RESUMEN
The accumulation, enrichment and provenance of selected trace metals (Ag, As, Cd, Cr, Cu, Hg, Ni, Pb, V and Zn) were studied in sediment cores collected from three lakes located in the Central Mexican Plateau, selected on the basis of their contrasting degree of urbanization: Santa Elena Lake, in a rural and remote area; El Tule Lake, in a rural and slightly urbanized area; and Chapala Lake, in a highly urbanized area. Grain size, magnetic susceptibility and sedimentary constituents such as organic carbon, calcium carbonate, as well as major (Al, Fe, Mn) and minor (Ca, Li, Rb, Sr, Th) elements were analyzed to explain the concentration trends of trace metals. Factor analysis (FA) was used to assess the provenance of the trace elements. The highest metal enrichment factor (EF) above natural concentration levels was found at Chapala Lake for Ag (EF = 3.9), although other trace element EF in all lakes was <2.0, indicating slight contamination. However, the concentration levels of Cr and Ni in all lakes, Hg and Zn in Chapala Lake, Cu in El Tule Lake and As in Santa Elena Lake were above international benchmarks for which adverse effects are expected to occur frequently, even for those metals only slightly enriched (e.g. As, Cr). Through FA, the terrigenous contribution was identified as the most important source of trace metals to the three lakes, most likely related to deforestation and erosion of the surrounding areas, followed by atmospheric transport of volcanic ashes, rather than to direct sources.
Asunto(s)
Monitoreo del Ambiente/estadística & datos numéricos , Contaminación Ambiental/análisis , Sedimentos Geológicos/química , Lagos/química , Radioisótopos de Plomo/análisis , Metales Pesados/análisis , Monitoreo del Ambiente/métodos , Análisis Factorial , México , Tamaño de la PartículaRESUMEN
We designed an in vitro assay to detect the presence of lactose in the tracheal aspirates of premature, ventilator-dependent infants. This method was employed to identify recurrent, unrecognized aspiration, which could prolong the requirements for ventilator support and contribute to the development of chronic lung disease. One hundred five determinations of lactose were performed on the tracheal fluid obtained from 42 ventilator-dependent infants who were receiving enteral feedings. There was a wide range of lactose levels (0 to 3,270 nmol lactose/ml tracheal aspirate). Six infants had samples that were highly suggestive of aspiration (greater than 200 nmol lactose/ml tracheal aspirate). Twenty infants had questionably positive samples (25 to 200 nmol lactose/ml tracheal aspirate), and 16 infants had samples that were considered negative for aspiration (less than 25 nmol lactose/ml tracheal aspirate).