Formaldehyde concentrations in household air of asthma patients determined using colorimetric detector tubes.

Formaldehyde is a colorless, pungent gas commonly found in homes and is a respiratory irritant, sensitizer, carcinogen, and asthma trigger. Typical household sources include plywood and particleboard, cleaners, cosmetics, pesticides, and others. Development of a fast and simple measurement technique could facilitate continued research on this important chemical. The goal of this research is to apply an inexpensive short-term measurement method to find correlations between formaldehyde sources and concentration, and formaldehyde concentration and asthma control. Formaldehyde was measured using 30-min grab samples in length-of-stain detector tubes in homes (n = 70) of asthmatics in the Boston, MA area. Clinical status and potential formaldehyde sources were determined. The geometric mean formaldehyde level was 35.1 ppb and ranged from 5 to 132 ppb. Based on one-way ANOVA, t-tests, and linear regression, predictors of log-transformed formaldehyde concentration included absolute humidity, season, and the presence of decorative laminates, fiberglass, or permanent press fabrics (P < 0.05), as well as temperature and household cleaner use (P < 0.10). The geometric mean formaldehyde concentration was 57% higher in homes of children with very poorly controlled asthma compared to homes of other asthmatic children (P = 0.078). This study provides a simple method for measuring household formaldehyde and suggests that exposure is related to poorly controlled asthma.

Phenotypic persistence and external shielding ultraviolet radiation inactivation kinetic model.

AIM: To develop an inactivation kinetic model to describe ultraviolet (UV) dose-response behaviour for micro-organisms that exhibit tailing using two commonly referenced causes for tailing: physical shielding of micro-organisms and phenotypic persistence. METHODS AND RESULTS: Dose-response data for Escherichia coli, Mycobacterium terrae and Bacillus subtilis spores exposed to UV radiation were fit to the phenotypic persistence and external shielding (PPES) model. The fraction of persistent micro-organisms in the original population (N(persistent)/N(total)) that exhibited reduced sensitivity to UV radiation was estimated by the PPES model as approx. 10(-7), 10(-5) and 10(-4) for E. coli, B. subtilis spores and Myco. terrae, respectively. Particle shielding effects were evaluated for Myco. terrae and resulted in additional reduction in UV sensitivity. CONCLUSIONS: Tailing occurred in laboratory experiments even when clumping and shielding were eliminated as major factors in UV resistance, suggesting that phenotypic persistence in addition to shielding may be important to consider when evaluating dose-response curves for disinfection applications. SIGNIFICANCE AND IMPACT OF THE STUDY: The PPES model provides a mechanistically plausible tool for estimating the dose-response behaviour for micro-organisms that exhibit tailing in dispersed and aggregated settings. Accurate dose-response behaviour (including the tailing region) is critical to the analysis and validation of all UV disinfection systems.