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Ecotoxicological information

Toxicity to soil microorganisms

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Reference
Endpoint:
toxicity to soil microorganisms
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Remarks:
Acceptable, well documented publication which meets basic scientific principles, restriction: test period was 6 days
Principles of method if other than guideline:
Two soils (Captina silt loam and McLaurin sandy loam) were sieved (6.3 mm and 2.0 mm) and moistened with distilled, deionized water to 80% base saturation and soil properties (soil saturation, pH, sulfur, particle size distribution, total phophorus and total nitrogen, cation exchange capacities) were measured. Total organic carbon in the soils was measured as the amount of dissolved organic carbon plus the amount in the solid sample. The test item was then added near the surface of 50-g soil samples contained in stoppered, 8x5 cm glass jars at a concentration of 1 mg/g soil dry weight. Soils were not mixed after addition of the chemicals so that increased losses from volatilization could be avoided. Triplicate treatments with matched controls for each soil were incubated at 20 +/- 0.4 °C in the dark. CO2 efflux was measured on an infrared gas analyzer (Model 300, Mine Safety Appliances Co., Pittsburgh, PA) at 24 h intervals over a 6 d incubation period by purging the headspace with moist, CO2-free air.
GLP compliance:
not specified
Test organisms (inoculum):
soil
Total exposure duration:
6 d
Moisture:
80% saturation (i.e. 190 µL/g silt loam, and 92 µL/g sandy loam)
Duration:
6 d
Dose descriptor:
NOEC
Effect conc.:
>= 1 g/kg soil dw
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
respiration rate

The o-dichlorobenzene led to a reduction in CO2 release in the first few days, this effect being more pronounced in the soil with the higher content of organic carbon. However, towards the end of the experiment (from days 4 to 6), the differences compared to untreated control samples were no longer significant.

Conclusions:
The o-dichlorobenzene applied at 1 g/kg dry soil to a silt loam soil and a sandy loam soil led to a reduction in CO2 release of soil micro-organisms in the first few days, this effect being more pronounced in the soil with the higher content of organic carbon. However, towards the end of the experiment (from days 4 to 6), the differences compared to untreated control samples were no longer significant. Thus, the NOEC is considered to be equal or higher than 1 g/kg dry soil.
Executive summary:

Walton et al. (1989a,b).

The o-dichlorobenzene applied at 1 g/kg dry soil to a silt loam soil and a sandy loam soil led to a reduction in CO2 release of soil micro-organisms in the first few days, this effect being more pronounced in the soil with the higher content of organic carbon. However, towards the end of the experiment (from days 4 to 6), the differences compared to untreated control samples were no longer significant. Thus, the NOEC is considered to be equal or higher than 1 g/kg dry soil.

Description of key information

The 1,2-dichlorobenzene applied at 1 g/kg dry soil to a silt loam soil and a sandy loam soil led to a reduction in CO2 release of soil micro-organisms in the first few days, this effect being more pronounced in the soil with the higher content of organic carbon. However, towards the end of the experiment (from days 4 to 6), the differences compared to untreated control samples were no longer significant. Thus, the NOEC (6 d) is considered to be equal or higher than 1 g/kg dry soil (Walton et al., 1989a,b).

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:
1 000 mg/kg soil dw

Additional information

Walton et al. (1989a,b) investigated the effect of 1,2 -dichlorobenzene on soil micro-organisms by applying 1,2 dichlorobenzene at 1 g/kg dry soil to a silt loam soil and a sandy loam soil. The results showed a reduction in CO2 release by soil micro-organisms in the first few days, this effect being more pronounced in the soil with the higher content of organic carbon. However, towards the end of the experiment (from days 4 to 6), the differences compared to untreated control samples were no longer significant. Thus, the NOEC (6 d) is considered to be equal or higher than 1 g/kg dry soil. Although the test period was 6 days, this was a well documented publication which meets basic scientific principles and therefore the NOEC of 1000 mg/kg dry soil has been used as the key value for toxicity to soil microorganisms.