It occurred to me that EVAs on the Martian surface would be liable to bring biologicals from Earth out into the Martian environment. A habitat will become contaminated with bacteria from the humans occupying it... Skin and GI flora, skin flakes, and other types of biologicals from experiments going on in the habitat. I was wondering if anyone has given any thought to how we're going to prevent this stuff from going out the airlock every time someone goes EVA.
While measures would be taken to limit the contamination for scientific investigation reasons, it is generally accepted that 100% containment would be impossible.
In fact, when the planetary protection regulations were originally established in the mid 1960's, a time limit of 50 years was set as the time, for example, required that Mars orbiters remain in orbit. Once they de-orbit, their unsterilized innards would potentially contaminate Mars. Why 50 years? Because it was considered obvious at the time that, surely, humans would be on Mars in less than 50 years. If humans are there, then we have clearly given up on preventing biological contamination, so let the orbiters auger in.
Alas, it has been 50 years, and there are no humans on Mars. But when there are, they and their habitats will certainly be a source of biological contamination.
Even so, there are approaches for collecting sub-surface samples in a contaminated environment that are not contaminated, so unsullied scientific investigations could and would be conducted.