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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Description of key information

This fish dietary bioaccumulation study was performed under OECD 305 guidelines (OECD 2013) to determine the tissue elimination rate constant (k_depuration) for the test substances in rainbow trout (Oncorhynchus mykiss). Data collected in this study were used to derive the elimination half-life (t½), the assimilation efficiency (α), the biomagnification factor (BMF) and the lipid-normalized biomagnification factor (BMF_L) for the test substance. The study included a 12-day uptake phase and 21-day depuration phase. This OECD 305 fish dietary fish bioaccumulation test is especially suitable for determining the bioaccumulation potential of substances with very low water solubility such as the test substance.

 

A single feed aliquot containing the dose was prepared containing two test substances and was administered to the test organisms via the diet. The control group was administered an untreated diet with no test substance. The treated and untreated diets were fed to the fish daily during the uptake phase for 12 days (on Days 0-11). On Day 12, clean untreated feed was fed to both the control and treatment fish for 21 days. A flow through exposure system was constructed to provide at least five volume replacements of water per day through each test chamber.

 

The mean concentration of the test substances in the fish tissue at the end of the uptake phase (mean feed conc. of 93.7 ppm) was determined to be 0.17 µg/g. Mean lipid content of tissues collected at Day 12 Uptake and Day 21 Depuration was determined to be 2.93%. No statistically significant differences were observed in mortality or growth rate for the treatment groups when compared to the control group.

 

The test substance had lipid-normalized biomagnification factor of 0.28, an assimilation efficiency of 3.3%, and the elimination half-life was 38 days.

 

The assimilation efficiencies (α) value for the test substance indicates uptake of the test substances. More importantly, the elimination half-lives (38 days) indicates that the test substance is effectively cleared from the fish (50% clearance within about 38 days), most likely as a result of metabolism. In addition, the experimental BMF values indicate that the test substance is not expected to biomagnify or bioaccumulate in rainbow trout under the conditions of the OECD 305 fish dietary bioaccumulation test (Burkhard, et al. 2011).

 

The test substance has been shown to be inherently biodegradable in OECD 301F ready biodegradability testing, showing that these materials are expected to be metabolized or biodegraded by aquatic organisms such as microbes. These substances should be expected to effectively be cleared in the liver of rainbow trout given the clearance half-lives found in this study.

 

QSAR-based model calculations further support the conclusion that the test substance has a low potential to bioconcentrate. The model-estimated log BCF value is 3.16. In addition, the substance has a calculated Log Kow of 11.0. Collectively, these calculations support the conclusion that mono-, and di-(sec-hexadecyl)naphthalene is unlikely to be bioaccumulative.

Key value for chemical safety assessment

Additional information

The potential for mono-, and di-(sec-hexadecyl)naphthalene to bioaccumulate is low.

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