Critical Comparison of Soil Pollution Indices for Assessing Contamination with Toxic Metals Chao Cai & Bijing Xiong & Youchi Zhang & Xinhu Li & Luis M. Nunes Received: 4 February 2015 /Accepted: 16 September 2015 # Springer International Publishing Switzerland 2015 Abstract Aggregation of environmental monitoring data into indices is a common procedure when the objective of the assessment is the evaluation of some environmental criterion for large areas, usually with planning purposes. Two types of aggregation functions are commonly used in the construction of indices: the weighted sum and the constant elasticity of substitution. Several criteria have been proposed for the selection of aggregation functions, namely, (i) ambiguity, which happens when all indicators indicate non-contamina- tion, but the index fails to reflect this observation; (ii) eclipsing, i.e., the index fails to reflect contamination indicated by one of the variables; (iii) rigidity occurs when the introduction of more variables result in increased failure in the classification given by the index, as indicated by a decrease of the index. The first two criteria are easily checked, but the latter is more difficult to evaluate. A method to assess rigidity is here proposed and applied. Two other criteria are also proposed: sen- sitivity and accuracy. The present study compares and discusses the use of pollution indices for the classifica- tion of soils as to heavy metal pollution, with both empirical and real-world data. In the end, some criteria for index selection are indicated, along with their rank- ing for different practical circumstances. The Nemerow pollution index and the ecological risk index complied with all the fundamental criteria making them good general-use indices. Keywords Pollution . Index . Ambiguity . Eclipsing . Rigidity . Sensitivity . Accuracy 1 Introduction Industrialization has been accompanied by increased concentrations of metals and semimetals in soils. Some, such as lead and cadmium, are non-essential, being potentially toxic even in very low concentrations; essen- tial ones, such as copper, nickel, zinc, and manganese, are fundamental for many metabolic activities, but be- come toxic for concentrations above a certain threshold. Increased concentrations of the former are usually linked to emissions from industrial production processes (such as metal smelting and refining, coal and oil fired power stations, and electroplating plants), road traffic, Water Air Soil Pollut (2015) 226:352 DOI 10.1007/s11270-015-2620-2 C. Cai : B. Xiong : Y. Zhang : X. Li : L. M. Nunes Key Lab of Urban Environment and Health, Institute of Urban Environment, Chinese Academy of Sciences, Xiamen 361021, China C. Cai e-mail: ccai@iue.ac.cn B. Xiong e-mail: bjxiong@iue.ac.cn Y. Zhang e-mail: yczhang@iue.ac.cn X. Li e-mail: xhli@iue.ac.cn L. M. Nunes (*) Civil Engineering Research and Innovation for Sustainability, University of Algarve, 8005-139 Faro, Portugal e-mail: lnunes@ualg.pt