Safe plastics for hygienic drinking water
Assessment criteria for plastics and other organic materials in contact with drinking water (KTW-BWGL) as a pioneer of the EU Drinking Water Directive
Sascha Hupach, Shimadzu Deutschland GmbH
Markus Janssen, Shimadzu Europa GmbH
Clean drinking water is an important commodity that thankfully we get reliably here in Europe. But the quality is of crucial importance. Manufacturers who make products such as pipes, hoses and other plastic parts that come into contact with drinking water face the challenge of meeting the stringent requirements of the EU Drinking Water Directive. To ensure that these products do not pose a risk to human health, they undergo extensive laboratory testing, including TOC analysis to detect unwanted organic components.
The public is becoming increasingly aware of harmful substances that can migrate from plastics into water, such as plasticizers. Manufacturers are therefore obliged to ensure that products that come into contact with drinking water are technically and hygienically suitable in order to guarantee consumer safety. Article 11 of the EU Drinking Water Directive [1] was consequently introduced for Europe and must be implemented in all member states as of this year.
Fortunately, testing the hygienic suitability of plastic materials and products is nothing new in Europe. Even before the EU Drinking Water Directive came into force, four EU member states, including Germany, had joined forces in what’s known as the “4 Member States (4MS) Initiative” and assumed a pioneering role.[2] Until 2021, Germany adhered to the KTW (plastics/drinking water) Guideline. To implement the EU directives, this was then replaced by the KTW-BWGL (assessment criteria for plastics and other organic materials in contact with drinking water).[3] This guideline helps to assess the hygienic suitability of organic materials for contact with drinking water and outlines the requirements that plastics must meet. The quality of the drinking water must not be impaired through contact with the materials from the systems or through contamination with extractable substances.
The requirements apply not only to plastics but also to organic coatings and lubricants. Aside from pipes or hoses, this also affects many different products or components, such as seals, taps, meters, supply lines, membranes for expansion vessels and much more.
These tests are designed to achieve a “confirmation of conformity of the drinking water hygiene suitability of products”, which are carried out by accredited institutions.
Testing plastics with migration waters
The suitability of plastics for use in drinking water is tested using what’s known as migration waters, which are produced in the laboratory. In accordance with the applicable specifications, eluates are prepared in a certain ratio of water to the surface of the product. These are then analyzed for odor, turbidity, coloration, foaming and TOC.
To produce the migration waters, the laboratory pretreats each specimen. This includes a rinsing phase and a stagnation phase. Drinking water is then added to the specimen being tested for at least three migration phases to generate the migration water. These migration periods can be carried out with cold water (72 hours at 23 °C) or hot water (24 hours at 60–85 °C), depending on the intended use of the component or material.
The procedure for a hose used in cold water applications is as follows:
For pretreatment, the specimen being tested (a hose section) is rinsed with cold water for 1 hour. The hose, filled with water, is then shut off and the water is left to stagnate for 24 hours. The hose is then prewashed again for 1 hour.
|
Criteria |
Organic materials |
Metallic materials |
Cementitious materials |
Enamels and ceramic materials |
|
Organoleptic tests |
||||
Odor and flavor |
X |
X |
||
Color and turbidity |
X |
X |
||
|
General hygiene assessments |
||||
Leaching of total organic carbon (TOC) |
X |
X |
||
Surface residues (metals) |
X |
|||
|
Migration testing |
||||
DWD-relevant parameters |
X |
X |
X |
X |
MTCtap of positive list substances |
X |
X1 |
||
Unexpected substances (GCMS) |
X |
X1 |
||
Compliances with composition lists |
X |
X |
||
Enhancement of microbial growth |
X |
X1 |
||
X1: Depending on the existence of organic substances in the material
Producing the migration water: After prewashing, the hose is filled with water and sealed. The water is left to stagnate over a migration period (in this case 72 hours at 23 °C). The migration water (analysis sample) is then removed and the tube is refilled – the next migration period begins. It is important here that the migration periods take place one after the other without being interrupted.
Once the migration waters have been produced, the required analyses are promptly carried out in accordance with the relevant standards.
The sum parameter TOC
The total organic carbon (TOC) is an important sum parameter. It indicates the sum of all organic components that have migrated into the water in a concentration value.
The laboratory uses the established method of determining the TOC using what’s called the direct or NPOC method. The water sample is mixed with a mineral acid for sample preparation, and any carbonates or bicarbonates present are converted to carbon dioxide. The CO2 is then removed from the sample using a purge gas. An aliquot of the prepared sample is then injected onto a hot platinum catalyst in an oxygen-containing atmosphere. The organic compounds are oxidized to carbon dioxide and transported through a carrier gas to a CO2-selective detector (NDIR). The area of the resulting peak is the equivalent of the TOC concentration.
Modern TOC analyzers, such as the TOC-L series from Shimadzu, handle the entire sample preparation (acidification and degassing) fully automatically – either in the autosampler or in the analyzer itself. They oxidize the organic compounds at a temperature of 680 °C on a highly effective platinum catalyst. The TOC-L systems have an automatic dilution function for samples as well as for standard solutions to create multi-point calibrations, even at equidistant concentration intervals. This allows 10-point calibrations to be created automatically from a stock solution, for example, saving the user a lot of time. The system can also extend the measurement range by automatically diluting the sample.
Guaranteeing the safety of our drinking water
Laboratories that perform product tests are a crucial part of guaranteeing the safety of our drinking water. They ensure that only materials and products that have passed stringent tests come into contact with our drinking water. This prevents substances from these materials leaching into our drinking water and contaminating it or making it undrinkable. For this purpose, migration waters are produced and analyzed. In addition to the sum parameter TOC, odor/taste, turbidity and coloration are also determined to ensure that the quality of our drinking water is not impaired. The EU Drinking Water Directive along with the KTW-BWGL provide the necessary guidelines that laboratories then put into practice to protect our water quality.
[1] https://eur-lex.europa.eu/eli/dir/2020/2184/oj
Application News. 05-SCA-130-406-EN. Janssen, Markus.