p-phenylenediamine

Biodegradation in water and sediment: simulation tests

Description of key information

Both ' biodegradation in water: simulation testing on ultimate degradation in surface water' and 'biodegradation in water:sediment simulation testing' are waived. The available information is deemed sufficient for the PBT assessment, classification and labelling and the chemical safety assessment. Thus, no further testing on biotic degradation is required, according to column 2 of Annex IX.

Additional information

Biodegradation is not a primary route of degradation for this substance. The substance is not readily nor inherently biodegradable as indicated by numerous studies many of which resulted in 0% biodegradation. Therefore, further studies on biodegradation of the substance are likely to result in limited biodegradation of the substance. However, the all of following degradation studies, summarized in IUCLID 5.2.2 with robust study summaries in IUCLID 5.6, in river water and aqueous matrices under laboratory conditions (not exposed to natural or simulated sunlight) demonstrate rapid degradation of the substance in water via abiotic oxidative mechanisms and two studies identify degradates (Picardo et al, 1990 and Corbett, 1972). These studies provide sufficient weight of evidence that degradation in water is rapid and provide identification of potential degradates.

 

In numerous aqueous matrices, degradation of the test substance was rapid. The half-life in aerated and non-aerated water is about 4 and 5.7 hours (E-29035). The oxidation study in aerated well water containing microbial biomass (10E2 to 10E4 colony forming units per mL) resulted in rapid loss of the substance (t(1/2) < 1 day; HL608-85). Picardo et al., 1990 also demonstrated rapid loss in buffered water, where 90% of the substance was degraded after 24 hours in buffer at pH 7.4. At pH 5.5, about 40% of the substance was degraded after 24 hours and 55% after 48 hours. The preliminary degradative pathway was oxidation to imminoquinone which was subsequently hydrolyzed to benzoquinone. Formation of several unstable intermediates have been observed which can transform into Bandrowski’s base or subsequent hydrolysis products of p-benzoquinonediimine. Several studies conducted by Corbett (1972) showed rapid loss of the test substance in aqueous solutions. These studies also demonstrated formation of Bandrowski’s base, an oxidation degradate, which increased with increasing substance concentration and oxygen content.