AN ALKALINE OXIDATION METHOD FOR DETERMINATION OF TOTAL ARSENIC AND SELENIUM IN SEWAGE SLUDGES

A simple and precise method was developed for determination of total A s and Se in sewage sludges by using hydride-generation atomic absorpti on spectrometry (HGAAS). It involves boiling a 50-mg sample with sodiu m hypobromite (NaOBr) solution to dryness in a sand bath (260-280 degr ees C), extraction of the As and Se in the digest with 1.25 M H2SO4, a nd determination of these elements by HGAAS after reducing As(V) and S e(VI) to As(III) and Se(IV), respectively. The proposed method gives q uantitative recovery of As and Se in standard reference materials (96- 103%) and of these elements added to sewage sludges (95-100%). The ave rage results of As (9.8 mg/kg) and Se (7.5 mg/kg) in 12 sewage sludges determined by the proposed digestion method agreed closely with those obtained by the acid digestion methods recommended by USGS and USEPA. Tests with 13 metals indicated that, at the concentrations expected i n sewage sludges, none of the metals interfered with determination of As and Se by the proposed method. A single operator can complete analy sis of one of the elements in 40 samples in a normal working day, or b oth elements in 1.5 d.