The current wisdom is that PP is one of the least problematic plastics wrt to leachate contaminating the contents. HDPE is also fairly well regarded. In theory LDPE is also considered 'food safe' but if you can smell the plasticizers evaporating off of LDPE (which I absolutely can) then what's it doing to your food?

I read something about PE in the environment recently but I can't recall if it said it was the hardest to break down or the easiest. I'm thinking the former though, since I came away from that article feeling better about PP and worse about PE.