Moderate to heavy contamination is easy to observe, but with low levels of contamination in an uncontrolled environment by an inexperienced person it's not likely. If you get one colony on the plate is that from the air, the analyst or the sample? I've witnessed an experienced microbiologist contaminate plates by mouth breathing while plating samples. It's distinguishable but you have to know what you're looking for.Around 2006 i had access to all different types of agar. I made some extra one day and smears some AAS oil on it. Nothing grew which was to be expected as I had filtered everything through a 0.22 and baked it.
Then my buddy kept having some issues characterized by redness and a lot of pain after injects. He never filtered his gear anything else. While it was already a punctured vial i did grab some of that oil and smeared it on a few different types of agar. I had cultures on all of them. I never cared enough to try to identify but obviously he tossed the vial.
My point being is im not sure it matters all that much to test for bacteria. I would just assume every time that UG gear is NOT perfectly sterile and all users should take the necessary precautions. for "fun" one could smear it on some agar and see and do the best you can not to contaminate it. Its kind of easy to tell if its truely a airborne contaminate though based on the pattern of growth on the agar so a full hood isnt needed. Heck in medical school we never used a hood when isolating and it worked out fine "most" of the time.
With respect to heavy metals. I believe the list you have is a good start. I have no useful info as to how to test for them these days. The tests i saw were on raw powders not oils and were likely posted on AFboard back in the day as that was the website i was most on around that era.
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