Dibenzylbenzene, ar-methyl derivative

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 216 (Soil Microorganisms: Nitrogen Transformation Test)

Deviations:

yes

Remarks:

The water amount added to the soil was not sufficient to achieve the recommended soil moisture content of 40% WHCmax, the test was conducted at 36% WHCmax. This deviation was not considered to have affected the outcome of the study objectives

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

no

Details on preparation and application of test substrate:

- Description of the test soil:
The soil substrate used for this study was a silty sand soil (according to German DIN), provided by Lufa Speyer (Soil type 2.3, batch F2.3 3819). The specifications of the soil are presented in Table 1 (See section "Any other informations").

The soil moisture (4.9%) and the Maximal Water Holding Capacity (WHCmax, 28.6%) were determined at the test facility. The soil was not pasteurized nor heat treated; no fertiliser or plant protection products were used.

The test soil was stored (around six weeks) prior to use. A pre-incubation was carried out for a period of 96h before the test initiation at a similar test temperature and moisture content that used in the test.

- Test units:
Glass beakers of 600 mL of nominal capacity were used for incubation of soils and were covered with perforated polyethylene foil to minimise water loss and to allow gas exchange during the test.

- Amendment with organic substrate:
The test and control soils were amended with a powdered lucerne-grass-green meal at the recommended lucerne-soil ratio of 5 g of lucerne per kilogram of soil (dry weight).

Test organisms (inoculum):

soil

Total exposure duration:

28 d

Test temperature:

The test was carried out in the dark at a room temperature of 20 ± 2 °C

Moisture:

4.9%

Organic carbon content (% dry weight):

0.65

Nitrogen content (% dry weight):

0.07

Nominal and measured concentrations:

As the test item is not an agrochemical, a geometric series of the following nominal concentrations was tested: 10.0, 22.0, 48.4, 106.5, 234.3 and 515.4 mg/kg sdw (Soil Dry Weight).

Reference substance (positive control):

yes

Remarks:

A toxic reference substance was used to confirm the sensitivity under the test conditions of the soil microorganisms: one single concentration of 20 g/kg sdw was tested with the objective to inhibit the microorganisms activity

Key result

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

515.4 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Details on results:

The results of the quantity of nitrate-N determined in the control at Day 0 are shown in Table 3 (See "Any other information"). Values for the amount of nitrate-N determined in the control and in each treatment group at Day 28 are presented in Table 4 (See "Any other information").

None of the tested concentrations showed inhibition of Nitrate production compared to the blank control. An increase of Nitrate production ranging from 9.7% and 21% was observed. There was no clear relationship between the test item concentration and the nitrates contents, as a consequence there was no inhibitory effect of the test item compared to the control on nitrate formation up to 515.4 mg/kg soil dry weight. The NOEC is therefore considered to be equal to or greater than 515.4 mg test item/kg soil dry weight.

In compliance with guideline OECD 216, the study can be regarded to be valid, since the variation of nitrate-N content between replicate control samples was less than 15% (i.e. 3.8%).

pH are presented in Table 5 (See "Any other information"). and were maintained between 6.3 and 6.4

The temperature was continuously recorded and ranged from 19.9 to 20.4°C (mean: 20.2°C).

Results with reference substance (positive control):

Results obtained with the toxic reference confirm the presence of the microorganism activity as it was strongly inhibited at day 28 (the nitrates content was 75.2% lower than the control group).

Table 3: Nitrate-N content determined at Day 0 in control soil

Replicate	Nitrate-N content (mg/L)			SD
	Measure 1	Measure 2	Mean
a	15.98	16.16	16.07	0.131
b	16.43	16.48	16.46	0.030
c	15.91	16.17	16.04	0.186
d	13.26	13.20	13.23	0.043

a, b & c: soil amended with Lucern

d: soil without Lucern

Table 4 : Nitrate-N content determined at Day 28:

Treatment (mg/kg sdw)	Replicate	Nitrate-N content (mg/L)			SD	RSD (%)	Deviation of measured contents from mean of controls (%)
		Measure 1	Measure 2	Mean
Control	a	65.90	65.56	65.73	0.24	0.36	Per replicate	Mean of replicates
	b	63.79	63.53	63.66	0.18	0.29
	c	68.72	68.66	68.69	0.05	0.07
Toxic Reference	a	17.15	16.98	17.07	0.12	0.72	-74.2	-75.2
	b	15.79	15.90	15.84	0.08	0.49	-76.0
	c	16.48	15.80	16.14	0.47	2.94	-75.6
10.0	a	79.47	79.22	79.34	0.18	0.22	20.2	14.4
	b	70.00	68.76	69.38	0.87	1.26	5.1
	c	78.15	77.80	77.98	0.24	0.31	18.1
22.0	a	73.28	72.90	73.09	0.27	0.36	10.7	9.7
	b	70.76	70.36	70.56	0.28	0.40	6.9
	c	73.60	73.70	73.65	0.07	0.10	11.5
48.4	a	75.79	75.45	75.62	0.24	0.32	14.5	11.8
	b	74.56	74.37	74.46	0.14	0.18	12.8
	c	71.60	71.04	71.32	0.40	0.56	8.0
106.5	a	72.27	72.08	72.17	0.13	0.18	9.3	12.0
	b	74.84	75.13	74.99	0.20	0.27	13.6
	c	74.74	74.51	74.63	0.17	0.22	13.0
234.3	a	80.46	80.87	80.67	0.29	0.36	22.2	21.0
	b	78.53	81.52	80.02	2.11	2.64	21.2
	c	78.42	79.72	79.07	0.92	1.16	19.8
515.4	a	74.37	73.92	74.14	0.32	0.43	12.3	16.6
	b	79.51	78.55	79.03	0.68	0.86	19.7
	c	77.70	77.95	77.82	0.18	0.23	17.9

< DL (0.06 mg/L): concentration lower than the Detection Limit

< QL (0.2 mg/L): concentration lower than the Quantification Limit

Table 5 : Measured pH at Day 28:

Treatment (mg/kg sdw)	pH T0	pH day 28
Control	6.4	6.4
10.0	6.4	6.3
515.4	6.4	6.3

 

Validity criteria fulfilled:

yes

Conclusions:

No inhibitory effect was observed up to the highest tested concentration (i.e. 515.4 mg test item/kg soil dry weight) 28 days after application. The NOEC is therefore considered to be equal to or greater than 515.4 mg test item/kg soil dry weight.
Since no dose-response relationship could be observed, the EC15, 50 values could not be calculated.

Executive summary:

This study was designed to investigate the long-term effects of the test item, after a single exposure, on nitrogen transformation activity of soil microorganisms, following the procedure described in the corresponding OECD 216 guideline.

 

As the test item is not an agrochemical, the test was performed as a dose-response test: a sieved soil was amended with powdered plant meal (Lucerne, Medicago sativa) and either treated with the test item or left untreated (blank control). The test soils were then incubated at 20±2 °C in the dark. The quantities of nitrate formed in treated and control samples were measured at the test initiation and after 28 days of incubation. The rate of nitrate formation in treated samples compared with the rate in the controls, and the percent deviation of the treated from the control were calculated.

 

Since no dose-response relationship could be observed, the EC10, 50 values could not be calculated. No inhibitory effect was observed up to the highest tested concentration (i.e. 515.4 mg test item/kg soil dry weight) 28 days after application. The NOEC is therefore considered to be equal to or greater than 515.4 mg test item/kg soil dry weight.

 

In compliance with guideline OECD 216, the study can be regarded to be valid, since the variation of nitrate-N content between replicate control samples was less than 15% (i.e. 3.8%).

Description of key information

No inhibitory effect was observed up to the highest tested concentration (i.e. 515.4 mg test item/kg soil dry weight) 28 days after application. The NOEC is therefore considered to be equal to or greater than 515.4 mg test item/kg soil dry weight.
Since no dose-response relationship could be observed, the EC15, 50 values could not be calculated.