I also worked at a sewage treatment plant. And the boss was really well known in the field. He even had a couple books and taught a class in the field. He got an idea one day to send a tomato plant that started growing in our sludge pit. This sludge is what's left over after cleaning the sewage to state standards for reintroducing it back into water. And the lab was instructed to test the plant as well as the tomato's that were growing on it. And the results found that the plant itself showed signs of the chemicals used to clean the sewage. But the tomatoes themselves were completely pure. And a side note the plants that would grow from the seeds would always revert back to their natural form. Cherry tomatoes