Styrene

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: sediment simulation testing

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 water samples with biometer flasks by measuring C converted to CO2.

GLP compliance:

not specified

Radiolabelling:

yes

Oxygen conditions:

not specified

Inoculum or test system:

natural water / sediment

Details on source and properties of surface water:

- Details on collection (e.g. location, sampling depth, contamination history, procedure):

- Beebe Lake, Ithaca, NY (pH 7.5, 50-60 mg of organic matter/L) (used within 2 h of collection)
- Groundwater containing traces of aquifer solids, Freeville, NY (pH 8.25, 30.5 mg of organic matter/L) (stored at 4°C before use)

Details on source and properties of sediment:

- Details on collection (e.g. location, sampling depth, contamination history, procedure):
- Sewage, primary settling tanks of the Ithaca, NY, sewage treatment plant (pH 7.0-7.4) (used within 1 h of collection)
- Aquifer solid, Freeville, NY, at a depth of 6.0 m (pH 6.95, 0.4% organic matter)

Duration of test (contact time):

33 d

Initial conc.:

2.5 - 1 000 µg/L

Based on:

other: styrene in Lake Beebe water

Initial conc.:

20 - 1 000 µg/L

Based on:

other: styrene in aquifer solid

Initial conc.:

1 000 µg/L

Based on:

other: styrene in sewage

Initial conc.:

1 000 µg/L

Based on:

other: styrene in groundwater

Parameter followed for biodegradation estimation:

other: percentage of styrene C converted to CO2

Details on study design:

TEST CONDITIONS
- Volume of test solution/treatment: 50 g samples of aquifer solid, 50 mL of groundwater, lake water and sewage
- Test temperature: 22 ± 2°C
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 250 mL biometer flasks (Bellco Glass Inc., Vineland, NJ)

- Test performed in closed vessels due to significant volatility of test substance: yes
- Details of trap for CO2 and volatile organics if used: CO2 trapped with 0.5 M NaOH

% Degr.:

> 50

Parameter:

CO2 evolution

Sampling time:

33 d

Transformation products:

not specified

Evaporation of parent compound:

not specified

Volatile metabolites:

not specified

Residues:

not specified

The graphical depiction of the results is given in the attachments (figs. 1 and 2). From this graphics the following results can be deduced:

Aquifer sand was amended with 1 mg of styrene/kg, and samples of sewage, groundwater, and lake water received styrene at 1 mg/L. Both the rate and the extent of mineralization varied appreciably in these samples (attachment, fig. 1). The rates were greatest in sewage, and the transformation was essentially linear with time until more than 30% had been converted to CO2; more than half of the C was mineralized in 33 days. An acclimation period of several days duration and lower rates and extents of mineralization characterized the conversion in groundwater and lake water. The rates and extents were lowest in aquifer sand, and only 10% of the compound was metabolized to CO2 in about 33 days. 14C02 was not formed in 33 days when labeled styrene was added to sterilized samples from the same environments.

The effect of low concentration was quite different in samples of lake water. On a percentage basis, the rate was not independent of concentration at 2.5, 10, and 100 µg/L but rather diminished as the concentration fell (attachemnt, fig. 2A, upper part). Thus, the rate was less at the lower concentrations than would be predicted if it is assumed that the absolute rate is a direct function of substrate level. These data suggest the existence of a threshold at a level somewhat below 2.5 µg/L. It is of interest that the percentage mineralized also diminished with decreasing concentrations. The conversion in aquifer sand was only measured at 20 and 100 µg/kg. The transformation in samples of this environment was particularly slow. Only 1.09 and 1.51% of the styrene added at 20 and 100 µg/kg, respectively, were mineralized in the test period (attachment, fig. 2B, lower part). In this instance, as in lake water, the rate at the lower level is less than would be predicted if it is assumed that the rate is a direct function of concentration.

Validity criteria fulfilled:

not applicable

Executive summary:

More than 50% of Styrene was degraded during the 33 d testing period.

Description of key information

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

Biodegradation also occurs in surface waters. This has been demonstrated in a laboratory with samples of lake water to which the compound was added to give 2.5 µg to 1.0 mg/L. 10 to 20% of the compound was mineralized in weeks. The transformation required several days for acclimation of the indigenous microorganisms (Fu and Alexander, 1992).

Additional information

 

Environment (1993) reports that styrene would degrade more slowly in groundwater than in surface waters. Howard et al. (1991) estimated a half-life in groundwater of between 4 and 30 weeks. Fu and Alexander (1992) report that anaerobic environment cultures of bacteria have been shown to convert styrene to a series of aromatic, alicyclic and aliphatic products and these probably persist.

Information on mechanisms of anaerobic styrene breakdown and involved ezymes is available in the review of Dirk Tischler and Stefan Kaschabek

(S.N. Singh (ed.) 2012, Microbial Degradation of Xenobiotics, Environmental Science and Engineering, Chapter 3, p. 67 -99).