Dear Susan: First, my apologies for taking so long to answer your question. We had some logistical and technical issues getting me connected to the Scienceman column, and I've been in and out of the office attending some exciting conferences since the end of March. Now, to your question. Plastics are great materials for reusable goods, or for goods that can be readily recycled. Two concerns about plastics are their use in throw-away goods (what a waste of resources!) and the possibility of toxic components making them unsuitable for certain applications (such as the use of PVC and polycarbonate for food contact applications). Seventh Generation automatic dishwasher detergents can be used with most plastics, including polyethylene terephthalate (PET, No. 1), high density polyethylene (HDPE, No. 2), low density polyethylene (LDPE No. 4), polypropylene (PP No. 5), and certain other plastics (No. 7). Like most automatic dishwasher detergents, Seventh Generation automatic dishwasher detergents are alkaline (pH 11 and above), which is not an issue for PET, HDPE, or LDPE. However, polycarbonate, used for many clear, rigid, water bottles may develop stress cracks from the high temperatures used in dishwashers, or from reaction with alkali. Dishwasher detergents with chlorine bleaches should definitely be avoided.