A demographics-based mass load model for estimating community drug use

Abstract

The high global consumption of illicit drugs, together with their inefficient removal during wastewater treatment, raises concerns over their potential impacts on water sources. Illicit drugs are potent psychoactive chemicals; their presence in receiving waters may pose risks to aquatic organisms and to human health. Their concentrations in sewage are typically within the nano-g/L to micro-g/L range, making them challenging and costly to measure. In this study, we apply a demographics-based mass load model to estimate the influent concentration of cocaine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA) in two mid-size wastewater treatment plants (WWTP). Both plants service fully-sewered areas; WWTP1 services a population of 100,000 while WWTP2 services a population of 200,000. Census data were combined with published age-based drug consumption rates and pharmacokinetic factors to determine average daily mass loads and drugs levels in the influents. Model predictions ranged from 1–102 ng/L, and were highest for MDMA and about the same for cocaine and methamphetamine. These were also compared with actual measurements from the WWTPs. Estimates were consistent with actual measurements for cocaine and methamphetamine but were overestimated for MDMA. Overall, findings suggest high consumption of the target drugs in the studied area. From the perspective of WWTP operation, model estimates can serve as a basis for establishing mass loads of illicit drugs entering the WWTP and for optimizing treatment processes to more effectively remove them during treatment.