Report No DWI0731

CONVERSION FACTORS FOR LEACHING TESTS (DWQ 9007)

DWI0731

Mar 1994

SUMMARY

Leaching tests on products for use in contact with drinking water are undertaken to assess whether the leaching of any impurity from the product would be acceptable or not as far water quality and human health are concerned.

Approval schemes in different countries take different approach how to make this assessment on the basis of results from leaching tests. These range from extensive field tests, simulating actual conditions of use, where the concentrations measured are used directly in the assessment, to a single standardised short-term test, where the test results are adjusted, using conversion factors (depending on the product and its intended use) to estimate the actual concentrations in field use.

CEN TC164/WG3/AHG2 is drafting standard methods for migration tests from non-metallic products which will include calculation of the actual concentration in field use from the test results. A number of conversion factors, derived from those used in the existing schemes, has been proposed and are being discussed within CEN.

This report reviews the current approaches in the UK, Germany, France, the Netherlands and the USA, and compares the different conversion factors for plastic pipes proposed for the CEN migration tests.

Most progress has been achieved in defining a factor F2, which should correct for differences between laboratory and field use conditions in surface area to volume ratio and contact time of water with the product, but a number of differences still exists.

Decisions are needed concerning adjustments due to decreasing migration with time (factor F1, extended leaching), and whether a typical or 'worst-case' situation should be used when calculating the F2 factor. Any solution to these questions need to satisfy regulations on water quality and should be based on expert toxicological advice.

Copies of this report may be available as an Acrobat pdf download under the 'Pre 2000 Reports' heading on the DWI website.