Pesticide residues are a big problem in museum collections. Particularly pesticide residues which remain tenacious over a long period of time - like arsenic.
Back in the day, it was common practice for museums and collectors to "poison" their collections - dipping them in some kind of chemical bath - to keep away the bugs, the rodents, and all manner of creepy crawlies which might eat the organic material in, say, a basket, a mask, or leather objects. It was recommended by the Smithsonian. This was wildly effective - there are many many beautifully preserved objects. To this day student museologists hear tales of small historical societies with volunteers who keep their cache of old pesticides on hand to treat incoming collections. The downside to the practice of poisoning collections is that the poisons which kill the creepy crawlies also tend to have detrimental health effects for humans as well.
This means that, unless museums have absolutely perfect records of the object from the time it was made through to the present day, we need to assume that an object is contaminated. Like this basket.
As I went to make a condition report of this basket, I noticed a white residue. Not exactly crystalline, but grainy and visible to the eye. Arsenic sometimes has this property over time (although I am not a chemist, nor do I play one on TV). But I wasn't taking any chances. I was already wearing my nitrile gloves (although not the brand linked to - we buy powder free gloves), because I am aware that pesticides are a likely issue in the collection. I began wearing a mask when handling this basket as well.
So I have a basket that I think might be contaminated with arsenic. What does it mean? It means that most of the collection is probably contaminated, as it has been moved over the years. But the nature of the residue made me feel that it might be removed by brushing or jostling. I do not wish that, because then there would be free floating contaminants. So I created a custom enclosed box which will help to isolate this basket and any poisonous residues which might be on it. I place a warning on the exterior box so that others are aware of the possible issues with this object.
Now, it's entirely possible that this is not pesticide residue. Maybe the white grains are some sort of paint splatter or old mold growth that looks unfamiliar to me. But I prefer to follow the old adage, better safe than sorry, and be careful.
The National Museum of the American Indian has a very good page of links on this topic, if you would like to know more.