Unsupervised pattern-recognition techniques to investigate metal pollution in estuaries

•We provide a clear classification of pattern-recognition techniques.•The main features of unsupervised pattern-recognition techniques are summarized.•Pattern recognition applied to pollution monitoring is an increasing area of concern.•The most important papers on pattern recognition in estuarine sediments are reviewed.•Multivariate techniques are mandatory to handle environmental data tables.

There has been a significant increase in the application of unsupervised pattern-recognition techniques to the analysis of long datasets emerging from the monitoring of metal pollution in estuaries. In this work, we thoroughly review the most important articles published on this topic in recent years.