Drug contamination test. Gloved hand of a chemist holding test tubes being used to carry out tests on river water, tap water, and sewage samples. The test here is the enzyme-linked immunosorbent assay (ELISA). This test checks for the presence of proteins such as antibodies and antigens, as well as allergens like pollen. Here, it is being used to test for the presence of the antibacterial drug triclosan. The yellow colour represents a low or zero concentration of triclosan, while the clear colour represents a high concentration of triclosan.