Tell them the truth. You did not leave the company for a silly reason. You left it because of the work environment that was harming you. So, explain the situation. Most of the times, when recruiters ask you why you quit your job, it is just to understand about your attitude towards work. You quit your job does not mean you did something wrong. Quitting job for a silly or a stupid reason would affect on your impression in front of the recruiter but when it is a genuine reason then it is fine. And until and unless you have good skills and you are good at your job, quitting job would not matter much.