OECD 111 – Hydrolysis as a Function of pH
OECD 111 assesses abiotic hydrolytic transformations of chemicals in aquatic systems at pH values normally found in the environment (pH 4 – 9).
OECD 111 is an important evaluation for determining how a chemical will react in an aqueous environment; hydrolysis itself is an important reaction controlling degradation. Abiotic hydrolysis is likely one of the most common reactions of organic compounds with water in aqueous environments. The abiotic hydrolysis process can help assess the environmental fate of a substance.
Hydrolysis is especially important for materials with low biodegradability that may persist in the environment after use and disposal. Chemicals with a better ability to transform and degrade in the environment generally have less potential for persisting as an environmental pollutant.
It can be especially important to evaluate the hydrolysis of chemicals that are used in applications like agriculture, where the chemical pesticide frequently comes into contact with surface waters by such routes as:
- direct application
- spray drift
- waste disposal
- industrial, domestic, or agricultural effluent
- atmospheric deposition and may be transformed in those waters by chemical (e.g. hydrolysis, oxidation), photochemical and/or microbial processes.
OECD 111 is performed to determine:
- the rate of hydrolysis of the test substance as a function of pH
- the identity rates of formation and decline of hydrolysis products to which organisms may be exposed.
The OECD 111 test method is commonly used as guidance to carry out other analytical OECD test methods. OECD 111 and the EPA 835.2120 Fate & Hydrolysis Transformation Test are examples of common methods used to evaluate the hydrolysis of chemical substance. This evaluation is commonly required for the degradation component of the Environmental fate section for US EPA pesticide registration and reregistration. Further information regarding these components can be found in the EPA document 40 CFR Part 158, Data Requirements for Registration.
40 CFR Part 158 outlines a variety of test categories and test types that need to be performed and documented for pesticide registration. Before performing a hydrolysis test for an Environmental fate analysis, it is beneficial to have the following information, if available, on the test substance:
- solubility in water (OECD 105)
- solubility in organic solvents
- vapour pressure
- n-octanol/water partition coefficient (OECD 107 and OECD 117)
- dissociation constant (OECD 112)
- direct and indirect phototransformation rate in water where appropriate