Sodium acrylate

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

13 Jan 1992 - 27 Aug 1992

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Principles of method if other than guideline:

Method according to U.S. EPA Pesticide Assessment Guidelines, Subdivision N, § 162- 1

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

other: Milton sandy loam

% Clay:

16

% Silt:

30

% Sand:

54

% Org. C:

3.2

pH:

7.7

CEC:

22.2 meq/100 g soil d.w.

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Somersham Cambridgeshire, USA
- Pesticide use history at the collection site: The soil has not been treated with any pesticide during the previous fifteen years, and had lain fallow (grass and wild plants) for two years prior to sampling
- Collection procedures: The soil was tilled to a depth of about 20 cm immediately prior to sampling and soil was taken from the tilled layer.
- Storage: stored in large plastic containers sunk into open ground at Huntingdon Research Centre
- Soil preparation: Vegetation was allowed to germinate and grow in the soil. Approx. one month prior to the study a large sample of this soil with vegetation was transferred to a large plastic container. This container was then maintained at ambient temperature indoors.

PROPERTIES OF THE SOILS (in addition to defined fields)
- Water holding capacity: 40.2 % by weight
- Water content at 75 % of 0.33 bar: 17.3 % by weight

Soil No.:

#1

Duration:

28 d

Soil No.:

#1

Initial conc.:

100 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

25.1 - 25.9 °C

Humidity:

75 %

Details on experimental conditions:

EXPERIMENTAL DESIGN
- Soil preincubation conditions: Aliquots of sieved (2 mm) soil equivalent to 100 g soil dw were put into 250-mL glass flasks. The glass Buchner flasks were acclimated in the dark for 18 days at 25 °C prior to dosing.
- No. of replication treatments: 3
- Details of traps for CO2 and organic volatile, if any: The trapping vessels contained a polyurethane foam bung, ethyl digol, 2 M aqueous potassium hydroxide, and a solution of ethanolamine/2-ethoxyethanol (1:3, v/v).

Test material application
- Volume of test solution used/treatment: 5 mL aliquots (nominal concentration of 2.0 mg/L)

Experimental conditions
- Moisture maintenance method: Humidified air was drawn through the soil flask
- Continuous darkness: Yes

SAMPLING DETAILS
- Single flasks of soil were taken for analysis at the following times after test substance application; 0, 1, 3, 7, 14 and 28 days
- Trapping solvents/solutions and bungs were taken for analysis and replaced with fresh material at 1, 3, 7, 14 and 28 days after test substance application

Key result

Soil No.:

#1

% Degr.:

72.9

Parameter:

CO2 evolution

Sampling time:

3 d

Key result

Soil No.:

#1

DT50:

> 0 - < 1 d

Type:

(pseudo-)first order (= half-life)

Temp.:

> 25.1 - < 25.9 °C

Transformation products:

yes

No.:

#1

Details on transformation products:

- Formation and decline of each transformation product during test:
The main transformation product was carbon dioxide: 27.9 % after 1 day, increasing up to 81.1 % after 28 days.

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

Details on results:

- Under aerobic conditions 14C-acrylic acid was rapidly degraded.
- The estimated half-life was less than 1 d.
- After 3 days incubation no detectable acrylic acid was present in soil.
- A large proportion (72.9 %) of the applied radioactivity was mineralised to radiolabelled carbon dioxide after 3 d and 81.1 % after 28 d.
- Non-extractable radioactivity peaked at 16.8 % of applied radioactivity after 3 d and declined to 10.1 % of applied radioactivity after 28 d.
- Solvent extractable radioactivity decreased dramatically over the first 3 days with only 2.9 % applied radioactivity extracted on Day 3. More vigorous extraction methods (reflux) were unsuccessful in extracting bound radioactivity.
- Volatile radioactivity was produced rapidly during the first 3 days with 73.9 applied radioactivity being trapped after this time. The major component in these volatiles was carbon dioxide, trapped by aqueous potassium hydroxide. A small proportion (ca. 1 % applied radioactivity) of volatile radioactivity was trapped by the ethyl digol trap, especially during the initial phase of the study. This, presumably, was volatilised acrylic acid. The rate of increase in carbon dioxide emissions fell sharply after Day 3, but levels continued to rise to reach 81.1 % applied radioactivity by Day 28 (82.1 % applied radioactivity total volatiles).
- Soil extracts were analysed by HPLC. The rapid degradation of acrylic acid was confirmed by these analyses. By Day 3 no acrylic acid was detected in soil extracts. Most extractable radioactivity took the form of polar material eluting at the solvent front. HPLC analysis of 14C-acrylic acid in the application solvent and all soil extracts showed the presence of a region of radioactivity eluting after acrylic acid. This material was detectable after 28 days of incubation with soil and was not considered relevant to the conclusions to be drawn from the study.

Extraction and recovery of radioactivity from aerobic soil samples after application of 14C-acrylic acid at a rate of 100 mg/kg dw (results are expressed as % of applied radioactivity)

Time (days)	extracted	not extracted	volatiles	carbon dioxide	total recovery
0	101.7	1.4			103.1
1	44.6	13.8	29.0	27.9	87.4
3	2.9	16.8	73.9	72.9	93.6
7	2.7	15.3	77.0	75.9	95.0
14	2.3	12.9	81.5	80.4	96.7
28	2.1	10.1	82.1	81.1	94.3

The trend exhibited in metabolism of acrylic acid in soil was bi-phasic. In the first phase, by Day 3, the vast majority (if not all) of the 14C-acrylic acid applied to the soil had been degraded. Most of the radioactivity was mineralised to carbon dioxide. The remainder probably became incorporated into soluble or insoluble organic material. The soluble material was extracted and visualised by HPLC analysis. The insoluble material remained bound. In the second phase the radiolabelled organic material appeared to remain bioavailable, but it was metabolised at a much slower rate (based on CO2 evolution data) so distinguishing it from, the more labile acrylic acid.

Description of key information

Based on the data of the structural analoge acrylic acid, sodium acrylate is readily biodegradable.

Key value for chemical safety assessment

Half-life in soil:

1 d

at the temperature of:

25 °C

Additional information

There are no experimental studies  available to assess the biodegradation potential of sodium acrylate in soil. Therefore, the evaluation of the endpoint biodegradadtion in soil is based on a weight of evidence approach using the data of the structural analogue acrylic acid (CAS 79-10-7) (for WoE information, see chapter 13.2). However, based on the results of the structural analogue acrylic acid the ready biodegradability of sodium acrylate is likely. Nevertheless, a well-documented and reliable test on biodegradation of acryl acid in soil (sandy loam) is available (BAMM, 1992). From the test design, the test can be rated as a simulation test in soil. Under aerobic conditions acrylic acid was rapidly metabolized. After 3 days no acrylic acid was detected in soil extracts. The half-life for acrylic acid under these conditions was estimated to be less than one day.

From the presented simulation test in soil it can be concluded that acrylic acid is readily biodegradable in sandy loam. Since the chemical structure of sodium acrylate is related to acrylic acid, ready biodegradability of the test substance in soil is to be expected.