You are begging the question. The claim 'there is no safe level' is based precisely on dubious epidemiological results like this, and this study is already being used to push exactly that claim. I am fine with <10ug in my blood because I am not yet aware of any natural or randomized experiments showing benefits from decreases in that level, as makes sense with any kind of plausible dose-response curve - the last few ug should matter the least.