Estimation of aggregate population cancer risk from dichloromethane for Japanese using atmospheric dispersion model.

The aggregate population cancer risk from dichloromethane exposure for each prefecture and for all of Japan was estimated using an atmospheric dispersion model and by considering the population within each calculation mesh (about 5 x 5 km). Indoor dichloromethane exposure was also taken into consideration. The number of lifetime dichloromethane-exposure-induced cancer cases for all of Japan was estimated to be only 1.3 (of 125 million people) using a most recently reported unit risk value. It was also found that the average ratio of the contribution to the aggregate population cancer risk attributable to outdoor emission sources (industrial factories) to the total emission sources was no more than 40% for all of Japan. From these results, it is believed that further reductions in dichloromethane emissions from industrial factories on a prefectural or a nationwide scale would not be effective in reducing cancer risk. It was also revealed that the average ambient concentration of dichloromethane measured at monitoring stations for hazardous air pollutants in each prefecture is a good measure of the average ambient dichloromethane concentration to which people in that prefecture are exposed. Therefore, it was suggested that the aggregate population cancer risk from dichloromethane exposure can be effectively estimated for entire Japan by simply using the average ambient concentration measured at monitoring stations in all of Japan taking into consideration indoor dichloromethane exposure.