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Biodegradation in water and sediment: simulation tests

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In accordance with Column 2 of REACH Annex IX, the simulation test on ultimate degradation in surface water and the sediment simulation test (required in Sections 9.2.1.2 and 9.2.1.4 respectively of the REACH regulation) do not need to be conducted as the substance is readily biodegradable. Identification of degradation products (required in Section 9.2.3 of the REACH regulation) is also not necessary because extensive mineralisation has been demonstrated. Measured degradation in sediment data are available for two analogous saturated alcohols (described below). In view of the similar adsorption coefficient and water solubility of (Z)-octadec-9-enol compared to these linear alcohols, for which simulation tests are available, it can be expected that biodegradation of (Z)-octadec-9-enol in similar substrates will be equivalent.

It is notable that significant technical difficulties were encountered during method development for a recent study of adsorption/desorption (OECD 106, Wildlife, 2015), with the structurally analogous substance decan-1-ol (CAS 112-30-1), using natural standard soils, in that it was not possible to detect sufficient substance and establish equilibrium in non-sterilised soil samples. Refer to the Discussion under Section 5.2.3 for a full description of the relevant findings. Half-lives in non-sterilised test soils were in the range approximately 15 minutes to 2 hours. The polar degradation product is most likely the corresponding carboxylic acid, though it was not definitively identified. The chromatograms show that decan-1-ol was effectively fully removed in all four soil types by the 24 h time point (in the case of 2 of the soil types, within 2 hours). Though sediments were not studied in this test, similar instability is to be expected and similar findings would be anticipated for hexan-1-ol.

Discussion of trends in the Category of C6 -24 linear and essentially-linear aliphatic alcohols

Sediment simulation testing

The degradation of C14 linear alcohol in sediments was determined in two studies conducted in accordance with OECD 314 test method and using radiolabelled (14C) test substance. After 92 days, 76.5% mineralisation to CO2 was obtained using sediment from Ohio River near Cincinnati, Ohio area (Federle T W and Itrich N R, 2010a). After 149 days, 83.6% mineralisation to CO2 was obtained using Lytle Creek sediments from Wilmington, Ohio (Federle T W and Itrich N R, 2010b).

The degradation of C18 linear alcohol in sediments was determined in a similar study, conducted in accordance with OECD 314 test method and using radiolabelled (14C) test substance (Itrich, 2010). After 60 days, 61.1% mineralisation to CO2was obtained using sediment from Ohio River, and 71.6% mineralisation to CO2 after 60 days was obtained using Great Miami River sediments.

The radiochemical analytical results for sediment-associated and aqueous alcohols in these three sediment degradation studies indicated that there are two pools of substance, understood to represent the strength of adsorption of the alcohol to sediment particles, which degrade at different rates.

In another study, using activated sludge and radiolabelled (14C) test substance, 76.7% mineralisation of C14 to CO2 after 48 h was determined in accordance with OECD 314B (Federle, 2005). In the same study, 66.3% mineralisation of C16 to CO2after 48h was determined. Another OECD 314 test using activated sludge and using radiolabelled (14C) test substance, indicates 95% mineralisation of C16 to CO2 in 31 days (Federle, 1993).

Activated sludge simulation testing

In another study, an activated sludge simulation test using similar methods to the sediment studies described above, was conducted with radiolabelled C12 alcohol.

 

A simulation of the biodegradation of Dodecanol in activated sludge was conducted under aerobic conditions in accordance with the OECD 314B guideline (Federle, 2005). A solution of radiolabeled Dodecanol (1-14C) was tested at 9.8 µg/L.  The inoculum was activated sludge obtained from Fairfield Wastewater Treatment Plant (Fairfield, OH), which receives predominantly domestic wastewater. The disappearance of parent and progression of metabolite formation and decay were monitored over time by thin layer chromatography with radioactivity detection. Production of CO2was determined by comparing total radioactivity in a bioactive treatment compared to that in an abiotic control using liquid scintillation counting (LSC).

 

After 48 h, 74% was mineralized, 20.7% was non-extractable (solids), 9.4% was metabolite, and 0.8% remained as parent. The rate constants for biodegradation of Dodecanol in activated sludge were:

Primary biodegradation: 113 h-1

Mineralization: 11 h-1

 

This biodegradation simulation test satisfied the guideline requirements for the OECD 314 B simulation tests to assess the biodegradability of chemicals discharged in wastewater.