For the assessment of the relevance of micropollutants, a precautionary and hazard-based approach was chosen by the “Federal Strategy on Micropollutants” Stakeholder Dialogue (in German): If a micropollutant found in water bodies fulfils one or more of the criteria of persistence, mobility and toxicity, a weight-of-evidence decision is taken whether it is regarded as a relevant micropollutant. For this approach, a risk assessment can be useful, i.e., the German Centre for Micropollutants compares the concentration of the micropollutant in water bodies with derived reference values (limit, guide, threshold or guideline values), which are derived from the results of human toxicological or ecotoxicological tests. If no test results are available, precautionary thresholds may be used. Here is a selection of the most important reference values:
WHO Drinking Water Guideline Values
The World Health Organisation (WHO) has derived health-based guideline values for a few chemicals in drinking water, based on observed health effects. A guideline value for a micropollutant represents the concentration that does not lead to a significant health risk during a lifetime consumption of 2 litres of drinking water per day by an adult person (60 kg body weight).
Drinking Water Limit Values According to the Ordinance on the Quality of Water Intended for Human Consumption (Drinking Water Ordinance)
The German Drinking Water Ordinance (TrinkwV) sets thresholds for microbiological parameters, chemical parameters and indicator parameters. A is the politically determined maximum concentration of microorganisms or a micropollutant or the politically determined maximum or minimum value of a physico-chemical parameter in drinking water. Political determination means that not only the health-related assessment but also technical-economic aspects (including available techniques for removal and their costs, available analytical methods or the protection of technical installations, e.g., from corrosion) and political reasons (e.g., minimisation principle) are factored in as well. The selection of TrinkwV chemical parameters for which a threshold value is determined is based on the relevance of the parameter’s occurrence in drinking water and its significance for health.
An indicator parameter is a parameter with an indicator function for which exceeding the corresponding threshold value or non-adherence to the requirements is an indication of an undesirable and possibly hygienically relevant change in the supply system for which it is necessary to determine the cause.
Acceptable / Tolerable Daily Intake (ADI and TDI Value)
The ADI value considers the oral intake of a micropollutant and indicates the total amount that can be ingested daily over a lifetime in air, food or drinking water without posing a health risk. The ADI is based on the “No-Observed(-Adverse)-Effect Level” (NOAEL) determined in studies with animals. This represents the (highest) dose of a chemical that no longer has a toxic effect. In addition, the ADI value takes various safety factors into account (e.g., extrapolation of the test duration, toxicodynamic and toxicokinetic differences between and within different species).
For pesticide active ingredients and additives in food, the value is called the Acceptable Daily Intake (ADI) value. The Tolerable Daily Intake (TDI) value indicates the tolerable daily intake of a non-intentionally added contaminant in food and drinking water.
Drinking Water Guideline Value
The phrase “guideline value” is not used in the TrinkwV (Drinking Water Ordinance). However, UBA uses the term in connection with drinking water to calculate the toxicologically based, maximum concentration of a micropollutant in drinking water which, if adhered to, is not likely to cause any damage to health even over lifelong exposure.
UBA sets corresponding guideline values when a complete toxicological assessment is possible. The highest non-effective dose (NOAEL) is used as the point of departure (POD) for the calculation. To calculate the drinking water guide value from the point of departure (POD), the first step is to calculate the total tolerable daily intake (TDI) for a human being – and in rare cases the tolerable weekly intake (TWI) as well. Based on the tolerable daily intake (TDI), the calculation of a drinking water guide value must take into account that the intake of a certain micropollutant by humans may not only occur via drinking water (allocation). The formula for calculating the drinking water guide value from the TDI is therefore:
Drinking water guide value = (TDI x body weight x allocation) / drinking water consumption
Default assumptions are used for body weight 70 kg, allocation 0.1 = 10% and drinking water consumption of 2 litres per day.
Health-Related Indicator Value (HRIV)
An HRIV is used to evaluate micropollutants in drinking water that have not been assessed at all or only in part to date and closes the time, data and legal gap between the analytical detection of a micropollutant in drinking water above 0.1 micrograms per litre (µg/l) and the existence of a guideline or threshold value. Falling below the HRIV provides sufficient human toxicological safety; exceeding the HRIV does not inevitably lead to a health effect or hazard due to the strong precautionary character. A health-related indicator value (HRIV) is derived when insufficient toxicological data is available to calculate a guide value. Depending on the data available, an HRIV may be between 0.01 µg/l and 3.0 µg/l.
If an HRIV is exceeded, an action HRIV can be derived based on the concept of action values, which can be up to ten times an HRIV for a limited period of time but not more than 10 µg/l. More on the HRIV (in German)
Environmental Quality Standard (EQS)
The environmental quality standard (EQS) is set for chemicals in waters under the EU Water Framework Directive and takes into account the aquatic ecosystem and human health. It is derived based on studies for the most sensitive endpoint. The annual average EQS (AA-EQS) is the average concentration over an entire annual cycle that must not be exceeded to prevent chronic toxic effects on humans and the ecosystem. In addition, a maximum allowable concentration (MAC-EQS) is set for pollutants with high acute toxicity. The MAC-EQS must not be exceeded by the measured maximum value in the water body.
Predicted No-Effect Concentration (PNEC)
The PNEC value is the maximum concentration of a chemical or its degradation product in the environment at which there are no adverse effects on the ecosystem. PNEC values are derived from ecotoxicological tests and also take a safety factor into account.
Regulatory Acceptable Concentration (RAC)
The RAC is a parameter from the approval procedure for plant protection products. As with the PNEC, it indicates the maximum concentration of a pesticide active substance or its degradation product in the environment at which no unacceptable effects on the ecosystem are to be expected. RAC values are determined based on ecotoxicological tests and a safety factor.
Target Values of European Drinking Water Suppliers for Rivers and Watercourses
A few European drinking water suppliers (IAWR, AWBR, ARW, RIWA-RIJN, IAWD, AWE, AWWR, RIWA-MAAS, RIWA-SCHELDE) have also defined target values for anthropogenic chemicals in rivers and watercourses in order to implement the precautionary approach according to the EU Water Framework Directive and to ensure their sustainable use as drinking water. The target values are maximum permissible values. The target value is
- 1.0 micrograms per litre (µg/L) for assessed micropollutants with no known effects on biological systems and microbially poorly degradable substances;
- 0.1 µg/L for evaluated micropollutants with known effects on biological systems, non-evaluated micropollutants insufficiently removable by semi-natural processes and non-evaluated micropollutants forming non-evaluated degradation/ transformation products.
The threshold values according to the German Groundwater Ordinance (GrwV 2010) are 0.1 micrograms per litre of groundwater (µg/L) for
- active substances in plant protection products, including the relevant metabolites,
- biocidal active substances, including relevant metabolic or degradation or reaction products, and
- substances of concern in biocidal products.