Hydroquinone

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

Study period:

Study initiation date : 26 january 2015; Experimental completion date : 24 April 2015

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:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

no

Vehicle:

yes

Details on preparation and application of test substrate:

PREPARATION OF TEST TREATMENTS
A stock solution of the hydroquinone was prepared at a nominal concentration of 100 mg a.i./mL by direct addition of hydroquinone (5.0059 g) to 50 mL of acetone. This stock solution was serially diluted to prepare solutions to dose the soil at 0.10, 1.00, 10.0,100 and 1000 mg hydroquinone/kg dry soil treatment levels.

AMENDMENT OF SOIL AND APPLICATION OF TEST SUBSTANCE TO SOIL
The hydroquinone solution preparation and dosed sand preparation took two hours and the test treatments were prepared as follows immediately afterwards.
A series of 1500 g (dry weight equivalent) aliquots of the pre-acclimated soil was weighed out into a stainless steel mixing bowl.
The test soil was amended with dry powdered lucerne at a rate of 2.5 g of lucerne/500 g of soil (dry weight equivalent) to the control and treatment groups by hand mixing prior to addition of the dosed sand.
The lucerne had a carbon content of 45.21% w/w and a nitrogen content of 3.14% w/w giving a C:N ratio of 14.4:1 (determined by Butterworth Laboratories Ltd, Teddington, Middlesex, TW11 8NY, United Kingdom, reported in a separate GLP compliant Study report ID 1404-0246). A copy of the report is in the raw data package.
The treated sand was then added to the soil with a volume of water to achieve a test moisture of 42 % of the MWHC.
The bulk dosed amended soil was mixed in a planetary mixer (Crypto Peerless, Halifax, UK) and then divided equally into replicate test vessels. Treatments were prepared in the following order: deionised water, solvent control followed by the test item dosed sand in ascending rates;


VEHICLE:
Acetone was used because hydroquinone is not stable in water.
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): acetone
- Evaporation of vehicle before use: no

Test organisms (inoculum):

soil

Total exposure duration:

28 d

Test temperature:

The vessels were maintained in the dark at 20°C +/- 2°C.
Temperature was monitored throughout the study using IceSpy (Skye Instruments, Powys, UK) electronic environmental data loggers.

Moisture:

A satellite moisture control vessel was included in the test for the sole purpose of monitoring moisture content. The moisture content of the soil was maintained at 42 % ± 5% MWHC and on a weekly basis, the weight of the moisture control vessel was determined as a guide to test vessel water loss. Weight loss since the previous sampling occasion was restored by the addition of deionised water to all replicates in all treatments, based on the assumption that all vessels had experienced similar moisture change.

Details on test conditions:

TEST SYSTEM
- Test vessels: Each replicate was contained within a 2.0 L plastic container (internal dimensions 16.7cm x 16.7cm x 9cm deep) with the lid perforated with a single 3 mm diameter hole to ensure aerobic conditions.
- Amount of soil: Each replicate contained 500 g (dry weight equivalent) of soil.
- No. of replicates per concentration, control water and control solvent: Three replicates were prepared for each treatment in the bioassay.

SOIL INCUBATION
- Method: bulk

SOURCE AND PROPERTIES OF SUBSTRATE (soil)
The study was carried out with a single, common agricultural soil as described in OECD Guideline 216 (2000). The soil used was LUFA standard soil type 2.3 (Batch number Sp2.30815) and was supplied by LUFA-Speyer, Obere Langgasse 40, 67346 Speyer, Germany.
The soil sampling was carried out according to ISO 10381-6 (1993) as recommended in OECD 216 (2000). Details of the soil characterisation data and soil collection, site history and soil treatment were provided by LUFA-Speyer.
- Geographical reference of sampling site: Germany, Rheinland-Pfalz / Offenbach - "rechts der Landauer Str.", Nr. 826/7.
- Date of sampling: 18/02/2015
- Vegetation cover: uncultivated in sampling year and 4 former years.
- Treatments with pesticides: No pesticides in sampling year and 4 former years.
- Treatments with fertilizers: no fertilization in 2015, fertilization in 2014: 3500 kg/ha CaO (05/06/2014), 3500 kg/ha CaO (24/09/2014), 3500 kg/ha CaO 1463 kk/ha MgO (15/12/2014); no fertilization the former 3 years.
- Accidental contamination: none reported
- Depth of sampling: ca. 20 cm.
- Soil texture: no data
- % sand: 59.7
- % organic carbon: 0.67
- microbial biomass: 2.11% of the total organic carbon content
- pH (in water): 6.6
- preparation of the soil: temperature : 16°C, drying at room temperature from 18/02 till 25/02/2015; presieving 10 mm mesh on the 25/02; last sieving on the 27/02 mesh 2 mm.
- at time packing : dry matter of the soil: 93%, water content: 7.6 g water/100 g soil dm; water capacity: 21.5 % (g water/100 g soil dm)
- Storage (condition, duration): Soil was received at CEMAS on the 06 March 2015 and was stored in the dark in a refrigerator (nominally at 4°C) until required.

SOIL ACCLIMATATION:
Acclimation of the soil used for the definitive study was started on 20 March 2015, where the soil was brought to a moisture content of 35 % (+/- 5 %) of the maximum water holding capacity (MWHC) of the soil, and left to acclimate in a test cabinet in the dark at 20 ± 2°C for six days before treatment.

SAMPLING AND EFFECT PARAMETERS MEASURED :
- Nitrogen transformation test :
As soon as possible after dosing approximately 50 g (dry weight equivalent) sub-samples were taken from each replicate for the determination of nitrate, ammonium and nitrite concentration. Further sub-samples were taken after 28 days. Inorganic ammonium, nitrate and nitrite were extracted in 250 mL of 2 M potassium chloride (KCl) solution, shaken for 2 hours and then centrifuged for 15 minutes. Approximately 15 mL of the supernatant was collected and these extracts were stored in the dark, under refrigeration (nominally at 4oC), prior to analysis on Day 28. The extracted solution was analysed for nitrate, ammonium and nitrite using the Bran + Luebbe Autoanalyzer AA3 system (method described in SOP CEM-3394 Determination of Nitrate-N, Ammonium-N and Nitrite-N in soil solutions and water).
- Analysis of nitrate and nitrite:
Total oxidised nitrogen (TON, sum of nitrate and nitrite) was determined as nitrate was reduced to nitrite after being passed through a copperised cadmium reduction column. The resulting nitrite was then diazotized with sulphanilamide and N-(1-napthyl)-ethylenediamine dihydrochloride to form a highly coloured azo dye, the absorbance of which was measured colorimetrically using a photometer fitted with a 550nm wavelength filter. Any nitrite in the extracts was also determined to ensure that the nitrate present was derived only from nitrate and that nitrite had not been formed in the soil.
- Analysis of ammonium:
Ammonium in the solutions was reacted with salicylate and dichloro-isocyanuric acid (nitroprusside was used as the catalyst for the reaction), to produce a blue compound, the absorbance of which was measured colorimetrically using a photometer fitted with a 660nm filter.
The concentrations of all analytes were determined by comparing the absorbance signal of prepared calibration standards of varying concentrations to that of the unknown solutions.

VEHICLE CONTROL PERFORMED: yes

RANGE-FINDING STUDY
- Test concentrations: concentration range of 0.01 µg hydroquinone /kg to 1000 µg hydroquinone/kg dry soil.
- Results used to determine the conditions for the definitive study: No dose response was observed and therefore higher concentrations were selected for the final study to determine an EC50 and a NOEC.

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

10 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Duration:

28 d

Dose descriptor:

EC10

Effect conc.:

17.6 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

54.2 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

10 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: quantity of nitrate formed in mg nitrate/kg dry weight soil

Duration:

28 d

Dose descriptor:

EC10

Effect conc.:

19.5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: quantity of nitrate formed in mg nitrate/kg dry weight soil

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

60.1 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: quantity of nitrate formed in mg nitrate/kg dry weight soil

Details on results:

- Nitrate, Nitrite and Ammonium Determinations
The soil nitrate and ammonium concentrations in the soil on Days 0 and 28 for the definitive assay are given in Table 1 and 2, respectively.
Changes in nitrate transformation rates (mg nitrate/kg/day) over the duration of the study are given in Table 3, as the changes in nitrate production from 0-28 days.

During the 0-28 day period the soil nitrate transformation rates (mg/kg dry soil/day) in the soil treated at concentrations of 0.10, 1.00, 10.0, 100 and 1000 mg hydroquinone/kg dry soil varied by +0.73%, -2.66%, 0.00%, -123.3%, and -139.2%, respectively, from the mean of the pooled control groups. The water control varied by -4.00% compared to the solvent control.
The nitrite results have not been reported as nitrite-N levels were all below the limit of detection of 0.5 mg/L. This is as expected in an aerobic soil system, however, due to the chemistry of the reaction that determines nitrate, it is incorrect to report the TON value as nitrate unless the absence of nitrite has been confirmed.

- Soil pH and Moisture Content
Soil pH values at Day 0 and Day 28 are given in Table 4. Hydroquinone at the rates tested showed a change in the soil pH values at the highest concentrations of 100 and 1000 mg hydroquinone./kg dry soil at both timepoints.

Soil moisture and dry matter was determined at the end of the 28 day exposure period and the treatments with hydroquinone showed slightly reduced moisture levels throughout, however, the soil moisture levels for the study were maintained at 42 % +/- 5 % of the MWHC of the soil (Table 5).

- Validity Criteria
All validity criteria for the study were met, as the variation in nitrate concentration in replicate water and solvent control samples ranged by -1.3% to +0.6% and -1.8% to +2.1 % respectively, at Day 28, which was no greater than +/-15 %.

CONCLUSIONS
Hydroquinone at 100 and 1000 mg hydroquinone/kg dry soil showed a significant inhibitory effect on soil nitrogen mineralisation compared to the control treatments in terms of both the amount of nitrate produced at the end of the 28 day test and the rate of nitrate production period (Dunnett’s two tail, p=0.05).

For the concentration on nitrate produced at day 28 , the EC10 , EC20 and EC50 were estimated at 19.5, 29.7 and 60.1 mg hydroquinone/kg dry soil, respectively. The NOEC was determined at 10.0 mg hydroquinone/kg dry soil and the LOEC at 100 mg hydroquinone/kg dry soil.

For the rate of nitrate production from 0 to 28 days , the EC10 , EC20 and EC50 were estimated at 17.6, 26.7 and 54.2 mg hydroquinone/kg dry soil, respectively. Again the NOEC and LOEC were determined as 10.0 mg and 100 mg hydroquinone/kg dry soil, repsectively.

At day 28 there was some ammonium present in the soil in the 100 mg hydroquinone/kg dry soil treatment. The accumulation of ammonium indicates that the process of nitrification (ammonium to nitrate) had been inhibited. The rate of nitrate production in this treatment and the 1000 mg hydroquinone/kg dry soil treatment at day 28 compared to the control treatments was greater than 25% which suggests there has been some long term effect on the soil microorganisms.

Reported statistics and error estimates:

The water and solvent controls were pooled before use in the hypothesis tests and point estimates, as there was no significant difference between the water and solvent controls for both data sets (concentration p=0.09, p=0.08). Differences between pooled controls and the treated soils were analysed using ANOVA and then Dunnett’s t-test followed by Linear Interpolation to estimate the ECx’s and confidence limits.

Table 1: Soil Nitrogen Concentrations: Day 0

LUCERNE AMENDED SOIL NITROGEN CONCENTRATIONS - Day 0 (Start)
Treatment Group	Replicate	Soil Ammonium mg/kg dry soil			Soil Nitrate mg/kg dry soil
Control (water)	1	3.05			77.85
	2	2.79			77.40
	3	2.92			78.76
Mean value		2.92			78.00
within treatment variation (%)		-4.55	to	4.55	-0.78	to	0.97
Acetone Control	1	2.72			77.62
	2	2.85			78.08
	3	2.79			77.85
Mean value		2.79			77.85
within treatment variation (%)		-2.38	to	2.38	-0.29	to	0.29
0.1	1	2.59			77.62
	2	2.65			76.71
	3	2.59			79.22
Mean value		2.61			77.85
within treatment variation (%)		-0.85	to	1.69	-1.46	to	1.75
1	1	2.65			80.13
	2	2.65			78.99
	3	2.59			78.76
Mean value		2.63			79.29
within treatment variation (%)		-1.68	to	0.84	-0.67	to	1.05
10	1	2.45			79.67
	2	2.52			80.36
	3	2.19			80.36
Mean value		2.39			80.13
within treatment variation (%)		-8.33	to	5.56	-0.57	to	0.28
100	1	2.39			78.99
	2	2.19			76.03
	3	2.92			82.18
Mean value		2.50			79.07
within treatment variation (%)		-12.39	to	16.81	-3.84	to	3.93
1000	1	3.65			81.72
	2	3.65			81.72
	3	3.72			83.09
Mean value		3.67			82.18
within treatment variation (%)		-0.60	to	1.20	-0.55	to	1.11

Table 2: Soil Nitrogen Concentrations: Day 28

Treatment Group	Replicate	Soil Ammonium mg/kg dry soil			Soil Nitrate             mg/kg dry soil
Control (water)	1	0.93			278.17
	2	0.80			283.63
	3	0.66			283.63
Mean value		0.80			281.81
within treatment variation (%)		-16.67	to	16.67	-1.29	to	0.65
Acetone Control	1	0.80			285.00
	2	0.80			289.10
	3	0.80			296.38
Mean value		0.80			290.16
within treatment variation (%)		0.00	to	0.00	-1.78	to	2.14
0.1	1	0.93			287.28
	2	0.80			287.28
	3	0.80			287.73
Mean value		0.84			287.43
within treatment variation (%)		-5.26	to	10.53	-0.05	to	0.11
1	1	0.93			280.90
	2	0.80			279.54
	3	0.80			285.00
Mean value		0.84			281.81
within treatment variation (%)		-5.26	to	10.53	-0.81	to	1.13
10	1	1.46			283.63
	2	0.93			289.55
	3	0.80			291.37
Mean value		1.06			288.19
within treatment variation (%)		-25.00	to	37.50	-1.58	to	1.11
100	1	24.81			34.60
	2	26.27			30.05
	3	26.94			26.86
Mean value		26.01			30.50
within treatment variation (%)		-4.59	to	3.57	-11.94	to	13.43
1000	1	1.33			0.91
	2	0.93			0.46
	3	1.06			0.46
Mean value		1.11			0.61
within treatment variation (%)		-16.00	to	20.00	-25.00	to	50.00

Table 3: Soil Nitrate Transformation Rates Day 0- 28

Treatment Concentrations	Replicate	Day 0-28 mg/kg/day
Control (water)	1	7.15
	2	7.37
	3	7.32
	mean	7.28
	% from acetone control	-4.00
Solvent Control (Acetone)	1	7.41
	2	7.54
	3	7.80
	mean	7.58
	% from control	n/a
0.10 mg/kg hydroquinone	1	7.49
	2	7.52
	3	7.45
	mean	7.48
	% from acetone control	-1.29
	% from pooled control	+0.73
1.00 mg/kg hydroquinone	1	7.17
	2	7.16
	3	7.37
	mean	7.23
	% from acetone control	-4.61
	% from pooled control	-2.66
10.0 mg/kg hydroquinone	1	7.28
	2	7.47
	3	7.54
	mean	7.43
	% from acetone control	-2.00
	% from pooled control	0.00
100 mg/kg hydroquinone	1	-1.59
	2	-1.64
	3	-1.98
	mean	-1.73
	% from acetone control	-122.9
	% from pooled control	-123.3
1000 mg/kg hydroquinone	1	-2.89
	2	-2.90
	3	-2.95
	mean	-2.91
	% from acetone control	-139.2
	% from pooled control	-138.4

Table 4: Soil pH (measured in water)

Treatment	Day 0^*	Day 28^*
Water control	6.7	6.5
Solvent control (Acetone)	6.7	6.5
0.10 mg hydroquinone/kg dry soil	6.7	6.7
1.00 mg hydroquinone/kg dry soil	6.8	6.6
10.0 mg hydroquinone/kg dry soil	6.8	6.6
100 mg hydroquinone/kg dry soil	7.0	7.2
1000 mg hydroquinone/kg dry soil	7.2	7.2

*Taken from bulk dosed soil on Day 0 and replicate 1 on Day 28.

Table 5: Soil Moisture Levels at Day 28

Treatment	Dry Matter %	Moisture %
Water control	87.9	12.1
Solvent control (Acetone)	87.9	12.1
0.10 mg hydroquinone/kg dry soil	88.0	12.0
1.00 mg hydroquinone/kg dry soil	88.2	11.8
10.0 mg hydroquinone/kg dry soil	88.3	11.7
100 mg hydroquinone/kg dry soil	88.1	11.9
1000 mg hydroquinone/kg dry soil	88.4	11.6

Targeted Moisture Level 42 % MWHC	Mean Dry Matter Day 28* (% w/w)	Mean Moisture Day 28* (% w/w)	Achieved % MWHC^b
Controls	87.9	12.1	41.7
All Treatments( inc.controls)	88.1	11.9	40.8

*Taken from the mean of replicate 1 vessel from each treatment.

^bMean moisture content divided by the MWHC of the soil (29.1 %), multiplied by 100.

Notes: Some values are calculated using un-rounded values.

Deviations from the Study Plan:

There were two deviations from the Study Plan.

There was a minor excursion from the study temperature limits of 18 to 22°C for a period between 3 to 4 hours on 15 and 16 April 2015 (Day 21) when the temperature reached a recorded maximum of 22.12°C.

In Section 9 of the Study Plan the results and the percentage effect were to be calculated from the solvent control and a dose response curve with estimates of ECx (% effect) values was be determined, if appropriate.

As there was no statistical difference between the water and solvent control treatments the statistical analysis of the data was undertaken using pooled controls rather than using the solvent control alone. This was conducted after consultation with the Sponsors and agreed as the use of pooled controls gives a stronger statistical model.

It was considered that there was no negative impact on the scientific integrity or validity of the study.

Validity criteria fulfilled:

yes

Conclusions:

The OECD TG 216 recommends to consider the quantity of nitrate formed to interpret the results for non-agrochemicals. The 28d EC10 and EC50 were estimated at 19.5 and 60.1 mg hydroquinone/kg dry soil, respectively. The NOECwas determined as 10.0 mg hydroquinone/kg dry soil.

Executive summary:

This study determined the effects of hydroquinone on the nitrogen transformation activity in a LUFA standard soil type 2.3, according to procedures described in OECD Guideline 216 (2000) and under GLP.

The soil used in the study had a sand content of 59.7%, a pH (measured in water) of 6.6, an organic carbon content of 0.67% w/w and a microbial biomass of 2.11 % of the total organic carbon (TOC).

A range finder assay was conducted across a concentration range of 0.01 µg hydroquinone /kg to 1000 µg hydroquinone/kg dry soil. Based on the result of the range finding assay, the concentrations used for the definitive test were as follows; 0.10, 1.00, 10.0, 100 and 1000 mg hydroquinone/kg dry soil. The test item was prepared in acetone and the test solutions dried down onto fine quartz sand. The soil was amended with powdered lucerne and the soil dosed with the treated sand. Each treatment group was replicated three times. The products of the process of mineralisation of organic nitrogen were extracted from the soil on Day 0 and then 28 after treatment and incubation at 20°C ± 2°C in the dark.

 

The solutions for extracted soil were analysed on Day 28 for nitrate, nitrite and ammonium nitrogen concentrations.

Hydroquinone at 100 and 1000 mg hydroquinone/kg dry soil showed a significant inhibitory effect on soil nitrogen mineralisation compared to the pooled control treatments in terms of both the amount of nitrate produced at the end of the 28 day test and the rate of nitrate production period (Dunnett’s two tail, p=0.05).

For the concentration on nitrate produced at day 28 , the EC10 and EC50 were estimated at 19.5 and 60.1 mg hydroquinone/kg dry soil, respectively. The NOEC was determined at 10.0 mg hydroquinone/kg dry soil and the LOEC at 100 mg hydroquinone/kg dry soil.

For the rate of nitrate production from 0 to 28 days , the EC10 and EC50 were estimated at 17.6 and 54.2 mg hydroquinone/kg dry soil, respectively. Again the NOEC and LOEC were determined as 10.0 mg and 100 mg hydroquinone/kg dry soil, respectively.

At day 28 there was some ammonium present in the soil in the 100 mg hydroquinone/kg dry soil treatment. The accumulation of ammonium indicates that the process of nitrification (ammonium to nitrate) had been inhibited. The rate of nitrate production in this treatment and the 1000 mg hydroquinone/kg dry soil treatment at day 28 compared to the control treatments was greater than 25% which suggests there has been some long term effect on the soil microorganisms.

 

All validity criteria for the study were met, as the variation in nitrate concentration in replicate water and solvent control samples ranged by -1.3 to +0.6 % and -1.8 to +2.1 % at Day 28, respectively, which was no greater than +/-15 % for either control.

Description of key information

A study performed according to the OECD TG 216 and under GLP is available. The OECD TG 216 recommends to consider the quantity of nitrate formed to interpret the results for non-agrochemicals. The 28d EC10 and EC50 were estimated at 19.5 and 60.1 mg hydroquinone/kg dry soil, respectively. The NOEC was determined as 10.0 mg hydroquinone/kg dry soil.

Key value for chemical safety assessment

Short-term EC50 for soil microorganisms:

60.1 mg/kg soil dw

Long-term EC10 or NOEC for soil microorganisms:

19.5 mg/kg soil dw

Additional information

One reliable key study is available for this endpoint. This study determined the effects of hydroquinone on the nitrogen transformation activity in a LUFA standard soil type 2.3, according to procedures described in OECD Guideline 216 (2000) and under GLP.

The soil used in the study had a sand content of 59.7%, a pH (measured in water) of 6.6, an organic carbon content of 0.67% w/w and a microbial biomass of 2.11 % of the total organic carbon (TOC).

A range finder assay was conducted across a concentration range of 0.01 µg hydroquinone /kg to 1000 µg hydroquinone/kg dry soil. Based on the result of the range finding assay, the concentrations used for the definitive test were as follows; 0.10, 1.00, 10.0, 100 and 1000 mg hydroquinone/kg dry soil. The test item was prepared in acetone and the test solutions dried down onto fine quartz sand. The soil was amended with powdered lucerne and the soil dosed with the treated sand. Each treatment group was replicated three times. The products of the process of mineralisation of organic nitrogen were extracted from the soil on Day 0 and then 28 after treatment and incubation at 20°C ± 2°C in the dark.

 

The solutions for extracted soil were analysed on Day 28 for nitrate, nitrite and ammonium nitrogen concentrations.

Hydroquinone at 100 and 1000 mg hydroquinone/kg dry soil showed a significant inhibitory effect on soil nitrogen mineralisation compared to the pooled control treatments in terms of both the amount of nitrate produced at the end of the 28 day test and the rate of nitrate production period (Dunnett’s two tail, p=0.05).

For the concentration on nitrate produced at day 28 , the EC10 and EC50 were estimated at 19.5 and 60.1 mg hydroquinone/kg dry soil, respectively. The NOEC was determined at 10.0 mg hydroquinone/kg dry soil and the LOEC at 100 mg hydroquinone/kg dry soil.

For the rate of nitrate production from 0 to 28 days , the EC10 and EC50 were estimated at 17.6 and 54.2 mg hydroquinone/kg dry soil, respectively. Again the NOEC and LOEC were determined as 10.0 mg and 100 mg hydroquinone/kg dry soil, respectively.

At day 28 there was some ammonium present in the soil in the 100 mg hydroquinone/kg dry soil treatment. The accumulation of ammonium indicates that the process of nitrification (ammonium to nitrate) had been inhibited. The rate of nitrate production in this treatment and the 1000 mg hydroquinone/kg dry soil treatment at day 28 compared to the control treatments was greater than 25% which suggests there has been some long term effect on the soil microorganisms.

 

All validity criteria for the study were met, as the variation in nitrate concentration in replicate water and solvent control samples ranged by -1.3 to +0.6 % and -1.8 to +2.1 % at Day 28, respectively, which was no greater than +/-15 % for either control.