Desk Based Review of Current
Knowledge on Pharmaceuticals in Drinking Water and Estimation of
The Drinking Water Inspectorate commissioned this review to identify
all relevant, robust studies that investigate pharmaceutical
concentrations in raw or treated water, or factors affecting those
concentrations. This summary of existing knowledge will be taken
forward and used for the systematic evaluation of the potential for
different pharmaceuticals to reach water.
There are about 3000 pharmaceuticals registered in the UK and
approximately 5000 substances listed as human pharmaceuticals were sold
over the counter in the UK in 2004. Consumption of active
pharmaceutical ingredients in industrial countries is estimated to be
between 50 and 150 g per person per year, with fewer than 50 compounds
making up 95% of the total amount of active pharmaceutical ingredient
consumption. In addition to the consumption of drugs for health care,
there is also significant consumption of ‘illegal’
drugs due to both recreational consumption and drug addiction, and for
enhancement of sporting performance.
The observed concentrations of pharmaceuticals in raw wastewater
indicate that the major source of pharmaceuticals to the environment is
via sewage treatment works effluent. Sewage treatment works use a wide
range of processes, e.g. primary screening, biological filtration, and
anaerobic digestion, and these are considered in detail in this report.
Reported removal rates for pharmaceuticals vary considerably between
and within studies. In addition, concentrations of some compounds have
been found to increase during the treatment process, probably as a
consequence of the transformation of conjugates back to the parent
compound. As well as the variances that can be ascribed to differences
in process type and sewage treatment works configuration, other
factors, such as heavy rainfall and seasonality, have been shown to
confound interpretation of removal rate efficiency.
Drinking water treatment works use a wider and technically more
advanced range of processes, but again these are not specifically
designed to remove pharmaceuticals and several compounds have been
reported in finished drinking water in different parts of the world.
Although no clear quantitative structural relationships have been
determined that describe the degree of removal of a pharmaceutical
during treatment processes, it is clear that the structure and nature
of individual compounds are key parameters in determining the
efficiency of removal. Only a few pharmaceuticals are oxidised to
smaller molecules by chlorine or chlorine dioxide, but for those
pharmaceuticals containing amino or phenolic moieties a complete
oxidative degradation can be expected. Most non-polar organic compounds
are the best candidates for the removal by activated carbon but the
removal rate may depend on the age of the carbon. Neutrally charged
pharmaceuticals are well removed from water using an oxidant such as
ozone or ultraviolet radiation. Reverse osmosis has been shown to be a
particularly effective process for removing a wide range of
pharmaceuticals but is an energy-intensive process. Removal of
pharmaceuticals by drinking water treatment works processes was
significant for almost all of the pharmaceuticals studied when the
treatment process included ozonation and activated carbon. This
combination, together with the more conventional DWTW processes, can
result in removal rates of >90% for a wide variety of
Very limited data were available for the concentrations of
pharmaceuticals or illegal drugs in UK drinking waters, but data from
the rest of Europe and the USA have shown that concentrations in
finished drinking water at treatment works are generally ≤100
ng.l-1. Data for UK rivers and streams has shown that median
concentrations of pharmaceuticals are almost always ≤100 ng.l-1.
Five drinking water treatment works scenarios based on UK catchments
were used for deterministic and probabilistic modelling to estimate
concentrations in UK drinking waters. The model was based on the simple
approach developed by the European Medicines Agency (EMEA) for
estimating concentrations of pharmaceuticals in surface waters.
Exposure ratios based on comparison of the estimated concentrations
with the minimum therapeutic dose were used to determine the
significance of the model outputs for pharmaceuticals and illegal drugs.
Worst-case modelling showed that even in the scenario with the highest
estimated concentrations, the exposure ratios (comparison of the
minimum therapeutic dose to the estimated intake from drinking water)
for most of the major used pharmaceuticals and illegal drugs were
significantly greater than 1000 and provided a high safety margin. Only
10 substances produced exposure ratios less than 1000 and four of these
were illegal drugs. In only one case was the exposure ratio less than
100 and this was the special case, using a combined total for all
NSAIDs at the lowest minimum therapeutic dose. It therefore appears
that even in this worst case situation there is no significant risk
from pharmaceuticals discharged to drinking water sources.
The use of probabilistic modelling provided a more realistic estimate
of likely concentrations in drinking water and showed that, as
expected, the estimated concentrations for all except one substance
were significantly lower than the estimated concentrations from the
worst case (deterministic model). Using the mean concentrations from
the probabilistic model, all of the substances have exposure ratios
significantly greater than 100 and only tetrahydrocannabinol also has
an exposure ratio less than 1000. It therefore appears that this more
realistic worst case probabilistic modelling confirms that there is no
significant risk from pharmaceutical usage.
The accuracy of the estimates of usage for the illegal drugs is unknown
and since many of them produced some of the lowest exposure ratios it
would be appropriate to revisit estimates of usage. In addition, since
they were assigned nominal, very low, minimum therapeutic doses it
would also be appropriate to search for data to provide more realistic
estimates. In addition it would be useful to collate data on the
percentage of active ingredients in cannabis that are absorbed during
use in order to obtain a better estimate of the quantities of
tetrahydocannabinol that might be available to reach wastewater.
Some pharmaceuticals produce significant quantities of metabolites
which are excreted and enter the environment via sewage treatment.
Worst case modelling of these metabolites for major use pharmaceuticals
would be worthwhile to determine their exposure ratios.
In view of the dearth of measured data on the concentrations of
pharmaceuticals and illegal drugs in UK drinking waters it would be
prudent to carry out a small scale survey. This survey could be guided
by the findings from this report and address those substances that have
the lowest exposure ratios, the highest predicted concentrations and
substances of potentially high public perception of hazard such as
cytotoxic drugs, depending on the available analytical methodology. In
addition, the monitoring could be carried out in the catchments that
provided the scenarios with the highest estimated concentrations or
where there is reason to believe that there may be a particular hotspot.
Copies of this report may be available as an Acrobat pdf download under the 'Post 2000 Reports' heading on the DWI website.