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Environmental fate & pathways

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The biodegradation of acrylonitrile in aqueous systems has been extensively studied using a range of experimental systems. Much of the earlier literature relates to experimental simulation tests, acclimation studies and BOD/COD tests, rather than assessment of biodegradability using current Annex V or OECD test methods. Although two recent ready biodegradability tests carried out indicate that acrylonitrile cannot be regarded as readily biodegradable, a third ready biodegradability study in seawater has demonstrated almost 80% degradation over a 28-day period. The majority of the earlier studies in the literature show extensive biodegradation by acclimated microbial populations. When the emission data from the majority of sites are also taken into account, the EU RAR (2004) concluded that acrylonitrile is rapidly biodegradable in situations where an adapted microbial population can be expected, such as in an industrial wastewater treatment plant.

Three independent studies of acceptable quality indicate that acrylonitrile does not meet the criteria for ready biodegradability. Acrylonitrile has an initial inhibitory effect on activated sludge systems and other microbial populations, and an acclimation period appears to be necessary before biodegradation is established. However, extensive biodegradation is seen in such acclimated systems, with greater than 95% biodegradation being reported in a number of studies which simulated conditions in a wastewater treatment plant. It can be concluded that acrylonitrile will be extensively degraded following a short acclimation period if emitted to WWTP from industrial point sources, either primary production or secondary processing plants. The experimental evidence also indicates that it will be rapidly degraded following discharge into a marine environment, and that it will be degraded, although at a slower rate, if released directly into the freshwater environment.

The EU RAR reports a study investigating the biodegradation of [14C]- acrylonitrile in a variety of surface soils, in which concentrations of up to 100 ppm were degraded in under 2 days. Over 50% of radioactivity was recovered as C02 after 6 days, with the transient formation of acrylamide and acrylic acid. Higher concentrations (500 and 1000 ppm) were degraded only slowly, and this correlates with experimental evidence that these levels inhibit respiration of soil microbes, with gradual acclimation. Wenzhonget al(1991) isolated 2 strains of bacterium,Corynebacterium hoffmaniiandArthrobacter flavescens, from nitrile-polluted soils. Aqueous cultures of these bacteria were able to degrade 5g/l acrylonitrile. Similar breakdown by microbial populations present in sediments is likely. Overall significant accumulation in the soil or sediment compartments is not anticipated.

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