Desk based review of current knowledge on pharmaceuticals in drinking water and estimation of potential levels
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 ingredie nts 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 pharmaceuticals.