When the drugs reach the works
Consumption of illegal drugs is a major fact of metropolitan life, says Frank Rogalla of Aqualia. But what happens when they leave the human body? European research provides some answers
This is possible even at the scale of a whole city. In 2008, researchers in the North-western US took one-day samples from 96 Oregon wastewater treatment plants (WwTPs) that volunteered to participate, testing for the presence of chemicals indicating methamphetamine, cocaine and ecstasy.
Cocaine showed up in 80% of the communities tested, whereas ecstasy, the one-time party drug, was detected half as often - but meth appeared in every test, from Oregon's smallest towns to its biggest cities.
Millions of people around the world use cocaine, heroin, amphetamine type stimulants, marijuana and other illegal drugs - in fact, the amount of illicit drugs consumed worldwide is comparable with the consumption of therapeutic drugs. In 2007, the UN Office on Drugs & Crime (UNODC) estimated that 16M people worldwide, corresponding to 0.4% of the population aged 15-64 years, have used cocaine, which is now the second most used illicit drug after cannabis.
The European Monitoring Centre for Drugs & Drug Addiction (EMCDDA) estimates that approximately 4.5M European residents aged 15-64 (1.3%) used cocaine in 2007; in Italy, Spain and the UK, the prevalence of cocaine use was over 2%. From the available data, it is clear that these compounds are present in wastewater influents, treated wastewaters and surface waters in several countries and there are potential impacts for aquatic organisms. In humans, cocaine is hydrolyzed rapidly to benzoylecgonine (BE) and ecgonine methyl ester (EME) and degraded further into some minor metabolites.
Only a small fraction of cocaine is excreted in urine as the parent compound, while the largest amount is excreted as BE, the most important metabolite. Because EME was undetectable in all water samples (<20ng/l) and cocaine is proven to be not stable in water, only the measured BE concentrations (in ng/l) can be used to back-calculate into an amount of used cocaine (as g/day).
Using 24-hour flow-dependent automatic samplers, influent wastewater was collected from 41 WwTPs across Belgium, covering approximately 3.7M inhabitants - about 35% of the total Belgian population. The plants were chosen based on the amount of residents they serve (>10,000) and on their geographical location, to give a general picture of cocaine consumption in Belgium. To evaluate differences in cocaine use during the week and at weekends, two samples were collected for each WwTP, one on Sunday and one on Wednesday. Two sampling periods were used - one in the summer of 2007 and one in the winter of 2007-08 (see figure 1).
While the average concentration is calculated to be around 0.5g/d per 1,000 inhabitants, the peak value in Antwerp was found to be more than three times higher at 1.8g/d per 1,000 inhabitants. A separate study in Dublin found an equivalent of 1.44g/d per 1,000 inhabitants in the influent of Ringsend WwTP. To estimate the annual cocaine consumption for the whole of Belgium, the results can be extrapolated from the 3.7M inhabitants from which wastewater was collected to the total population of 10.5M, resulting in an average annual cocaine consumption close to 2t per year. On the assumption that an average administered dose consists of 100mg cocaine and an average cocaine user consumes around 0.65g/ week, the number of estimated cocaine users is around 60,000, or 0.6% of the total population - a percentage that doubles if an age bracket of potential users for people aged 15-44 is chosen.
In a study on the occurrence of several psychoactive drugs in water resources from North-eastern Spain, most of the studied controlled drugs (eight out of 11) were found in both influent and effluent samples from several WwTPs. Cocaine and its metabolite were detected in wastewaters at concentrations ranging from 4ng/l to 4.7ìg/l and from 9ng/l to 7.5ìg/l respectively while concentrations of amphetamine type stimulatory drugs ranged from 2 to 688ng/l.
Removal percentages were estimated by sampling eight WwTPs in Catalonia. Cocaine and benzoylecgonine removal percentages were higher than 88%, while those of amphetamine-type stimulants varied ranging from 40% to more than 99%. Daily variability was also evaluated by performing a sequential survey, which revealed important fluctuations in the concentrations of nicotine, paraxanthine, amphetamine and ecstasy during the week. In the Netherlands, compared with the provisional drinking water limits of 1ìg/l, the concentrations of drugs measured in wastewater effluents was about 100-1,500 times less - with the exception of the tranquilizers oxazepam and temazepam, which could reach values of up to three times higher in treated wastewater than the maximum concentration allowed in potable water.
Therefore, the removal of psychoactive stimulatory drugs in raw waters used for drinking water production is important, and was evaluated in a Spanish drinking water treatment plant. The surface waters- exhibited cocaine, its metabolite benzoylecgonine (cocaine metabolite), amphetamine, methamphetamine as well as MDMA (ecstasy) in mean concentrations ranging from 4 to 350ng/l. Nicotine, caffeine, and their metabolites were also found at the ìg/l level.
Amphetamine-type stimulants (except MDMA) were completely removed during prechlorination, flocculation, and sand filtration steps, yielding concentrations lower than their limits of detection (LODs).
Further, ozone treatment was shown to be effective in partially eliminating caffeine (76%), while subsequent granulated activated carbon (GAC) filtration removed cocaine (100%), MDMA (88%), benzoylecgonine (72%), and cotinine (63%).
Post-chlorination achieved the complete elimination of cocaine and nicotine. Only one parent compound (caffeine), and two metabolites (cotinine and benzoylecgonine) persisted throughout treatment, although reductions of 90% for caffeine and benzoylecgonine and 74% for cotinine were obtained. In the Netherlands, 12 out of the total number of 35 compounds investigated were detected in concentrations up to 68ng/l in surface waters of the rivers Rhine and Meuse :
- The amphetamine-type stimulants methamphetamine and MDMA
- The opiates codeine, morphine and methadone
- Cocaine and its major metabolite benzoylecgonine
- The barbiturates pentobarbital, phenobarbital and barbital
- The benzodiazepines oxazepam and temazepam
It was the latter three compounds (benzoylecgonine, phenobarbital, oxazepam, temazepam) that were most frequently detected, present at > 70% of the total of 14 surface water sampling locations. In finished drinking water, out of the total number of 35 compounds investigated, only the three barbiturates (pentobarbital, phenobarbital and barbital) were detected, at concentrations up to 12ng/l.
From the 17 finished drinking water samples, six samples (35%) contained one or more barbiturates above the Limit Of Quantification (LOQ). When also the monitoring results < LOQ (2-4ng/l) are taken into account, more than twice as many samples (76%) contained one or more barbiturates.
Barbiturates appear only to get partly removed during drinking water treatment, as they were detected most frequently, mainly in water produced from bank and dune filtrate, and could be related to the greater share of older groundwater in these sources. Barbital, a tranquilizer that has been used as a human medicine since the beginning of the 20th century, is still detected although it is no longer available as a prescription drug.
Barbiturates have now largely been replaced by benzodiazepines in routine medical practice - for example, in the treatment of anxiety and insomnia - mainly because benzodiazepines are significantly less dangerous in overdose. In the Netherlands, the Dutch drinking water act recommends for organic compounds of anthropogenic origin concentrations of less than 1ìg/l, and all traces of drugs found in surface water were well below that general signal value. For the substances that are detected in raw water (benzoylecgonine, sum of benzodiazepines, and sum of barbiturates), the provisional drinking water limit is between 300 and 7,000 times higher than the concentrations detected.
For the surface waters of the rivers Rhine and Meuse, the provisional drinking water limits for all substances are more than 1,000 times higher than the concentrations detected, except for the benzodiazepines.
For the only drugs still detected after treatment, three barbiturates found in finished drinking water, the provisional drinking water limit is about 1,800 times higher than the actual concentrations measured.
To assess possible risks to human health, provisional toxicological limits for drinking water were derived based on the currently available toxicological knowledge. Based on this information, effects on public health are not expected.
However, possible effects of combined exposure to multiple compounds in low concentrations are less clear. Ongoing research with respect to possible effects of combined exposure to multiple compounds in low concentrations needs attention, as well as the development of analytical techniques to detect possible new emerging contaminants.
Only first screening results of limited monitoring campaigns are available, lacking detail on variability in time and space. In order to be able to better evaluate the presence of DOA, a more thorough derivation of human and ecotoxicological health standards for DOA in surface waters and drinking water is required, as well as the investigation of the contributions of WwTPs with respect to amounts of DoAs that are discharged into surface waters, what kinds of processes occur within the plants, their effects on the fate of the compounds and the final concentrations that are detected in effluents.