It is suggested that assessments of chemicals of emerging concern can be rationally structured around a multistage process in which fate and risk are evaluated with increasing accuracy as new data become available. An initial tentative and approximate assessment of fate and risk can identify key data gaps and justify and direct further investigations, which progressively improve the reliability of the assessment. This approach is demonstrated for a class of chemicals, the polybrominated diphenyl ethers (PBDEs), which is of increasing concern, but about which there is presently a lack of comprehensive data on properties, sources, fate and effects. Specifically, 20 PBDE congeners are investigated using the suggested approach and research needs are identified. 相似文献
Cross-border transport of ozone is one of the most contentious issues of air pollution management in the U.S. Yet, both the modeling and observational studies are lacking. Models are normally validated by comparing predicted and observed ozone concentrations. However, proper validation of cross-border transport model requires a comparison of predictions against observation-based benchmarks of cross-border ozone transport. Such benchmarks are unavailable, as published observation-based studies always deal only with a combination of local production and cross-border transport, not a cross-border transport itself. We show how to extract necessary benchmarks from observations of rural monitoring sites near state borders. On example of the western border of New York, we find that in about two-thirds of the most polluted days all the ozone came in a steady cross-border inflow after previously passing over one or more large urban areas to the west. In all the enumerated days with direct cross-border inflow, daily maximum 8-hr concentrations of ozone just upwind of the border were over 60 ppb, with an average value of 68 ppb, just short of the 70 ppb ozone regulatory threshold, information also useful to state air pollution authorities.
Implications: The purpose of the cross-border ozone pollution models is to predict cross-border transport of ozone, so the ability of the model to accurately represent observed ozone concentrations is necessary but not sufficient for model validation. The accuracy of predicted ozone concentrations is not necessarily the same as the accuracy of the predictions of ozone transport. Proper model validation requires comparisons against observation-based benchmarks of cross-border transport. Such observations, so far absent, can be obtained from rural monitoring sites near state borders, as illustrated by the example of western New York. 相似文献
This research examines the pattern of sediment contamination of an urban bayou of New Orleans (formerly a natural waterway) and the potential for human exposure from consumption of fish caught in the bayou. Sediments and soils of Bayou Saint John were evaluated for lead (Pb), zinc (Zn), and cadmium (Cd). Sediment cores were collected at bridges (n = 130) and sites between the bridges (n = 303) of the bayou. In addition, soil samples (n = 66) were collected along the banks of the bayou. Sediments below the bridges contain significantly more (p-value approximately 10(-7)) Pb and Zn (medians of 241 and 230 mg kg(-1), respectively) than bayou sediments located between bridges (medians of 64 and 77 mg kg(-1), respectively). Sediments below bridges of the upper reaches of the bayou contain significantly larger amounts of metals (p < 10(-14) for Pb and Zn and p approximately 10(-8) for Cd) (medians of 329, 383 and 1.5, respectively) than sediments below bridges in the lower reaches of the bayou (medians of 43, 31 and 0.5 for Pb, Zn and Cd, respectively). Likewise, medians for sediments located between bridges contain significantly (p < 10(-14)) higher quantities of Pb, Zn and Cd (170, 203 and 1.8 mg kg(-1), respectively) in the upper bayou than Pb, Zn, and Cd (48, 32, and 0.8 mg kg(-1), respectively) in the lower reaches of the bayou. The potential risk for human exposure may be magnified by the fact that fishing generally occurs from the numerous bridges that cross the bayou. Poor and minority people do most of the fishing. Most people (87%) indicated they ate fish they caught from the Bayou. 相似文献
Summary The production of volatile secondary plant substances during the evolution of terrestrial plants is reviewed in regard to the defensive systems of plants to microorganisms and herbivores. Plant volatiles can be produced by both anabolic and catabolic processes. Although attraction of pollinators is a well-studied phenomenon, functions of volatiles range from excretion of waste products to the production of compounds attracting natural enemies of herbivores. During the evolution of the angiosperms a diversity of volatiles were selected to defend generative parts against microorganisms. Many of these allomones were related to or even identical with sex pheromones of insects. As a result flowers of angiosperms became utilized as a mating site. Consequently insects visiting flowers became involved in pollination, facilitating the steps from anemophily to entomophily. The efficiency of entomophily was increased because of nutritional rewards.An evolutionary scenario for the impact of plant volatiles on insects is presented and the role of volatile allomones in the establishment of plant-insect relationships is emphasized by (1) their strong antimicrobial properties, (2) strategies to protect symbiotic microorganisms, (3) their function as repellents and deterrents, (4) the use of volatile allomones as kairomones. These facts speak for an adaptation of insects to plant physiology and a limited importance of phytophagous insects in selection pressure upon plants. Herbivorous insects have realized specific adaptations to be able to discriminate between complex odour blends, but the utilization of chemical groups among insect taxa is different.The main theories on plant chemical defence do not discuss the impact of volatiles on host plant selection and may be apt to revision when pheromones, allomones, kairomones and synomones are not taken into account. 相似文献
The present study utilizes meta‐analytic techniques to examine the literature on sleep and work performance. In line with previous meta‐analytic research, results indicate that sleep and work performance have a positive relationship. However, more importantly, results from moderator analyses reveal that the type of sleep measurement (sleep quantity and sleep quality), work performance measurement (task performance, organizational citizenship behavior, and counterproductive work behavior), analysis method (between‐person and within‐person), sleep report source (self‐report, other report, and objective), sleep recall window (day, week/month, and more than 1 month), and study setting (field and laboratory) differentially influence the strength of the sleep–work performance relationship. Furthermore, meta‐analytic SEM results indicate that certain mediators (affect, job attitudes, and cognitive resources) provide stronger explanations (i.e., stronger indirect effects) for the relationship between sleep and work performance, depending on the specific type of performance being examined. In general, results highlight the importance of construct operationalization and methodology decisions when conducting sleep–work performance research and provide greater insight into explanations for the relationship between sleep and work performance. Research implications, practical implications, potential limitations, and future directions are also discussed. 相似文献