Risk assessments for forest trees: the performance of the ozone flux versus the AOT concepts

Published ozone exposure-response relationships from experimental studies with young trees performed at different sites across Europe were re-analysed in order to test the performance of ozone exposure indices based on AOTX (Accumulated exposure Over a Threshold of X nmol mol(-1)) and AF(st)Y (Accumulated Stomatal Flux above a threshold of Y nmol m(-2) s(-1)). AF(st)1.6 was superior, as compared to AOT40, for explaining biomass reductions, when ozone sensitive species with differing leaf morphology were included in the analysis, while this was not the case for less sensitive species. A re-analysis of data with young black cherry trees, subject to different irrigation regimes, indicated that leaf visible injuries were more strongly related to the estimated stomatal ozone uptake, as compared to the ozone concentration in the air. Experimental data with different clones of silver birch indicated that leaf thickness was also an important factor influencing the development of ozone induced leaf visible injury.     

Reproducibility and imputation of air toxics data

Ambient air quality datasets include missing data, values below method detection limits and outliers, and the precision and accuracy of the measurements themselves are often unknown. At the same time, many analyses require continuous data sequences and assume that measurements are error-free. While a variety of data imputation and cleaning techniques are available, the evaluation of such techniques remains limited. This study evaluates the performance of these techniques for ambient air toxics measurements, a particularly challenging application, and includes the analysis of intra- and inter-laboratory precision. The analysis uses an unusually complete-dataset, consisting of daily measurements of over 70 species of carbonyls and volatile organic compounds (VOCs) collected over a one year period in Dearborn, Michigan, including 122 pairs of replicates. Analysis was restricted to compounds found above detection limits in > or =20% of the samples. Outliers were detected using the Gumbell extreme value distribution. Error models for inter- and intra-laboratory reproducibility were derived from replicate samples. Imputation variables were selected using a generalized additive model, and the performance of two techniques, multiple imputation and optimal linear estimation, was evaluated for three missingness patterns. Many species were rarely detected or had very poor reproducibility. Error models developed for seven carbonyls showed median intra- and inter-laboratory errors of 22% and 25%, respectively. Better reproducibility was seen for the 16 VOCs meeting detection and reproducibility criteria. Imputation performance depended on the compound and missingness pattern. Data missing at random could be adequately imputed, but imputations for row-wise deletions, the most common type of missingness pattern encountered, were not informative. The analysis shows that air toxics data require significant efforts to identify and mitigate errors, outliers and missing observations, and that these steps are essential and should be performed prior to using these data in receptor, exposure, health and other applications.     

Bioaccumulation of trace elements in pelagic fish from the Western Indian Ocean

Trace elements were analyzed in fish of commercial interest to determine their importance in marine systems of the Western Indian Ocean and their bioaccumulation patterns. The results are equivalent or lower than levels reported in ichthyofauna worldwide. Certain values of muscular Cd, Hg, Pb and Zn were, however, above thresholds for human consumption. Levels varied among tissues, species and fish length, but were seldom influenced by the nutritional condition of the fish, its gender and its reproductive status. Correlations between hepatic Hg and Se levels in Swordfish (r2=0.747) and Yellowfin Tunas (r2=0.226), and among metallothionein linking metals imply the existence of detoxification processes in these species. Level differences between fish from the Mozambique Channel and Reunion Island reflect differences of diets rather than differences of elemental availability in both environments.     

Imputing Unmeasured Explanatory Variables in Environmental Epidemiology With Application to Health Impact Analysis of Air Pollution

This paper presents the results of a reconsideration of earlier work that finds an association between daily hospital admissions for respiratory distress and daily concentrations of sulphate (lag 1) as well as daily maximum concentrations of ozone (lags 1 and 3). These associations are found even after clustering the data by hospital of admission and accounting for the effects of temperature. We use an adaptation of their generalized estimating equation technique for clustered data, that daily data being for southern Ontario summers from 1983 to 1988. Like them, we adjust for daily maximum temperatures. However, unlike the earlier work returned to ours includes daily average humidity as a potential explanatory variable in our model. Our analysis also differs from theirs in that we cluster the data by census subdivision to reduce the risk of confounding pollutant levels with population size within regions. Moreover, we log-transform the explanatory variables and then high-pass filter the resulting data. We also deviate from the earlier analysis by taking account of measurement error incurred in using surrogate measures of the explanatory variables. To do so we use new methodology designed for our study but of potential value in other applications. That methodology requires a spatial predictive distribution for the unmeasured explanatory variables. Each day about 700 missing measurements for each of these variables can then be imputed over the geographical domain of the study. With these imputations we get a measure of imputation error through the covariance of the predictive distribution. Along with the predictive distribution we require an impact model to link-up with the predictive distribution. We describe that model and show how it uses the imputed measurements of the missing values of the explanatory variables. We also show how through that model, uncertainty about these values is reflected in our analysis and in commensurate uncertainties in the inferences made. Apart from its substantive objectives, our analysis serves to test the new methods with the earlier results serving as a foil. The reassuring qualitative agreement between our findings and the earlier results seems encouraging.     

Alpha-male paternity in elephant seals

The aim of this study was to assess paternity of males that dominated mating in harems at northern (Mirounga angustirostris) and southern (M. leonina) elephant seal rookeries using DNA fingerprinting and microsatellite DNA analysis. Southern alpha males had greater reproductive success than most northern alphas at similar-sized harems. Comparison of the relatedness between pups within harems also suggested that fewer males achieved matings in the southern elephant seal population. This was consistent with behavioral observations that suggest greater competition for mates in northern elephant seal harems. Reproductive success was consistent with estimates of mating success in some cases, but lower than expected for some northern elephant seal alpha males. A lower reproductive success than predicted from mating behavior may arise from a variety of factors including sperm competition, male sperm depletion from frequent mating, or reduced fertility. The alternatives are discussed in the context of environmental and historical factors. Received: 17 August 1998 / Received in revised form: 28 March 1999 / Accepted: 30 May 1999     

The influence of career stage on the work attitudes of male and female accounting professionals

The present study compared work commitments, overall job satisfaction, intrinsic and extrinsic rewards satisfactions, and organizational and professional turnover intentions of 718 male and female accounting professionals at different career stages. Career stage was measured by professional tenure. The results indicate that there are some differences in work attitudes across career stages for male accounting professionals. Job involvement, organizational commitment, and intrinsic and extrinsic rewards satisfaction are positively related to professional tenure. Organizational turnover intentions are negatively related to professional tenure for male accounting professionals. There are no significant differences in work attitudes across career stages for female accounting professionals. An examination of reasons for differences in work attitude patterns between male and female accountants suggests the need for research to determine whether later career stages (advancement and maintenance) differ for men and women. The results also suggest that future research should consider defining career stage in terms of the overlap between stages defined using alternate career stage measures.     

A novel hydrothermal method to synthesize brookite titanium dioxide nanosquares for efficient pollutant degradation

Environmental Chemistry Letters - Photocatalysis is a cost-effective method to degrade and remove pollutants, using semiconductor catalysts such as titanium dioxide. The brookite form of titanium...     

Evaluation of analytical strategies for the determination of metal concentrations to assess landfill leachate contamination

Due to the complex nature of landfill leachates, metal and metalloid analyses prove to be tricky and suffer from a lack of standard protocols. A complete approach has been adopted to investigate the influence of the different steps during the sample processing of French landfill leachates. The validation of the entire protocol has been achieved using a laboratory reference material. This material, which is a real landfill leachate, is representative of real samples. Its evaluation has allowed a quality control for metal and metalloid analyses in landfill leachates. Precautions concerning storage temperature, aeration and filtration are proposed to perform accurate metal analyses in these complex matrices. The sample processing has been applied to the seasonal monitoring of a French landfill. The assessment of major leachate metallic contaminants such as As, Cr, Sb, Sn, has been performed by evaluating the relative enrichment of metals and metalloids in comparison with rain water and groundwater. In addition, hydrological data are useful and complementary information for pointing out the main factors affecting metal concentrations and thus their potential remobilisation pathways.     

Turbulent flow over a D-section bluff body: a numerical benchmark

Environmental Fluid Mechanics - A numerical benchmark of different turbulence closures was performed to investigate the turbulent wake flow behind a submerged D-shaped bluff body. The numerical...