Thought I'd give you my 2 cents on this as it's up my alley.
Polyvinyl chloride is a plastic derived from oil used in such things as water and sewer pipes, shower curtains and a number of other household products. In it's solid state it is fairly inocuous (not harmful) at least from the present knowledge. In its' liquid state it's one of the most toxic substances that I can think of with maybe the exception of Vx. The problem with PVC is that it off gasses the chemicals used to produce it. This is just like the formaldehyde problem with the Kitrina trailers but unlike the trailers PVC gives off more than one chemical. Three of the off gassing chemicals are the components of gasoline that includes: toluene, ethylbenzene, xylene. Toluene is a known carcinogine and the others are not too kind to your system either.
So what to do about the problem. You can switch to other types of curtains like nylon, polyester, or cotton. There is one other solution if the manufacturers would take the time and expense. That would be to treat the curtains to a process of ozone for a few days. The ozone process bonds oxygen to the plastic preventing additional release of the gasses. It's the same process nature uses to eliminate odors. It isn't an expensive process but it does take several days to complete. And no it not something you'd want to try at home although that could be done.