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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
The study was not conducted under GLP, although a LIMS was used to produce and stored the data
Qualifier:
according to guideline
Guideline:
other: equivalent or similar other guideline: DIN 38414 Teil 8
Principles of method if other than guideline:
A defined quantity of the test item was added to the inocculum
GLP compliance:
no
Remarks:
Data were produced and documents according to WinLims-Nr P-0705665
Test type:
other: anaerobic degradation in STP digester tower
Oxygen conditions:
anaerobic
Soil classification:
other: digested sludge was used
Year:
2007
Details on soil characteristics:
Sludge from STP Düsseldorf-Süd (domestic) which was digested almost completely (age of sluge: almost 27 days). The sludge was spiked with 5% concentrated raw sludge (aerobic)to maintain viability of microorganisms (zoogloea)
Soil No.:
#1
Duration:
50 d
Soil No.:
#1
Initial conc.:
174.4 other: mg per 500 mL slude
Based on:
other: TOC
Soil No.:
#1
Initial conc.:
404 other: mg per 500 mL sludge
Based on:
test mat.
Parameter followed for biodegradation estimation:
TOC removal
Soil No.:
#1
Temp.:
35
Microbial biomass:
500 mL digested sludge with unknown composition
Details on experimental conditions:
500 mL reactors were used to conduct the test.
Two test groups were set-up (in duplicate): Test concentration & blank control, i.e., digested sludge without test substance.
The pH of the inocculum was adjusted to pH 7 (plus/minus 0.2) by adding an appopriate buffer (acc. to EN 12176, Part 5).
Test substance and inocculum were filled into the reactord anaerobically and homogenized prior to connecting to the Eudiometer.
During the test, samples were mixed once a day.
Volumes of digester gas were analysed daily (without few exceptions)



DT50:
ca. 40 d
Type:
other: Graphical estimation
Details on results:
77% of the test item were degraded within 21 days, after a lag phase of 29 days
Conclusions:
The results show that 77% of the test substance was degraded to CO2 and methane, within 21 days, following a lag phase of 29 days.
Executive summary:

Following DIN 38414 Part 8, the test substance was incubed under anaerobic conditions for 50 days. Sludge, which had been digested almost completely at domestic STP Düssedorf-Süd, was mixed with 5% raw, aerobic sludge from the same STP. The thus combined sludge was mixed with the test item, 174.4 mg TOC/L sludge. The specimen were incubated at 35 plus/minus 1°C in 500 mL reactor, attached to the following system: Behrotest Eudiometer Unit FH 10 acc. to DIN 38414 S8. Test solutions were homogenized at the beginning of the test and one daily therafter. Digester gaz volumes were measured daily in treatment and control test group. CO2 was removed by precipitation through alkaline solutions. Volumes of methane, released from test group and control were compare with each other. Total incubation time was 50 days. The results showed that 77% of the test item were degraded within 21 days following a lag phase of 29 days. The test is considered valid, since the blank sludge volume produced 849 mL digester gas, which is well comparable with the STP digester tower production performance (600 to 1500 mL per comparable quantity of inocculum).

Endpoint:
biodegradation in soil: simulation testing
Data waiving:
other justification
Justification for data waiving:
the study does not need to be conducted because the substance is readily biodegradable

Description of key information

In accordance with EC 1907/2006, Annex IX, point 9.2.1.3, column 2, soil simulation testing  is not required since Docusate Sodium is readily biodegradable, as shown in study section 4.1.2.1.2 and since (2) Docusate Sodium is not considered highly adsorptive to soil (Koc 953 L/kg).

Key value for chemical safety assessment

Additional information

One study is available, which investigated the anaerobic degradation of Docusate Sodium to methane during a digestion tower simulation test, with the purpose to assess whether use of digested sludge in agriculture poses a risk for the soil environment (Cognis, Bendt 2007). The study however demonstrates that Docusate Sodium is biodegradable under anaerobic conditions, since 77% were digested within 21 days, after the sludge had been adapted. The adaptation period duration was four weeks.