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Based on the bioconcentration factors from the fish study summarized above, bioaccumulation of residues in the terrestrial compartment is unlikely to occur. The rapid dissipation of cloquintocet-mexyl in soil (see IUCLID Section 5.2.3) adds to the weight-of-evidence for a lack of bioaccumulation in the terrestrial compartment.

In general, predicted BCF values (whether from QSAR or read-across) can be used for the initial assessment of secondary poisoning and human dietary exposure. The QSAR model of Jager (1998; see ECHA R.7c) is recommended as a reasonable worst case for an initial assessment of the earthworm bioconcentration factor, and provides a description of this tool. The only input term required is the octanol-water partition coefficient (Kow), and an application range of log Kow 1-8 is advised. The following equation is used:

BCFearthworm = (0.84 + 0.012 × Kow) / RHOearthworm

Taking account of the log Kow of cloquintocet-mexyl (i.e. 5.2) and the bulk density of worm (RHOearthworm = 1 kg/L), the calculated BCF for earthworms is 1903. The corresponding value for the metabolite (based on log Kow -0.99) is 0.84.

It should be noted that the above estimate of BCF for cloquintocet-mexyl is likely to present a gross overestimation of bioaccumulation potential in earthworms, since the rapid environmental dissipation is not taken into account. Indeed, comparison between predicted and measured BCF value for fish indicates that the use of the QSAR approach is highly inaccurate. Therefore, crude surrogate measures of bioaccumulation for the terrestrial compartment are likely to be grossly misleading and are not considered further. It is recognized that the ability of fish to metabolise xenobiotics will likely exceed that of earthworms, nevertheless, surrogate measures are considered misleading. The evidence for a lack of persistence in the environment is sound evidence for a lack of bioaccumulation.