Pesticide Registration Toolkit

#999 Ready biodegradability

Objective of the study

The objective of this study is to assess whether the pesticide is readily biodegradable and consequently rapidly degradable in the environment.

Principle of the study

A solution, or suspension, of the test substance in a mineral medium is inoculated and incubated under aerobic conditions in the dark or in diffuse light.

In general, degradation is followed by the determination of parameters such as dissolved organic carbon (DOC), CO2 production and oxygen uptake. Measurements are taken at sufficiently frequent intervals to allow the identification of the beginning and end of biodegradation.Normally, the test lasts for 28 days. However, tests may be ended before 28 days, i.e. as soon as the biodegradation curve has reached a plateau for at least three determinations.

Information on the chemical's solubility, vapor pressure and adsorption characteristics is essential to select the most appropriate method. The chemical structure or formula should be known in order to calculate theoretical values and/or check measured values of parameters, e.g. Theoretical oxygen demand (ThOD), Theoretical carbon dioxide (ThCO2), dissolved organic carbon (DOC), Total organic carbo (TOC), and Chemical oxygen demand (COD).

Circumstances under which the study is recommended to be required

Data with the technical-grade active ingredient (TGAI) are recommended to support all outdoor end-use product uses.

Test substance

The study is conducted with the technical grade active ingredient of the pesticide.

Typical endpoints of the study

The pass levels for ready biodegradability are 70% removal of DOC and 60% of ThOD or ThCO2 production for respirometry methods. These pass values must be reached in a 10-day window within the 28-day period of the test, except some special cases. Chemicals which reach the pass levels after the 28-day period are not deemed to be readily biodegradable.

Testing guidelines

The following test guidelines may be used for determination of ready biodegradability:

  • OECD Guidelines for the Testing of Chemicals. Test No. 301 (A-F): Ready Biodegradability.

    In this Guideline six methods are described that permit the screening of chemicals for ready biodegradability in an aerobic aqueous medium. They are:

    • 301 A: DOC Die-Away

    • 301 B: CO2 Evolution (Modified Sturm Test)

    • 301 C: MITI (I) (Ministry of International Trade and

    • Industry, Japan)

    • 301 D: Closed Bottle

    • 301 E: Modified OECD Screening

    • 301 F: Manometric Respirometry