breastfeeding storage question

Ra

So I just started trying to store my breast milk BUUUUT I put it in a ZipLoc Baggy...

I just read in google not to use ZipLoc, but doesnt say why...

Is it Harmful? Can I use it still? What Precautions should I take while doing so?

We're REALLY REALLY low on money so I cant afford to buy actual BM storage bags.. but Im going back to work, running low on formula... and gotta do what I gotta do for at least 2 weeks til I get paid