Glossary

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Term Main definition
Health Orientation Value

The HOV is a theshold value for substances present in drinking water which can either not be or only partially assessed from a human toxicological aspect. It is used by the German Commission for Drinking Water Safety ("Trinwasserkommission"). From a hygienic aspect values > 3 μg/l can be permanently tolerated without further testing if at least one chronically oral study is present, on the basis of which the contaminants are toxicologically (almost) completely appraisable and the assessment does not refer to a value below 3 μg/l. Indications of this type for tentatively hygienically tolerable concentrations of non or only partially appraisable substances in drinking water above the HOV = 0.1 μg/l should however only be approved on a case by case basis by the German Federal Environmental Agency at a national level. (https://www.umweltbundesamt.de/sites/default/files/medien/374/dokumente/gow-empfehlung_2003_46.pdf, https://www.umweltbundesamt.de/sites/default/files/medien/374/dokumente/kommentar_stoffe_im_tw_n_bewertbar.pdf)
As a substitute the rating of the contaminants by QSAR in the overall range >0,1 µg/l to 3 µg/l is then recommended, if scientifically appropriate resilient expectation statements about the relationship between structure and biochemical toxicological potential of the contaminants are present ("Structure/activity relationship, QSAR") 

The HOV value is measured in such a way that a later, complete human toxicological evaluation of a non-genotoxic material/material with effectiveness threshold and the majority of genotoxic materials/materials without an effectiveness threshold securely leads to a lifelong hygienically tolerable or acceptable hygienic guide value at the level of the guide value of the HOV. For the lesser number of "strongly" genotoxic substances which can enter drinking water, the restriction of the HOV to a maximum exposure time of 10 years is recommended.

  • An HOV of 0.1 μg/l  serves as the first evaluation basis.
  • HOV ≤ 0.3 μg/l: The substance is demonstrably not genotoxic, i.e. in vitro primarily negative data about genotoxicity and/or the initial carcinogenic potential of the contaminant are present, otherwise no significant experimental toxicological data.
  • HOV ≤ 1 μg/l: The substance is demonstrably not genotoxic (see above). Significant in vitro and in vivo data about oral neuro-toxicity of the contaminant and its potential to harm germ cells are present. These data however do not refer to values below 0.3 μg/l.
  • HOV ≤ 3 μg/l: The substance is neither genotoxic nor harmful to germ cells or neurotoxic (see above). In addition significant in vivo data from at least one study of the subchronic oral toxicity of the contaminant are present. These data however do not refer to values below 1 μg/l.
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