At least in my city, contaminated cars are handled by private contracts.
Before bloated government unions, they used to just hire kids for this job. As a teen, I had a job for our town - cutting grass, mopping floors, painting etc... I was assigned to the local PD for one summer. Cleaning out the patrol cars was pushed all the way down the hierarchy - to me. It usually vomit - from the DWI arrests. Once or twice it was some blood (this was before HIV, etc..) Never had a "brown alert," thankfully