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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:
key study
Study period:
2017
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Soil (10 g air-dried weight) was added to sterile 125 mL amber glass serum bottles capped with butyl rubber aluminum crimp caps, adjusted to approximately 75% of field capacity (Table 1) using sterile water, and preincubated for 5 days at 22 ± 2 °C to establish a steady-state
microbial activity. Soils for sterile controls were autoclave sterilized. After pre- incubation, a set of soil microcosms were autoclaved (hereafter referred to as autoclave-sterilized
controls) three times at 103.4 KPa and 121 °C for 2 h on day 1, 2, and 4. All glassware and deionized water were also autoclave-sterilized.
All experiments were conducted with individual bisphenol chemicals (BPs) in triplicate for microbially active systems and in duplicate for autoclave-sterilized controls. Individual target compounds were added to soil microcosms through a talc carrier to target an initial soil concentration of 100 μg/kg. BP coated talc was prepared by mixing 10 mL of an individual chemical stock solution (10 mg/L) dissolved in MeOH with 10 g of talc in a Petri dish followed by evaporating MeOH and homogenizing dry BP-coated talc. Single compound amended
talc (100 mg) was added to each microcosm resulting in the mass of talc not exceeding 1% of the soil weight. In previous studies, no significant influence of the talc on chemical degradation including phenolic-based compounds or differences
compared to using ethanol as the target compound carrier. Talc was considered to allow for a more even distribution in the soil, thus is often selected as the carrier of choice for low solubility compounds. Compound concentrations were monitored for 180 days with sampling times selected based on expected degradation patterns and adjusted accordingly depending on observed degradation trends. Headspace O2 and CO2 levels were measured by sampling 5 mL of headspace in a subset of microcosms using a monoject 6 mL needle syringe at designated incubation times to confirm aerobic conditions and biological activity were maintained.. Headspace samples were injected directly onto an Agilent 7890A gas chromatograph (GC) equipped with a thermal conductivity detector (TCD).
At each sampling time, triplicate microcosms were extracted three times sequentially with 25 mL of MeOH each time. After each extraction, bottles were equilibrated end-overend at 35 rpm for ∼24 h at room temperature (22 ± 2 °C), and centrifuged at 1700 rpm for 60 min. Aliquots (1 mL) of individual extracts were added to an HPLC vial and d8-BPA (0.5 mL) was added uniformly to all vials.
GLP compliance:
not specified
Test type:
laboratory
Radiolabelling:
no
Soil classification:
other: Two surface clay loam soils were used in this study: one sampled in a forested area close to the Purdue campus (FRST-50) and one sampled from the Purdue Student Organic Farm (PSF-51)
Year:
2017
Soil no.:
#1
Soil type:
other: FSRT-50
% Clay:
28
% Silt:
36
% Sand:
36
% Org. C:
2.7
pH:
5.8
CEC:
11.3 other: cmol/kg
Soil no.:
#2
Soil type:
other: PSF-51
% Clay:
30
% Silt:
34
% Sand:
36
% Org. C:
1.5
pH:
6.2
CEC:
6.9 other: cmol/kg
Soil No.:
#1
Initial conc.:
0.1 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
0.1 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Soil No.:
#1
Temp.:
22 °C
Humidity:
20.2%
Soil No.:
#2
Temp.:
22 °C
Humidity:
16.5%
Key result
Soil No.:
#1
DT50:
0.935 d
Type:
(pseudo-)first order (= half-life)
Temp.:
22 °C
Key result
Soil No.:
#2
DT50:
0.649 d
Type:
(pseudo-)first order (= half-life)
Temp.:
22 °C
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
Details on transformation products:
#1 Formula: C12H10O8S; Mass 314.01; SMILES: c1c(O)c(O)ccc1S(=O)(=O)C(C=CC(=O)O)=CC(=O)O
#2 Formula: C12H10O7S; Mass: 298.01; SMILES: c1cc(O)ccc1S(=O)(=O)C(C=CC(=O)O)=CC(=O)O
#3 Formula: C8H8O4S; Mass 200.01; SMILES: c1cc(O)ccc1S(=O)(=O)C(=O)C

Description of key information

Aerobic soil biodegradation of 4,4'-sulphonyldiphenol was investigated for up to 180 days in a forest soil and an organic farm soil. Based on compound mass recovered from soils compared with to the mass applied, 4,4'-sulphonydiphenol had short half-lives of < 1 day in both soils.

Key value for chemical safety assessment

Half-life in soil:
1.1 d
at the temperature of:
22 °C

Additional information