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Environmental fate & pathways

Biodegradation in soil

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In a test according to EPA OPPTS 835.3300 & ASTM D5988 the biodegradation in soil was ≥79 % ThCO2 after 42 d, 60 % within 10-14 days (readily biodegradable);
t50 (0.8 mgC/g soil) = 6.6 d
t50 (3.2 mgC/g soil) = 9.4 d
t50 (12 mgC/g soil) = 43 d
In a further test according to ASTM D 5338 & ASTM D 598 the biodegradation in actively aerated compost was 64.9 % ThCO2 after 45 d (readily biodegradable);
t50 (17.2 mgC/g soil) = 33.4 d

Key value for chemical safety assessment

Additional information

In a test on biodegradation in soil according to EPA OPPTS 835.3300 and ASTM D5988 (Farrell, 2000) triethyl citrate (TEC) was found to be readily biodegradable. Decay rates decreased as a function of substrate concentration. Consequently, the time required to achieve 50 % mineralization (t50) or 60 % mineralization (t60) increased as the TEC concentration in the soil increased. Nevertheless, at all substrate concentrations, net mineralization of the TEC was greater than that of the positive control (cellulose). Moreover, biodegradation of the TEC met or exceeded the ‘pass levels’ defined in the ASTM, FDA, and EPA guidelines. That is, conversion of substrate-C into CO2exceeded 50 % ThCO2within the 64-day time limit set by the equivalent FDA soil biodegradation test (USFDA, 1987) and 60 % ThCO2within the time limits set by the equivalent ASTM (≤ 180 days) and USEPA (≤ 64 days) test methods (ASTM, 1999; USEPA, 1998b). These results – plus that fact that at substrate concentrations in the range recommended by the FDA and EPA tests (≤ 5 mg substrate-C g-1 soil), conversion of substrate-C into CO2exceeded 60 % ThCO2within a 10–14 day window following the lag period – indicate that TEC can be considered readily biodegradable (US EPA, 1998a).

In another test on ultimate biodegradation in actively aerated compost according to ASTM D 5338 and ASTM D 5988 (Farrell, 2000), mineralization of the test substance reached 64.9 % ThCO2in 45 days. Both the TEC and cellulose reference achieved total, net mineralization values ≥ 50 % ThCO2during the 45-day test exposure, cellulose was the only test material to exceed the 60 % ThCO2pass level defined in the ASTM guideline during the test exposure. Nevertheless, the calculated t60for the TEC was 53 days – well within the time limit defined in ASTM Standard D 6002 (i.e., during a test exposure of up to 180 days).