ORGANIC MATTER AS AN INFLUENCING FACTOR ON COPPER AND CADMIUM ADSORPTION BY SOILS G. PETRUZZELLI, G. GUIDI, and L. LUBRANO Laboratorio per la Chimica del Terreno, Via Corridoni, 78, 56100 Pisa, Italy (Received 1 April, 1977; revised 28 September, 1977) Abstract. Soil organic matter influence on Langmuir isotherms for Cu and Cd in four Italian soils of different pedogenetic origin was investigated. Adsorption processes were carried out either on the whole soils or on soils after destruction of organic matter. Organic matter removal produced a noteworthy decrease of Cu adsorption contrasted by a smaller decrease or even a slight increase of Cd adsorption. Addition of increasing amounts of Cu on soil previously enriched with Cd did not significantly change the Cu adsorption while a rather different pattern was observed when increasing quantities of Cd were adsorbed on the same soil after Cu enrichment. In this case Cu already present in the soil reduced the amount of Cd adsorbed. These findings suggest that the differences found in the adsorption process of such metals primarily depend on the different chelating effectiveness of soil organic matter in the respect to Cu and Cd. 1. Introduction Industrial growth has led to increased soil contamination by a wide variety of toxic substances. Among these substances, heavy metals are particularly insidious because their nonbiodegradable nature produces long term problems of toxicity; plants growing in polluted soils may accumulate heavy metals in amounts toxic to animal and human health. Heavy metals adsorption by soil has received increasing attention in recent years. Several studies have investigated adsorption processes by means of the Langmuir isotherm and showed that in many cases it provided useful information (Riffaldi and Levi-Minzi, 1975; Shuman, 1975,1976; Udo etal., 1970). In our laboratory two metals have been selected as models. Copper, a biological metal, which becomes toxic when its concentration exceeds certain limits in plants (Mukherji and Das Gupta, 1972; Walsh et al., 1972) and Cd which is toxic at very low concentrations and may be very dangerous for human health (John et al., 1972; Friberg et al., 1974; Hiatt and Huff, 1975). Previously we have investigated the influence of soil organic matter on Cu and Cd availability to wheat seedlings (Petruzzelli and Guidi, 1976; Petruzzelli etaL, 1977). The purpose of this study is to investigate how organic matter influences adsorp- tion of heavy metals by soils. This was accomplished by evaluating whether metal adsorption with and without the organic matter removed conformed to the Langmuir isotherm. Water, Air, and Soil Pollution 9 (1978) 263 -269. All Rights Reserved Copyright © 1978 by D. Reidel Publishing Company, Dordrecht, Holland