The phrase "already contaminated" is correct and usable in written English.
It can be used to describe something that has been contaminated prior to a certain point in time or before an action is taken.
Example: "The water supply was already contaminated before the testing began, raising concerns about public health."
Alternatives: "previously contaminated" or "contaminated beforehand".
Frequently the raw material is already contaminated when this selection occurs and thus the detection of the contamination became very difficult.
Of course, the virus has already contaminated a passenger jet, causing it to crash.
Returning refugees, soldiers and reporters may have already contaminated or disturbed many sites.
The ground on the site is already contaminated with benzene left behind from its days as a coal transfer station.
Ortega did not ameliorate those concerns when he declared, a few months ago, that the lake was "already contaminated".
At work, if an inconsiderate oaf has already contaminated what is supposed to be segregated waste, the damage is already done for those who follow.
Plastic already contaminates huge tracts of land and ocean.
Mining waste and discharge from the strip mine, according to state agency surveys, are already contaminating the groundwater and Grindstone Creek, a historic watershed that served the first mills in the region.
The laboratory has already excavated contaminated soil around the building and shipped out contaminated fuel, cooling fans and a leaking underground sump.
We note however that if a given equation is already in canonical form, then one may not assume that the damping has already been folded into (q(x)); as equation (6) shows, the given (q(x)) may already be contaminated by the (-b'(x)/2) term, which may not be acting as pure damping.
Both the air and water are already alarmingly contaminated, as my colleagues Sharon LaFraniere and Bettina Wassener have reported.
