Objective of the study

The objective of the study is to characterize the bioaccumulation potential of pesticides in fish, using aqueous or dietary exposure, and establish a bioconcentration factor (BCF) or biomagnification factor (BMF).

Bioaccumulation is generally referred to as a process in which the chemical concentration in an organism achieves a level that exceeds that in the respiratory medium (e.g., water for a fish), the diet, or both.

Bioconcentration is the increase in concentration of the test substance in or on an organism (or specified tissues thereof) relative to the concentration of test substance in the surrounding medium.

Biomagnification is the increase in concentration of the test substance in or on an organism (or specified tissues thereof) relative to the concentration of test substance in the food.

Circumstances under which the study is recommended to be required

Bioconcentration potential of the active ingredient shall be assessed if:

1. the log P_ow is greater than 3, or there are other indications of bioconcentration; and
2. the substance is considered stable, i.e. less than 90% loss of the parent compound over 24 hours via hydrolysis.

For strongly hydrophobic substances (log P_ow greater than 5 and a solubility below approximately 0.01-0.1 mg/L), testing via aqueous exposure may become increasingly difficult. For these highly hydrophobic substances the dietary test may be recommended.

Principle of the study

The study aims to characterize the bioaccumulation potential of a pesticide in fish, using aqueous or dietary exposure, under flow-through conditions (but semi-static regimes are permissible). Independent of the chosen exposure method, the study consists of two phases: exposure (uptake) and post-exposure (depuration). During the uptake phase (usually 28 days but can be extended), a group of fish of one species is exposed to the test substances at one or more chosen concentrations (depending on the properties of the test substance). For the depuration phase they are then transferred to a medium free of the test substance, or fed with clean, untreated feed. A depuration phase is always necessary unless uptake of the substance during the uptake phase has been insignificant.

Test organism

Important criteria in the selection of species are that they are readily available, can be obtained in convenient sizes and can be satisfactorily maintained in the laboratory. Other criteria for selecting fish species include recreational, commercial, ecological importance as well as comparable sensitivity, past successful use, etc.

Test substance

A radiolabelled active ingredient, using the C¹⁴-labelling technique, is recommended and labelling should normally be in the most stable part(s) of the molecule.

Typical endpoints of the study

• Information on any adverse effects observed
• For a (aqueous) bioconcentration study:
  • Steady-state bioconcentration factor (BCFSS), if steady-state is (almost) achieved; or
  • Kinetic bioconcentration factor (BCFK) and derived uptake and depuration rate constants, if steady-state has not been reached
• For a (dietary) biomagnification study:
  • "Raw" dietary biomagnification factor (BMF), and
  • Lipid and growth-dilution corrected kinetic biomagnification factor (BMFKgL)

Testing guidelines

The following test guidelines may be used for determination of bioaccumulation potential in fish:

• OECD Guidelines for the Testing of Chemicals. Test No. 305. Bioaccumulation in Fish: Aqueous and Dietary Exposure

• US EPA OCSPP Harmonized Test Guidelines. Ecological Effects Test Guidelines: OCSPP 850.1730 Fish Bioconcentration Factor (BCF)