Because human DNA is deposited onto objects in the environment, this implies people may frequently ingest trace amounts of DNA from making contact with contaminated objects like doorknobs and then touching the mouth, as happens with germs, does this contribute in any way to complications from karma among individuals who otherwise lead separate lives?

While this would seem to be a potential negative influence, physical traces of DNA are a minor aspect of the crosstalk that happens among the human community members. The exchange of feelings and ideas through the collective unconscious and the proximity to the thought forms of others, and being recipient to many psychic attacks from the negative energies projected from the minds of millions of other human beings, are a greater source of perturbation that can, in some ways, strengthen the bonds among members of the tribe, so to speak, as well as create discord and suspicion depending on the nature of the energies projected and how they are perceived. You cannot escape being a member of the human community no matter how you might wish to isolate yourself. So the environmental route for physical transfer of intact DNA is very, very inefficient as only trace amounts will survive and have an opportunity to be taken up within the body, as this will not take place through the skin because it is an efficient barrier, so there must be contact with membranes in the orifices, and even then, length of survival is fairly minimal, so this is not a major avenue for influence.