Aeolian dust in Colorado Plateau soils: nutrient inputs and recent change in source.

Aeolian dust (windblown silt and clay) is an important component in arid-land ecosystems because it may contribute to soil formation and furnish essential nutrients. Few geologic surfaces, however, have been characterized with respect to dust-accumulation history and resultant nutrient enrichment. We have developed a combination of methods to identify the presence of aeolian dust in arid regions and to evaluate the roles of this dust in ecosystem processes. Unconsolidated sandy sediment on isolated surfaces in the Canyonlands region of the Colorado Plateau differs greatly in mineralogical and chemical composition from associated bedrock, mainly aeolian sandstone. Detrital magnetite in the surficial deposits produces moderately high values of magnetic susceptibility, but magnetite is absent in nearby bedrock. A component of the surficial deposits must be aeolian to account for the abundance of magnetite, which formed originally in far-distant igneous rocks. Particle-size analysis suggests that the aeolian dust component is typically as much as 20-30%. Dust inputs have enriched the sediments in many elements, including P, Mg, Na, K, and Mo, as well as Ca, at sites where bedrock lacks calcite cement. Soil-surface biologic crusts are effective dust traps that apparently record a change in dust sources over the past several decades. Some of the recently fallen dust may result from human disturbance of land surfaces that are far from the Canyonlands, such as the Mojave Desert. Some land-use practices in the study area have the potential to deplete soil fertility by means of wind-erosion removal of aeolian silt.

Respirable particles in the excimer laser plume.

PURPOSE: To determine whether respirable-size particles are present in the excimer laser plume following ablation of the corneal stroma. SETTING: Outpatient laser vision correction facility. METHODS: In this experimental study, an excimer laser was used to ablate 2 eye-bank corneas. Material from the plume was collected with filter paper that was coupled to a smoke evacuator. The filter paper was examined and photographed with an electron microscope. The particle size was measured with a computer program using digitized images of the photographs. As a control, room air was sampled using a smoke evacuator connected to a holder containing filter paper prior to the tissue ablation. RESULTS: Ninety-eight particles were measured. The mean diameter was 0.22 microm +/- 0.056 (SD). No particles were seen on the control filter paper. CONCLUSIONS: The plume created during excimer laser ablation of the cornea contained respirable-size particles. It is not known whether inhalation of these particles poses a significant health hazard. However, we recommend that a mask be worn by the surgeon and technical personnel assisting in excimer laser surgery. The plume should also be evacuated.