Fraunhofer Institute for Molecular Biology and Applied Ecology IME
The OECD Guideline TG 321 describes the “Hyalella azteca Bioconcentration Test (HYBIT)”, a standardized method for investigating the bioaccumulation of chemicals in aquatic systems using an invertebrate organism. The aim is to determine the uptake and elimination behavior of substances in Hyalella azteca and to derive bioconcentration factors (BCF) from these data. The test consists of two phases: an uptake phase, in which the organisms are exposed to the substance, and a depuration phase, in which they are transferred to clean water. During the test, concentrations in water and in the organisms are measured in order to calculate kinetic parameters such as uptake and elimination rates. The method can be conducted under both flow-through and semi-static conditions. Special requirements apply to the stability of test concentrations, water quality, and the analytical determination of the substance.
OECD TEST GUIDELINE 321: Hyallela azteca Bioconcentration Test (HYBIT)
Bioconcentration Studies with Hydrophobic Organic Compounds
Conducting bioconcentration tests with Hyalella according to OECD TG 321 requires the ability to produce stable, measurable concentrations of test substances in aqueous solution. For highly hydrophobic organic chemicals (HOCs; log Kow > 6), testing via aqueous exposure becomes increasingly difficult. At Fraunhofer IME, a solid-phase desorption dosing system (Fig. 1) is available, which is suitable for providing stable HOC concentrations required for determining bioconcentration in fish and represents a practical alternative to the use of solvents for preparing test solutions.
Sample Analysis
With our modern analytical instruments, we are able to quantify a wide range of compounds in the different matrices (water, Hyalella) obtained during the studies. Investigations can be performed using isotopically labelled substances (14C). The combination of highly specific analytical methods and isotopically labelled compounds enables the identification of metabolites of organic substances in the test organisms. BCF values are typically normalized based on the lipid content of the invertebrate organisms. Suitable extraction techniques are available to ensure complete extraction of total lipids from Hyalella samples.