Background: Wastewater analysis can provide estimates of illicit drug (ID) consumption in local communities.
Methods: We used repeated raw wastewater analysis in urban wastewater treatment plants to estimate loads of cocaine, heroin, methamphetamine, and cannabis consumed daily by the inhabitants of two cities in Northern Italy, Milan and Como, from 2005 to 2009.
Results: Daily cocaine loads did not change in Milan from 2005 to 2008 but fell 45% in 2009 (ANOVA, p<0.001, followed by Tukey-Kramer HSD test [2009 vs. others], p<0.05), and there was a similar drop in Como (41%, p<0.0001, t-test). Heroin also fell from 2008 to 2009 in Milan (66%, ANOVA, p<0.001, followed by Tukey-Kramer [2009 vs. others], p<0.05) and Como (26%, p=0.017, t-test). However, methamphetamine, which had risen in Milan from 2005 to 2008, rose further in 2009 (Kruskal-Wallis test, p<0.001, followed by Steel-Dwass [2009 or 2008 vs. previous], p<0.05), and cannabis, which was falling from 2005 to March 2009, rose again in September 2009 (40%, p=0.027, t-test).
Conclusions: Results suggest a trend toward a decrease in consumption of costly ID, such as cocaine and heroin. This might be due to a reduction in the number of consumers and/or to a change in their behaviour since there was also an increase in the consumption of less expensive ID. This itself might reflect a drop in consumers' money supply, caused by the economic crisis. Wastewater analysis was useful to estimate ID consumption levels in local communities in real time and promptly identify changes in trends.
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