Differential effects of air conditioning type on residential endotoxin levels in a semi-arid climate.

Residential endotoxin exposure is associated with protective and pathogenic health outcomes. Evaporative coolers, an energy-efficient type of air conditioner used in dry climates, are a potential source of indoor endotoxins; however, this association is largely unstudied. We collected settled dust biannually from four locations in homes with evaporative coolers (n=18) and central air conditioners (n=22) in Utah County, Utah (USA), during winter (Jan-Apr) and summer (Aug-Sept), 2014. Dust samples (n=281) were analyzed by the Limulus amebocyte lysate test. Housing factors were measured by survey, and indoor temperature and relative humidity measures were collected during both seasons. Endotoxin concentrations (EU/mg) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons. Endotoxin surface loads (EU/m2 ) were significantly higher in homes with evaporative coolers from mattress and bedroom floor samples during both seasons and in upholstered furniture during winter. For the nine significant season-by-location comparisons, EU/mg and EU/m2 were approximately three to six times greater in homes using evaporative coolers. A plausible explanation for these findings is that evaporative coolers serve as a reservoir and distribution system for Gram-negative bacteria or their cell wall components in homes.

Specific gravity adjustment of urine analysis results.

Analysis of urine samples for compounds such as lead, phenol, or 4,4'-methylene bis (2-chloroaniline) (MBOCA) are often adjusted for specific gravity following a recommendation in a NIOSH Benzene Criteria Document. The adjustment normalizes all results to a specific gravity of 1.024 by multiplying the analytical result in microgram/liter by 24/G where G is the last 2 digits of the specific gravity of the urine sample. The adjustment calculation is based on a suggestion by Levine and Fahy, who found that the urine solids content is roughly proportional to 24/G. We believe this adjustment to be inappropriate based on the following considerations.