P-dichlorobenzene emission rates from moth repellents and leakage rates from cloth storage cases

Emission rates of p-dichlorobenzene (pDCB) from five kinds of commercially available moth repellents and leakage rates from six kinds of commercially available cloth storage cases were measured. The emission rates from moth repellents immediately after purchase (E(max)), which were obtained as the slope of the total emission amount vs. time elapsed, were 0.0033 to 0.035 g/h at 25 degrees C. Moth repellents from different manufacturers differed greatly in emission rates at 0.0033, 0.0060, and 0.011 g/h, even if the moth repellent pieces were of similar shape and initial weight. This is thought to be because emission rates depended on the diffusion resistance of the repellent packing material used by each manufacturer. Therefore, the manufacturer-specific apparent mass transfer coefficients (K) were calculated for each moth repellent from the measured emission rates and a calculated saturated concentration. The apparent mass transfer coefficient K and the concentration gradient between the in-case (inside a cloth storage case) bulk air and the air at the surface of a moth repellent (pDCB tablet) were used for the calculation of the general emission rates. The leakage rates, defined as the air-exchange rate for a cloth storage case, from six cloth storage cases ranged from 0.41 to 78/h. Despite the large difference (more than 100 times) in the leakage rates of the cloth storage cases, the differences in emission rates of pDCB from these cloth storage cases to the indoor environment were small (<30%). This is because the concentration gradients between the in-case bulk air and the air at the surface of a repellent piece were almost the same among the storage cases. This suggests that pDCB emissions from cloth storage cases into the indoor environment should be reduced by making the storage cases more tightly sealable so that the leakage rate is <0.01/h. The results of adsorption tests of pDCB onto woollen clothes showed that the adsorption of pDCB on the clothes was assumed to be very strong and the transfer between the gas phase and the cloth phase in the cloth storage case was assumed to be small.

The use of pDCB provides benefits such as moth control and deodorizing, but on the other hand, poses potential risks to human health. There is a risk-benefit tradeoff, i.e. a tradeoff between risks of pDCB to human health and benefit of moth control effects. The pDCB concentration in the cloth storage case and in the indoor air can be estimated by using emission rates and the leakage rates obtained in this study. By comparing the concentration to the deterrent efficiency of pDCB, the risk for the use of pDCB moth repellents can be managed.