Relative importance of school bus-related microenvironments to children's pollutant exposure

Real-time concentrations of black carbon, particle-bound polycyclic aromatic hydrocarbons, nitrogen dioxide, and fine particulate counts, as well as integrated and real-time fine particulate matter (PM2.5) mass concentrations were measured inside school buses during long commutes on Los Angeles Unified School District bus routes, at bus stops along the routes, at the bus loading/unloading zone in front of the selected school, and at nearby urban "background" sites. Across all of the pollutants, mean concentrations during bus commutes were higher than in any other microenvironment. Mean exposures (mean concentration times time spent in a particular microenvironment) in bus commutes were between 50 and 200 times greater than those for the loading/unloading microenvironment, and 20-40 times higher than those for the bus stops, depending on the pollutant. Although the analyzed school bus commutes represented only 10% of a child's day, on average they contributed one-third of a child's 24-hr overall black carbon exposure during a school day. For species closely related to vehicle exhaust, the within- cabin exposures were generally dominated by the effect of surrounding traffic when windows were open and by the bus's own exhaust when windows were closed. Low-emitting buses generally exhibited high concentrations only when traveling behind a diesel vehicle, whereas high-emitting buses exhibited high concentrations both when following other diesel vehicles and when idling without another diesel vehicle in front of the bus. To reduce school bus commute exposures, we recommend minimizing commute times, avoiding caravanning with other school buses, using the cleanest buses for the longest bus routes, maintaining conventional diesel buses to eliminate visible emissions, and transitioning to cleaner fuels and advanced particulate control technologies as soon as possible.     

Sources of variability in plant toxicity testing

Published literature is investigated regarding the response of plants to various substances to determine the sensitivity of agricultural plants versus other species, the similarity of effects seen at different taxonomic levels, sensitivity of plants growing outdoors versus in a greenhouse, and the sensitivity of different measurement endpoints. We find that agricultural species are not consistently more or less sensitive to the herbicides tested than non-crop species. Genus and family taxonomic groupings may show similar responses among species, but this similarity quickly decreases as the comparison progress between orders and classes. Results from field and greenhouse studies are less in agreement between studies than data from the other topics. Shoot length will be affected at concentrations lower than for other vegetative endpoints for most species tested for inorganic substances, but for organic substances root and shoot mass were more sensitive. Overall, there is no one species or endpoint that is consistently the most sensitive for all species or all chemicals in all soils, and differences in bioavailability among compounds may confound comparison of test results. Therefore, species sensitivity distributions, adjusted for bioavailability when possible, should be considered in order to better evaluate effects to non-target terrestrial plants.     

The endocrinology of sunlight and darkness

Information from autoradiographic studies and follow-up indicates that 1,25(OH)2 vitamin D3 (soltriol) is a somatotrophic activator and modulator, regulated by the amount of sunshine and the endocrine status of the individual, with the purpose of promoting development, reproduction, and maintenance of life. Regulation of calcium homeostasis is only one of its many functions. A close link to the pineal hormone system is apparent. Evidence supports the new concept that the skin-derived hormone of sunlight and the pineal hormone(s) of darkness are messengers with comprehensive actions on endocrine, autonomic, sensory, skeletal, and motor functions. In a complementary fashion, both hormone systems appear to correlate biological activities with the daily and seasonal changes of our solar environment.