Use of dust fall filters as passive samplers for metal concentrations in air for communities near contaminated mine tailings.

Mine tailings are a source of metal exposures in many rural communities. Multiple air samples are necessary to assess the extent of exposures and factors contributing to these exposures. However, air sampling equipment is costly and requires trained personnel to obtain measurements, limiting the number of samples that can be collected. Simple, low-cost methods are needed to allow for increased sample collection. The objective of our study was to assess if dust fall filters can serve as passive air samplers and be used to characterize potential exposures in a community near contaminated mine tailings. We placed filters in cylinders, concurrently with active indoor air samplers, in 10 occupied homes. We calculated an estimated flow rate by dividing the mass on each dust fall filter by the bulk air concentration and the sampling duration. The mean estimated flow rate for dust fall filters was significantly different during sampling periods with precipitation. The estimated flow rate was used to estimate metal concentration in the air of these homes, as well as in 31 additional homes in another rural community impacted by contaminated mine tailings. The estimated air concentrations had a significant linear association with the measured air concentrations for beryllium, manganese and arsenic (p < 0.05), whose primary source in indoor air is resuspended soil from outdoors. In the second rural community, our estimated metal concentrations in air were comparable to active air sampling measurements taken previously. This passive air sampler is a simple low-cost method to assess potential exposures near contaminated mining sites.

Resonant-cavity-enhanced thin-film AlGaAs/GaAs/AlGaAs LED's with metal mirrors.

Resonant-cavity-enhanced light-emitting diodes (RCE LED's) are of increasing interest as a low-cost alternative to lasers for short-distance applications. We report on the characteristics of thin-film AlGaAs/GaAs/AlGaAs double-heterostructure RCE LED's with metal mirrors on both sides fabricated by means of epitaxial liftoff and bonded to silicon host substrates. The devices exhibit typical turn-on voltages of 1.3 V, operating resistances of 31 Ω, linewidths of 10.4 nm, efficiencies of 1.4%, dispersion half-angles of 23.7°, and stable output over more than 1700 h. These devices exhibit significant improvement over conventional LED's without additional complicated processing or growth steps, resulting in a manufacturable, low-cost device.