Environmentalists have long been concerned that the pollution caused by the production of electric cars negates the benefits of driving an exhaust-free vehicle. Now Bloomberg reports that one large ingredient in lithium-ion batteries — graphite — is causing particular concern in China, where much of it is mined. Authorities there have already shut down dirty mines that produce roughly 10 percent of supply in an effort to stem "graphite rain" and polluted water supplies.

Unfortunately, the crackdown comes just as demand is ramping up from companies like Tesla, which could double its graphite needs when its battery factory in California opens. For his part, Tesla CEO Elon Musk says on Twitter that the graphite used in its lithium-ion batteries is mined "in a very clean way" and comes from Japan. Nevertheless, it all could significantly raise prices and cause trouble for the growing electric and hybrid car industry, which can use over 100 pounds of the substance per car. You can read the full report over at Bloomberg.

Update: This article has been modified to include Tesla CEO Elon Musk's comments on the Bloomberg article, which he called "beyond ridiculous." The headline has been updated to reflect his statement.