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Biodegradation in water and sediment: simulation tests

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Toräng et al. (2002) performed 38 laboratory batch tests using Rhine water from upstream and downstream spots of the BASF wastewater outlet. The method used was equvalent to OECD guideline 309. Batch experiments in the laboratory were performed in duplicate in 2 l glass flasks with 1.5 l of river water at 15 or 21 °C and incubated in darkness. Aniline was spiked to an initial concentration in the range from 4.4 to 557 µg/l as either unlabeled aniline or as 14C-labeled aniline. Primary degradation of aniline in laboratory batch tests were measured by GC headspace methodology while the mineralization rates were estimated by 14C techniques.

  

Short lag phases before significant degradation of aniline commenced ranged between 0.9 and 3.7.

 

Estimated biodegradation rate constants from the laboratory batch test ranged from 1.0 to 4.1 day-1. Attempts failed to correlate the estimated rates with such variables as up/downstream sample location or origin; test methodology or selected water quality characteristics. A clear trend of increase in rate was however observed with increasing initial test concentration and with incubation temperature. A higher pseudofirst- order rate constant were estimated at 100–600 µg/l than at lower concentrations from 1 to 19 µg/l.

 

When taking only batch experiments performed at realistic low initial concentration (<25 µg/l) into account, first-order rate constants were estimated as 1.5 and 2.0 day-1 at a temperature of 15 and 20 °C, respectively.

The primary degradation of aniline in riverwater was also examined by Bayer AG (1992). 10 μg/L aniline was added to the river water and incubated at 22°C in the dark. After 3 days a primary degradation of > 95% was achieved.

In several tests the mineralisation of 14C-labelled aniline in natural seawater at low concentrations was examined: The test results show that aniline in environmental relevant concentrations can be mineralised in both freshwater and seawater. Nyholm (1991) found in a shake flask test employing an aniline concentration of 20μg/l a half-life for mineralisation of 12 days. The sample was incubated at 15°C. With the same test design Nyholm et al. (1992) examined the mineralisation of aniline

concentrations ranging from 2 to 40μg/l in two different seawater samples. The half-lifes for mineralization ranged from 11 to 31 days. These great differences can partly be explained by the test temperature, the site-specific characteristic of the microflora and the composition of the water sample.

No study on sediment degradation is available. Comparable to the fate in soils, aniline forms chemical bonds with the organic matter. For the reaction product, the same half-life as for soils (350 d) was used for the upper (aerobic) sediment layer, leading to a half-life of 3,500 days for the total sediment (EU Risk assessment report, Aniline, 2004).