1,4-Dichlorobenzene (p-Dichlorobenzene)

Para-dichlorobenzene (p-DCB) was developed as an alternative to naphthalene mothballs beginning in the 1940s and became the dominant mothball formulation in the US [1]. Its strong characteristic odor — described as similar to old urinal cakes — also made it popular as a deodorizer for toilet bowls, urinal blocks, and room air fresheners. By the 1990s it was used in millions of American homes and was detectable in the blood of nearly every American sampled in CDC biomonitoring studies [2]. p-DCB is also used as a chemical intermediate in pesticide and pharmaceutical production. Industrial sources include its manufacture and use in dye synthesis, pharmaceutical production, and as a fumigant for soil and stored products. Like other chlorinated aromatics, it is volatile and persistent, accumulating in indoor air from products and in body fat from dietary exposure [3].

Household use of p-DCB mothballs and solid air fresheners is the most universal exposure pathway — these products are designed to sublimate into the air, which is precisely what makes them release p-DCB into indoor air [1]. In homes using these products, indoor air concentrations can significantly exceed outdoor air. The chemical also accumulates in carpets, fabric, and furniture in rooms where products are used. CDC's National Biomonitoring Program found 2,5-dichlorophenol (a p-DCB metabolite) in 96% of Americans tested, reflecting essentially universal background exposure [2]. Dietary exposure occurs through contaminated water and food. Drinking water contamination near production facilities and industrial discharge points is documented. Occupational exposure in chemical manufacturing and dye production can be significant [3].

p-DCB is classified as a possible human carcinogen (IARC Group 2B), with clear evidence for liver and kidney tumors in animal studies and suggestive human evidence for non-Hodgkin lymphoma [1]. It accumulates in fatty tissues and is slow to be eliminated from the body. The liver and kidney are primary targets of chronic toxicity — p-DCB causes hepatotoxicity (elevated liver enzymes, fatty liver) and nephrotoxicity (protein in urine, kidney cell damage) in exposed animals and at high occupational exposures in humans [2]. The central nervous system is affected at higher exposures: headache, fatigue, and neurological symptoms are reported in people with heavy home exposure to p-DCB from mothballs or air fresheners used in enclosed spaces. Chronic indoor use in enclosed rooms creates exposures far higher than background [3].

People who use p-DCB mothballs or solid room deodorizers in enclosed spaces — particularly in small bedrooms, closets, or bathrooms without adequate ventilation — face the highest indoor exposures [1]. Infants and toddlers in rooms where p-DCB products are used breathe a higher proportion of room air per body weight. Workers in p-DCB production, dye manufacture, and pharmaceutical synthesis face occupational exposures [2]. Frequent users of public toilet facilities with urinal blocks are exposed in the short term.

Replace p-DCB mothballs and room deodorizers with safer alternatives: cedar chips, lavender sachets, sealed clothing storage, good ventilation, and baking soda for odor control accomplish the same goals without the carcinogen [1]. If you currently use p-DCB products, remove them, ventilate the space thoroughly, and air out stored items. Never use mothballs in living spaces, bedrooms, or areas accessible to children [2]. Look for toilet deodorizer products labeled "free of paradichlorobenzene" — alternatives exist. Check cleaning product labels for dichlorobenzene. In workplaces, use engineering controls and local exhaust ventilation for any process involving p-DCB [3].