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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Using standard ready biodegradation test conditions, the test chemical displays negligible degradation. As a consequence the biodegradation potential of DAPD was further assessed in a number of inherent biodegradation studies.
In these inherent biodegradation tests it was demonstrated that slow inherent biodegradation of DAPD does occur, yielding 23 to 37% of mineralisation after 56-63 days. Furthermore, primary degradation of DAPD into water soluble metabolites was found to occur much faster and lead to the complete removal of the parent compound from the test system within 28 days.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

Two studies are available addressing the ready biodegradability of 1,4 -benzenediamine, N,N’-mixed Ph and tolyl derivs. (DAPD) (Kung, 1995 and Hartmann, 1990). In both studies, the test chemical was subjected to aerobic degradation conditions in the presence of activated sludge for 28 days using the oxygen uptake monitoring. Under these conditions, no biodegradation of 1,4-benzenediamine, N,N’-mixed Ph and tolyl derivs. was observed.

 

Both tests fulfil the validity criterion as the used positive control substance showed a high degree of biodegradation. In the study by Kung (1995) one of the test flasks contained test chemical, control substance and inoculum. From this test run it could be concluded that 1,4 -benzenediamine, N,N’-mixed Ph and tolyl derivs. did not show microbial toxicity, as the control substance was degraded without any problem. It should be noted however, that these tests require the use of high levels of test compound (100 mg/L) in incubation media, far in excess (> 100 x) the water solubility of the the constituents of DAPD. As biodegradation can only occur for chemicals in solution, this test might not be the most appropriate one to evaluate the chemicals (realistic) biodegradation potential.

As a consequence the biodegradation potential of DAPD was further assessed in a number of inherent biodegradation studies. In these studies a surfactant is added to the test bottles in order to enhance the water solubility of the test substance, a lower concentration of test substance is used and an elevated sludge concentration when compared to a ready biodegradation test.

 

In total 3 studies have been undertaken to assess the inherent biodegradability of1,4 -benzenediamine, N,N’-mixed Ph and tolyl derivs. (DAPD (Commander and Daniel, 2011a, Commander and Daniel 2011b, Commander, Daniel and Mc. Cormack 2011). In the first study (Commander and Daniel, 2011a), the oxygen uptake of the test substance was again chosen as the parameter to be monitored. In this test, no degradation was observed at a DAPD concentration of 20 mg/L. Additionally, the test substance appeared to have some inhibitory effect on the respiration rate of the inoculum. There was, however, sufficient viability in the inoculum to degrade sodium benzoate when this positive control substance was added to the test vessels after 11 days of incubation.

 

The second test (Commander and Daniel, 2011b) made use of radiolabelled test substance R898. The formation of14C-CO2 and the distribution of the remaining14C over the aqueous phase and the sludge solids were examined. Due to the higher sensitivity of the methods used for the quantitation of the test chemical and the degradation products (14C-CO2) a test concentration closer to the water solubility could be implemented. As a consequence, in this experiment test substance concentrations of 100, 10 and 1 µg/L were used.

The test results showed about 23% of mineralisation (CO2-formation) after 56 days, which demonstrates the inherent biodegradation potential of DAPD. Furthermore, it was found that a large portion of the radioactivity remained associated with the sludge solids, whereas no parent compound could be detected in the aqueous phase of the test system after 28 days.

 

The third test (Commander, Daniel and Mc. Cormack 2011) used the same principle and test substance concentrations (100 and 10 µg/L) as the previous one, but additional effort was put into the analysis of breakdown products. In this study, the maximum mineralisation was observed in the10 µg/L experiment) and yielded up to an average of 37% in 63 days. Furthermore, incorporation of the test substance into intracellular components (DNA/RNA, lipids, proteins et cetera) of the biomass was observed. It was also confirmed that no test substance remained in the aqueous test phase, although14C levels of up to 55% of the applied radioactivity were found in the aqueous fraction. This suggests that water soluble metabolites were formed. However, due to their multiplicity and/or difficulties with the chemical separations they could not be characterized.

 

 

Overall, it can be concluded from the full set of experimental results that DAPD does not fulfil the criteria for ready biodegradation. Nevertheless, slow inherent biodegradation of DAPD does occur, yielding 23 to 37% of mineralisation after 56-63 days. Furthermore, primary degradation of DAPD into water soluble metabolites was found to occur much faster and lead to the complete removal of the parent compound from the test system within 14 days.