TlI and TlIII presence in suspended particulate matter: speciation analysis of thallium in wastewater

Environmental context Thallium occurs in the environment in two oxidation states, with Tl-III being 1000-fold more toxic than Tl-I. We present a fractionation and speciation study of thallium in suspended particulate matter from highly polluted wastewater samples, and elucidate the dominant forms of thallium. Abstract Thallium (Tl) is a toxic element, whose toxicity is affected by its redox state. Compared with Tl-III, Tl-I is thermodynamically more stable and less reactive; therefore in aquatic environments, dissolved thallium is mostly present as Tl-I. However, Tl-III could be 1000 times more toxic than Tl-I. A combination of a fractionation and a speciation study carried out in highly polluted wastewater samples from a mining area in southern Poland in order to characterise chemical speciation of Tl in physically defined fractions is presented here. Total, particulate and dissolved thallium was determined. A leaching experiment based on forming Tl-III complexed with diethylene triamine penta-acetic acid - a Tl-III-DTPA complex - was performed in filters containing suspended particulate matter after single (0.45 mu m) and sequential filtration (15 + 0.45 mu m) of wastewater samples. This is the first speciation study of Tl carried out in suspended particulate matter. The results obtained indicate that the dominant form of Tl in suspended particulate matter is Tl-I, but Tl-III could be found in suspended particulate matter fractions larger than 0.45 mu m.