Lessons learned from more than two decades of research on emerging contaminants in the environment.

In the last twenty years, thousands of research papers covering different aspects of emerging contaminants have been published, ranging from environmental occurrence to treatment and ecological effects. Emerging contaminants are environmental pollutants that have been investigated widely only in the last two decades and include anthropogenic and naturally occurring chemicals such as pharmaceuticals and personal care products and their metabolites, illicit drugs, engineered nanomaterials, and antibiotic resistance genes. The advancement in our knowledge on emerging contaminants has been the result of the appearance of highly sensitive and powerful analytical instrumentation that rapidly developed, allowing identification and trace quantification of unknown contaminants in complex environmental matrices. High efficiency chromatographic separations coupled to high-resolution mass spectrometers have become more common in environmental laboratories and are the pillars of environmental research, increasing our awareness and understanding of the presence of emerging contaminants in the environment, their transformation and fate, and the complex ecological consequences that they pose on exposed biological systems. This introductory paper for the Virtual Thematic Issue on Emerging Contaminants presents a brief literature overview on key research milestones in the area of emerging contaminants, focusing on pharmaceuticals and personal care products and endocrine disrupting compounds, and highlighting selected research papers previously published in the Journal of Hazardous Materials during the period of January 2012 to December 2015.