Zinc is a very important metal for healthy bodies; however extreme doses of zinc are poisonous. Excessive intake of zinc has been shown to suppress iron and copper absorption. Acute toxic oral doses of zinc lead to nausea, vomiting, diarrhea and abdominal cramps and gastric bleeding. The free zinc ion has been shown to be a powerful Lewis acid that is corrosive; as a result the presence of hydrochloric acid in the stomach reacts with zinc to give zinc chloride which is corrosive.
This is what causes stomach upsets and in severe cases bleeding. The presence of zinc in the oral gastrointestinal tract causes burning in the mouth and throat, pharyngitis, esophagitis, hypocalcaemia and pancreatitis. Ingestion of zinc phosphide which metabolized under acidic conditions in the stomach to produce phosphine gas causes abdominal pain, lethargy, hypotension, cardiac arrhythmias, circulatory collapse, pulmonary edema, seizures, renal damage, leucopenia and coma. Inhalation of freshly formed zinc oxide, mainly as a result of welding of galvanized materials has been seen to cause zinc chills or zinc shakes. If not detected early and treated zinc poisoning can cause fungal sepsis and gastrointestinal bacteria whose effects are usually fatal. If no urgent medical action is taken, death can occur in days to weeks (Opresko, 2009). Chronic oral exposures to zinc causes hypo chromic microcytic anemia. Others include metal fume fever, gastrointestinal distress and liver failure. Currently, the accepted RfD for both sub chronic and chronic exposures is 0.2 mg/kg/day while that of zinc phosphide is 0.0003 mg/kg/day and the sub chronic RfD is 0.003 mg/kg/day (Opresko, 2009; McCarthy, 2008).