A Brief History of Chemical Residues in Drinking Water

Population growth and increased abstraction of water leads to lower dilution for sewage and industrial effluents that discharge to watercourses. If sewage treatment is not improved, this leads inevitably to higher concentrations of chemical residues and an increased possibility that some residues, or the products of their reactions with water treatment disinfectants, will appear in drinking water derived from surface water sources. The organic matter that occurs naturally in water also has a role in the production of unwanted by-products in drinking water. Indeed the interest in disinfection by-products (DBP) that emerged in the 1970s stemmed from the identification of trihalomethane (THM) compounds, produced when chlorine reacts with humic substances in water.

Two decades of research into DBP formed by chlorine and other disinfectants, coupled with an expanding toxicology database, led to limits in the 1998 Drinking Water Directive for THM and bromate (formed by reaction of ozone with the bromide salts present in most water sources and in hypochlorite from high bromide brine). Recent proposals for revision of the 1998 Directive include limits on haloacetic acids (formed by reaction of chlorine with organic matter) and chlorite and chlorate (breakdown product of disinfection with chlorine dioxide and decomposition product in stored sodium hypochlorite).

Most DBP are toxic and some are potential human carcinogens. Numerous ecological studies have been carried out to investigate risks to health from chlorinated drinking water. In general, these studies have compared the health outcomes in populations served by chlorinated drinking water derived from surface water sources with equivalent populations receiving unchlorinated water or water from groundwater sources where DBP levels are insignificant. These studies have looked for possible associations between long-term exposure to very low DBP concentrations in drinking water and incidence of specific cancers, cardiovascular disease or adverse pregnancy outcomes, including birth defects.

Some studies have reported positive associations between adverse health outcomes and total or individual THM levels, while others have produced contradictory results. An authoritative assessment of the significance of these studies can be found in the WHO document “Environmental Health Criteria 216: Environmental Health Criteria 216: Disinfectants and Disinfectant By-products”. In Part IV the following conclusions are drawn:

The overriding conclusion of this WHO report is that the microbiological quality of drinking water is paramount and new data have not changed these conclusions. Water treatment processes must be operated to minimise DBP formation but maintaining microbiological quality must be given priority over minimisation of DBP.

A new concern about chemicals in drinking water emerged in the early 1990s with the publication of research findings on the feminisation of male fish. The then Department of the Environment (DOE) had been funding research on inter-sex fish in the River Lea throughout the 1980s. When this work was eventually published, it complemented the findings of other research studies on the environmental impact of endocrine disrupting compounds (EDC). These are natural or synthetic compounds that mimic hormones or disrupt the function of the endocrine system, which regulates the production and release of hormones. The DOE research findings showed that natural oestrogens and components of the contraceptive pill were present at trace levels in sewage effluents and that exposure of male fish to sewage effluents caused a change in their hormone levels that was indicative of feminisation. As other EDC studies had linked endocrine disruptors to adverse biological effects in animals, this gave rise to concern that low-level, long term exposure might cause similar effects in human beings. The media promptly latched on to the ready made conspiracy theory that the Government had been suppressing “secret” research evidence of “gender bending” chemicals in the water supply. Media interest reached fever pitch in 1994 when an article in The Lancet1 suggested that the low sperm count exhibited by men living in the London area might be caused by EDC in the tap water.

Further research on the inter-sex fish revealed that the effect was observable only at points close to the discharge of sewage effluents. An authoritative assessment of the implications for water supplies is available in the UKWIR report2 on contraceptive pill steroids in water sources and their fate in water treatment processes. This report confirmed (1) that steroids could not be detected in any water sources at the point of abstraction for drinking water treatment and (2) that conventional water treatment processes would effectively remove any steroid residues that were present.

Knowledge about the nature of chemical residues in drinking water sources expanded still further in the 1990s. A steady stream of scientific papers reported on pharmaceuticals, personal care products and other man-made chemical preparations that are flushed down the drain, eventually reaching watercourses as sewage effluent. This was not a new issue; pioneering work on DBP in the 1980s at the Water Research Association3 (the predecessor to WRc) had tentatively identified pharmaceutical residues in concentrated extracts prepared from River Thames water. Now, with the increased sensitivity and selectivity of modern analytical instrumentation it was possible to identify common high use pharmaceuticals in water sources and in some cases, drinking water.

1 J. Ginsburg, S. Okolo, G. Prelevic and P. Hardiman, The Lancet, Vol. 343 No. 8891 p 230
2 Steroid Concentration in Treated Sewage Effluents and Water Courses -98/TX/01/1
3 M Fielding et al. (1981) Organic Micropollutants in Drinking Water. Water Research Centre Technical Report (TR) 159

Drinking water identifications undoubtedly represented extreme worst-case situations. An example was the identification in 1994 of up to 0.17μ/l of clofibric acid in Berlin’s tap water4. At the time, clofibric acid was commonly prescribed at doses of up to 2g per day for reduction of blood cholesterol. The molecule is highly water soluble and resistant to degradation in the environment. The water source was a river carrying a high proportion of treated sewage effluent and the relatively sophisticated water treatment processes were not designed for removal of the substance in question.

Most of the published work on pharmaceuticals in water throughout the 1990s was based on European and American studies, although a useful review of human pharmaceuticals in the environment was published by the Environment Agency in 2000. That review included tables of the quantities of prescribed drugs in the UK and information on their environmental fate, as well as available data on the concentrations reported in sewage effluents, environmental waters and drinking water. Many of the report’s conclusions were especially relevant to drinking e.g. reported detection levels of pharmaceuticals were extremely low, usually of the order of ng/l; the major source of input to the environment was patient excretion, rather than disposal of unwanted drugs with solid waste; there was a need for accurate information on the quantities of prescription and over-the-counter products and this information, in conjunction with data on metabolism/excretion rates and environmental fate should be used to prioritise targeted analysis of the most persistent chemicals.

4 Stan, H. -J., Heberer, Th., Linkerhägner, M. Vom Wasser (83) 57-68 (1994) (English summary included in proceedings of “Issues in the analysis of environmental endocrine disrupters” American Chemical Society, San Francisco, 26-30 March 2000).

A 2008 report commissioned by DWI “Desk based review of current knowledge on pharmaceuticals in drinking water and estimation of potential levels” DWI 70/2/213 indicated that there was still little information available on pharmaceuticals in UK water supplies. The report concluded that, based on data from the USA and Europe, concentrations of individual pharmaceuticals in drinking water were likely to be less than 0.1mg/l. The report echoed the recommendation of the 2000 EA report in respect of the need for modelling of the fate of high usage pharmaceuticals. The report also recommended a small-scale survey of pharmaceuticals in drinking water based on concentrations predicted by modelling and supplemented by analysis of chemicals of “potentially high public perception of hazard such as cytotoxic drugs”. The Daily Telegraph publicised the DWI report under the headline “British drinking water 'may be tainted with prescription drugs'

The current state of knowledge on pharmaceutical residues in UK water supplies is inadequate for the purposes of a rigorous risk assessment. On the other hand, estimates of exposure levels suggest that the effective dose will be tens of thousands of times lower than the therapeutic dose level. One of the key conclusions of a WHO expert group in 2009 was that “appreciable adverse impacts on human health are unlikely at current levels of exposure associated with drinking water”.