Occurrence of Human-Excreted Contaminants Within a Decantation Tank: A Clue of Their Historical Consumption?

Summary This study investigated the occurrence of drug target residues (DTR) in a decantation tank. This installation trapped the coarse fractions of a unitary sewer system, collecting both stormwater and wastewater. While this 17 m deep underground building could constitute a nonesuch opportunity to study the historical evolution of illicit and licit drug consumption in the catchment, the deposition processes and the record of DTRs remain largely unknown at present. Five cores were acquired from 2014 to 2017. 152 sediment samples were extracted using a mixture of water:methanol (1:1) prior to the DTRs quantification in the extracts. Several classical sedimentological analyses such as total organic carbon, facies description and granulometry were also performed on these samples, in order to understand the most important factors impacting their deposition. The key-role of the speciation of DTRs was highlighted by the higher contents in neutral and anionic DTRs in organic layers, whereas only cationic DTRs were found in mineral layers. The considerable modifications in the sediments’ properties are therefore the most important driver impacting their DTR concentrations in decantation tank sediments. Further research remains necessary to fully understand the deposition process, but this study provides new clues explaining these temporal evolutions.