BACKGROUNDExperimental data were used to study the impact of pH and organic matter on soil pollution indices, with the view to express them as a function of the above two variables. RESULTSData were from an experiment performed in a greenhouse using 12 wastewater and sludge treatment combinations in four replications, using Lactuca sative var Longifolia as a test plant. The experimental data were analyzed by means of linear multiple regression analysis, and the equations found were considered as revised forms for the calculation of pollution indices, which could be used as a tool for the assessment of the level of soil pollution by heavy metals. CONCLUSIONTentative critical levels of the pollution indices were established on the basis of the reference revised Index PLIn. However, additional work is necessary, such as calibration of the revised indices on the basis of percentage crop yield loss, towards a more accurate assessment of the heavy metal soil pollution levels. (c) 2018 Society of Chemical Industry