The problems of getting at Lake Vostok (and of preventing organisms from the surface from contaminating it) are, give or take the billion kilometre spaceflight required to get there, the same as those that would arise in any attempt to get a probe into Europa's putative oceans.
Whether the presence of acid conditions or surface active digestive substances in the guts of such marine organisms can desorb and release contaminants in significant quantities to cause such effects, or whether such a response is to their physical presence, remains to be answered.
Microplastics have larger surface to volume ratios, potentially facilitating contaminant exchange and have been shown to be ingested by a range of organisms.