1-Propanol, 2-methyl-3-[(1,7,7-trimethylbicyclo[2.2.1]hept-2-yl)oxy]-

Bioaccumulation: terrestrial

Description of key information

The BCF in earthworms was estimated with the equation from Jager (1998) which is incorporated in the EUSES model and is applicable to substances with a log Kow value ranging from 1-8: BCFworm = (Fwaterworm + Flipidworm*Kow) /RHO worm where Fwaterworm = 0.84, Flipidworm = 0.012 and RHO worm = 1 kg ww/l. Entering the log Kow value of 3.86 for the substance will result in a BCFearthworm of 87.8 l/kg ww.

Bioaccumulation in air-breathing organisms: The substance fulfils the screening criteria for bioaccumulation of air-breathing organisms when using the Koa predictor of EpiSuite. When using the  Log Pblood-air partition coefficient the criteria are not met because the value is 4.0, which is < 5 (Koa cut off). In addition, the substance is metabolised (OECD Toolbox and Xenosite) and is excreted via the kidneys as seen in the male rat. Therefore there is no bioaccumulation in air-breathing organisms.

Additional information

Bornafix and its bioaccumulation assessment for Air-breathing organisms

Introduction: The substance fulfils the screening criteria for concern for bioaccumulation in air breathing organisms: log Koa (8.6: > 5). This is based on its measured log Kow of 3.86, vapour pressure of 0.67 Pa and water solubility of 57.8 mg/l.

Background: The concern for bioaccumulation in air breathing organisms is related to their distinct respiratory pathways and their ability to accumulate substances primarily through dietary exposure (Armitage and Gobas, 2007, Kelly et al., 2004). It is understood that chemicals that may not necessarily bioaccumulate in water respiring organisms can potentially bioaccumulate in air breathing organisms. Water respiring organisms such as fish and aquatic invertebrates readily exchange chemicals to water via gill ventilation and/or skin to soil via pore-water contact. Elimination of chemicals through lungs via the lipid-air exchange process in air breathing organisms (e.g., mammals, birds and reptiles) is a much slower elimination pathway. This can result in a potential underestimation of bioaccumulation when considering fish studies.

While the physiological differences between water breathing and air breathing organisms lead to differences in chemical clearance, the same principals apply; bioaccumulation concerns only exist if the substance is not readily metabolized and/or excreted (Gobas et al., 2020). Based on the terrestrial bioaccumulation model developed by Armitage and Gobas (2007), the bioaccumulation potential of a contaminant is effectively negated if it possesses a biological elimination rate constant of 0.3 d^-1 or a biological half-life of < 2.5 days in an air breathing organism. Furthermore, Armitage and Gobas (2007), in agreement with Hendriks et al. 2001, state that, “as the size of the organism increases, the elimination rate constant required to counteract the bioaccumulative potential of the contaminant in question drops”.[1] Rodents and other small mammals are therefore conservative indicators of the extent chemicals need to be biotransformed and/or eliminated to reduce their inherent bioaccumulation potential. Goss et al. (2013) demonstrate that the elimination rate constant, k2, can be used to derive the elimination half-life, EL_0.5 and for air breathing mammals, an EL_0.5 < 70 days will keep the biomagnification factor at a safe level of < 1. The thresholds reported by these authors represent points of comparison for the substance toxico-kinetics and in particular elimination rates in relevant biological compartments.

The substance and bioaccumulation for air-breathing organisms: there is several available information that can shed light on the potential for air breathing organisms to bioaccumulate for this substance. 1) The log Koa is a screening tool for possible bioaccumulation in air-breathing organism only based on physico-chemical parameters. A log Koa of > 5 and absence of metabolism would possibly indicate a bioaccumulation potential for air-breathing organisms. The substance has log Koa of 8.6 and further information is needed. Instead of the log Koa, a better estimate for the substance remaining in the body is the log Pblood/air partition coefficient (see Toxico-kinetic section for formula) based on human and rat data as derived by Buist et al (2012). This value for the substance  is 4.0  and is well below the log Koa criterion of 5 and based on this no bioaccumulation in air-breathing organisms is expected; 2) The presence of metabolism presents absence of this bioaccumulation: a) The primary alcohol functionality of the substance, can be oxidised during Phase 1 metabolism into an acid as presented by OECD Toolbox and/or will be glucuronidated at this site (Scheme is presented in the Toxico-kinetic section).  The repeated dose toxicity studies show that kidney effects in males indicate excretion via kidneys.

Conclusion: The substance fulfils the screening criteria for bioaccumulation of air-breathing organisms when using the Koa predictor of EpiSuite. When using the  Log Pblood-air partition coefficient the criteria are not met because the value is 4.0, which is < 5 (Koa cut off). In addition, the substance is metabolised (OECD Toolbox and Xenosite) and is excreted via the kidneys as seen in the male rat.

References

Armitage, J.M., and Gobas, F.A.P.C, 2007, A terrestrial food-chain bioaccumulation model for POPs, Environ. Sci. Techn., 41, 4019-4025.

Buist, H.E., Wit-Bos de, L., Bouwman, T., Vaes, W.H.J., 2012, Predicting blood:air partition coefficient using basis physico-chemical properties, Regul. Toxicol. Pharmacol., 62, 23-28.

Gobas, F.A.P.C., Lee, Y-S, Lo, J.C., Parkerton, T.F, Letinski, D.J., 2020, A Toxico-kinetic framework and analysis tool for interpreting organization for economic co-operation and development guideline 305 dietary bioaccumulation tests, Environ. Tox. Chem., 39, 171-188.

Goss, B. and Endo, 2013, Elimination half‐life as a metric for the bioaccumulation potential of chemicals in aquatic and terrestrial food chains, Environ. Tox. Chem. 32, 1663-1671. Hendriks, A. J. et al. , 2001, The power of size. 1. Rate constants and equilibrium ratios for accumulation of organic substances related to octanol‐water partition ratio and species weight, Environ. Tox. Chem., 20, 1399-1420.

Kelly, Gobas, F.A.P.C, and McLachlan (2004). "Intestinal absorption and biomagnification of organic contaminants in fish, wildlife, and humans, Environ. Tox. Chem., 23,2324-2336.