Phosphorodithioic acid, mixed O,O-bis(iso-Bu and pentyl) esters, zinc salts

Short-term toxicity to aquatic invertebrates

Administrative data

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

16 August 2004 - 10 March 2005

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Guideline study. Restriction due to lack of analytical monitoring of test material concentration (nominal concentration used)

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2005

Report date:

2005

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts

EC Number:

283-392-8

EC Name:

Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts

Cas Number:

84605-29-8

IUPAC Name:

Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
PHYSICO-CHEMICAL PROPERTIES
- Melting point: liquid at room temperature
- Boiling point: decomposes before boiling
- Vapour pressure: 0.0069 Pa at 25 deg. C
- Henry's law constant (for volatie substances): no data
- Water solubility (under test conditions): 2736 ppm at 22 deg. C
- Solubility in organic solvents: no data
- log Pow: 0.56
- pKa: no data
- Base or acid catalysis of test material: no data
- UV absorption: no data
- Stability of test material at room temperature: stable
- pH dependance on stability: hydrolytically stable at pH 4 and 7 for 5 days at 50 deg. C (OECD 111, Tier 1 preliminary study)

OTHER PROPERTIES (if relevant for this endpoint)
- Toxicity to microorganisms: EC50 > 10,000 mg/L (OECD 209)
-Biodegradability: 1.5% in 28 d (OECD 301B)

Sampling and analysis

Analytical monitoring:

no

Details on sampling:

- Concentrations: 10, 18, 32, 56, and 100 mg/L loading rate WAF

Test solutions

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: Due to the low aqueous solubility and complex nature of the test material for the purpose of the definitive test the test material was prepared as a Water Accommodated Fraction. Amounts of test material were each separately added via syringe to the surface of 2.5 liters of reconstituted water to give the 10, 18, 32, 56 and 100 mg/L loading rates. After the addition of the test material, the reconstituted water was stirred by magnetic stirrer using a stirring rate such that a vortex was formed to give a slight dimple at the water surface. These were stirred for 24 hours. The stirring was stopped and the mixtures allowed to stand for 1 hour. The aqueous phase or WAF was removed by mid depth siphoning. Microscopic inspection of the WAFs showed no microdispersions or undissolved test material to be present.

- Differential loading: Preparation of test solutions with individually prepared loading rates
- Controls: Untreated negative control

- Concentration of vehicle in test medium (stock solution and final test solution): Not applicable.
- Evidence of undissolved material (e.g. precipitate, surface film, etc): After siphoning and for the duration of the test the 10, 18, 32, 56, and 100 mg/L loading rates were observed to be clear colorless solutions. Microscopic inspection of the WAFs showed no microdispersions or undissolved test material to be present.

Test organisms

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM
- Common name: Water Flea

- Source: In house laboratory cultures with a known history
- Age at study initiation (mean and range, SD): less than 24 h old
- Weight at study initiation (mean and range, SD): no data available.

- Length at study initiation (length definition, mean, range and SD): no data available.
- Valve height at study initiation, for shell deposition study (mean and range, SD): no data available.
- Peripheral shell growth removed prior to test initiation: no data available.
- Method of breeding: parthenogenises
- Feeding during test : The daphnids received no food during exposure
- Food type: Not applicable.
- Amount: Not applicable.
- Frequency: Not applicable.

ACCLIMATION
- Acclimation conditions (same as test or not): Not applicable.
- Type and amount of food: Each culture was fed daily with a suspension of freshwater algae
- Feeding frequency: daily
- Health during acclimation (any mortality observed): Culture conditions ensured that reproduction was by parthenogenesis. The diet and diluent water are considered not to contain any contaminant that would affect the integrity or outcome of the study.

QUARANTINE (wild caught)
- Duration: Not applicable.
- Health/mortality: Not applicable.

Study design

Test type:

static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Post exposure observation period:

Any immobilization or adverse reactions to exposure were recorded at 24 and 48 hours after the start of exposure. The criterion of effect used was that Daphnia were considered to be immobilized if they were unable to swim for 15 seconds after gentle agitation.

Test conditions

Hardness:

The reconstituted water had an approximate theoretical total hardness of 250 mg/L as CaCO3

Test temperature:

20.6ºC to 21.2ºC

pH:

pH values ranged from 7.6 to 8.0 in controls and all test concentrations at the beginning of the test and ranged from 7.8 to 8.0 at the end of the 48 duration.

Dissolved oxygen:

There were no treatment related differences in oxygen concentration (range from 8.7 to 8.9 at start of test and 8.4 to 8.6 at end of test)

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal loading rates of 10, 18, 32, 56, and 100 mg/L

Details on test conditions:

TEST SYSTEM
- Test vessel: 250 mLglass jars containing approximately 200 mL of test solution
- Type (delete if not applicable): glass jars covered with aluminum foil to reduce evaporation
- Aeration: No
- Type of flow-through (e.g. peristaltic or proportional diluter): Not applicable.
- Renewal rate of test solution (frequency/flow rate): static.

- No. of organisms per vessel: ten first instar daphnids per vessel
- No. of vessels per concentration (replicates): 2 vessels
- No. of vessels per control (replicates): 2 vessels
- No. of vessels per vehicle control (replicates): Not applicable.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: reconstituted water used for both the range finding and definitive tests was the same as that used to maintain the stock animals. All chemicals were of analytical grade (CaCl2.2H2O; MgSO4.7H2O; NaHCO3; KCl) and deionised water was used to prepare the reconstituted water.

- Total organic carbon: NDA
- Particulate matter: NDA
- Metals: NDA
- Pesticides: NDA
- Chlorine: NDA
- Alkalinity: NDA
- Ca/mg ratio: NDA
- Conductivity: NDA
- Culture medium different from test medium: No difference
- Intervals of water quality measurement: N/A

OTHER TEST CONDITIONS
- Adjustment of pH: NA
- Photoperiod: 16 hours light and 8 hours darkness cycle with 20 minute dawn and dusk transition periods
- Light intensity: NDA

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
At 24 hours and 48 hours, the criterion of effect used was that Daphnia were considered to be immobilised if they were unable to swim within approximately 15 seconds after gentle agitation of the test vessel.

TEST CONCENTRATIONS
- Justification for using less concentrations than requested by guideline: NA
- Range finding study. The loading rates to be used in the definitive test were determined by a preliminary range finding test. In the range finding test Daphnia magna were exposed to a series of nominal loading rates of 1.0, 10, and 100 mg/L. The test material was prepared as a WAF. Ten daphnids were placed in each test and control vessel and maintained in a temperature controlled room at approximately 21 degrees C.
- Results used to determine the conditions for the definitive study: No immobilization was observed at the 1 and 10 mg/L loading rate WAFs. However immobilization was observed at the 100 mg/L loading rate WAF. Based on this information loading rates of 10, 18, 32, 56 and 100 mg/L using a stirring period of 24 hours followed by a one hour standing period were selected for the definitive test.

Reference substance (positive control):

no

Results and discussion

Effect concentrations

Effect concentrations 1

Duration:

48 h

Dose descriptor:

EL50

Effect conc.:

23 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: 20 - 25 mg/L

Effect concentrations 2

Duration:

48 h

Dose descriptor:

NOELR

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Effect concentrations 3

Duration:

24 h

Dose descriptor:

NOELR

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mobility

Results with reference substance (positive control):

n/a

Reported statistics and error estimates:

Analysis of the immobilization data was by the probit method at 24 hours and the trimmed spearman karber method at 48 hours based on the nominal loading rates.

Any other information on results incl. tables

Results based on read across and Justification for read across:

Table 1. Cumulative Immobilisation Data in the Definitive Test (EC 283 -392 -2)

Nominal Loading Rate (mg/L)	Cumulative Immobilised Daphnia (10 per replicate)
	24 hours				48 hours
	R1	R2	Total	%	R1	R2	Total	%
Control	0	0	0	0	0	0	0	0
10	0	0	0	0	0	0	0	0
18	1	0	1	5	2	1	3	15
32	2	4	6	30	10	10	20	100
56	2	5	7	35	10	9	19	95
100	5	5	10	50	10	10	20	100

Justification for Read Across from Analogue EC 283-392-8 

 

Common Manufacturing Process: The test substance (EC 270-608-0) and the analogue (EC 283-392-8) are produced under a common manufacturing process in which a phosphorodithioic acid ester intermediate, (RO)₂PS₂H, is produced by the reaction of phosphorus pentasulfide with a mixture of two alcohols of a similar class - branched alcohols containing C4 and C5 carbons (test substance) and C3 and C6 carbons (analogue ). The intermediate is neutralized with zinc oxide to produce the final multicomponent substance.The reaction is performed in the presence of a highly refined base oil which accounts for 8 – 10 % of the final products. 

 

Impurities: The level of impurities in the submission substance and the analogue is minimal (0.09 % wt and < 0.15% wt, respectively). Impurities have been identified as residual, unreacted alcohols from the production of the phosphorodithioic acid ester intermediates (isobutyl alcohol and pentyl alcohol isomers in the submission substance and isopropyl and 1,3-dimethylbutyl alcohols in the analogue).

 

Same Chemical Category: The submission substance (EC 270-608-0) and the analogue (EC 283-392-8), generically referred to as ZDDPs, have been shown to have sufficient structural similarities to be included in the Zinc Dialkydithiophosphate Category (ZDDPs) in the United States Environmental Protection Agency High Production Volume (HPV) Chemical Challenge Program.

 

Structural Similarity: The primary feature accounting for the similarity of the test substance (EC 270-608-0) and the analogue (EC 283-392-8) is the common organometallic core structure consisting of a central zinc metal bonded to four alkyldithiophosphate esters (ligands) by coordinate covalent bonds -Zn[(S₂P(OR)₂]_2. Structural variations between the test substance and the analogue are related to the alkyl (R) groups of the alkyldithiophosphate ligands.

 

Both substances contain a distribution of several different zinc dialkyldithiophosphates (ZDDPs).  The type and distribution of the zinc dialkyldithiophosphates is determined by the alcohol mixture and charge ratios of the alcohols used in the manufacturing process.

 

The test substance (EC 270-608-0) is a mixture of ZDDPs containing all isobutyldithiophosphate ligands, all pentyldithiophosphate ligands, and components containing both isobutyldithiophosphate and isomeric pentyldithiophosphate ligands resulting in a multicomponent substance with a molecular weight range of 548 – 604 (for monomers).            

 

The analogue (EC 283-392-8) is a multicomponent mixture of ZDDPs containing all isobutyl dithiophosphate ligands, all pentyl dithiophosphates ligands and ZDDPs containing both isobutyl and isomeric pentyl dithiophosphates with a molecular weight range of 492 – 660 (for monomer).

 

Tanimoto Fingerprint (ToxMatch Version 1.06 software) gives a similarity index greater than 0.8 (values range from 0, no similarity to 1, identical). Peer reviewed literature indicates that values greater than 0.6 are significantly similar. DSSTox similarity was 80% between the submission substance and the analogue.

Similarity of Physicochemical Properties: In addition to the structural similarities, similar physicochemical properties further support the justification for read across from the analogue. Both the test substance and analogue have similar physical states, densities and the same order of magnitude of vapour pressures and partition coefficients (logPow). Both were shown to be hydrolytically stable at pH 4, 7 and 9 in an OECD 111 preliminary hydrolysis study.

 

In evaluating the evidence for read across, significant consideration was given to water solubility. Water solubility studies conducted on the test substance and the analogue show the lower molecular weight ZDDP monomers are preferrentially dissolved in water with solubility decreasing with increasing alkyl chain lengths (molecular weights) of the alkyldithiophosphate ligands.  In this respect, the water soluble composition of the test substance (EC 270-608-0) and the analogue (EC 283-392-8) are considered to be sufficiently close to reasonably expect a similar mode of action and toxicological effects in aquatic toxicity studies. The slightly lower molecular weight of the water solubles in the analogue would represent the “worst case” with respect to bioavailability and potential for toxicity to daphnia.

                                Data Matrix for Read Across from Analogue                                       

Property	Submission Substance (Target)	Analogue   (Data Source)
EC	270-608-0	283-392-8
CAS	68457-79-4	84605-29-8
Chemical Name	Phosphorodithioic acid, mixed O,O-bis(iso-Bu and pentyl) esters, zinc salts	Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts
Physical	Viscous liquid	Viscous liquid
Boiling Point	Decomposes before boiling	Decomposes before boiling
Density @ 15.6 deg. C   (ASTM D4052)	1.17 mg/L	1.2 mg/L
Vapour Pressure @ 25 C   (EU method A.4)	0.0025 Pa	0.0069 Pa
Water Solubility @ 22 deg. C (OECD 105)	1658 mg/L	2764 mg/L
Identity of water soluble components (% = GC area %)	ZDDPs containing 76% isobutyl (C4) dithiophosphate ligands + 24% containing mixed isobutyl (C4) and pentyl (C5) dithiophosphate ligands	ZDDP containing 95% isopropyl (C3) dithiophosphate ligands + 5% containing mixed isopropyl and 1,3 -dimethylbutyl dithiophosphate ligands
Average molecular weight of water solubles (weighted average based on GC peak area %)	562	500.4
Partition Coefficient, logPow (OECD 107)	0.69	0.56
Hydrolysis as a function of pH (OECD 111, Tier 1 preliminary study at pH 4,7 and 9)	Hydrolytically stable at pH 4, 7 and 9	Hydrolytically stable at pH 4, 7 and 9

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Conclusions:

The acute toxicity of the test material to the freshwater invertebrate Daphnia magna has been investigated and gave a 48-Hour EL*50 value of 23 mg/L nominal loading rate with 95% confidence limits of 20 to 25 mg/L. The No Observed Effect Loading rate at 48 hours was 10 mg/l nominal loading rate.

Executive summary:

Introduction.A study was performed to assess the acute toxicity of the test material to Daphnia magna. The method followed that described in the OECD 202 Guidelines, “Daphnia sp, Acute Immobilisation Test and Reproduction Test”.

Methods.  Following a preliminary range finding test, twenty daphnids (2 replicates of 10 animals) were exposed to water accommodated fractions of the test material over a range of nominal loading rates of 10, 18, 32, 56, and 100 mg/L for 48 hours at a temperature of 21 degrees C under static test conditions. The number of immobilized Daphnia were recorded after 24 and 48 hours.

 

Results.The 48-Hour EL50 for the test material to Daphnia magna based on nominal loading rates was 23 mg/L with 95% confidence limits of 20 to 25 mg/L.

The No Observed Effect Loading rate was 10 mg/l nominal loading rate WAF.

 

Given that toxicity cannot be attributed to a single component or mixture of components but to the test material as a whole, the results were based on nominal loading rates only.