To expose and extract coal seams buried deep under mountains, miners blast through rock with explosives in a method called mountaintop removal mining. In Appalachia where such mining is widespread, people who live or work near mines have a greater incidence of lung cancer than the general population. Scientists have hypothesised that exposure to dust from mountaintop removal mining can cause cancer, but until now, they havent demonstrated the link experimentally. A new study, published in the journal Environmental Science & Technology, has now shown that human lung cells exposed to airborne dust from homes within a mile of a mountaintop removal mining site adopt cancer-like properties and, when implanted in mice, can promote tumours in mice. Sudjit Luanpitpong and Yon Rojanasakul, cancer researchers at West Virginia University, and their colleagues collected air samples on 5-?m mesh filters over several weeks from two West Virginia homes within a mile of an active mountaintop removal mining site. They also collected samples from homes in a rural part of the state where there is no mining activity. They extracted the particulates from the filters and then analysed their composition using scanning electron microscopy with energy-dispersive X-ray spectroscopy. The researchers then exposed cultured human lung cells to a non-lethal dose, 1 ?g/mL, of the particulates from either a mining site or a non-mining one for three months. By comparing the exposed surface area of the lung cells to that of human lungs, they estimate that this dose is equivalent to eight to nine years of human exposure to average air concentrations of particulates in these areas. Cells exposed to particulates from near the mine adopted cancer-like properties: They formed colonies when grown on soft agar, a common test of transformation into cancer cells. These cells also grew faster and migrated farther. In contrast, cells treated with particulates from non-mining areas did not show these characteristics. In addition, the team investigated why mining dust might cause this transformation. They exposed cells to silica and molybdenum, the two main inorganic components of these particulates. Adding molybdenum trioxide, a suspected carcinogen, caused the cells to adopt cancer-like properties. But to the teams surprise, silica, a known carcinogen, had no or minimal effect. To test whether these cells could cause tumour formation, the team injected mice with cells from the earlier experiments. None of the cells initiated tumour formation in mice. So to see if the cells might promote the growth of existing tumours, they injected the cells from each treatment into mice together with lung cancer cells. In this case, the cells that had been treated with particulates from mining areas or with molybdenum promoted three to four times as much tumour growth as cells treated with particulates from the non-mining sites. Exposure to these particles may not induce cancer, says Rojanasakul, but may enhance the effect of other carcinogens, such as those in cigarette smoke. Regina M. Santella, an environmental health researcher at Columbia University, says the study is valuable because it demonstrates cancer-promoting effects with samples collected from areas where people are being exposed to dust from mining activities. It shows that higher exposure to these particulates is potentially a risk, she says. An important next step, she adds, would be to test the particulates in an inhalation study in animals to gauge the cancer risk they pose.
Chemical & Engineering News, 3 November 2014 ;http://pubs.acs.org/cen/news ;