Air pollution due to hydraulic fracturing might add to acute or chronic health issues for those living near natural gas drilling sites, U.S. researchers said. Lead author Lisa McKenzie of Colorado School of Public Health said the findings, based on three years of monitoring, found a number of potentially toxic petroleum hydrocarbons -- including benzene, ethylbenzene, toluene, xylene, heptane, octane and diethylbenzene -- in the air near wells. Benzene has been identified by the Environmental Protection Agency as a known carcinogen, McKenzie said. \"Our data show that it is important to include air pollution in the national dialogue on natural gas development that has focused largely on water exposures to hydraulic fracturing,\" McKenzie said in a statement. \"Our results show that the non-cancer health impacts from air emissions due to natural gas development is greater for residents living closer to wells. The greatest health impact corresponds to the relatively short-term, but high emission, well completion period.\" The researchers calculated there were elevated cancer risks for residents living nearer to the wells as compared to those residing further away, the report said. However, benzene was the major contributor to lifetime excess cancer risk from both scenarios.