They're manufacturing their solar cells in enormous quantities...and then dumping the manufacturing byproducts into the soil untreated. Many of those solar cells then get exported and China continues to burn cheap coal instead.
Communist governments love to make big gestures to show how they're winning by some metric they think people care about without examining the underlying reason why people care. Diversifying the currency is another example, where they're just trading one boss for another.
These kinds of problems are structural and very difficult to change because entrenched interests are tightly integrated into the government and the government has a relatively low level of accountability to the public. Worse, they don't think there is a problem. They're the world leader in Green technology, Beijing should have pristine air and there should be no trouble with heavy metal contamination in the rice, right?
Well, the guys who own the Solar Cell factories make a ton of money, and their government buddies get a cut, and that's all that matters.