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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

Key value for chemical safety assessment

BCF (aquatic species):
391 dimensionless

Additional information

Bioconcentration and metabolism of OTNE in Lepomis macrochirus was investigated according to international guidelines (OPPTS 850.1730 / OECD Guideline 305) under GLP. Validity criteria for the test were met. OTNE was extensively metabolised by the fish, therefore the BCF was determined both by the kinetic approach (k1/k2) and by the steady state approach (Cf/Cw). There is no significant difference between these BCFs, nor between the BCFs for the high and low dose treatment. In the steady state approach, the BCF was also calculated with the measured OTNE concentration in the premix chamber.

The results show that the BCF is 603 and 593 in the low and high treatment. Based on total radioactivity in fish and the premix chamber containing no metabolites, the corresponding BCF value is 747 and 736. This indicates that part of the extracted radioactivity in the fish is to be attributed to metabolites. The DT50 was found to be 1.2 day.

OTNE was extensively metabolised by the fish. A total of 6 components including OTNE were detected in fish fillet. In fish viscera, OTNE (approximately 50% of TRR) as well as two major polar metabolites (comprising 30% to 35% TRR) were observed. In viscera approximately 7-10 components were detected. Most of the metabolites present in the viscera samples were also present in the water in the aquaria, indicating that these were actively excreted from the fish into water.

The average lipid content of the fish was 7.7%. For subsequent calculations the empirical BCF of 603 was converted to a standard fish with a lipid content of 5%. Thus a BCF of 603/7.7 * 5 = 391 is used for the further evaluations. 

Mass balance calculations based on the study report indicate that 80 -93% of the residual radio-activity in the water can be explained by the presence of excreted metabolites.

Mass balance (further calculations based on study report):

Most of the metabolites present in the viscera samples were also present in the water in the aquaria, indicating that these were actively excreted from the fish into water (Madsen et al 1999). Analysis of the water suggested that the metabolism of OTNE in fish tissues was relatively rapid. OTNE levels in water at steady state were less than 40%, in spite of the high daily turnover rate of 7.3 – 8 times for the test solution. This implies that around 60% of the test material can be attributed to metabolites.

Mass balances were calculated based on the loss of radioactivity k2multiplied with the plateau concentration TRR at day 21 for the whole fish. Multiplication of this ‘loss’ by the average fish-to-water loading rate (0.93 g/l day-1) gives the nominal concentration of ‘lost’ radioactivity in water leaving the system: 0.65 μg/l in the low treatment and 5.60 μg/l in the high treatment. Comparing these concentrations to the average measured concentrations of metabolites in water (day 14 and 21): 0.7 μg/l for the low treatment and 7.02 μg/l for the high treatment, shows that 93% and 80% of the totally applied radioactivity can be accounted for.