In 2002, the Office of the Inspector General noted: "EPA cannot assure the public that current land application practices [of sewage sludge] are protective of human health and the environment.” Here are just a few of the ways that sewage sludge can be harmful:
1.) Persistent Organic Pollutants: Industrial chemical compounds such as PCBs and dioxins cannot be degraded and “persist” in the environment. They can bioaccumulate up the food chain as they are taken up by plants, which are in turn eaten by animals, which are in turn eaten by other animals. Many POPs are known to be carcinogens and have been implicated in endocrine, reproductive, and immune disorders.
2.) Heavy Metals: Heavy metals such as lead, mercury, molybdenum, cadmium, and thallium – a toxin hazardous to humans in very small doses – can be taken up by plants in neutral and basic soils and poison both animals and people.
3.) Harmful Pathogens: Some pathogenic bacteria, viruses, parasites, and fungi survive sewage treatment and thrive in the nutrient-rich sludge. These can include salmonella, campylobacter, listeria, hepatitis, diarrhea-causing protozoa, and parasitic worms that can lead to neurological problems and nutritional deficiencies. Because of the antibiotic residues commonly found in waste, sewage sludge is the perfect way to select for extremely hardy and antibiotic-resistant bacteria, which can be deadly.
4.) Nanomaterials: Nanomaterials are used in several cosmetics, such as sunscreen, and enter sewage treatment plants when washed off in the sink or shower. Nanomaterials are physically distinct from their bulk counterparts and act in ways that are not yet fully understood. Exposure to nanomaterials can cause potentially devastating plant and animal harms and should not be released into the environment until fully assessed.
5.) Hormones: Pharmaceutical residues from hospitals, animals treated to promote growth, and people on prescription doses for various reasons can also be found in sewage sludge. These hormones can act as endocrine disruptors and interrupt reproductive cycles, in rare cases leading to premature puberty and cancer.