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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

The bioaccumulation and depuration of cloquintocet-mexyl in bluegill sunfish (Lepomis macrochirus) was investigated in one study (Burri, 1993). Bioconcentration of cloquintocet-mexyl is not considered to be of concern as it is rapidly metabolised and eliminated in fish, whilst the primary metabolite of cloquintocet-mexyl (CGA153433) has negligible bioaccumulation potential.

Key value for chemical safety assessment

BCF (aquatic species):
621 dimensionless

Additional information

The bioaccumulation and depuration of cloquintocet-mexyl (log Pow= 5.2) in bluegill sunfish (Lepomis macrochirus) was investigated by Burri (1993) using a dynamic flow-through system. The study was GLP compliant, conducted to guideline 305 and is considered to be reliable without restrictions. The fish were continuously exposed (flow-through system) to 14C-labelled cloquintocet-mexyl for 17 days. In the exposure water, cloquintocet-mexyl was partially hydrolyzed to the free acid CGA153433. The residual radioactivity in fish body increased rapidly and reached a maximum after about one day of exposure. The residues in the edible and non-edible tissues were mainly comprised of CGA153433. It is assumed that residual radioactivity in fish parts initially represented accumulated cloquintocet-mexyl, which was then immediately metabolised into CGA153433. Therefore, bioconcentration of cloquintocet-mexyl is not considered to be of concern as it is rapidly metabolised and eliminated in fish, whilst the primary metabolite of cloquintocet-mexyl (CGA153433) has negligible bioaccumulation potential.

Based on the total radioactivity in fish, the BCF values are calculated to be 122, 877, and 621 in edible tissues, non-edible tissues, and whole fish respectively. After transferring the fish to clean flowing water, the radioactivity decreased very rapidly with half-lives ranging from 0.3 to 0.6 days. After 10 days depuration, residual radioactivity was below the limit of quantification.  

Therefore, bioconcentration of cloquintocet-mexyl is not considered to be of concern as it is rapidly metabolised and eliminated in fish and since the primary metabolite of cloquintocet-mexyl (CGA153433) has negligible bioaccumulation potential.

An estimated BCF for cloquintocet mexyl can also be calculated using a QSAR approach. ECHA R.7b indicates that for substances with a log Kow of 2-6 the following linear relationship can be used as developed by Veith et al. (1979):

log(BCFfish) = 0.85 × log(Kow) − 0.7

Taking account of the Log Kow of 5.2, an estimated BCFfish of 5248 can be calculated. When compared against the measured value (621), it is clear that this represents significant overestimate of bioaccumulation potential. This is due to the fact that the QSAR approach does not take account of rapid metabolism of the substance.