These are micro-organisms such as cryptosporidium and giardia, often of animal or human origin, transmitted by the faecal-oral route
can cause significant damage to the central nervous system. Toxic effects on the liver
Chlorine and its organic compounds, including trichloromethanes which are believed to be carcinogenic, can also cause nerve damage and metabolic disorders
lead, copper, aluminium, mercury, etc.
e.g. bisphenol A and oestradiol: can cause hormonal imbalances. Radon is radioactive.