Exposure to environmental contaminants has been shown to alter normal thyroid function in various wildlife species, including the American alligator (Alligator mississippiensis). Abnormalities in circulating levels of the thyroid hormone thyroxine (T4) have been reported in juvenile alligators from several contaminated lakes in Florida. To further elucidate these functional thyroid abnormalities, this study examines the structure of thyroids and circulating T4 concentrations from juvenile alligators collected from three sites of varying contamination on Lake Okeechobee, Florida. The following variables were used to characterize thyroid morphology: epithelial cell height, width and area, percent colloid, and follicle area. These variables were compared among study sites and between genders. No difference was detected in epithelial cell height, epithelial cell area, or follicle area among the sites, whereas significant differences in epithelial cell width (p=0.02) and percent colloid (p=0.008) were found. Animals from the most contaminated site (Belle Glade) had significantly greater epithelial cell widths and significantly less colloid present in their follicles compared to animals from the reference site (West). Gender did not have a significant interaction with site for any variable measured. Thyroxine (T4) concentrations were elevated in the intermediately contaminated site (Conservation Area 3A) compared to the other sites (p<0.0001). It is proposed that the disruptions seen in Lake Okeechobee alligators are due to disruptions at both the thyroid and extra-thyroidal tissues. 相似文献
Objectives: The objective of this study was to examine the association between dangerous student car drop-off behaviors and historical child pedestrian–motor vehicle collisions (PMVCs) near elementary schools in Toronto, Canada.
Methods: Police-reported child PMVCs during school travel times from 2000 to 2011 were mapped within 200 m of 118 elementary schools. Observers measured dangerous student morning car drop-off behaviors and number of children walking to school during one day in 2011. A composite score of school social disadvantage was obtained from the Toronto District School Board. Built environment and traffic features were mapped and included as covariates. A multivariate Poisson regression was used to model the rates of PMVC/number of children walking and dangerous student car drop-off behaviors, adjusting for the built environment and social disadvantage.
Results: There were 45 child PMVCs, with 29 (64%) sustaining minor injuries resulting in emergency department visits. The mean collision rate was 2.9/10,000 children walking/year (SD = 6.7). Dangerous drop-off behaviors were observed in 104 schools (88%). In the multivariate analysis, each additional dangerous drop-off behavior was associated with a 45% increase in collision rates (incident rate ratio [IRR] = 1.45, 95% confidence interval [CI], 1.02, 2.07). Higher speed roads (IRR = 1.27, 95% CI, 1.13, 1.44) and social disadvantage (IRR = 2.99, 95% CI, 1.03, 8.68) were associated with higher collision rates.
Conclusions: Dangerous student car drop-off behaviors were associated with historical nonfatal child PMVC rates during school travel times near schools. Some caution must be taken in interpreting these results due small number of events and limitations in the data collection, because collision data were collected historically over a 12-year period, whereas driving behavior was only observed on a single day in 2011. Targeted multifaceted intervention approaches related to the built environment, enforcement, and education could address dangerous drop-off behaviors near schools to reduce child PMVCs and promote safe walking to school. 相似文献
Low birth weight (LBW) is associated with a number of maternal environmental exposures during pregnancy. This study explored the association between soil metal concentrations around the home where the mother lived during pregnancy and the outcome of LBW. We used a retrospective cohort of 9,920 mother–child pairs who were insured by Medicaid during pregnancy and lived in ten residential areas, where we conducted soil sampling. We used a grid that overlaid the residential areas and collected soil samples at the grid intersections. The soil was analyzed for the concentration of eight metals [arsenic (As), barium (Ba), chromium (Cr), copper (Cu), lead (Pb), manganese (Mn), nickel (Ni), and mercury (Hg)], and we then used Bayesian Kriging to estimate the concentration at the actual maternal addresses, since we had the GIS coordinates of the homes. We used generalized additive modeling, because the metal concentrations had nonlinear associations with LBW, to develop the best fitting multivariable model for estimating the risk of LBW. The final model showed significant associations for female infants, maternal smoking during pregnancy, non-white mothers, Cu, and As with LBW. The As variable was nonlinear in relation to LBW, and the association between higher concentrations of As with LBW was strong (p = 0.002). We identified a statistically significant association between soil concentrations of arsenic around the home of pregnant women and an increased risk of LBW for her infant. 相似文献
Poly(lactic acid) (PLA) has been modified using twin-screw reactive extrusion to improve its melt properties and crystallinity. In this work lauroyl peroxide was used as an alkyl free radical source, abstracting hydrogen atoms from the PLA backbone leading to branching and chain extension reactions. Once the linear viscoelastic region was determined for these polymers, changes in dynamic rheology (dynamic viscosity real and loss modulus) were measured. Gel permeation chromatography showed that the molecular weight and polydispersity increased to a maximum with the addition of 1.00 and 0.50?wt% peroxide, respectively. Low temperature ?? transitions in dynamical mechanical thermal traces gave further evidence that branching had also occurred. G?ttfert Rheotens measurements showed a three fold increase in melt strength due to both increased chain length and branching. Thermal analysis showed the level of crystallisation had decreased also possibly due to branching. Reductions in crystallinity and improved melt strength are known to be critical for film and foam formation. 相似文献
Predation exerts tremendous selection pressure on all organisms. In this study, we exposed embryos of convict cichlids (Amatitlania siquia) twice daily to one of the following: (1) chemical alarm cues of damaged conspecifics + odour of a novel predator (Polypterus endlicheri), (2) chemical alarm cues of damaged conspecifics + water or (3) blank water. No chemical cues were presented after the eggs hatched. When the larvae were 9 days old (mean total length?=?5.7 mm), they were exposed to either predator odour or water. Those larvae that had been conditioned as embryos on alarm cues + predator odour showed a significant reduction in activity (i.e. anti-predator behavioural response) to predator odour relative to the other treatments. This is the first demonstration of acquired predator recognition by fish embryos. 相似文献
We propose a space-time stick-breaking process for the disease cluster estimation. The dependencies for spatial and temporal effects are introduced by using space-time covariate dependent kernel stick-breaking processes. We compared this model with the space-time standard random effect model by checking each model’s ability in terms of cluster detection of various shapes and sizes. This comparison was made for simulated data where the true risks were known. For the simulated data, we have observed that space-time stick-breaking process performs better in detecting medium- and high-risk clusters. For the real data, county specific low birth weight incidences for the state of South Carolina for the years 1997–2007, we have illustrated how the proposed model can be used to find grouping of counties of higher incidence rate. 相似文献
Terrestrial CO2 flux estimates are obtained from two fundamentally different methods generally termed bottom-up and top-down approaches. Inventory methods are one type of bottom-up approach which uses various sources of information such as crop production surveys and forest monitoring data to estimate the annual CO2 flux at locations covering a study region. Top-down approaches are various types of atmospheric inversion methods which use CO2 concentration measurements from monitoring towers and atmospheric transport models to estimate CO2 flux over a study region. Both methods can also quantify the uncertainty associated with their estimates. Historically, these two approaches have produced estimates that differ considerably. The goal of this work is to construct a statistical model which sensibly combines estimates from the two approaches to produce a new estimate of CO2 flux for our study region. The two approaches have complementary strengths and weaknesses, and our results show that certain aspects of the uncertainty associated with each of the approaches are greatly reduced by combining the methods. Our model is purposefully simple and designed to take the two approaches’ estimates and measures of uncertainty at ‘face value’. Specifically, we use a constrained least-squares approach to appropriately weigh the estimates by the inverse of their variance, and the constraint imposes agreement between the two sources. Our application involves nearly 18,000 flux estimates for the upper midwest United States. The constrained dependencies result in a non-sparse covariance matrix, but computation requires only minutes due to the structure of the model. 相似文献
Synchronous and intermittent reproduction in long-lived plants, known as mast seeding, is induced by climatic cues, but the mechanism explaining variation in masting among neighboring but edaphically segregated species is unknown. Soil nutrients can enhance flowering, and thus, populations on nutrient-rich soils may require less-favorable growing temperatures to flower. We tested this hypothesis by predicting the probability of flowering in response to air temperature for five species of alpine Chionochloa grasses in South Island, New Zealand, over 37 years and relating our predictions to soil N supply (NH4(+) + NO3(-)). Summer air temperatures better predicted flowering than spring air temperatures, which were correlated with soil N mineralization. Species on N-rich soils required lower mean temperatures to induce flowering and/or responded more consistently across a gradient of air temperatures, contributing to the higher probability of their tillers and tussocks flowering at low summer temperatures. Our results suggest that flowering primarily occurs in response to warm summer temperatures, but species on N-rich soils require less favorable growing conditions because they invest relatively less N in seeds. Thus, predicting masting requires a consideration of the interactions among climate, the internal resources of plants, and mineral nutrient uptake. 相似文献