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Environmental fate & pathways

Biodegradation in soil

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Reference
Endpoint:
biodegradation in soil, other
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
259 days
Reliability:
4 (not assignable)
Rationale for reliability incl. deficiencies:
documentation insufficient for assessment
Remarks:
Non standard dissipation study, not carried out according to any guideline.
Guideline:
other: no guideline followed
Principles of method if other than guideline:
Soils were either amended with sewage sludge or spiked with a mixed standard solution of chlorobenzenes, including 1,2 dichlorobenzene. Each soil treatment was investigated in four different experimental conditions; normal, sterilized, sterilized and shaded and sterilized, shaded and sealed. In addition there was a control, untreated soil. Each 1000 g (dry weight) soil was put in jars 20 cm tall and 10 cm in diameter except the soil in the sealed system. This system contained 60 g (dry weight) soil and was put in 100 mL glass bottles. All soils were placed in a glass house over 259 days where the temperature varied from 20C to 30C.
GLP compliance:
no
Test type:
other: greenhouse
Radiolabelling:
no
Oxygen conditions:
aerobic
Soil classification:
not specified
Details on soil characteristics:
Soil taken from 1-15 cm depth range of a plot with no history of sludge or farmyard manure applications
Details on experimental conditions:
Temperature ranged from 20°C to 30°C and the moisture for the standard spiked soil was 18% with a pH 6.07.
DT50:
191 d
Type:
other: Second degradation step
Temp.:
30 °C
DT50:
8.63 d
Type:
other: first degradation step
Temp.:
30 °C
Transformation products:
not specified
Details on results:
Degradation of 1,2 dichlorobenzene in soil was reported as a two step process with a DT50 of 8.63 days reported for step 1 and a DT50 of 191 days reported for step 2.
Conclusions:
Degradation of 1,2 dichlorobenzene in soil was reported as a two step process with a DT50 of 8.63 days reported for step 1 and a DT50 of 191 days reported for step 2. As a worst case, the DT50 in the second step (191 days) was taken to represent the DT50 of 1,2 dichlorobenzene in soil. As the study was carried out at variable temperature, the DT50 of 191 days was assumed to represent degradation at 30°C as a worst case. Therefore the equivalent degradation rate at 12°C was calculated to be 806 days according to the EU-TGD (2003).
Executive summary:

This study investigated the degradation of 1,2 dichlorobenzene in soil in a greehouse at variable temperature. The study was carried out in light conditions and with no trapping of volatiles, therefore removal processes such as volatilisation or photolysis were not accounted for. Degradation of 1,2 dichlorobenzene in soil was reported as a two step process with a DT50 of 8.63 days reported for step 1 and a DT50 of 191 days reported for step 2. As a worst case, the DT50 in the second step (191 days) was taken to represent the DT50 of 1,2 dichlorobenzene in soil. As the study was carried out at variable temperature, the DT50 of 191 days was also assumed to represent degradation at 30°C as a worst case. Therefore the equivalent degradation rate at 12°C is calculated to be 806 days according to the EU-TGD (2003). Although this study was not carried out to a guideline and has some deficiencies, it does allow a conservative DT50 in soil of 806 days to be calculated.

Description of key information

A waiver based on REACH annex XI section 1 is presented based on the EAWAG Pathway Prediction System. Metabolistaion due to bacterial attack was found to be unlikely. This fact is supported by a non-guideline study containing several deficiencies but yielding a half-life of 806 days at 12°C.

Key value for chemical safety assessment

Additional information

Wang and Jones (1994) investigated the degradation of 1,2 dichlorobenzene in soil in a greehouse at variable temperature. The study was carried out in light conditions and with no trapping of volatiles, therefore removal processes such as volatilisation or photolysis are not accounted for. Degradation of 1,2 dichlorobenzene in soil was reported as a two step process with a DT50 of 8.63 days reported for step 1 and a DT50 of 191 days reported for step 2. As a worst case, the DT50 in the second step (191 days) was taken to represent the DT50 of 1,2 dichlorobenzene in soil. As the study was carried out at variable temperature, the DT50 of 191 days was also assumed to represent degradation at 30°C as a worst case. Therefore the equivalent degradation rate at 12°C was calculated to be 806 days according to the EU-TGD (2003). Although this study was not carried out to a guideline and has some deficiencies, it does allow a conservative DT50 in soil of 806 days to be calculated.