Q: What symptoms do I look for if a chin is suffering from mold exposure?
A: Symptoms of an upper respiratory infection.
Here is a case study:
http://www.chinchillaclub.com/members/mag/0804gut.htmlHere is a good article about sickness in general if you haven't seen it:
http://www.chinchillaclub.com/members/mag/1004sickchin.htmlHere is a article from the Merck Veterinary Manual:
http://www.merckvetmanual.com/mvm/index.jsp?cfile=htm/bc/171504.htmIf you would like more information I'll be glad to find more.
Q: There does seem to be a finish on the desk top. Is it possible that the finish could have blocked urine absorption...
A: I hope so. If the surface is bubbled, cracked, or peeling over the exposed area, then probably not.
If it is not bubbled and it is just discolored then try scrubbing to make sure you get it clean as possible. Discoloring is an indication that the surface has absorbed something. It doesn't necessarily mean it's molded, it's more than likely just stained and will be permanent. I wouldn't worry about mold if the surface is still smooth or if you don't see any black spots.
Hope the articles don't scare you too badly, but keep in mind that there's mold and there's mold. Considering that you can't really smell it unless you're close to it tells me it's not horrible but it should be scrubbed and disinfected. I would think the kind of mold that can cause a chin to get sick would be the if large areas of the carpet or your walls were affected such as a leaky roof or something along those lines. Mold infections of chinchillas are usually contracted through moldy food that was improperly stored or processed. Mold has to have moisture to thrive. In an area that's poorly ventilated on a surface that's porous (like uncoated particle board) this is a major problem, but since it took so long to notice the problem (smelling it) I suspect that is not the case.
Since you can't remove the chins from the room long enough to use bleach you'll just have to use soap and water and a scrub brush or a cleaning pad if you haven't already. Dish soap works. If you already have then hit it again and see if it still stinks. Scrub it with a brush and with a dish cleaning pad that is not too abrasive to roughen the surface.
If you decide you can move your chins out for a couple of hours (fumes will likely be gone in about 10 minutes if you dry it with a towel) and can use bleach a 1 cup to 1 gal solution should kill any mold it comes into contact with but you still have to scrub it first. It will penetrate a little bit and probably do what you need it to do. Again, you probably don't want to do this with chins in the room as this is a pretty strong concentration.