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Environmental fate & pathways

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Fugacity modelling and physical chemical properties show that this substance will partition primarily into water. The substance degrades primarily via abiotic processes and to a much lesser extent via biotic processes such as microbial degradation. Abiotic degradation occurs rapidly when the substance is exposed to light and oxygen and can lead either to the formation of higher molecular weight molecules (dimer, trimer and Bandrowski’s base) or to benzoquinone depending on concentration.

Rapid photodegradation (Freitag et al., 1985) and oxidation (CSR section 5.2.2) of the substance indicate that the substance is unlikely to persist in air. In addition, the vapour pressure (0.0104 Pa) and the Henry's law constant (3.63E-5 Pa m3/mol) of the substance indicate that the substance is not likely to volatilise extensively from surfaces into air under dry conditions or from water. Therefore, any concentrations of the substance in air are considered negligible.

Rapid degradation of the substance is also expected in aerobic aquatic environments and water bodies with penetration of natural sunlight. Exposure of the substance to sunlight in water and humic acid amended water demonstrated rapid indirect and direct photodegradation [overall (t1/2) = 0.12 days (2.88 hrs)]. In aerated and non-aerated river water, aerated well water, and buffered water in the absence of natural sunlight, degradation was also rapid (CSR section 5.2.2 and 5.6). Half-lives were longer at lower pHs (pH 5.5 vs 7.5), at higher concentrations (25 vs 2.5 mg/L) and in non-aerated versus aerated water. The non-aerated river water half-life of 5.7 hrs is representative of behaviour expected in the environment. Degradation pathways were identified in the buffered water studies by Picardo et al. (1990), with the primary degradative pathway being oxidation to p-benzoquinonediimine and subsequent hydrolysis to benzoquinone. Oxidation of the substance to p-benzoquinonediimine in aqueous solutions was also documented with Bandrowski’s base the primary rearrangement product (Corbett, 1972). Given the rapid oxidation of the substance, storage recommendations during and prior to use include keeping the substance in well-closed containers, protected from light (Merck Index, 1996).

Biodegradation is not expected to be a primary route of degradation in the environment. The substance is not readily biodegradable as demonstrated by 30% biological oxygen demand after 28 days with no further loss after extending the study to 84 days. Nor is the substance inherently biodegradable as indicated by 0% biodegradation after 27 days in an OECD 302A study. Further, many supporting studies show minimal biodegradation (See IUCLID section 5.2.1).

The pKa value (6.22) indicates that the substance will distribute between the protonated and the neutral form in the environment. The Koc value (12.91 L/kg) estimated using ACD labs (www.acdlabs.com) with reference to supporting batch measurements on aniline which sorbs via similar mechanisms, indicates that the substance will exist primarily in the water compartment. However, in soils with lower pH, the substance may sorb to soil via cation exchange.

Budavari S (ed.) (1996). The Merck Index - An Encyclopedia of Chemicals, Drugs, and Biologicals, p. 1255, Merck and Co., Inc.

 

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