Hydroxylammonium chloride

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

20 - 21 Apr. 2017

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 209 (Activated Sludge, Respiration Inhibition Test

Version / remarks:

2010

GLP compliance:

yes (incl. QA statement)

Remarks:

Department of health of the government of the United Kingdom

Analytical monitoring:

no

Vehicle:

no

Test organisms (species):

activated sludge of a predominantly domestic sewage

Details on inoculum:

- Name and location of sewage treatment plant where inoculum was collected: sludge return line at Burley Menston sewage treatment works (West Yorkshire, UK)
- Pretreatment: transported in a closed container with an adequate headspace. On arrival at the test facility, the sludge was aerated. The suspended solids concentration was determined gravimetrically following homogenisation and adjusted using dechlorinated tap water to 3 g/L (± 0.3 g/L). The sludge was maintained at 20 ± 2°C with aeration. During storage it was maintained at 20 ± 2°C and fed with synthetic sewage concentrate at a rate of 50 mL/L.
- Initial inoculum concentration: 3 g/L (determined before the test)

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

3 h

Test temperature:

20 ± 2°C

pH:

7.00 - 7.81

Nominal and measured concentrations:

Nominal: 30, 72, 180, 400 and 1000 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: glass conical flasks
- Fill volume: 250 mL
- Aeration: yes, 3 h
- No. of vessels per concentration (replicates): 6
- No. of vessels per control (replicates): 6
- Synthetic sewage concentration: 32 mL/L
- Inoculum: 500 mL/L
- Suspended solids concentration: 1.5 g/L
- Nitrification inhibitor used: 11.6 mg/L N-allylthiourea (ATU) added to appropriate test and reference vessels

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: dechlorinated tap water

OTHER TEST CONDITIONS
- Adjustment of pH: yes with 2M NaOH
- Details on termination of incubation: at the end of the 3 h incubation period, 20 mL of each vessel was transferred to a sample tube containing a stirrer. For those samples requiring amendment with ATU, this was undertaken at least 10 min prior to oxygen consumption measurement. The dissolved oxygen electrode was sealed in the neck of the flask, ensuring air was completely excluded. Oxygen consumption was measured over a period of up to 10 min. Respiration rates (mg O2/L/h) were determined by measuring the gradient of the linear portion of the graph. Measurements at high (> 7.0 mg/L) or low (< 2.0 mg/L) dissolved oxygen levels were avoided, where possible.

EFFECT PARAMETERS MEASURED: inhibition of total, heterotrophic and nitrification respiration

TEST CONCENTRATIONS
- Range finding study: yes
- Test concentrations: 1, 10, 100 and 1000 mg/L
- Results used to determine the conditions for the definitive study: range-finder test showed inhibition of total, nitrification and heterotrophic respiration at 100 and 1000 mg/L (61% to 67% for total, nitrification and heterotrophic respiration). Based on these data, the definitive test was conducted at test substance concentrations of 30, 72, 180, 400 and 1000 mg/L.

Reference substance (positive control):

yes

Remarks:

3,5-dichlorophenol

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

1.7 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

2.9 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of nitrification rate

Duration:

3 h

Dose descriptor:

EC10

Effect conc.:

1.5 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of heterotrophic respiration

Results with reference substance (positive control):

- Results with reference substance valid? yes
- Relevant effect levels: EC50 (total respiration) = 10.4 mg/L, EC50 (nitrification respiration) = 4.7 mg/L
- Blank control total respiration rate: 55 mg/L/h (coefficient of variation of the blank control respiration rates was ≤ 30%)

VALIDITY CRITERIA

Table 1: Validity criteria

Criterion from the guideline	Outcome	Validity criterion fulfilled
The blank controls (without the test substance or reference substance) oxygen uptake rate should not be less than 20 mg oxygen per one gram of activated sludge (dry weight of suspended solids) in an hour.	The blank control respiration rate was ≥ 20 mg/g/h	yes
The coefficient of variation of oxygen uptake rate in control replicates should not be more than 30% at the end of definitive test.	The coefficient of variation of the blank control respiration rates were ≤ 30%	yes

BIOLOGICAL DATA

Table 2: Further effect concentrations

	3 h effect concentrations in mg/L
	Total Respiration	Heterotrophic	Nitrification
LOEC	30	30	30
EC20	6.5	5.1	15
EC40	36	33	40
EC50	49	53	48

Table 3: Inhibition Data

Test Substance Nominal Concentration mg/L	Total Respiration Inhibition (%)	Heterotrophic Respiration Inhibition (%)	Nitrification Respiration Inhibition (%)
Control	n.a.	n.a.	n.a.
30	34	39	25
72	62	57	71
180	79	77	82
400	75	81	67
1000	80	86	71

Validity criteria fulfilled:

yes

Remarks:

For further details please refer to “Any other information on results incl. tables”.

Description of key information

EC10 (3 h) = 1.7 mg/L (nominal, OECD 209)

Key value for chemical safety assessment

EC10 or NOEC for microorganisms:

1.7 mg/L

Additional information

One study testing the toxicity of hydroxylammonium chloride (CAS 5470-11-1) to microorganisms is available. The test was conducted according to the OECD guideline 209 and GLP. Activated sludge of a predominantly domestic sewage plant was exposed to 30, 72, 180, 400 and 1000 mg test item/L (nominal) in a static, aerobic, freshwater test system for 3 h. The inhibition of total, heterotrophic and nitrification rate by the test item was followed. The test resulted in a 3 h EC10 (total respiration rate inhibition) of 1.7 mg/L (nominal).