Application of enantiomeric analysis of illicit drugs in wastewater-based epidemiology and beyond

Wastewater-based epidemiology (WBE) is a methodology used to estimate (illicit) drug abuse by analyzing raw wastewater. However, the application of WBE can be complicated when drug use estimations need to be derived from the concentration of the parental drugs because no other suitable biomarkers (metabolites) are available, since the presence of unchanged form in sewage can derive from multiple sources, not necessarily from illicit use. This is the case of three relevant illicit substances, viz.: amphetamine, methamphetamine and methylenedioxymethamphetamine (MDMA), among other drugs. In such cases, chiral analysis can be particularly useful to avoid misinterpretation of the results. This chapter is devoted to review the applications of chiral analysis in WBE of those drugs, by providing a quick overview of such technique, considering licit and illicit sources of the abovementioned drugs in wastewater, the existing analytical methods and the most relevant applications. Furthermore, a short description of the chemical behavior of those drugs during wastewater treatment and subsequent release in the receiving natural media is provided. Finally, some further applications, particularly in the analysis of ephedrine/pseudoephedrine and ketamine, among others, are presented.