From what I can tell from the article, direct injection does not solve the problem of cancerous particulates coming out of the tailpipe. Bummer. But that was not the main reason for the adoption of direct injection anyway.
If I recall correctly, direct injection was adopted for fuel efficiency, which it does indeed do better than the old fuel injection engines. So GDI is environmentally better in that it saves fuel, even though it does not lower the rate of cancerous particles exiting the rear of the car.
Pobudy's Nerfect.
GDI is still an useful technology that helps the environment and saves gas. And new technologies are usually slowly improved over time, so GDI still might help with particulate levels in the future. Plus, the study found that adding a cheap ceramic particulate filter helped significantly (a filter that should last the life of the car). So in the end the study finds a way to inexpensively help the environment. So in "trying to save environment," the study seems to be helpful for the environment. And GDI tech does seem to help the environment in other ways (given the fuel savings).