I'd also suggest pool chemicals as a leading cause. I bought a pair of trek 220s from 1997 and 1999 respectively that had already been through 2 sets of kids, my daughter commuted to school on it year round and were loaned to a 4th set of kids before being sent off to a fifth set, I know from the previous owner and myself they lived on the south shore of LI near the ocean from at least 2006 and they don't look anywhere near that bad, actually barely rusted when we gave them away 2 years ago and they were even ridden on the beach, that has to be largely chemical. Personally, I'd lean towards replacing the wheels, everything is severely corroded and replacement wheels might be cheaper than replacement spokes depending on your online searching skills. Evapo-rust is also a good solution for everywhere else but don't soak the frame of the paint will come off.