p-Dichlorobenzene and naphthalene : emissions and related primary and secondary exposures in residential buildings



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p-Dichlorobenzene (p-DCB) and naphthalene are compounds classified as Group C carcinogens according to the USEPA. Sources of p-DCB and naphthalene include moth repellents and deodorizers typically used in closets, garment bags, and toilet bowls found in pure form. In this study, laboratory, closet, and garment bag experiments were used to determine emission rates of p-DCB and naphthalene from consumer products (closet air freshener, toilet bowl deodorizer, and moth repellent). 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 a closed closet or garments bag, relative to products placed in well-ventilated chambers. Experimental mass emission rates were used in conjunction with a well-mixed reactor model to predict indoor p-DCB and naphthalene concentrations for a range of reasonable residential scenarios. Results suggest that exposures under worst-case scenarios could lead to excess lifetime cancer risks of greater than 20,000 in a million (2%) for those who use consumer products that are pure p-DCB, a risk that dwarfs any reported environmental cancer risks over large segments of the US population. Since such products are typically used where clothing is kept, significant chemical adsorption onto clothing is possible following sublimation from the solid product. Chamber experiments were used to determine the amount of p-DCB and naphthalene mass that adsorbs onto selected clothing materials made of cotton, polyester, or wool. Cloth specimens were kept inside a chamber through which an air stream containing p-DCB or naphthalene was passed for one month. After this time, p-DCB or naphthalene were chemically extracted from the cloth specimens. Polyester was determined to be the most adsorbent material, while cotton was the least adsorbent for each chemical. Equilibrium partition coefficients of 0.01 m³/g for p-DCB and 0.02 m³/g for naphthalene were determined experimentally for wool. Desorption rates were determined in both laboratory chambers and a closet in a test house. Results suggest prolonged persistence of p-DCB and naphthalene on polyester and wool, e.g., half-lives of 12 to 20 days after a moth repellent is removed from the clothes storage environment. An exposure scenario was also carried out to compare the inhalation and dermal exposure risks associated with contaminated clothing.