Bear in mind this was nearly a decade ago, and I no longer work there. Yes, we did consider contamination from the brushes and the rest of the cleaning equipment, which consisted of a stainless steel tub and funnel, and several beakers. The entire set of cleaning equipment was cleaned in our lab sink at the conclusion of each round of testing. At one point, for thoroughness, we did a test after cleaning the set once, and another test after cleaning the set three times. There was no difference. We also examined our parts and the elements of the cleaning equipment that would fit, under our microscope. The debris was present on the parts before testing, and present in much lower amounts on the cleaning equipment. I don't remember if I mentioned any of this in previous posts, but we eventually found the main source of the stuff was in the parts cleaning system the parts were cleaned in. We ended up creating a preventive maintenance protocol and schedule to drain the cleaning tanks, scrub and rinse them, and wipe down the air dry chamber. The particle size and quantity went way down after implementing that.