EU CPDW: WP1 (2001-2003)
Contract No.: EVK1-2000-00622
Development of harmonised tests to be used in the European Approval Scheme concerning Construction Products in contact with Drinking Water
WP1: Assessment of the microbial growth support potential of products in contact with drinking water
A harmonised test method is needed for determining the microbial growth promoting properties of construction products in contact with drinking water (CPDW). To achieve this goal, the characteristics of existing methods have been evaluated (Mean Dissolved Oxygen Difference (MDOD) test (UK), W270 method (Germany), the Austrian test and the Biomass Production Potential (BPP) test (Netherlands)).
Adenosine triphosphate (ATP) was to be used in the investigations as parameter for microbial biomass. The test procedure itself was to be evaluated within the project. It was decided to design a test based on semi-static conditions, i.e. a batch test with regular water replacement, using tap water as test water. Also the surface area to volume ratio (S/V) of 0.16 cm-1 as used in the MDOD and the BPP tests was to be maintained. An incubation temperature of 30°C was considered most appropriate, nethertheless initial experiments were conducted at 25°C. A limited variety of CPDW, viz. Glass, HDPE, Nitrile Rubber, PVC-C, PVC-P, Silicone Rubber and Stainless Steel, was selected to determine the microbial growth support potential at different test conditions.
Using a test determining the growth potential of the water, each participant selected an appropriate (tap) water type to be used in the investigations. Water types with a maximum Biomass Production (BP) below 10 ng ATP/l were considered suitable. Moreover it was decided to use 1% river water inoculum in the test.
The effect of water replacement on the biomass production of selected products was tested. Products with relatively strong growth-promoting properties (Nitrile Rubber, PVC-P) had higher BP values when the water was replaced, suggesting that a lack of oxygen and/or inorganic nutrients may limit growth under test conditions where the water is not replaced. A water replacement once a week was considered most appropriate.
The reproducibility of the BPP test with water replacement was tested. The BPP value is the mean of the BP values observed on days 56, 84 and 112. The BPP of the selected products tested at 25°C ranged from about 25 pg ATP/cm² (glass) to more than 40.000 pg ATP/cm² (PVC-P). The relative standard deviation (RSD) of the mean of the BP values ranged from 3% to 73% with a median value of 33%. Differences in average RSD values between laboratories indicated that further improvement of the test is achievable. The coefficient of variation of reproducibility (VCR) ranged from 34 to 107% for the test conducted at 25°C (six products in five laboratories) and from 20 to 34% for the test conducted at 30°C (three products in three labo-ratories). Critical factors to improve the performance of the method are the quality (biostability) of the test water and the quality of the ATP analysis (calibration).
Temperature had a distinct impact on the BPP values, with lower values at higher temperature for most tested products. Taking into account these effects, it is concluded that an incubation temperature of 30°C is preferred to 25°C.
The collected data demonstrated that the BPP test with water replacement once a week and a duration of 16 weeks is a promising method for determining the growth-promoting properties of CPDW. The test covers BPP values ranging from less than 50 pg ATP/cm² (as observed for glass, stainless steel and PVC-C) to more than 40.000 pg ATP/cm² (PVC-P).
Further comparison with existing methods and studies aiming at determining the effect of biofilm concentrations on the microbiological quality of water intended for human consumption is required to establish pass-fail criteria for CPDW, based on BPP testing.
WP1: Assessment of the microbial growth support potential of products in contact with drinking water
A harmonised test method is needed for determining the microbial growth promoting properties of construction products in contact with drinking water (CPDW). To achieve this goal, the characteristics of existing methods have been evaluated (Mean Dissolved Oxygen Difference (MDOD) test (UK), W270 method (Germany), the Austrian test and the Biomass Production Potential (BPP) test (Netherlands)).
Adenosine triphosphate (ATP) was to be used in the investigations as parameter for microbial biomass. The test procedure itself was to be evaluated within the project. It was decided to design a test based on semi-static conditions, i.e. a batch test with regular water replacement, using tap water as test water. Also the surface area to volume ratio (S/V) of 0.16 cm-1 as used in the MDOD and the BPP tests was to be maintained. An incubation temperature of 30°C was considered most appropriate, nethertheless initial experiments were conducted at 25°C. A limited variety of CPDW, viz. Glass, HDPE, Nitrile Rubber, PVC-C, PVC-P, Silicone Rubber and Stainless Steel, was selected to determine the microbial growth support potential at different test conditions.
Using a test determining the growth potential of the water, each participant selected an appropriate (tap) water type to be used in the investigations. Water types with a maximum Biomass Production (BP) below 10 ng ATP/l were considered suitable. Moreover it was decided to use 1% river water inoculum in the test.
The effect of water replacement on the biomass production of selected products was tested. Products with relatively strong growth-promoting properties (Nitrile Rubber, PVC-P) had higher BP values when the water was replaced, suggesting that a lack of oxygen and/or inorganic nutrients may limit growth under test conditions where the water is not replaced. A water replacement once a week was considered most appropriate.
The reproducibility of the BPP test with water replacement was tested. The BPP value is the mean of the BP values observed on days 56, 84 and 112. The BPP of the selected products tested at 25°C ranged from about 25 pg ATP/cm² (glass) to more than 40.000 pg ATP/cm² (PVC-P). The relative standard deviation (RSD) of the mean of the BP values ranged from 3% to 73% with a median value of 33%. Differences in average RSD values between laboratories indicated that further improvement of the test is achievable. The coefficient of variation of reproducibility (VCR) ranged from 34 to 107% for the test conducted at 25°C (six products in five laboratories) and from 20 to 34% for the test conducted at 30°C (three products in three labo-ratories). Critical factors to improve the performance of the method are the quality (biostability) of the test water and the quality of the ATP analysis (calibration).
Temperature had a distinct impact on the BPP values, with lower values at higher temperature for most tested products. Taking into account these effects, it is concluded that an incubation temperature of 30°C is preferred to 25°C.
The collected data demonstrated that the BPP test with water replacement once a week and a duration of 16 weeks is a promising method for determining the growth-promoting properties of CPDW. The test covers BPP values ranging from less than 50 pg ATP/cm² (as observed for glass, stainless steel and PVC-C) to more than 40.000 pg ATP/cm² (PVC-P).
Further comparison with existing methods and studies aiming at determining the effect of biofilm concentrations on the microbiological quality of water intended for human consumption is required to establish pass-fail criteria for CPDW, based on BPP testing.
