3-mercaptopropionic acid

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-02-29 to 2008-04-01

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Alga, Growth Inhibition Test)

Qualifier:

according to guideline

Guideline:

EU Method C.3 (Algal Inhibition test)

GLP compliance:

yes (incl. QA statement)

Remarks:

Swiss Federal Office of Public Health, Consumer protection directorate, Notification Authority for Chemicals, 3003 Bern, Switzerland

Analytical monitoring:

yes

Details on sampling:

For measurement of the actual concentrations of the test item, duplicate samples were taken from the test media of all test concentrations at the start of the test (without algae) and at the end of the test (containing algae). At the same sampling times, duplicate samples were also taken from the control.

For sampling at the end of the test, the test medium of the treatment replicates was pooled. Immediately after sampling, all samples were buffered to pH 5 (for details see analytical phase report) in order to stabilize the latter during the storage period. Thereafter, all samples were stored deep-frozen (at about -20°C). In pre-experiments for investigation of the storage stability of the samples (non-GLP), the test item proved to be stable under these storage conditions.

Vehicle:

no

Details on test solutions:

The test medium of the highest nominal concentration of 100 mg/L was prepared by dissolving 100.7 mg of the test item completely in 1000 mL of test water using intense stirring for 15 minutes at room temperature. The test medium of the highest test concentration was diluted with test water to prepare the test media of the lower test concentrations. The test media were prepared just before the start of the test.

Test organisms (species):

Raphidocelis subcapitata (previous names: Pseudokirchneriella subcapitata, Selenastrum capricornutum)

Details on test organisms:

TEST ORGANISM
- Common name: Pseudokirchneriella subcapitata (Formerly Selenastrum capricornutum)
- Strain: 61.81 SAG
- Source (laboratory, culture collection): Collection of Algal Cultures, University of Goettingen, Germany
- Age of inoculum (at test initiation): inoculum culture was set up three days before the start of the test
- Method of cultivation: cultivation in RCC's laboratories under standardised conditions according to the test guidelines

ACCLIMATION
- Culturing media and conditions (same as test or not): same as test

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

72 h

Hardness:

calculated: 0.24 mmol/L (= 24 mg/L as CaCO3)

Test temperature:

22°C; for measured values see below ("remarks on results including tables and figures");
Water temperature of test media recorded daily.

pH:

for measured values see below ("remarks on results including tables and figures");
pH was measured in each treatment at the start and end of the test.

Dissolved oxygen:

not determined (not recommended by the algae guidelines)

Nominal and measured concentrations:

nominal (mg/L): 100, 46, 22, 10, 4.6, 2.2 , 0 (control)
initially measured (mg/L): 78, 30, 19, 8.0, 4,1, n.d., 0 (control)

Details on test conditions:

TEST SYSTEM
- Test vessel:
- Type (delete if not applicable): open
- Material, size, fill volume: glass, 50 mL, 15 mL
- Aeration: no
- Initial cells density: 10000 algal cells/mL
- Control end cells density: increase by a factor of 124 (over 72 h)
- No. of vessels per concentration (replicates): 3
- No. of vessels per control (replicates): 3
- No. of vessels per vehicle control (replicates): no vehicle control


GROWTH MEDIUM
- Standard medium used: yes


OTHER TEST CONDITIONS
- Photoperiod: 24 h/day
- Light intensity: approx. 6400 Lux (range: 5800-7000 Lux) (continuous illumination with fluorescent tubes (Philips TLD 36W/840))


EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
- Determination of cell concentrations: fluorimeter


TEST CONCENTRATIONS
- Spacing factor for test concentrations: 2.145

Reference substance (positive control):

yes

Remarks:

potassium dichromate (tested separately twice a year)

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

32.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: nomonal, recalculated based on mean recovery

Key result

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

21.3 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: recalculated based on mean recovery

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

17 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% confidence intervals: 6.0-21 mg/L

Duration:

72 h

Dose descriptor:

EC20

Effect conc.:

19 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% confidence intervals: 9.8-23 mg/L

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

26 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: 95% confidence intervals: 21-34 mg/L

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

4.1 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

LOEC

Effect conc.:

8 mg/L

Nominal / measured:

meas. (initial)

Conc. based on:

test mat.

Basis for effect:

growth rate

Details on results:

corresponding 72 hour EyC values (yield; also based on initial measured test item concentrations), in mg/L (values in brackets are the 95% confidence intervals):
EC10: 6.8 (0.00-12)
EC20: 9.0 (0.01-14)
EC50: 16 (2.5-30)
NOEC: 4.1
LOEC: 8.0

Results with reference substance (positive control):

The result of the latest positive control test performed in 2007 (RCC Study No. B67342) showed the sensitivity of the test system was within the historical range of the laboratory:  2007 test: 72-hr EC50 for growth rate = 1.20 mg/L Range of the 72-hr EC50 for growth rate from 2000 to 2007: 0.71 - 1.74 mg/L.

Reported statistics and error estimates:

The 72 h EC10, EC20 and EC50 values for the inhibition of average growth rate and yield and their 95% confidence intervals were calculated by Probit Analysis. For the determination of the LOEC and NOEC, average growth rate and yield at the test concentrations were compared to the control values by Dunnett's tests.

The test item could be shown to be instable at pH > 6.0 (pre-experiments, non-GLP). As the pH of all test concentrations (except 100 mg/L) was > 6.0 and additionally the algal growth causes an increasing pH, the degradation/modification (probably oxidation [6]) of the test item could not be avoided. However, pretests with the modified test item at pH 8 have shown also 100% inhibition of the algal growth. Thus, it can be assumed that the modified test item shows a similar toxicity as the parent compound at low pH. Therefore, the following biological results are based on the initial measured concentrations of the test item.

 

The measured concentrations of the test item in the freshly prepared test media of the nominal concentrations of 2.2 to 100 mg/L were between 65 and 90% of the nominal values, as shown below:

Nominal test conc.(mg/L)	Initial measured conc. test item
	(mg/L)	(% of nominal)
2.2	n.d.	-
4.6	4.1	90
10	8.0	80
22	19	88
46	30	65
100	78	78

 

After 72 hours test duration, the concentrations of the test item were determined to be below the LOQ (1.27 mg/L) at the nominal test concentrations of 4.6 to 46 mg/L. At the highest nominal test concentration of 100 mg/L, 45% of the nominal value was found at the end the test period.

 

The test item had a significant inhibitory effect on the growth of the algae (growth rate and yield) after the test period of 72 hours at the concentration of 8.0 mg/L (initially measured) and at all higher test concentrations (results of Dunnett's tests, one-sided,  = 0.05). Thus, this concentration was determined to be the 72-hour LOEC.

 

The 72-hour NOEC was determined to be 4.1 mg/L (initially measured), since up to and including this test concentration the growth rate and yield of the algae after 72 hours were not significantly lower than in the control.

 

The following biological results are based on the initial measured concentrations (mg/L) of the test item:

Parameter (0-72 hr)	Growth Rate	Yield
EC10 (95%CI)	17 (6.0-21)	6.8 (0.00-12)
EC20 (95%CI)	19 (9.8-23)	9.0 (0.01-14)
EC50 (95%CI)	26 (21-34)	16 (2.5-30)
NOEC	4.1	4.1
LOEC	8.0	8.0

 

Mean measured light intensity: approximately 6400 Lux (range of 5800 - 7000 Lux). At the start of the test, the pH measured in the treatments was between 5.4 and 8.4. At the end of the test, pH values of 6.2 to 9.3 were measured. The increase of the pH during the test was caused by the uptake of CO2 by the algae due to their growth. The water temperature during the test was 22 °C.

 

The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 100 mg/L and the algal cells in the control. The shape and size of the algal cells was obviously not affected by the test item up to at least this concentration.

 

No remarkable observations were made concerning the appearance of the test media. All test media were clear solutions throughout the test period.

 

All validity criteria for OECD TG 201 were met.

Validity criteria fulfilled:

yes

Conclusions:

The effect levels based on nominal concentrations are: ErC10 = 21.3 mg/L; ErC50 = 32.6 mg/L; NOEC = 4.6 mg/L

Executive summary:

The influence of the test item 3-Mercaptopropion ic acid on the growth of the freshwater green algal species Pseudokirchneriella subcapitata (formerly Selenastrum capricornutum) was investigated in a 72-hour static test according to the OECD Guideline 201 (2006) and the EU Commission Directive 92/69/EEC, C.3 (1992).
The nominal concentrations of the test item of 2.2, 4.6, 10, 22, 46 and 100 mg/L were tested in parallel with a control.
The measured concentrations of the test item in the freshly prep ared test media of the nominal concentrations of 2.2 to 100 mg/L were betw een 65 and 90% of the nominal values. After 72 hours test duration, the concentrations of the test item were determined to be below the LOQ (1.27 mg/L) at the nominal test concentrations of 4.6 to 46 mg/L. At the highest nominal test concentration of 100 mg/L, 45% of the nominal value was found at the end the test period.

The test item had a significant inhibitory effect on the growth of the algae (growth rate and yield) after the test period of 72 hours at the concentr ation of 8.0 mg/L (initially measured) and at all higher test concentrations. The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 100 mg/L and the algal cells in the control.

The results can be summarized as follows (on the basis of the initially measured concentrations of the test item): ErC10 = 17 (6.0-21) mg/L, EcR50 =26 (31-34) mg/L, NOErC = 4.1 mg/L.

Due to instability of the substance in aqueous media and since the transformation products are less toxic than the parent substances (no free –SH groups) regulatory endpoints calculated on the basis of nominal concentrations represent a realistic worst case approach.

The effect levels based on nominal concentrations are: ErC10 = 21.3 mg/L; ErC50 = 32.6 mg/L; NOEC = 4.6 mg/L

Description of key information

EC50 (72 h, growth rate) = 26 mg/L (Pseudokirchneriella subcapitata);
NOEC (72 h, growth rate) = 4.1 mg/L (Pseudokirchneriella subcapitata)

Key value for chemical safety assessment

EC50 for freshwater algae:

26 mg/L

EC10 or NOEC for freshwater algae:

4.1 mg/L

Additional information

The influence of the test item 3-Mercaptopropion ic acid on the growth of the freshwater green algal species Pseudokirchneriella subcapitata (formerly Selenastrum capricornutum) was investigated in a 72-hour static test according to the OECD Guideline 201 (2006) and the EU Commission Directive 92/69/EEC, C.3 (1992).
The nominal concentrations of the test item of 2.2, 4.6, 10, 22, 46 and 100 mg/L were tested in parallel with a control.
The measured concentrations of the test item in the freshly prep ared test media of the nominal concentrations of 2.2 to 100 mg/L were betw een 65 and 90% of the nominal values. After 72 hours test duration, the concentrations of the test item were determined to be below the LOQ (1.27 mg/L) at the nominal test concentrations of 4.6 to 46 mg/L. At the highest nominal test concentration of 100 mg/L, 45% of the nominal value was found at the end the test period.

The test item had a significant inhibitory effect on the growth of the algae (growth rate and yield) after the test period of 72 hours at the concentr ation of 8.0 mg/L (initially measured) and at all higher test concentrations. The microscopic examination of the algal cells at the end of the test showed no difference between the algae growing at the nominal test concentration of 100 mg/L and the algal cells in the control.

The results can be summarized as follows (on the basis of the initially measured concentrations of the test item): ErC10 = 17 (6.0-21) mg/L, EcR50 =26 (31-34) mg/L, NOErC = 4.1 mg/L.

Due to instability of the substance in aqueous media and since the transformation products are less toxic than the parent substances (no free –SH groups) regulatory endpoints calculated on the basis of nominal concentrations represent a realistic worst case approach.

The effect levels based on nominal concentrations are: ErC10 = 21.3 mg/L; ErC50 = 32.6 mg/L; NOEC = 4.6 mg/L