Analysis of psychoactive substances in surface waters

Abstract

The changes in the law to keep drug trafficking and consumption under control have increased illicit market of psychoactive substances (PAS) and the synthesis and introduction of new psychoactive substances (NPS). On the other hand, many PAS are chiral and available either as racemate or enantiomerically pure and determination of the enantiomeric fraction is essential for a comprehensive analysis of drug consumption and evaluation of environmental risk. These substances reach the environment through different ways such as direct disposal by industry, illegal discharges and manly as humans excretion products (of parent compounds and/or metabolites) through the effluents of wastewater treatment plants (WWTP). Occurrence of PAS in surface waters can give insights about their consumption in a specific region and EF can provide valuable information about synthetic pathways and distinction between direct disposal or consumption. Therefore, the aim of this work was to develop and validate an indirect method by gas chromatography-mass spectrometry (GC-MS) based on the formation of diastereomers using (R)-(-)-α-methoxy-α- (trifluoromethyl) phenylacetyl chloride ((R)-MTPA-Cl) as chiral derivatization reagent, for enantiomeric quantification of eight PAS including three amphetamine like substances namely amphetamine (AMP), methamphetamine (MAMP), 3,4-methylenedioxymethamphetamine (MDMA), the metabolite norketamine (NK), and four synthetic cathinones, buphedrone (BPD), butylone (BTL), 3,4-dimethylmethcathinone (3,4-DMMC) and 3-methylmethcathinone (3-MMC). Also, two illicit piperazines (PP) namely 1-benzylpiperazine (1-BP) and 1-(4-metoxyphenyl)-piperazine (1,4-MPP) were included. PP were also derivatized with (R)-MTPA-Cl. The optimized conditions allowed the quantification of the target PAS (a total of 16 diastereomers and two PP derivatives) in less than 24.0 min. The method was validated according to the International Conference on Harmonization (ICH) in terms of selectivity, linearity, limit of detection (LOD), limit of quantification (LOQ), accuracy, intra and inter-precision and recovery. The method showed to be selective and correlation coefficients were higher than 0.98. The LOD ranged from 17 to 100 ng L-1 and LOQ varied between 50 and 300 ng L-1. The method demonstrated to be accurate (82.4 to 116.9%), precise (up to 8.5%) and recoveries ranged from 25 to 105.5%. The method was used to evaluate the occurrence, spatial distribution, and the EF of the target PAS in Portuguese surface waters in the Great Porto region and effluents from two WWTPs. For that, 1 L of surface estuarine water samples were collected at five sampling points along the Douro river estuary. Further, effluents samples were collected from two WWTPs that discharge their treated wastewaters for Douro river tributaries. Of the 18 compounds included in this work, 5 were detected in estuarine water and 6 in WWTPs. Both enantiomers of AMP, and only one enantiomer of MAMP, MDMA and BPD were found in estuarine waters, but below LOQ. Effluents samples showed only one enantiomer of AMP, BPD, 3,4-DMMC, but both enantiomers of MDMA (present though at concentrations below the LOQ). MAMP was also detected in both WWTPs in range of <LOQ - 57.30 ng L-1 with enantiomeric fraction (EF) ≅1. These results showed the occurrence of AMPs and for the first time the presence of illicit synthetic cathinones in Douro river estuary and effluents. Occurrence of MAMP in both surface waters and effluent samples suggests consumption rather than direct disposal. The occurrence of synthetic cathinones, namely BPD was found and reported for the first time in Portuguese surface waters. Analysis of effluent samples also detected for the first time the occurrence of synthetic cathinones (BPD and 3,4-DMMC) and EF suggests enantioselective processes. Further studies are needed considering the elution order of the diastereomers for a comprehensive analysis of the data. Though data from this study was obtained from one sampling period, results show the potential of the method to monitor the target PAS.