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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Weight of evidence:
Low mobility in soil under aerobic conditions, Directive 95/36/EC, Brandelli 2001a.
Rapid degradation under aerobic conditions, half-life between 0.8 and 1.3 days, Directive 95/36/EC, Schulze-Aurich 1998.
Rapid degradation under aerobic conditions, half-life between 2.9 and 27.0 days, Directive 95/36/EC, Brandelli 2001b.
Rapid degradation under aerobic conditions, half-life between 0.6 and 1.1 days, Directive 95/36/EC, Ellgenhause & Morgenroth 1998.
Rapid degradation under aerobic/anaerobic conditions, half-lives ranged from 0.448 to 2.20 days, EPA 162-2 & 162-3, Geldhill 2001.
Low potential for bioaccumulation under anaerobic, half-lives ranged from 0.4 to 1.7 days, EPA 162-3, Spare 2000.
Rapid degradation under aerobic-anaerobic conditions, half-lives ranged from 0.5 to 6.2 days, Directive 95/36/EC, Morgenroth 1999.
Rapid degradation under aerobic/anaerobic conditions, half-lives ranged from 0.5 to 3.4 days, Directive 95/36/EC, Ellgenhausen 1999.
Rapid bi-phasic degradation under aerobic conditions, primary half-life 0.6 days, secondary half life 220 days, EPA 162-1, Scott 1998.
Rapid metabolism under aerobic conditions, primary half-life 0.62 to 0.52 days, secondary half-life between 189.90 and 341.45 days, EPA 162-1, Cruz 1997.

Key value for chemical safety assessment

Additional information

Ten studies have been provided on a weight of evidence basis. The consensus of which is that the test material has a low mobility in soil, degrades rapidly and has little potential for bioaccumulation. The half-life of the test material is bi-phasic, where <90 % is degraded within the primary phase of approximately 0.6 days. The secondary phase was much slower ranging from 189.90 341.45 days. Degradation was considered to be dependent on microbial viability of the soil, where the fasted degradations were observed in viable, moist, aerobic soils incubated at ambient temperature. Several major and minor degradated were identified.

Brandelli (2001a) demonstrated that the test material has a low mobility in soil, with a penetration depth of between 5 and 10 cm into the soil columns. Three metabolites major metabolites were identified, one in the soil and three in the leachate. Only small amounts of radioactivity were detected in the leachate (between 0.0 to 29.0 %), consisting of degradation compounds only.

Schulze-Aurich (1998) determined that the test material degraded rapidly in the three soils under aerobic conditions, with a half-life ranging from 0.8 to 1.3 days. Three major metabolites were identified, with half-lives ranging from 2.1 to 53.8 days.

Brandelli (2001b) determined that the test material rapidly degraded in biologically active soils with half-lives ranging from 2.9 to 27.0 days. Representing a much reduced persistency in all three soils. Three major metabolites were identified in the three soils during incubation, although there profiles displayed variation between the soil types.

Ellgenhause & Morgenroth (1998) determined that the test material rapidly degraded in soil subject to various aerobic environmental conditions. The half-life of the test material ranged from 0.6 to 1.1 days. The half-life of the test material was unaffected by the application rate, although a decreased soil moisture produced a slightly longer half-life. Three main metabolites were identified with half-lives ranging from 1.6 to 153 days under the various conditions. End products were bound residue and carbon dioxide.

Rapid dissipation of the test material was observed under aerobic/anaerobic conditions Geldhill (2001). The degradation profiles of the test material were similar regardless of whether the test system was incubated under anaerobic conditions from the start, or converted to from aerobic to anaerobic conditions shortly after dosing. The same three major metabolites were identified in both samples.

Spare (2000) determined that the test material degraded rapidly in the water column and showed little potential for bioaccumulation in the soil phase. The test material degraded with a half life of 0.4 days in the water phase, and 1.7 days in the total system. Three major and two minor metabolites were identified. These resulting degradation products remain primarily with the water and show little potential for movement into the soil phase.

Morgenroth (1999) determined that the test material rapidly degraded in biologically active soil. Metabolism under aerobic conditions was faster in comparison to anaerobic conditions, with half-lives of 0.5 and 1.9 days respectively. A reduced temperature also increased the degradation time of the test material. No degradation occurred in sterile soil. Degradation to the test material was thus considered to be driven mainly by microbial degradation. In total eight metabolites were identified, however their profiles varied under the different environmental conditions, half-lives ranged from 2.1 to 48.1 days.

Ellgenhausen (1999) determined that the test material had a half-life of 0.5 days in aerobic incubations and a longer half-life of 3.4 days under anaerobic conditions. Three major and seven minor metabolites were identified in aerobic incubations with half-lives ranging from 1.6 to 6.5 days. Four minor and five major metabolites were identified in anaerobic incubations with half-lives ranging from 15.3 to 59.7 days. Anaerobic end products of incubation were mainly carbon dioxide and bound residue, the latter also further degrading to form carbon dioxide. Therefore no accumulation can be expected of the parent compound or its aerobic and anaerobic metabolites.

Scott (1998) determined that the degradation of the test material under aerobic conditions was bi-phasic, with primary and secondary half-lives of 0.6 and 220 days respectively. Exposure at difference dose levels showed no significant differences in the metabolic patterns. Three major metabolites were identified. Calculated metabolite half-lives ranged from 2.43 to 218.72 days.

Schocken (1996), provided as supporting information, showed that soil-associated radioactivity accounted for an average of 104 % of the applied dose for the samples in kinetic and degradate viable soil and kinetic sterile soil and 100 % for the degradate sterile soil samples after 366 days of incubation. Furthermore the production of volatiles accounted for less than 3 % in kinetic and degradate viable samples. All volatile radioactivity was trapped in the duplicate aqueous potassium hydroxide traps. No significant volatile production (≤0.01 %) was detected for either of the sterile test systems. Samples were further analysed in Cruz (1997).

Cruz (1997) analysed soil samples incubated in Schocken (1996), and showed that the test material was rapidly metabolised in viable soil, regardless of the dose rate. The test material displayed bi-phasic degradation in viable samples with a primary half-life ranging from 0.52 to 0.62 days, and a secondary half-life between 189.90 and 341.45 days. Degradation was slower in sterile samples. Four major metabolites were identified in viable samples, whereas only one was identified in sterile samples. The degradation of the test material is considered to be dependent on microbial viability of the soil.

All studies was performed to a high standard, in line with GLP and in accordance with standardised guidelines and has thus been assigned a reliability score of 1 in line with the principles for assessing data quality set out in Klimisch (1997).

The available data are considered to be complete and the conclusion that the test material is rapidly degradable in soil at 20 °C has been taken forward for risk assessment.

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