Assessment of micro-pollutants from a water supplier’s perspective


Heinz-Jürgen Brauch and Frank Sacher
DVGW-Technologiezentrum Wasser (TZW), Karlsruher Straße 84, 76139 Karlsruhe, Germany
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Abstract

More and more man-made chemicals are found in the aquatic environment in very low concentrations. These “micro-pollutants” might endanger the usage of water resources, particularly for drinking water preparation. The issue of micro-pollutants is a major challenge for water suppliers as adequate ­­­­­­­information on the occurrence, fate and assessment of the respective chemicals is often missing. In this paper an approach for the assessment of these micro-pollutants is described that combines the results of monitoring activities and lab-scale experiments with general information on physical, chemical and biological properties of individual chemicals under investigation. The outcome should enable water suppliers to decide on different management options and to communicate the issue to consumers and the public in an appropriate manner.

Key Words: micro-pollutants, assessment, water supply, water treatment, benzotriazoles, isothiazolinones

Introduction

The provision of safe drinking water to the consumer is the major task of any water supplier. To fulfil this task and to permanently guarantee high quality drinking water, most water suppliers usually apply the so-called multiple barrier concept which is composed of three key principles:
  • comprehensive source water protection,
  • adequate treatment,and
  • reliable distribution systems.
By applying this concept, water supplies in Central Europe have successfully achieved compliance with drinking water directives and have gained the trust and confidence of their consumers.
In recent years, however, an increasing number of reports in newspapers, journals and on television have discussed the discovery of chemicals in drinking water, which threaten the health of consumers. Although these reports are usually not completely unfounded, a closer look most often reveals that such reports are attention-grabbing and may contain single aspects that are inexact or even wrong from a scientific perspective. For example, in most cases the reports do not make a clear distinction  between findings of chemicals in wastewaters or surface waters and the occurrence of these compounds in drinking water.



Furthermore, the concentration levels of the identified chemicals are generally completely ignored. State-of-the art analytical instrumentation enables the detection of many chemical compounds at the ng/L level or even below. Most often the detection of such concentrations is comparable to the finding of a sugar cube in a large reservoir. Although there are chemicals that exhibit adverse health effects even at such low concentrations, the harmful effect levels of most compounds are far above these concentrations. Thus, even if adequate safety margins are taken into account, the occurrence of trace levels of a chemical in drinking water is not necessarily related to any harmful effects on consumers. Consumers, however, expect their water suppliers to adequately respond to any potential threat originating from chemical compounds (“micro-pollutants”) in their raw and drinking waters. Thus, water suppliers need to have a strategy for addressing this issue and communicating to the public.
The current paper presents two examples of organic micro-pollutants which are not regulated by current European drinking water directives but which occur almost ubiquitously in the urban water cycle. A concept of how to assess the relevance of non-regulated organic micro-pollutants from a water supplier’s perspective will be discussed here.