Drugs and hormones Antibiotic, antithyroid and antiparasitic drugs, clenbuterol, etc. These substances are given to animals, legally or illegally, to treat and prevent pathological processes and to fatten livestock, leaving residues at low concentrations in the foods. The effects on humans of repeated doses over long periods of time, however, are not known. Milk and dairy products can become contaminated with penicillin, as bovine mastitis is treated with intramammary penicillin, which is 80–90% eliminated in the milk. In theory, these substances have the potential to be hepatotoxic, nephrotoxic, ototoxic, teratogenic, allergenic, carcinogenic, and to cause hematologic disorders and antibiotic resistance. We can also ingest drugs (analgesics, antibiotics, antidepressants, etc.) and hormones (for example, estrogens) in drinking water. It has been reported that one in four Europeans washes medications down the sink. These substances are difficult for treatment plants to detect and eliminate, so we end up unintentionally consuming trace amounts of them in our water. Moreover, aquatic organisms living in rivers are the first to be directly affected by these. They ingest drugs, estrogens (which act as endocrine disruptors that give rise to hermaphrodite fish) and even the ingredients in sunscreens. Consumption of these pollutants is rising, and water treatment plants are unable to eliminate them. They reach fish, changing their metabolism…