Hey OP. I think you got a bit of a rough deal on here, and I speak as one of the diehard MN feminist vipers over there on the 'Feminism, Not The Fun Kind' board you are probably, right this minute, being told is 'feral' MN at its worst over on that Reddit thread you started. 
Actually I WILL fill out your questionnaire. My younger son is just about within your age frame. I think it's annoying that your university questionnaire protocols make you include a question asking about gender, rather than sex, and contend that we members of the public would find being asked our sex 'offensive' or divisive. I know that British universities will take a long time to catch up to the evolving public opinion on this, but no - the vast majority of people are not, and never would have been, 'offended' to be asked for their sex on a standard questionnaire. Gender is, as I'm sure you're aware, different from sex, which is biologically determined. MN is possibly the most likely forum in the UK today where you will get your arse handed to you on a plate if you ask a poster's gender rather than sex on a questionnaire, so I do actually feel some compassion for you. 
Now, as to your actual questionnaire, I do have some issues with the way you're phrasing questions, and the information you're giving participants (or not).
I would say, 'chemicals' makes me shrug and say 'meh', as chemicals are literally EVERYTHING.
My A-level Chem/Biology student is rolling his eyes. (He's also drawing me some diagrams which I absolutely don't need in order to state this.) Look OP, your query is fine but I don't think you gave your participants enough information about WHAT chemicals, in what sorts of concentrations, whether these 'chemicals' are part of the actual fibres, or a treatment that the fabric was subjected to, and what the relative risks of buying clothing with these 'chemicals' in are - compared to ... what? Wearing totally organic cotton and wool? Going naked? And if I wash my clothing in a detergent containing a particular chemical it'll probably be absolutely fine for my skin. If I drink that same detergent I'll probably end up very ill. Do you see?
I ask questions of those who are telling my my choices are risky, and often enough I find that the person postulating that something is harmful doesn't actually understand the concepts of 'risk' and 'harm'.
If you want meaningful answers for your research, you have to ask meaningful questions, and without any background information on what you mean by 'harmful/toxic chemicals' you're not asking questions that will garner very meaningful responses. Unless, of course, some of your participants happen to be passing petrochemical experts or similar.
End of the day - 'chemicals' are in and ARE everything. Including wool, cotton, linen. We are made of chemicals.