences and magnitudes of changes in the interpreted air photo data in a multi-level panel model that included soil quality and slope of sample areas and agricultural activities and employment reported in the U.S. Censuses of Agriculture and Population. We conclude that land retirement programs and production subsidies have worked at cross purposes, destabilizing micro-level patterns of land use in recent decades, increasing levels of switching between cropland and grassland and reducing the size of remaining areas of native grassland in the U.S. Great Plains.

Land Use and Family Formation in the Settlement of the U.S. Great Plains

In agricultural settings, environment shapes patterns of settlement and land use. Using the Great Plains of the United States during the period of its initial Euro-American settlement (1880-1940) as an analytical lens, this article explores whether the same environmental factors that determine settlement timing and land use-those that indicate suitability for crop-based agriculture-also shape initial family formation, resulting in fewer and smaller families in areas that are more conducive to livestock raising than to cropping. The connection between family size and agricultural land availability is now well known, but the role of the environment has not previously been explicitly tested. Descriptive analysis offers initial support for a distinctive pattern of family formation in the western Great Plains, where precipitation is too low to support intensive cropping. However, multivariate analysis using county-level data at 10-year intervals offers only partial support to the hypothesis that environmental characteristics produce these differences. Rather, this analysis has found that the region was also subject to the same long-term social and demographic changes sweeping the rest of the country during this period.

Household and farm transitions in environmental context

Recent debate in the literature on population, environment, and land use questions the applicability of theory that patterns of farm extensification and intensification correspond to the life course of farmers and to the life cycle of farm families. This paper extends the debate to the agricultural development of the United States Great Plains region, using unique data from 1875 to 1930 that link families to farms over time in 25 environmentally diverse Kansas townships. Results of multilevel statistical modeling indicate that farmer's age, household size, and household structure are simultaneously related to both the extent of farm operations and the intensity of land use, taking into account local environmental conditions and time trends as Kansas was settled and developed. These findings validate farm- and life cycle theories and offer support for intergenerational motivations for farm development that include both daughters and sons. Environmental variation in aridity was a key driver of farm structure.

The consequence of encouraging girls to be active for weight loss

The purpose of the study, conducted in Pennsylvania, USA, was to assess the prospective effect of parental encouragement of physical activity (PA) for weight loss on adolescent girls' concern about weight, Body Mass Index (BMI) and objectively-measured PA. Non-Hispanic White girls (N = 177) and their parents were assessed when girls were 9, 11, 13 and 15 years old. At each age, girls' concern about their weight, pubertal development, BMI, and dietary intake were measured along with mothers' and fathers' encouragement of PA for weight loss, modeling of PA, and logistic support for PA. At ages 13 and 15 years, girls' PA was assessed using accelerometry. At age 11, girls' PA was measured using a combination of self-report measures and a standardized assessment of cardiovascular fitness. Parents of obese girls reported the highest encouragement of PA for weight loss; however, girls from all weight categories were exposed to encouragement of PA for weight loss and showed similar age-related increases in parental encouragement. Encouragement of PA for weight loss was prospectively associated with higher concern about weight and higher BMI, independent of pre-existing levels of these constructs and covariates. Encouragement of PA for weight loss was not associated with girls' objectively-measured PA. Parental encouragement of PA for weight loss was therefore not an effective strategy in this sample. Findings are consistent with research on parental child feeding practices, where parental control has been linked with unintended negative dietary and psychosocial outcomes among children.

Analysis of PCB congeners related to cognitive functioning in adolescents

To investigate the characteristics of PCBs that are linked to cognitive functioning, those congeners that were concurrently found in 271 Mohawk adolescents were grouped according to structure (dioxin-like or non-dioxin-like) and persistence (persistent or low-persistent). After the effects of the congener groups were orthogonalized, regression analyses (controlling for a number of variables found to be related to the cognitive outcomes) examined the relationship of each congener group to scores on three cognitive tests (the non-verbal Ravens Progressive Matrices, the Test of Memory and Learning, and the Woodcock Johnson-Revised). Five subtests from these cognitive tests were found to be associated with one or more PCB congener groups, most often at a moderate level. Two measures of long-term memory (Delayed Recall and Long Term Retrieval) were associated with all four congener groups. Nevertheless, examination of the role of individual congeners in the significantly related congener groups revealed that almost all congeners associated with cognitive outcomes were non-dioxin-like and ortho-substituted. A notable exception was the Ravens test where scores were associated only with dioxin-like congeners. This finding adds to the limited evidence of neurotoxic effects of dioxin-like congeners. Auditory Processing was related only to the persistent congener group. The association of the non-persistent congener group with three cognitive test scores (Delayed Recall, Long Term Retrieval and Comprehension-Knowledge) suggests that the Mohawk adolescents have experienced continuing or recent environmental exposure to PCBs that is sufficient to result in detectable cognitive decrements. Comparison of our findings with those of other human studies was limited by the relative lack of specificity of both PCB measures and cognitive outcome measures in much previous work.

A longitudinal assessment of the links between physical activity and self-esteem in early adolescent non-Hispanic females

PURPOSE

For decades, researchers have proclaimed the positive psychosocial benefits of participation in physical activity. However, recent meta-analyses of the literature have found infrequent and inconclusive empirical support for the link between physical activity and psychosocial well-being. In this study, we use data from a longitudinal study to explore the links between participation in physical activity and global self-esteem among girls from childhood into early adolescence and the direction of this relationship.

METHODS

Participants included 197 non-Hispanic white girls. Girls' participation in physical activity and their global self-esteem were assessed when they were 9, 11, and 13 years old. Panel regression was used to assess the lagged effect of physical activity on self-esteem and the lagged effect of self-esteem on physical activity, controlling for family socioeconomic status (SES) and girls' body mass index (BMI).

RESULTS

A significant lagged effect of physical activity on self-esteem was identified. Specifically, higher physical activity at ages 9 and 11 years predicted higher self-esteem at ages 11 and 13 years respectively, controlling for covariates. Positive effects of physical activity on self-esteem were most apparent at age 11 and for girls with higher BMI. No support was gained for the lagged effect of self-esteem on physical activity.

CONCLUSIONS

Results suggest that participating in physical activity can lead to positive self-esteem among adolescent girls, particularly for younger girls and those at greatest risk of overweight. These findings highlight the necessity of promoting physical activity among adolescent girls as a method of fostering positive self-worth.

Are the correlates of cigarette smoking initiation different for black and white adolescents?

BACKGROUND

Studies of adolescent smoking suggest that the causes of smoking initiation may differ for Blacks and Whites.

METHODS

Correlates of smoking initiation were examined among 1,277 nonsmokers, ages 12-14, who completed questionnaires in their homes. The analyses examined relationships between smoking initiation and 11 explanatory variables using logistic regression with the combined sample and with Black and White samples.

RESULTS

Over two years, 24 percent of Whites and 14 percent of Blacks started to smoke. Whites were more likely to start smoking at age 12 and Blacks at age 14. Having a best friend who smoked increased the odds of initiating smoking over twofold for Whites but had no effect on the odds of smoking for Blacks.

CONCLUSIONS

Whites initiate smoking earlier than Blacks and are more likely to be influenced by friend behavior.

Mobility and adjustments: paths to the resolution of residential stress

In theory, residential mobility is a response to environmental stress only if households do not reduce dissatisfaction through other alternatives, such as housing improvements or repairs. Despite the attention given to stress-reducing alternatives, however, no attempt has been made to test empirically the residential satisfaction model with adjustments. Using data from the Annual Housing Survey: 1978-1981, I model three stages in the mobility process and investigate potential sources of specification error in previous tests. Blocks of family cycle, background/action state, and location/housing variables are shown to affect adjusting significantly. Residential satisfaction strongly affects mobility preferences; and all theoretically relevant blocks of explanatory variables predict mobility. Alternatives to mobility should be included in the residential satisfaction model.

Mobility and adjustments: Paths to the resolution of residential stress

In theory, residential mobility is a response to environmental stress only if households do not reduce dissatisfaction through other alternatives, such as housing improvements or repairs. Despite the attention given to stress-reducing alternatives, however, no attempt has been made to test empirically the residential satisfaction model with adjustments. Using data from the Annual Housing Survey: 1978–1981, I model three stages in the mobility process and investigate potential sources of specification error in previous tests. Blocks of family cycle, background/action state, and location/housing variables are shown to affect adjusting significantly. Residential satisfaction strongly affectsmobility preferences; and all theoretically relevant blocks of explanatory variables predict mobility. Alternatives to mobility should be included in the residential satisfaction model.