Styrene

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil, other

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

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

Mineralization of styrene was measured in environmental soil samples with biometer flasks by measuring C converted to CO2.

GLP compliance:

not specified

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

not specified

Soil classification:

not specified

Soil no.:

#1

Soil type:

other: Lima loam

pH:

7.23

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Lima loam (7.5% organic matter) was collected from Aurora, NY, USA
- Soil preparation: air dried and 2 mm sieved; for experiments involving sterile environmental samples, samples were irradiated with 60Co (2.5 Mrad)

Soil No.:

#1

Duration:

33 d

Soil No.:

#1

Initial conc.:

0.005 - 4 000 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

other: percentage of styrene C converted to CO2

Soil No.:

#1

Temp.:

22 ± 2°C

Humidity:

appr. 1 bar moisture tension

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil condition: air dried
- Soil (g/replicate): 50 g
- No. of replication treatments: 2
- Test apparatus (Type/material/volume): 250 mL biometer flasks (Bellco Glass Inc., Vineland, NJ)
- Details of traps for CO2 and organic volatile, if any: NaOH in side arm of the biometer flask to trap CO2

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: appr. 1 bar moisture tension
- Continuous darkness: Yes

Soil No.:

#1

% Degr.:

16 - 62

Parameter:

other: Styrene C converted to CO2

Sampling time:

33 d

Transformation products:

not specified

Evaporation of parent compound:

not specified

Volatile metabolites:

not specified

Residues:

not specified

Details on results:

TEST CONDITIONS
- Aerobicity, moisture, temperature and other experimental conditions maintained throughout the study: Yes

Because abiotic mineralization did not occur, the mineralization in samples of all environments tested resulted from microbial activity.

 

Table: Effect of styrene concentration on its degradation in Lima loam:

 

concentration mg/kg of soil	rate µg/kg/h	% mineralized
		per h	in 30 days
0.005	0.016	0.32	55
0.020	0.083	0.41	62
0.10	0.32	0.32	50
1.0	2.2	0.22	47
5.0	4.3	0.087	31
10	7.6	0.076	27
50	39	0.077	26
100	63	0.063	20
500	199	0.040	16
1000	320	0.032	16
4000	1700	0.043	17

 

An investigation was conducted to assess mineralization in samples of different environments. Lima loam was amended with 1 mg of styrene/kg. The transformation was essentially linear with time until more than 30% had been converted to C02; more than half of the C was mineralized in 33 days. 14C02 was not formed in 33 days when labeled styrene was added to sterilized samples.

A further study was conducted to evaluate the effect of different styrene concentrations on the rate of its mineralization in Lima loam maintained at a moisture tension of 1 bar. Eleven concentrations were used at levels extending from 5 µg to 4 g per kilogram of soil. Biodegradation occurred at all concentrations, but the percentage of styrene C converted to CO2 in 30 days generally decreased with increasing styrene concentrations and ranged from 62% for 20 µg/kg to 16% for 1000 mg/kg (see table). At concentrations greater than 100 mg/kg, mineralization began after a short acclimation period and then proceeded rapidly, and the rapid conversion was followed by a period of slow formation of 14CO2. At concentrations below 100 mg/kg, biodegradation began with no apparent lag period. Mineralization at low concentrations was initially rapid and linear, and this phase was followed by a slow release of 14CO2. The rates shown in the table were calculated from the activity at 0-5 days at concentrations of 0.005-1.0 mg/kg and 5-14 days at higher concentrations, which excluded the acclimation periods and nonlinear portions of the curves. The absolute rate of mineralization increased with increasing concentration. On a percentage basis, however, the rates at levels of 1.0 mg/kg or lower were not greatly affected by initial concentrations. The similarity in percentage mineralized per hour at 0.005, 0.020, 0.10, and 1.0 mg/kg of soil shows that the rate is directly correlated with concentration. The percentage mineralized in 30 days declined with increasing concentrations.

Executive summary:

An investigation was conducted to assess mineralization in samples of different environments. Lima loam was amended with 1 mg of styrene/kg. The transformation was essentially linear with time until more than 30% had been converted to C02; more than half of the C was mineralized in 33 days. 14C02 was not formed in 33 days when labeled styrene was added to sterilized samples.

Description of key information

The test item is readily biodegradable therefore further experimental studies are not required.

Additional information

Fu and Alexander (1992) used a range of concentrations, extending from as low as 5 µg up to 4 g/kg. As determined by the amount metabolized, the rate increased with increasing concentration und was even rapid at 4 g/kg. At concentrations up to 1.0 mg/kg, the rate was 0.22 to 0.41 mineralized per hour, that is, the rate in terms of actual amount degraded was directly correlated with concentration. Even at levels of 0.5 to 4.0 g/kg of saul, 0.032 to 0.043% was destroyed per h. Below 100 mg/kg of soil, aerobic degradation was detectable even very shortly after the chemical entered the soil, but it was only was evident after a short period at higher concentratians. The rate of degradation was proportional to concentration at 1.0 mg/kg or lower, suggesting first-order kinetics at the low concentrations. The rate of microbial transformation varied in different soils and was notably slow in an acid silt loam (pH 4.87). Near the soil surface, volatilization and biodegradation occurred simultaneously, but the main loss mechanism in soil at some depth below the surface is probably chiefly microbial, provided conditions favour biological activity.