Determining the frequency of asbestos use in automotive brakes from a fleet of on-road California vehicles.

Asbestos is a known human carcinogen, and recent regulation in California limits asbestiform fibers in brakes to trace levels beginning in 2014, although there is no corresponding federal requirement. In order to gauge the current prevalence of asbestos use in automotive brake applications, the California Air Resources Board tested brake linings from 137 light- and medium-duty vehicles and 54 heavy-duty vehicles. Only about 3% of the light- and medium-duty vehicle brake linings contained chrysotile asbestos. All of those brake linings were drum-type shoes, which are generally being phased out. No asbestos was found in low mileage vehicles presumed to have their original stock linings from the vehicle manufacturer. Additionally, no asbestos was found in the heavy-duty vehicle brake shoe linings sampled. Given the small percentage of vehicle brake linings with asbestos observed, it appears that the prior federal ban that was subsequently overturned, in combination with a threat of litigation, has reduced asbestos use in brake linings. However, our study was limited in scope and without a national ban, the current and future prevalence of asbestos in brakes is uncertain, suggesting the need for continued monitoring of materials released as toxic air contaminants in normal braking operations.

Insect sociality and its consequential effects on intraspecific competition.

The phenomenon of colonialism which characterizes many insect groups is considered in terms of its potential effect on intraspecific competition. Intraspecific competition is assumed to be a function of the number of distinct pair encounters between 2 individuals of differing colony origin. A model is offered which describes the reduction in the number of potential competing encounters as a result of colonialism, and as such, combinatorial formulae are appropriate. For 2-colony and multi-colony systems, there is a proportionately smaller number of potential competing encounters as the size of the colonies becomes more inequitable and greater than 100 individuals in combined total. As a consequence, large inequitabilities in colony sizes are expected for nearest neighbor pairs, and thus a generally large variance in colony size for groups of colonies is also expected. Empirical data from various sources is presented and in good agreement with the predictions generated from the model.