Trace metals in municipal sludges

An evaluation of 12 total trace metals in 2 municipal sludges was made using 6 modified plant and soil methods. The presence of organic and inorganic constituents in roughly equal proportions required method modification from that usually employed. The procedures tested were: wet oxidation - H₂O₂, repeated wetting and drying; wet oxidation - HNO₃+H₂0₂, repeated wetting and drying; wet oxidation - HNO₃ + HClO₄, heat digestion; Parr Bomb; dry ashing - with HNO₃ predigestion + HF; and Na₂CO₃ fusion. Because of the great resistance of the organic matter of the sludges to complete oxidation by wet methods, the fifth and sixth methods were found to be the most effective and reliable. Sodium interferes with many trace-metal determinations by the atomic absorption spectroscopy limiting its use to only a few elements.