Sewage Water Analyses Drugs in 56 European Cities: What do Statistics Show?

March 7, 2018

Today the European Monitoring Centre for Drugs and Drugs Addiction (EMCDDA) presents the 2017 results of the so-called sewage water analyses for drugs. Trend data of Amsterdam, Eindhoven, and Utrecht were presented for the Netherlands. Noteworthy were the high drug residue loads measured in Amsterdam for MDMA and in Eindhoven for amphetamine. But what do these statistics really show?

The statistics presented by the EMCDDA are derived from a European study (SCORE). Starting in 2011, a total of 7 measurements have been taken in an increasing number of European cities. In 2017 it was done in 56 cities in 19 European countries. For the Netherlands, (trend) data were presented for Amsterdam, Eindhoven, and Utrecht.

  • Of all cities, the highest load (measured in mg per 1000 people per day) of MDMA (ecstasy) was found in Amsterdam. High measures also were found in Eindhoven. Cocaine loads in Amsterdam are also relatively high, but there are more European cities with high numbers, such as Barcelona, Antwerp, and Bristol.
  • High loads for amphetamine were found in Eindhoven as well as in Antwerp. These are much higher than in Amsterdam and Utrecht.
  • Reference years show an erratic pattern for cocaine and amphetamine in the Dutch cities, without any clear trend. In Amsterdam and Eindhoven, loads for MDMA clearly are higher in 2017 than in 2011.
  • Looking at data from surveys among the general population, the Netherlands finds itself in the highest ranges of MDMA and amphetamine for last year’s percentage of users.

Interpretation of the statistics
Interpretation of the statistics is difficult (see below). The analysis that was used (usually) does not distinguish between dumping and human consumption. Dumping is, for instance, when a quantity of ecstasy pills is being flushed through the toilet during a raid. The higher score in Amsterdam may indicate a peak in consumption, even though there were no large festivals in the period measured. Amsterdam does have a continual flow of tourists and the city attracts party-goers. In other words, often people visit the city to use drugs. Sewage water analyses do not provide information about user groups or patterns. Eindhoven is situated in a region where much ecstasy and amphetamine is produced. Here too outcomes may be explained by dumping. It cannot be excluded that the high statistic in Amsterdam in 2017 has to do with dumping.

It is also noteworthy that methamphetamine was found in the sewage water analyses in Amsterdam. The load, however, is much lower than that of other stimulants and also lower than, for instance, in the Czech Republic, Slovakia, and Northern Europe. For some years now, several agencies have reported that the use of this stimulant is increasing. Yet this does not show in several prevalence studies, nor in the Amsterdam Antenna survey, which measures the use of drugs among the population of Amsterdam. There are some indications that the substance is used in certain circles, especially among gay and bisexual men, during sex.

 The Trimbos Institute annually reports developments in the drugs situation in the Netherlands to the EMCDDA. They do so in cooperation with the Research and Documentation Center (WODC), commissioned by the Ministry of Health, Welfare and Sport (VWS) and the Ministry of Justice and Security. This is done by all Focal Points in the EU member states. The data of the sewage water analyses are derived from SCORE, a European study that the EMCDDA is cooperating with.

Sewage water analysis: advantages and disadvantages

In contrast to survey questionnaires from a representative sample of respondents out of the registered population, this relatively new approach works by analyzing samples from sewage water in a specific time frame (often one week) and within a geographic area. An advantage of sewage water analysis is that this method can give a better idea about the total quantity of drugs consumed, as compared to estimations based on questionnaires and self-reporting. In this last ‘traditional’ method there can be an underestimation, for instance because the heaviest users are underrepresented, or the respondent cannot remember which drugs and how often and how much was used in a particular time frame, or people are unwilling to admit to their use of drugs. Fast market developments also can be monitored with sewage water analyses, but in the Netherlands this is done already via the Drug Information and Monitoring System.

Monitoring by using sewage water analyses also has disadvantages. There are difficulties and inaccuracies in calculating the concentrations of drugs found in the sewage water back to the actual quantities that were used. In addition to that, it is not possible to make a link between the estimated quantity of drugs and the number of users and their characteristics, as well as the potency and the purity of the drugs. Any visitors, such as tourists and party-goers that are not part of the population, cannot be taken into account in the statistics. Also, sewage water analyses cannot help in determining whether a small number of older (addicted) persons consume large quantities of crack daily, or many young people (whether from abroad, from other regions, or not) sniff occasionally in the weekend. The same is true for other risk factors, which can be addressed in questionnaires among users.

It is also difficult to make a distinction between human consumption and dumping of substances for which no degradation products can be measured (or are as yet not being measured), such as for MDMA and amphetamine. It is expected that in due course the classic method of questionnaires and the innovative method of sewage water analysis will complement one another.

Read the EMCDDA press release.

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