Essentially what the title says. I use that bucket to store all the measurement equipment, hydrometer, etc. but also yeast nutrient, stabilisers and chemical sanitisers. The smell that came out from the bucket was pretty strong and sharp, leaving a tingly feeling in my nostrils for some minutes after getting a big whiff of it. I have a bunch of strawberries I have just thawed for wine making and I wanted to check that this wasn't a product of some kind of nasty chemical reaction and the bucket is still safe to use once it gets a good clean. Can Homebrewing Stack Exchange advise?
After some research I think I discovered a potential source of the problem. Potassium metabisulfite decomposes into, amongst other compounds, sulphur dioxide - a gas which is irritating and toxic at higher concentrations. SO2 reacts with water to form sulphuric acid (nasty!), and that includes water in mucus membranes, which explains why I experienced a a sharp acidic odour and burning feeling in my nose.
Only since recently the bucket was stored in a pretty humid place, which apparently can accelerate potassium metabisulfite's decomposition which explains why I only ever got that effect now!