Boron carbide

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil macroorganisms except arthropods: short-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Mar 11–May 17, 2010

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 207 (Earthworm, Acute Toxicity Tests)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.8 (Toxicity for Earthworms: Artificial Soil Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

ISO 11268-1 (Effects of Pollutants on Earthworms. 1. Determination of Acute Toxicity Using Artificial Soil Substrate)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

The Principles of Good Laboratory Practice (GLP), (Chemikaliengesetz, attachment 1, Germany). The OECD Principles of Good Laboratory Practice.

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

Eisenia fetida

Animal group:

annelids

Details on test organisms:

TEST ORGANISM:
The test species was Eisenia fetida (Michaelsen), sub-species Eisenia fetida andrei. The organisms used for this study were obtained from a healthy laboratory rearing stock of the testing facility. Earthworms for these tests were between 7 and 8 months old. They were adult - with clitella - and had an individual weight between 32I and 468 mg at the beginning of the study.

ACCLIMATION:
48 h before test initiation, the earthworms were transferred from the rearing medium into moist, untreated test substrate for acclimatisation. Just prior to the introduction into the test containers, the earthworms were rinsed, blotted dry quickly and weighed individually. Afterwards ten earthworms meeting appropriate criteria were placed onto the soil surface of each test container in a non-systematic manner. The jars were covered with glass lids allowing ventilation and were incubated under test conditions for 14 days.

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

yes

Total exposure duration:

14 d

Remarks:

mortality checked after 7 and 14 days

Test temperature:

18.5–20.5 °C

pH:

pH of the control at the beginning and the end of the test were 6.46 and 6.75, respectively.
pH of the test substrate at the beginning and the end of the test were 6.36 and 6.74, respectively.

Moisture:

control: 37.1% (day 0) and 34.8% (day 14)
test substrate (37.4% (day 0) and 36.0% (day 14)

Details on test conditions:

Artificial Soil Components:
-10 % sphagnum peat (close to pH 5.5-6.0; no visible plant remains, finely ground, air dry);
-20 % kaolin clay (kaolinite content above 30 %);
-70 % industrial sand (fine sand dominant with more than 50% of the particles between 50 and 200 microns);
-0.24 % calcium carbonate - precipitated extra pure (the soil pH is adjusted to 6.0 ± 0.5 at the start of the test before adding the test item);
The water holding capacity of the artificial soil used for the test was 37.81 %.
The dry components were blended and mixed thoroughly in an electric mixer.

Preparation of the Test Substrate:
In order to achieve a water content of approx. 35% of the dry weight, a total amount of 195 g deionised water was added to 545 g dry soil. The water was mixed with the artificial soil 24 h prior to the test in order to achieve a homogeneous distribution. To avoid evaporation, the moistened substrate was stored in a closed container until use.
The test item was weighed directly on quartz sand on the day of test initiation. Each aliquot of moistened artificial soil (740 g) was mixed with 10 g treated sand for the treatment group and 10 g untreated quartz sand for the control at high speed using an electric mixer ('Kenwood', stainless steel), see table 1.
Immediately after mixing, the test substrate was placed loosely into the test containers (1 L glass vessels). For each treatment group four test containers were prepared.

Test Design:
The test comprised one treatment group (1000 mg / kg sdw Boron Carbide) and a control group. Each group consisted of four replicates with ten worms.

Test Conditions:
Incubation of the test containers was carried out at 18.5–20.5°C under continuous light with a light intensity between 500 and 750 lux.

Nominal and measured concentrations:

The nominal concentration was 1000mg/kg soil dry weight

Reference substance (positive control):

yes

Remarks:

2-Chloroacetamide

Duration:

14 d

Dose descriptor:

NOEC

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Duration:

14 d

Dose descriptor:

LOEC

Effect conc.:

> 1 000 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Details on results:

No mortalities have been observed at 1000mg/kg sdw boron carbide and in the control group, respectively.
The average body weight loss of the test organisms in the test item treatment group was 13.4 % compared to the initial weight. In the control group the average body weight loss was 10.2 % of the initial weight (table 2).

Results with reference substance (positive control):

The toxic reference item 2-chloroacetamide was tested in a separate 14-day toxicity study. The LC50 was determined to be 11.7 mg/kg soil dry weight using Spearman-Kärber estimator. The NOEC and the LOEC were determined to be 8 mg and 13 mg/kg soil dry weight, respectively.

Reported statistics and error estimates:

The mean relative body weight change per treatment was determined using the means of worm weight per replicate. Data of the mean weight change per replicate in percent were used for statistical evaluation.
At tested concentration of Boron Carbide the biomass loss was not statistically significantly different from the control treatment (t-test, pooled, left-sided, p < 0.05).
Statistics not relevant due to no observed mortalities.

Table 2: Earthworm body weight at the beginning and after 14 days of exposure to the test item

 

Test item	Test start		After 14 days
[mg/kg]^1	Mean [mg/worm]	SD ±	Mean [mg/worm]	SD ±	Mean weight change  [mg/worm]	Mean weight change [%]
control	403. 8	39.8	362.3	37.5	- 41.5	10.2
1000	385.3	39.3	333.7	37.6	- 51.6	13.4

¹based on soil dry weight; SD: standard deviation

Validity criteria fulfilled:

yes

Remarks:

According to the guidelines this study can be regarded as valid, since in the control and the positive control treatment the required validity criteria were met

Conclusions:

In this 14-days limit test the acute toxicity of boron carbide to the earthworm Eisenia fetida was assessed. Since no significant effects on mortality and biomass development were observed at the test item concentration of 1000 mg/kg soil dry weight, the NOEC and LOEC for both mortality and biomass development are equal to, repectively greater than 1000 mg/kg soil dry weight.

Executive summary:

To determine the toxicity of the test item, a test with one single concentration of boron carbide was carried out. Aliquots of wet artificial soil were mixed with the test item at 1000 mg/kg soil dry weight and filled into 1 L volume glass vessels. For the test item group and control group four glass vessels were prepared and ten adult earthworms (age between two and twelve months, with clitella) added respectively. Aliquots treated with untreated quartz sand served as control. A toxic reference item (2-chloroacetamide) was tested in the testing facility in a separate study to confirm the sensitivity of the earthworms against compounds with known effects under the test conditions. The results of the most recently performed toxic reference item test showed validity of the test. Earthworm mortality and behavioural changes were recorded after 7 and again after 14 days. The criterion of death was the absence of a reaction to a gentle mechanical stimulus to the anterior end, or the absence of worms. The assessment of earthworm weight was carried out immediately before exposure to the test item and at the end of the 14 day exposure period.

Since no significant effects on mortality and biomass development were observed at the test item concentration of 1000 mg/kg soil dry weight, the NOEC and LOEC for both mortality and biomass development are equal to, respectively greater than 1000 mg/kg soil dry weight.

Description of key information

The NOEC for soil macroorganisms except arthropods has been determined in a Limit Test (OECD 207, Acute Toxicity  on Earthworms, Eisenia fetida Artificial Soil Test). The nominal concentration was 1,000 mg/kg soil dry weight. As no mortalities or statistical relevant weight changes have been observed after 14 days, the NOEC is 1,000mg/kg soil dry weight boron carbide.

Additional information

This study has been chosen as key study because it is a valid study according to OECD guidelines (OECD 207, GLP compliant).

Due to the low water solubility of boron carbide (<1mg/L) and its inability to cross biological membranes a limit test has been performed.