China’s booming electric vehicle market is about to run into a mountain of battery waste, by Echo Huang.

China’s push to promote electric cars comes with a lot of benefits for a country that suffers from terrible air pollution from its reliance on fossil fuels. But there’s always a downside—electric car batteries are toxic if not disposed of properly, and China’s on the verge of having to deal with a slew of batteries that can no longer hold a charge.

In just a few years, China has become the world’s biggest electric vehicle market, with the help of subsidies. It saw 336,000 new electric car registrations in 2016, according to the International Energy Agency. That includes both battery-only and hybrid models. Including other types of vehicles, China says it sold a total of half a million “new energy” vehicles last year. This month, China also said that it would eventually phase out sales of all fossil-fuel cars.

That fast-growing market, however, is also producing batteries at a faster rate too. The average lifespan of a lithium-iron phosphate (LFP) battery, the dominant type in China’s electric vehicles, is around five years …

But recycling these batteries isn’t easy, due to the sophisticated chemical procedures involved. If it’s not done properly the heavy metal contained in the battery can lead to contamination of soil and water. …

China’s not the only one facing a recycling headache. In the European Union, only 5% (pdf) of lithium-ion batteries, another common type of battery power used in electric vehicles are recycled, according to data from non-governmental environment advocacy group Friends of the Earth Europe, which pointed out that “most of the current lithium is either dumped in landfill or incinerated.”