Methylthiouracil

Toxicity to aquatic algae and cyanobacteria

Administrative data

Endpoint:

toxicity to aquatic algae and cyanobacteria

Type of information:

experimental study

Adequacy of study:

key study

Study period:

01/02/2018 - 23/07/2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2018

Report date:

2018

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 201 (Freshwater Alga and Cyanobacteria, Growth Inhibition Test)

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Methylthiouracil

EC Number:

200-252-3

EC Name:

Methylthiouracil

Cas Number:

56-04-2

Molecular formula:

C5H6N2OS

IUPAC Name:

methylthiouracil

Test material form:

solid: crystalline

Specific details on test material used for the study:

Batch manufactured and supplied by : Korde Chemicals Pvt Ltd.
W-13, TTC Pawane MIDC, Navi Mumbai 400705 INDIA

Test item : 6-METHYL-2-THIOURACIL

CAS No. : 56-04-2

Chemical name (IUPAC) : 6-METHYL-2-SULFANYLIDENE-1H-PYRIMIDIN-4-ONE

Physical appearance : White powder

Purity as per CoA : 98.46%

Batch No. : 151117

pH 0.1 % : 6.20

Manufactured date : 15 November 2017

Expiry date : 14 November 2019

Recommended storage condition : Ambient (+15 to +25°C)

Sampling and analysis

Analytical monitoring:

not specified

Test solutions

Vehicle:

yes

Details on test solutions:

Test medium was algal medium as described in the OECD test guideline 201 (OECD, 2006) and the preparation details are given in Appendix 5.

Chemical Batch No. Manufacturer
MgCl2. 6H2O MF6M 561553 Merck Specialities Private Limited, Mumbai, India
ZnCl2 B0755316248
CaCl2. 2H2O D14A/1314/0804/31 s.d. fine chem. Limited
Mumbai, India
NH4Cl D14A/2314/2103/31
MgSO4. 7H2O H14A/1813/1707/31
Na2EDTA. 2H2O J08W/2908/2209/31
MnCl2. 4H2O E13A/1613/1204/13
CoCl2. 6H2O H09Z/1709/2203/31
CuCl2. 2H2O G09Z/2109/0106/31
Na2MoO4. 2H2O L15A/3315/0912/31
H3BO3 A16A/1115/0705/31
NaHCO3 D14A/1414/0702/31

Chemical Batch No. Manufacturer
KH2PO4 0000136538 Himedia Laboratories Private Limited, Mumbai, India
FeCl3. 6H2O 161215 Central Drug House (P) Limited, New Delhi, India

Test organisms

Test organisms (species):

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

Details on test organisms:

Pseudokirchneriella subcapitata ATCC 22662

This algal species was used as the test system as it is a recommended algal species in the guideline.
6.1.2.1 Source
American Type Culture Collection
P.O. Box 1549
Manassas, VA 20108
USA
6.1.2.2 Culture Maintenance
Algal cells were maintained at the test facility through sub-culturing once in 5 to 10 days from the continuous culture into fresh medium in a conical flask. These conical flasks were incubated between 21 and 25°C (±2°C) under a continuous illumination of 8000±1600 Lux.

Study design

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

72 h

Test conditions

Hardness:

not specified

Test temperature:

22.3

pH:

7.79-7.84

Dissolved oxygen:

not specified

Salinity:

not specified

Conductivity:

not specififed

Nominal and measured concentrations:

0.2, 0.64, 2.05, 6.56, 20.0 and 64.0 mg/L

Reference substance (positive control):

yes

Results and discussion

Effect concentrations

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

1.834 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The EC values calculated for growth rate and yield on the basis of the nominal concentration of the test item are presented below:

At 72 hours EC values (mg/L)
ErC50 8.187
ErC20 2.3767
ErC10 1.245
EyC50 1.834
EyC20 0.4968
EyC10 0.2509

Note: ErC refers to growth rate and EyC refers to yield.

Executive summary:

The effect of6-Methyl-2-Thiouracilwas tested on the growth of freshwater single cell green algaPseudokirchneriella subcapitata.

 

Range finding test was carried out to select the test concentrations for the definitive test. In the range finding test, the tested concentration was 0.001, 0.01, 0.1, 1, 10 and 100 mg/L with single replicate. The test item exhibited 0, 2.19, 1.82, 27.74, 82.48 and 100.0 % reduction in cell biomass at the tested concentrations of 0.001, 0.01, 0.1, 1, 10 and 100 mg/L at 72 h.

 

The alga was exposed to the test item at the nominal concentrations of 0.2, 0.64, 2.05, 6.56, 20.0 and 64.0 mg/L (factor of about 3.2) along with a negative control and a reference substance (Potassium dichromate) at 0.9 mg/L. The cell growth was measured at 24, 48 and 72 hours after the initiation of the test.

 

The concentration/effect relationship was determined using two factors namely growth rate and yield at the end of the test (72 hours). The per cent inhibition of growth rate was 3.37, 5.91, 13.86, 35.63, 73.02 and 100 % and the percent yield inhibition was 13.63, 22.68, 45.36, 79.32, 96.94 and 100 % at the nominal concentrations of 0.2, 0.64, 2.05, 6.56, 20.0 and 64.0 mg/L, respectively, when compared to the negative control. There was 20.78 % and 59.69 % inhibition of average growth rate and yield of alga, respectively, in the reference substance group at
0.9 mg/L. Observed cells were found morphologically normal.

 

The EC values calculated for growth rate and yield on the basis of the nominal concentration of the test item are presented below:

 

At 72 hours	EC values (mg/L)
ErC50	8.187
ErC20	2.3767
ErC10	1.245
EyC50	1.834
EyC20	0.4968
EyC10	0.2509

 

Note: E_rCrefers to growth rate and E_yC refers to yield.