Background: in the last years, the presence of new contaminants in water has been rising. There are only few studies which analyze such presence. The aims were to determine the occurrence of drugs of abuse and their metabolites in the influent and effluent of the Sewage Treatment Plant (STP) in Talavera de la Reina, and the River Tagus, as well as to evaluate the STP removal efficiency in the elimination of these substances and to estimate the consumption of drugs in Talavera.
Methods: whe samples were taken on June 28, 2010. The presence of 5 groups of drugs (10 drugs of abuse and 9 metabolites) was quantified. The efficiency was calculated from the percentage of reduction of the concentration in the influent and effluent of the STP. Drug consumption was calculated from influent concentrations. Using a specific methodology, based on the assumption the drugs after they are consumed and metabolized in the human body are excreted as parent compounds or metabolites. Whose metabolic pathways are known, and the amount of drug or metabolite quantified corresponds to the dose consumed.
Results: ten substances were detected. In all sampling points appeared: Benzoiclegonina (BE) (cocaine metabolite), ephedrine, methadone and its metabolite EDDP. The highest concentrations were of BE (239 ng/L), and THC-COOH (35 ng/L), both in influent. In the Tagus River, the highest concentrations were of BE (5.38 ng/L) and EDDP (4.4 ng/L). The STP removal efficiency was up to 80% for all substances except for methadone (which was zero) and EDDP (increasing to leave the STP). The estimated consumption shows that the most consumed substances were cannabis (1.88 grams / day) and cocaine (0.46 grams / day).
Conclusion: the presence of drugs of abuse in River Tagus in Talavera demonstrates that these substances are not eliminated completly by STPs. Drug consumption estimate indicates that the population of Talavera mainly consumed cannabis and cocaine. Thus this methodology can complement epidemiological surveys.