Dimethyl disulphide

Long-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

long-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: according to guideline and GLP requirements

Qualifier:

according to guideline

Guideline:

OECD Guideline 211 (Daphnia magna Reproduction Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

The concentrations of DMDS were measured in fresh test solutions collected from parent solutions on days 0, 6, 13, and 20 and corresponding spent test solutions which were collected after compositing replicate solutions by treatment on days 1, 7, 14, and 21. The working standard solutions used to prepare test solutions were sampled and analyzed along with each set of fresh test solutions on day 0, 6, 13, and 20 as well as with the spent solutions on day 1. Additional samples of the working standard solutions used to prepare the 0.0013, 0.0025, and 0.0050 mg/L test solutions were collected one day after the termination of the definitive test due to a dilution error during the preparation of the corresponding dosing solutions on day 20. A sample volume of approximate 10 mL was collected from the controls and each test substance treatment. Due to the instrument sensitivity limitations of the analytical method, samples were not diluted prior to being vialed for analysis by HPLC-UV.

Vehicle:

yes

Details on test solutions:

Primary standard solutions were prepared on 24 and 31 August and 07 September 2011. A 1.6 mg a.i./mL primary standard solution was prepared by transferring approximately 0.0160 g of the test substance (approximately 0.0160 g corrected for purity) to a 10-mL class A volumetric flask and bringing the flask to volume with DMF. Working standard solutions were prepared by serially diluting the 1.6 mg a.i./mL solution to a volume of 10-mL with DMF to concentrations of 0.052, 0.10, 0.20, 0.40, and 0.80 mg a.i./mL. Test solutions were prepared by diluting 0.050-mL volumes of the appropriate working standard to a volume of 2.0 L with dilution water, which resulted in nominal solution test concentrations of 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.i./L. The vehicle control was prepared by diluting 0.050 mL of DMF to a volume of 2.0 L with dilution water. The concentration of DMF in the vehicle control and the treated test solutions was 0.025 mL DMF/L. The control solution consisted only of dilution water.

Test organisms (species):

Daphnia magna

Details on test organisms:

Source: In-house culture

Culture: All daphnids were cultured at approximately 20°C during the holding period, fed a suspension of the algal species Pseudokirchneriella subcapitata at least once a day supplemented by a prepared artificial diet consisting of a wheat grass, salmon starter, and yeast suspension. Approximately one day prior to neonate selection, the adult daphnids were isolated by transferring the adults to a fresh culture with a water/food suspension. The adults were considered acceptable with no signs of stress, disease or physical damage. No adult mortality occurred during the 48-hour period immediately prior to production of neonates used in test initiation.

Acclimation: Since the culturing and testing environmental parameters were equivalent (i.e., temperature, dilution water, and lighting), no acclimation period was necessary.

Feeding: The daphnids were fed daily a diet consisting of 1.0 mL of a 3.0 x 107 cells/mL concentrated algal suspension (Pseudokirchneriella subcapitata, formerly Selenastrum capricornutum) and 0.5 mL of a 1.08 g/L or 1.71 g/L YTC daphnid feed mixture.

Age of Test Organisms at start of the Test: <24 h

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

21 d

Hardness:

142-146 mg CaCO3/L

Test temperature:

20.0 - 20.9

pH:

8.1 - 8.5

Dissolved oxygen:

7.0 - 8.7

Salinity:

not relevant

Nominal and measured concentrations:

Nominal concentrations: 0 (control), 0 (vehicle control), 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.s./L
The data are based on nominal DMDS concentrations since the test concentrations were outside the range of the analytical method, with the exception of the top test concentration of 0.020 mg/L DMDS.

Details on test conditions:

The test vessels were 125 mL glass jars sealed with PTFE lined screw on lids. The jars for each test were filled with the appropriate volume of control, vehicle control, or test substance solution so as to minimize headspace within the sealed vessel. The test chambers were maintained at 20 ± 1°C in a temperature-controlled water bath. Fluorescent lighting was maintained on a 16-hour daylight photoperiod with two 30 minute simulated dawn and dusk periods. The light intensity during the definitive test was 561 lux as measured on Day 0.

Observations were made daily on the number of surviving adult daphnids, occurrence of abnormalities, and production of neonates. Immobile daphnids, defined as those organisms not able to swim within 15 seconds after gentle agitation of the test vessel or gentle disturbance of the individual, were discarded; therefore, immobility was synonymous with mortality.

Each day, the adult daphnids (i.e., parental generation) were transferred to clean test chambers containing freshly prepared test solutions. After the release of broods by the adult daphnids, only the adult daphnids were transferred to fresh test solutions. The neonates produced between each renewal and at termination were counted and discarded.

At test termination, the length (head to base of spine) of each surviving adult was measured. Mean adult dry weight for the controls and each test substance treatment was determined after combining the surviving adult daphnids by treatment and drying the samples at approximately 60°C for approximately 48 hours.

Reference substance (positive control):

no

Duration:

21 d

Dose descriptor:

NOEC

Effect conc.:

0.003 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

21 d

Dose descriptor:

LOEC

Effect conc.:

0.005 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Details on results:

In order to estimate more reliable NOEC and LOEC concentration for reproduction, the reproduction of all first generation daphnids that were observed as immobile during the 21 day exposure was eliminated from the statistical evaluations. The total numbers of live young produced by surviving first generation daphnids after a 21-day exposure were 1,798, 1,771, 1,602, 1,395, 1,539, 1,435, and 1,201 in the 0 (control), 0 (vehicle control), 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.i./L treatments, respectively. The total numbers of live young produced per surviving first generation daphnids were 180, 177, 178, 174, 154, 159, and 150 in the 0 (control), 0 (vehicle control), 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.i./L treatments, respectively. Based on the total numbers of live young produced per surviving first generation daphnids, the 21-day NOEC and LOEC were 0.0025 and 0.0050 mg a.i./L, respectively. The MATC for reproduction was 0.035 mg a.i./L.
Mean day of first brood release were 8, 8, 8, 8, 8, 10, and 8 in the 0 (control), 0 (vehicle control), 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.i./L treatments, respectively. There was a significant increase in days to first brood release in the 0.010 mg a.i./L treatment compared to the control. However, this statistically significant difference was not considered to be a concentration dependent response in terms of the determination of the NOEC and LOEC values as the 0.020 mg a.i./L treatment was determined not to be significant. Based on days to first brood, the 21-day NOEC and LOEC values were 0.020 and >0.020 mg a.i./L, respectively.
Individual lengths (helmet-to-spine) of all surviving daphnids at day 21 was measured. Mean length of the daphnids were 4.6, 4.6, 4.5, 4.4, 4.4, 4.4, and 4.2 mm for the 0 (control), 0 (vehicle control), 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.i./L treatments, respectively. Based on length, the 21-day NOEC and LOEC were 0.010 and 0.020 mg a.i./L, respectively. The MATC for individual lengths was 0.014 mg a.i./L.
Mean dry weights of the daphnids were 1.05, 0.98, 1.02, 0.89, 1.00, 1.07, and 0.91 mg for the 0 (control), 0 (vehicle control), 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.i./L, treatments, respectively. Because the dry weight determinations were made by treatment, the lack of replication makes a statistical evaluation of the data unreliable and no statistical evaluation was performed. However, no concentration dependent response is apparent in the data.

Validity criteria fulfilled:

yes

Conclusions:

The test acceptability criteria were met for this study. The mortality of the parent animals in the control did not exceed 20% at the end of the test. The mean number of live young produced per surviving adult daphnid at the end of the test was =60. This study is classified as acceptable and satisfies the guideline requirement for a reproduction test with Daphnia magna. Total young per surviving adult was the most sensitive biological parameter.
Results based on nominal concentrations of dimethyl disulfide (DMDS):
Biological Parameter NOEC (mg a.i./L) LOEC (mg a.i./L) EC50 as mg a.i./L (95% confidence limits) MATC
Adult Survival 0.020 >0.020 >0.020 NA
Days to 1st Brood 0.020 >0.020 NA NA
Reproduction (a) 0.0025 0.0050 NA 0.0035
Adult Length 0.010 0.020 NA 0.014
(a) Reproduction expressed as total young per surviving adult daphnid.

Executive summary:

A freshwater 21 day static-renewal chronic toxicity test withDaphnia magnawas performed according to US EPA 850.1300 (1996) and OECD Guideline 211 to assess the toxicity of DMDS at nominal test concentrations of 0 (control), 0 (solvent control), 0.0013, 0.0025, 0.0050, 0.010, and 0.020 mg a.s./L (concentrations selected on the basis of the results of a range finding test). The definitive test was conducted for 21 days commencing when daphnids (<24 hours old at the start of the test) were added to the test chambers. 10 replicates (1 daphnid per test container) were included and the daphnids were fed daily. Each day the parental generation daphnids were transferred to clean test chambers containing freshly prepared test solutions. Observations were made daily on the number of surviving adult daphnids, occurrence of abnormalities, and production of neonates. The neonates produced between each renewal and at termination were counted and discarded. At test termination, the length of each surviving adult was measured and the mean adult dry weight for the controls and each test substance treatment was determined after combining the surviving adult daphnids by treatment. Water quality measurements and water temperature were monitored throughout the test. Statistical analysis was performed to assess the effects of DMDS on adult survival, reproduction and adult length.

 

There was no significant reduction in survival in any test treatment as compared to the dilution water control survival. Based on survival, the 21-day NOEC and LOEC were 0.020 and >0.020 mg a.s./L, respectively. The 21-day EC₅₀based on immobilization of the first generation daphnids is estimated to be >0.020 mg a.s./L, the highest test substance treatment. Based on the total numbers of live young produced per surviving first generation daphnids, the 21-day NOEC and LOEC were 0.0025 and 0.0050 mg a.s./L, respectively. The MATC for reproduction was 0.035 mg a.s./L. Based on length, the 21-day NOEC and LOEC were 0.010 and 0.020 mg a.s./L, respectively. The MATC for individual lengths was 0.014 mg a.s./L. Since the dry weight determinations were made by treatment, the lack of replication makes a statistical evaluation of the data unreliable and no statistical evaluation was performed. However, no concentration dependent response is apparent in the data.The results are based on nominal concentrations of DMDS since the test concentrations were outside the range of the analytical method, with the exception of the top test concentration.

Description of key information

Effect on reproduction of Daphnia magna has been examined (OCDE 211). The NOEC was calculated to be 0.0025 mg/L.

For marine water invertebrates, a life-cycle test on Americamysis bahia (OPPTS 850.1350) provided a NOEC = 0.464 mg/L

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Dose descriptor:

NOEC

Effect concentration:

0.003 mg/L

Marine water invertebrates

Marine water invertebrates

Dose descriptor:

NOEC

Effect concentration:

0.464 mg/L

Additional information

The half-life of DMDS was calculated to be 4.2 hours in fresh water, and 4.3 hours in sea water. DMDS is a volatile compound which is not expected to remain in the water column when released in the environment. Long term exposure of aquatic organisms to DMDS is therefore not expected. In spite of this, effect on reproduction of Daphnia magna has been examined (OCDE 211). The NOEC was calculated to be 0.0025 mg/L. For marine water invertebrates, a life-cycle test on Americamysis bahia was carried out according to OPPTS 850.1350: the most sensitive endpoint was a NOEC = 0.464 mg/L for the mean number of young per surviving female.