On the subject of the mothers diet and if they have consumed more than 2 glasses of alcohol, or recreational drugs. I would assume that the mothers who chose to go out of their way to donate would already be diligent breastfeeders who watched what they ate closely.

From personal knowledge of a couple of women who chose to drink (even occasionally) and 1 who smoked pot while BF - they are definately not the women who would actually think of donating.

If on the other hand women were paid for the donations thats when I think you would have more of a chance in women with these extra-curricular activities donating.