Occurrence of Stimulant Drugs of Abuse in a San Diego, CA, Stream and their Consumption Rates in the Neighboring Community

Abstract

Levels of amphetamine, methamphetamine, cocaine, and benzoylecgonine (BE), the metabolite of cocaine, were quantitated by solid phase extraction and liquid chromatography with tandem mass spectrometry (LC/MS/MS) in Forester Creek in San Diego County, CA, and in raw wastewater from the region’s sewage treatment plant. Drug residues in these surface waters were detected with 100% frequency. Mean concentrations were 0.022 ± 0.016, 0.450 ± 0.398, 0.024 ± 0.014, and 0.019 ± 0.012 μg/L for amphetamine, methamphetamine, BE, and cocaine respectively. Nonparametric testing by Spearman rank correlation showed significant (p < 0.05) positive correlations between the illicit drugs and traditional chemical markers (caffeine and sucralose) of sewage, with the exception of cocaine and sucralose. Because BE is a metabolite unique to human excretion, its presence in both wet and dry weather stream flows suggests a chronic and continuous condition of human sewage contamination in this urban southern California stream. Wastewater-based analysis also provided a direct way of measuring drug use within the population. Back-calculations of per-capita community drug consumption rates yielded values for amphetamine, methamphetamine and cocaine at 591, 5397, and 751 mg/d/1000 people, respectively. Notably, methamphetamine per-capita consumption rates determined in the present study for this southern California community were among the highest rates ever reported for the U.S. or Europe, and serve to confirm that methamphetamine use is surging in this area of southern California close to the USA-Mexico border.