p-Dichlorobenzene (p-DCB) and naphthalene are classified as hazardous air pollutants and rank highly among chronic chemical hazards in US. residences. Sources of p-DCB and naphthalene include moth repellents and deodorizers typically used in closets, garment bags, and toilet bowls. Nearly pure concentrations of p-DCB and naphthalene are found in these products. p-DCB and naphthalene mass emission rates were determined for four different products placed in well-ventilated laboratory chambers as well as closets in a test house and in a garment bag. Concentrations were measured in bedrooms adjacent to closets where products were used. Emission rates varied considerably between products that contain p-DCB, primarily due to product packaging, and were generally suppressed when the product was used in closed closet or garments bags relative to products placed in well-ventilated chambers. This reduction appears to be due to lower air speeds in closets and garment bags as opposed to chemical accumulation. Variations in air temperature within typical ranges observed in homes can significantly influence emission rates of p-DCB and naphthalene. Concentrations of p-DCB and naphthalene in bedrooms adjacent to closets where moth repellents are used can exceed or approach odor thresholds. For this study, the concentrations exceeded or were within the upper few percentiles of those previously reported in residential indoor air. Based on a comparison of whole-house emission rates derived in a previous study, it appears that somewhere between 2% and 12% of homes in that study had active sources of p-DCB and between 5% and 15% had active sources of naphthalene.
Implications: Inhalation of p-DCB and naphthalene has been linked to several health effects. Several off-the-shelf consumer products are nearly pure p-DCB or naphthalene, thus leading to potential for high emission rates and gas-phase concentrations in indoor environments where such products are used. Knowledge of p-DCB and naphthalene emission rates and variability in emissions with environmental conditions should provide for improvements in predictions of indoor concentrations of these compounds, which are in turn needed to complete exposure and inhalation risk assessments.