OECD 111 – Hydrolysis as a function of pH (OECD, 2004b)
This Test Guideline describes a laboratory test method to assess abiotic hydrolytic transformations of chemicals in aquatic systems at pH values normally found in the environment (pH 4 – 9). This Guideline is designed as a tiered approach; each tier is triggered by the results of the previous tier.
Sterile aqueous buffer solutions of different pH values (pH 4, 7 and 9) are treated with the non-labelled or labelled test substance (only one concentration, which should not exceed 0.01 M or half of the saturation concentration). They are incubated in the dark under controlled laboratory conditions (at constant temperatures). After appropriate time intervals, buffer solutions are analysed for the test substance and for hydrolysis products. The preliminary test should be carried out for 5 days at 50 ± 0.5°C and pH 4.0, 7.0 and 9.0. The second tier consists of the hydrolysis of unstable substances, and the third tier is the identification of hydrolysis products. The higher Tier tests should be conducted until 90 % hydrolysis of the test substance is observed or for 30 days whichever comes first.
OPPTS 835.2120 – Hydrolysis (US EPA, 2008)
This harmonised OPPTS test guideline is based largely on OECD Guidelines for the Testing of Chemicals, OECD 111 hydrolysis as a function of pH (OECD, 2004b) with clarifications derived from 40 CFR 796.3500 hydrolysis as a function of pH at 25 ºC and OPP 161-1 hydrolysis studies Pesticide Assessment Guidelines Subdivision N – Chemistry: Environmental Fate (EPA report 540/9-82-021, October 1982) for testing under TSCA and FIFRA, respectively.
OPPTS 835.2130 – Hydrolysis as a function of pH and temperature (US EPA, 1998)
The source material used in developing this harmonised OPPTS test guideline are OPPT 796.3510, OPP 161–1 Hydrolysis Studies, and OECD 111 Hydrolysis as a Function of pH (OECD, 2004b). This guideline was developed to determine the hydrolysis rate constants and half-live of substances at any environmentally relevant pH and temperature anywhere in the United States.
To determine the rates of hydrolysis at a fixed temperature hydrolysis experiments are carried out at three pH values (typically 3, 7 and 11)
To determine the rates of hydrolysis as a function of temperature, hydrolysis experiments are carried out at 3 pH values as above but at three different temperatures. From these data the half-life of the compound can be determined at any relevant environmental pH and temperature.