Test No. 315: Bioaccumulation in Sediment-dwelling Benthic Oligochaetes

This Test Guideline describes a method to assess bioaccumulation of sediment-associated chemicals in endobenthic oligochaetes worms. It applies to stable, neutral organic chemicals having log Kow values between 3.0 and 6.0, superlipophilic substances that show a log Kow of more than 6.0, or stable metallo-organic compounds which tend to associate with sediments. The test consists of two phases. During the uptake phase, worms are exposed to sediment spiked with the test substance, topped with reconstituted water and equilibrated as appropriate. Groups of control worms are held under identical conditions. The duration of the uptake phase is by default 28 days, unless a steady-state has been reached before. For the elimination phase, the worms are transferred to a sediment-water-system free of test substance. This second phase is terminated when either the 10% level of steady state concentration, or of the concentration measured in the worms on day 28 of the uptake phase, is reached, or after a maximum of 10 days. Change of the concentration of the test substance in/on the worms is monitored throughout both phases of the test. The uptake rate constant (ks), the elimination rate constant (ke) and the kinetic bioaccumulation factor (BAFK = ks/ ke) are calculated. Radiolabelled test substances may be used to determine whether metabolites identification and quantification should be made. The minimum number of treated replicates for kinetic measurements should be three per sampling point throughout uptake and elimination phase. To ensure the test validity (cumulative mortality of the worms < 20% of the initial number), toxicity tests should also be conducted at regular intervals. Besides, the worm lipid content, the sediment total organic carbon content and the residue level in worms at the end of the elimination phase are useful for the interpretation of the results.