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DIN Standards Committee Piping and Boiler Plant

Overview

Water intended for human consumption comes into contact with construction products during storage, transportation and distribution, including water systems inside buildings. The materials used in these products are selected on the basis of technical requirements and criteria regarding their influence on the water quality, for example release of substances and effects on odour, flavour or colour of the water. However, water quality problems may also arise when such materials enhance the multiplication of micro-organisms. A test method to determine the enhancement of microbial growth is required as organic substances present in non-metallic materials (either as ingredients, contaminants or process by-products) are capable of being utilized by micro-organisms and can give rise to a noticeable deterioration in the organoleptic, physical or microbiological quality of the water with which they are in contact. Microbial growth may occur in the water itself or at the material/water interface. Materials with the potential of supporting microbial growth do not necessarily lead to a deterioration in water quality in every situation due to the influence of various environmental factors, for example microbial quality of the water, temperature, presence of residual disinfectant or other growth limiting factors. The purpose of this standard is to describe three European test methods that can be applied to determine the ability of non-metallic materials to enhance microbial growth in drinking water: a) Method 1 determines the Biomass Production Potential (BPP) by using changes in ATP concentrations as a surrogate measure for active biomass. This method, developed by the Dutch, has been further enhanced as part of the CPDW project 2003 and 2006; b) Method 2 uses a volumetric measurement of the biofilm. This, German method, was first published as DVGW W 270 in 1984 and is used for certification purposes with limit values established for many years; c) Method 3 uses dissolved oxygen depletion in water as a surrogate measure of microbial activity (Mean Dissolved Oxygen Difference - MDOD). This test method, embodied in British Standard BS 6920-2.4:2000, is used in the United Kingdom for materials approval with limit values. Each method thus uses different performance characteristics, which allows its use for specific materials or product types but also has limitations. For example, multi-layer pipes cannot currently be tested with the BPP (Method 1) and the MDOD-method (Method 3), and greases or lubricants cannot currently be tested with the BPP (Method 1) and Volumetric-method (Method 2). For each type of material, harmonised product standards will define the hygienic requirement "resistance to drinking water" for which procedure(s) is (are) to be applied. In this connection it should be noted that the methods only allow testing of a single type of material or a product in which only one material is in contact with drinking water. They are not suitable for use on composite products where more than one material is exposed to water. All three methods use natural mixtures of aquatic organisms to assess the enhancement of growth by the sample of material. The natural flora comprises many strains that are adapted to living in a relatively hostile environment like drinking water and the results of tests using natural floras have been shown to correlate well with growth on materials in practice. The numbers, types and growth requirements of harmless micro-organisms present in drinking water vary considerably and no single cultural technique exists to enumerate all the aquatic micro-organisms that may be present in a sample of water. Therefore, overall numbers of micro-organisms are generally assessed by using simple indirect measurements of their activity. The technique for assessing enhanced microbial growth is different in each of the test methods described in this European Standard. In the BPP method described in Method 1 surface and planktonic microbial growth is determined using adenosine triphosphate (ATP) as a surrogate method for active biomass determination. In the Volumetric method (DVGW) described in Method 2, the sum of both active and non-active biofilm on the surface of the test material (living and dead micro-organisms as well as extracellular polymeric substances) is determined volumetrically. In the MDOD method described in Method 3 the measurement of dissolved oxygen uptake is used as a surrogate measure of the growth of both biofilm and planktonic aquatic micro-organisms (most of the organisms which give rise to appreciable microbial growth respire aerobically and exert an influence on the concentration of oxygen dissolved in the water in the test systems). A variety of factors may influence the capacity of living organisms to respond in a predictable manner and thus validation procedures are an essential part of any biological assay. In all three methods validation is achieved through the use of reference materials and systems. It is important to note that none of the three methods allows conclusions to be made on the physical, chemical or toxicological behaviour of materials nor on their resistance to detergents or disinfectants. Additionally, none of the methods provides information on the pathogenicity of any micro-organisms whose numbers may be increased by nutrients leaching from the test material. The tests described in this document should only be carried out in laboratories with suitable facilities and by suitably qualified persons with an appropriate level of chemical and microbiological expertise. Standard microbiological procedures should be followed throughout. This standard represents an extremely sensitive compromise, developed after lengthy negotiations, from the practice established thus far in the Member States in CEN/TC 164/WG 3 CEN/TC 164/WG 3 "Effects of materials in contact with drinking water" (secretariat: NEN, Netherlands). The responsible German standards committee is NA 119-07-09-01 UA "Europäische Prüfverfahren zur trinkwasserhygienischen Eignung von Werkstoffen (Supporting Standards, Mandat M/136)" ("European test methods for the suitability for drinking water hygiene of materials (Accompanying standards, mandate M/136")) at DIN Standards Committee Water Practice (NAW).

Document: references other documents

Document: referenced in other documents

Responsible national committee

NA 119-07-09 AA - Materials in contact with drinking water  

Responsible european committee

CEN/TC 164/WG 3 - Effects of materials in contact with drinking water