Sorption of toxic organic compounds on primary, mixed-liquor, and digested solids from municipal wastewater treatment plants has been correlated with octanol/water partition coefficients and with modified Randic indexes. The correlations developed are useful for assessing the role of sorption in the treatment of toxic or hazardous compounds in conventional biological wastewater treatment plants. Correlations developed provide a basis for predicting the concentration of toxic compounds associated with wastewater solids at a given equilibrium concentration in the aqueous phase. Organics in sludge can impact anaerobic digestion, land spreading, incineration and ocean dumping of sludges. Estimates of the concentration of toxics in sludge allows assessment of the impact of toxics on sludge disposal options. (Copyright (c) 1989 American Chemical Society.)