Sodium acrylate

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

30 October - 27 November 1991 (experimental)

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

GLP guideline study

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 217 (Soil Microorganisms: Carbon Transformation Test)

Deviations:

no

Principles of method if other than guideline:

- OECD Chemicals Testing Programme UPEC/3 "Guidelines for assessing the toxicity of chemicals to soil micro-organisms; Carbon cycle", 4th draft 1981
- Guidelines for the official testing of plant protection products Part VI, March 1987 "Effects on the activity of soil micro-flora" of the Federal Biological Research Centre for Agriculture and Forestry, Braunschweig, Germany

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

yes

Details on preparation and application of test substrate:

APPLICATION OF TEST SUBSTANCE TO SOIL
- Method:
- Acrylic acid was dissolved in distilled water to give a concentration of 100000 mcg/mL and a series of ten-fold dilutions prepared in the same medium to give concentrations down to 10 mcg/mL.
- 2.5 mL volumes of these solutions were then added to 250 g quantities of soil plus nitrogen source to give concentrations in the soil of 1000 down to 0.1 µg/g soil (= ppm). To effect homogeneous mixing, the soil was spread in a thin layer on a tray and the 2.5 mL volume of test compound sprinkled as evenly as possible over the surface of the soil, which was then mixed by hand and then transferred to a tumbling device for further mixing.

Test organisms (inoculum):

soil

Total exposure duration:

28 d

Test temperature:

18 - 22 °C

Moisture:

40 - 60 % of water holding capacity

Details on test conditions:

SOURCE AND PROPERTIES OF SUBSTRATE
- Geographical reference of sampling site: Welbeck, Nottinghamshire, U.K.
- History of site:
- Treatments with pesticides: none during the 5 preceding years
- Depth of sampling: the top 20 cm
- Particle size:
- 2 - 0.6 mm: 4 %
- 0.6 - 0.2 mm: 55 %
- 0.2 - 0.1 mm: 20 %
- 0.1 - 0.06 mm: 6 %
- 0.06 - 0.002 mm: 8 %
- < 0.002 mm: 7 %
- Organic carbon: 0.3 %
- Cation exchange capacity: 7.2
- Water holding capacity: 33.25
- Moisture content: 1.3*
- Texture classification: loamy sand
- pH: 6.5

*Moisture content of the soil was re-determined at HRC prior to study start and was found to be:
Sandy soll: 1.561 %

SOIL PRETREATMENT
- Method: Soil was sieved (2 mm) to remove coarse plant parts and macro fauna and was held at 18 - 22 °C for approx. 2 weeks. Then the soil was transferred to a refrigator at 4 °C for a few weeks and then replaced at 18 - 22 °C five days before study start. A sufficient quantity of Lucerne was added to the soil to give an input of approx. 150 µg nitrogen per gram of soil.

EXPERIMENTAL DESIGN
The following mixtures of soil, nitrogen source, acrylic acid and controls were set up:
(1) Soil only
(2) Soil plus nitrogen source
(3) Soil plus nitrogen source, plus 1000 ppm acrylic acid
(4) Soil plus nitrogen source, plus 100 ppm acrylic acid
(5) Soil plus nitrogen source, plus 10 ppm acrylic acid
(6) Soil plus nitrogen saurce, plus 1.0 ppm acrylic acid
(7) Soil plus nitrogen source, plus 0. 1 ppm acrylic acid
(8) Sterile soil plus 1000 ppm acrylic acid

RESPIROMETRY
- 100 g amounts of each of the soil mixtures were distributed into 100 g amounts in duplicate respirometers
- Respirometer flasks were connected to an air pump via a gas scrubbing system as described by Greaves et al. (1) consisting of a molecular sieve (Type 5A, 1/8" pellets), silica gel, soda asbestos 6 - 12 mesh (Carbazorb, BDH), a moisture trap, CO2-free water and precision bore capillary tubing to regulate thee air flow. Air exiting from the respirometer flasks was led into Drechsel bottle CO2-traps each containing 40 mL 1 M NaOH.
- The respirometers were maintained in a temperature controlled room set at 18 - 22 °C.
- The NaOH from each trap was transferred to a 100 mL volumetrie flask and fllled to valume with CO2-free water; 20 mL of this was used for titration, using a Radiometer TIT 85 Autotitrator
- The solution was adjusted manually to approx. pH 10 with 0.5 M sulphuric acid and then further adjusted to pH 8.3 with 0.05 M sulphuric acid using die Autotitrator. This solution was then titrated from pH 8.3 to pH 3.8 using the Autotitrator and the volume of 0.05 M sulphuric acid used was noted.

EFFECT PARAMETERS MEASURED: Respiration after 2, 7, 14, 21, 28 days

Nominal and measured concentrations:

Nominal test concentrations: control, 0.1, 1, 10, 100, 1000 ppm (corresponding to approx. 0.1, 1, 10, 100, 1000 mg/kg dry weight)

Reference substance (positive control):

not specified

Key result

Duration:

28 d

Dose descriptor:

EC0

Effect conc.:

ca. 100 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Duration:

28 d

Dose descriptor:

EC100

Effect conc.:

ca. 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Reported statistics and error estimates:

Differences between the control and treated soils were evaluated by Dunnett's test.

Concentrations of acrylic acid in soil up to 100 ppm (corresponding to 100 mg/kg d.w.) had no effect on the respiration of the microflora, but a concentration of 1000 ppm acrylic acid (corresponding to 1000 mg/kg d.w.) completely suppressed respiration.

Validity criteria fulfilled:

yes

Description of key information

Concentrations of the structural analogue acrylic acid in a sandy loam soil up to 100 ppm (= mg/kg soil ww) had no effect on the respiration of the micro-flora, but a concentration of 1000 ppm acrylic acid completely suppressed respiration.
EC0 = 100 mg/kg soil ww (Sandy loam soil, OECD TG 217, draft)

Additional information

No experimental data on the test substance is available. Sodium acrylate (NaA) is dissociating fast in aqueous media (Henderson – Hasselbach calculation). Therefore, the evaluation of the endpoint toxicity to soil microorganisms is based on a weight of evidence approach using the data of the structural analogue acrylic acid (AA) (CAS 79-10-7) (for WoE information, see chapter 13.2).

An experimental study similar to the OECD guideline 217 (Soil Microorganisms: Carbon Transformation Test) and GLP regulations was conducted with the structural analogue AA to assess the toxicity to soil microorganisms (BAMM, 1992). Due to good data quality and high adequacy of the study, it was rated as highly reliable (Klimisch score 1). AA was dissolved in water and mixed with soil of the soil type sandy loam. The microoganisms were exposed to the test concentrations: 0.1, 1, 10, 100, and 1000 ppm (= mg/kg soil ww). Portions of the treated soil, together with non-treated controls, and a sterile control were placed in triplicate respirometer flasks connected to an air-pump via a suitable gas-scrubbing system to remove CO2 for a test period of 28 days. A closed system was assured, and respiratory gases were collected by CO2-traps of a sodium hydroxide solution. The carbon dioxide evolved by control and treated soils was determined. At a concentration of 1000 ppm the respiration was depressed to a similar level than the respiration rate in the sterile controls. For lower concentrations no significant respiration depression was observed. Thus, it was concluded that AA in lower concentrations up to 100 ppm were non-toxic to the soil microorganisms while a concentration of 1000 ppm was highly toxic.