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Biodegradation in water and sediment: simulation tests

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Johnson et al. (2000) studied octylphenol biodegradation in river water and sediments samples taken from the Aire and Calder rivers in the United Kingdom, running through urban/industrial areas, as well as the Thames River running through a more rural area using laboratory microcosms (incubation of 100 µg/l and 600 µ/kg OP spiked river water samples and sediment samples, respectively, at 20 °C). The degradation of the test substance was followed by HPLC (river water samples) and GC (bed sediments). Methods used were similar to OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test) and EPA OPPTS 835.5154 (Anaerobic Biodegradability in the Subsurface).
In addition, Ying and Kookana (2003) studied the degradation of 4-tert-Octylphenol similar to the methods laid down in EPA Guideline OPPTS 835.3180 at initial concentrations of 5 µg/l and 1µg/g in seawater and marine sediments, respectively, for 56 (saltwater) and 70 days (marine sediments) at 20 °C under aerobic (-> seawater and sediment) and anaerobic (-> sediment only) conditions. The degradation of the test substance was followed by HPLC.
Besides, Tanghe et al. (2000) measured the aerobic biodegradation of branched octylphenol and the formation of degradation products formed by a Sphingomonas sp. strain isolated from activated sludge with and without the addition of an easily assimilable carbon source (sodium acetate). Octylphenol degradation and the formation of intermediates was determined in minimum mineral salts medium (MMO) as well as in resting cell cultures. The removal of octylphenol was monitored using HPLC, the formation of degradation products was followed by means of GC-MS.

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In the laboratory microcosms Johnson et al. (2000) obtained half-lives of 8 to 50 d for the river water samples, with most curves fitting a zero-order reaction. Shorter half-lives were generally seen in more urban and industrialised rather than upland and rural areas, which suggests that some form of acclimation may occur. However, even then, half-lives varied within the river for samples of river water taken at different times, although a similar degradation rate was noted for a range of concentrations from 0.3 to 100 µg/L.

Consequently this work demonstrates that 4-tert-Octylphenol could be degraded in river samples taken from a range of urban and rural reaches (with the possible exception being a sample taken from an upland stream). No degradation was observed over 83 days when bed sediments were spiked with 4-tert-Octylphenol and incubated under anaerobic conditions.

 

Ying and Kookana (2003) observed a significant loss in seawater samples in the first 13 days for 4-tert-Octylphenol in the sterile control. After this initial loss, the concentration of 4 -tert-Octylphenol in the sterile seawater remained stable with little change. A comparison of sterile and non-sterile treatments showed that following the initial abiotic loss due to volatilization and adsorption to glass surfaces of the incubation flasks, biodegradation was mainly responsible for the further loss in non-sterile seawater.

Aerobic degradation of 4-tert-Octylphenol in seawater and marine sediments was relatively slow with half-lives of 60 d and > 20 d, respectively, based on first-order reaction kinetics. Approximately 98 % of the test substance has been degraded in seawater under aerobic conditions within 49 days.

 

No degradation could be observed in marine sediments under anaerobic conditions after 70 days of incubation at 20 °C.

 

In summary, this study demonstrates that 4-tert-Octylphenol is degraded under aerobic conditions in seawater and marine sediments, but seems to be persistent in marine sediments under anaerobic conditions. Therefore, it can be concluded that 4-tert-Octylphenol is likely to be persistent and may accumulate in anoxic marine sediments.

 

 

From the studies conducted by Johnson et al. (2000) and Ying & Kookana (2003) it can be concluded that 4-tert-Octylphenol can be aerobically degraded in freshwater, marine water, and marine sediments. No degradation was observed in freshwater bed sediments and marine sediments under anaerobic conditions.

Tanghe et al. (2000) observed 94.5 % and 99 % degradation of octylphenol with and without the addition of sodium acetate, respectively. In both cases the formation of the metabolite 2,4,4-trimethyl-2-pentanol, representing the intact alkyl chain as a tertiary alcohol, was observed. Since the octylphenol degradation rate was not affected by the presence of acetate, this strain did not show any diauxic metabolic behaviour when incubated with octylphenol and sodium acetate as the sources of carbon and energy.

The formation of 2,2,4-trimethyl-2-pentanol as the most prominent intermediate detected in the Sphingomonas sp. culture in all test series implies that the alkyl side chain may remain intact as a tertiary alcohol after fission of the aromatic ring of the parent compound (octylphenol).