In most geochemical analysis, log-ratio techniques are required to analyze compositional data sets. In such studies, some chemical elements are present at low concentration levels. When these concentrations are so low as to be undetectable, they are usually identified as values below the detection limit and added to the data set either as zero values or simply attaching a less-than label. In any case, the ocurrence of such concentrations prevent us for applying the log-ratio approach. Consequently, a prior treatment of these values is required. In this article, a review of some of the more recent such treatments is carried out. We introduce their theoretical background, give some practical advice, and their performance is illustrated through geochemical examples.