Thallium is metal of IIIa group of Periodic table of the elements. It rarely occurs in elementary condition and usually occurs in minerals. There is little thallium in pyrite and it can get from this mineral during the production of sulphate acid. It present in lead and copper ores. Thallium-sulphate used for ants extermination, but from 1975. it is not in use any more. It is using in photocells like infrared detector, in glass production, electronic industry as alloy and in pharmacy.
Origin in water
It can be presence in underground waters, but in very small quantities.
Pharmacy industry is using thallium for treatment of skin infection.
There are some suspicions that thallium is cancerous for people. There were not final rules untill 1992. when USEPA gives rules for thallium in water, because of potential effect of thalium on kidneys, liver and brain.
Maximal allowable concentrations
From 1994. there is MCLG from 0,00005 mg/1 and MCL from 0,002 mg/1 (De Zitane, 1997).