Zinc, O,O-mixed (iso-Bu), (iso-Pr), (pentyl) phosphorodithioate

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Justification for type of information:

REPORTING FORMAT FOR THE CATEGORY APPROACH
Please refer also to the read-across statement attached in section 13

1. HYPOTHESIS FOR THE CATEGORY APPROACH (ENDPOINT LEVEL)
The target and the source substances are structurally similar substances that share 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 target and the source substances are related only to the alkyl (R) groups of the alkyldithiophosphate ligands. The substances in this category give thus rise to an (identical) common compound, Phosphorodithioic acid moiety, that can be released by the breakage of ester bonds and dissociation from the Zinc complex to which the organism would be exposed if the target substance was tested in the toxicity studies. Exposure to the parent compounds (non-transformed constituents) and to the counter alkyl alcohols, possibly released by hydrolysis of P-O bonds – non-common compounds – would not influence the prediction of the (eco)toxicological properties because they are considered to have the same biological targets and to cause the same type of effects through a common underlying mechanism due to the same functional groups (zinc cation, phosphorodithioic cation and aliphatic alcohol anionic moieties). The impurities of the target and the source substances are not expected to impact the prediction because they are identical or, if slightly structural different, belong to the same class of compounds with the same functional groups and their percentages are very low.

2. CATEGORY APPROACH JUSTIFICATION (ENDPOINT LEVEL)
The target substance is considered to follow similar hydrolysis pattern as the source substance, because it has the same structural features. Moreover, there is sufficient weight of evidence that the entire range of substances of ZDDP category including the source substance are hydrolytically stable, it is therefore a high probability that the target substance is also hydrolytically stable. There are no other structural alerts of the target substance pointing to a hydrolysis pattern different from the source substance. Therefore, it is predicted that the target substance would possess the same hydrolysis rate as the source substance if it was tested in a hydrolysis study.

Preliminary study:

In the 5-day Tier 1 preliminary study, 94.3% of the parent compound was recovered at pH 4. At pH 7 and 9, the recovery was 100%.

At pH 9, the zinc metal of the parent complex was exchanged for the sodium of the buffer forming a sodium dialkyldithiophosphate product and an insoluble sediment of zinc oxide. The 31P-NMR spectrum showed a single peak at 112 ppm indicating the alkyldithiophosphate ligands remained intact after the metal exchange. The sodium dialkyldithiophosphate product was confirmed by ICP analysis which showed 0% zinc and the presence of sodium in the test mixture after the 5-day study which was not present in the starting mixture.

A < 10% change in the concentration of the dialkyldithiophosphate ligands of the parent compound at pH 4, 7 and 9 meets the OECD 111 criterion for a hydrolytically stable material. A full hydrolysis study is not required.

Test performance:

The pH and temperature were maintained throughout the 5-day study. There were no unexpected occurrences that would have affected the test results. Test mixtures were cloudy and a slight oil slick was observed at all pHs. At pH 9, the zinc metal of the parent complex precipitated as zinc oxide. These observations were expected as the test substance contains a mixture of oil and zinc metal complexes with organic ligands of different water solubilities. All analyses were performed on the clear supernatants.

Transformation products:

no

% Recovery:

94.3

pH:

4

Temp.:

50 °C

Duration:

5 d

% Recovery:

100

pH:

7

Temp.:

50 °C

Duration:

5 d

% Recovery:

100

pH:

9

Temp.:

50 °C

Duration:

5 d

Key result

Remarks on result:

hydrolytically stable based on preliminary test

Validity criteria fulfilled:

not specified

Conclusions:

Based on the results of a Tier 1 preliminary study, the test substance is hydrolytically stable at pH 4, 7 and 9 as defined by the OECD 111 criterion of a < 10% change in the concentration of the parent compound. A full hydrolysis study is unnecessary.

Executive summary:

A Tier 1 preliminary hydrolysis study was performed according the OECD 111 guideline, Annex 1, tiered hydrolysis scheme. Mixtures of the test substance were prepared in buffers at pH 4, 7 and 9 and maintained at 50°C for 5 days. Following the 5 day incubation, mixtures were evaluated by 31P-NMR (phosphorus-Nuclear Magnetic Resonance) spectroscopy for depletion of the alkyldithiophosphate signals between 112 - 108 ppm and the appearance of other peaks which could be identified as hydrolysis products.

 

At pH 4, 7 and 9, the 31P-NMR spectra showed a change of < 10% in the concentration of the alkyldithiophosphate ligands bound to the zinc metal indicating the substance meets the OECD 111 criterion for a hydrolytically stable material.

 

At pH 9, the zinc metal was exchanged for the sodium of the buffer forming a sodium salt with the alkyldithiophosphate ligands remaining intact. In the exchange, the zinc metal was precipitated as insoluble zinc oxide/hydroxide. No other peaks besides the alkyldithiophosphates (between 112 – 108 ppm) were detected in the NMR spectrum.

 

Based on the results of the 5-day Tier 1 preliminary test, the substance was determined to be hydrolytically stable and a full study is not required.

Reference 2

Endpoint:

hydrolysis

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

weight of evidence

Justification for type of information:

REPORTING FORMAT FOR THE CATEGORY APPROACH
Please refer also to the read-across statement attached in section 13

1. HYPOTHESIS FOR THE CATEGORY APPROACH (ENDPOINT LEVEL)
The target and the source substances are structurally similar substances that share 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 target and the source substances are related only to the alkyl (R) groups of the alkyldithiophosphate ligands. The substances in this category give thus rise to an (identical) common compound, Phosphorodithioic acid moiety, that can be released by the breakage of ester bonds and dissociation from the Zinc complex to which the organism would be exposed if the target substance was tested in the toxicity studies. Exposure to the parent compounds (non-transformed constituents) and to the counter alkyl alcohols, possibly released by hydrolysis of P-O bonds – non-common compounds – would not influence the prediction of the (eco)toxicological properties because they are considered to have the same biological targets and to cause the same type of effects through a common underlying mechanism due to the same functional groups (zinc cation, phosphorodithioic cation and aliphatic alcohol anionic moieties). The impurities of the target and the source substances are not expected to impact the prediction because they are identical or, if slightly structural different, belong to the same class of compounds with the same functional groups and their percentages are very low.

2. CATEGORY APPROACH JUSTIFICATION (ENDPOINT LEVEL)
The target substance is considered to follow similar hydrolysis pattern as the source substance, because it has the same structural features. Moreover, there is sufficient weight of evidence that the entire range of substances of ZDDP category including the source substance are hydrolytically stable, it is therefore a high probability that the target substance is also hydrolytically stable. There are no other structural alerts of the target substance pointing to a hydrolysis pattern different from the source substance. Therefore, it is predicted that the target substance would possess the same hydrolysis rate as the source substance if it was tested in a hydrolysis study.

Preliminary study:

In the 5-day Tier 1 preliminary study, 93.4% of the parent compound was recovered at pH 7. At pH 4 and 9, the recovery was 100%.

At pH 9, the zinc metal of the parent complex was exchanged for the sodium of the buffer forming a sodium dialkyldithiophosphate product and an insoluble sediment of zinc oxide/hydroxide. The 31P-NMR spectrum showed a single peak at 108 ppm indicating the alkyldithiophosphate ligands remained intact after the metal exchange. The sodium dialkyldithiophosphate product was confirmed by ICP analysis which showed 0% zinc and the presence of sodium in the test mixture after the 5-day study which was not present in the starting mixture.

A < 10% change in the concentration of the dialkyldithiophosphate ligands of the parent compound at pH 4, 7 and 9 meets the OECD 111 criterion for a hydrolytically stable material. A full hydrolysis study is not required.

Test performance:

The pH and temperature were maintained throughout the 5-day study. There were no unexpected occurrences that would have affected the test results. Test mixtures were cloudy and a slight oil slick was observed at all pHs. At pH 9, the zinc metal of the parent complex precipitated as zinc oxide. These observations were expected as the test substance contains a mixture of oil and zinc metal complexes with organic ligands of different water solubilities. All analyses were performed on the clear supernatants.

Transformation products:

no

% Recovery:

100

pH:

4

Temp.:

50 °C

Duration:

5 d

% Recovery:

93.4

pH:

7

Temp.:

50 °C

Duration:

5 d

% Recovery:

100

pH:

9

Temp.:

50 °C

Duration:

5 d

Key result

Remarks on result:

hydrolytically stable based on preliminary test

Table 1. Results of 5 -day Preliminary Hydrolysis Test (at 50 °C)

pH	4	7	9
Buffer System	phthalate	tris/maleate	borate
Approx. saturation concentration (ppm)	2700	2700	2700
Starting Concentation (ppm)	1000	1000	1000
% recovery after 5 days	100	93.4	100^(1)

⁽¹⁾100% recovery of dialkyldithiophosphate with an exchange of zinc in the parent compound for the sodium of the pH 9 buffer occurred.

Validity criteria fulfilled:

not specified

Conclusions:

Results of a Tier 1 preliminary study indicated the test substance is hydrolytically stable at pH 4, 7 and 9 as defined by the OECD 111 criterion of a <10% change in the concentration of the parent compound. A full hydrolysis study is not required.

Executive summary:

A Tier 1 preliminary hydrolysis study was performed according to the OECD 111 guideline, Annex 1, tiered hydrolysis scheme. Mixtures of the test substance were prepared in buffers at pH 4, 7 and 9 and maintained at 50 °C for 5 days. Following the 5 day incubation, mixtures were evaluated by 31P-NMR (phosphorus-Nuclear Magnetic Resonance) spectroscopy for depletion of the alkyldithiophosphate signals between 112 - 108 ppm and the appearance of other peaks which could be identified as hydrolysis products.

 

At pH 4, 7 and 9, the 31P-NMR spectra showed a change of < 10% in the concentration of the alkyldithiophosphate ligands bound to the zinc metal indicating the substance meets the OECD 111 criterion for a hydrolytically stable material.

 

At pH 9, the zinc metal was exchanged for the sodium of the buffer forming a sodium salt with the alkyldithiophosphate ligands remaining intact. In the exchange, the zinc metal was precipitated as insoluble zinc oxide/hydroxide. No other peaks besides the alkyldithiophosphates (between 112 – 108 ppm) were detected in the NMR spectrum.

 

Based on the results of the 5-day Tier 1 preliminary test, the substance was determined to be hydrolytically stable and a full study is not required.

Description of key information

source substance Phosphorodithioic acid, mixed O,O-bis(iso-Bu and pentyl) esters, zinc salts (CAS 68457 -79 -4): non GLP, preliminary hydrolysis study, according to OECD 111, pH 4, 7, 9; 50 °C for 5 days: Based on the results of the 5-day Tier 1 preliminary test, the substance was determined to be hydrolytically stable and a full study is not required.

source substance Phosphorodithioic acid, mixed O,O-bis(1,3-dimethylbutyl and iso-Pr) esters, zinc salts (CAS 84605 -29 -8): non GLP, preliminary hydrolysis study, according to OECD 111, pH 4, 7, 9; 50 °C for 5 days: Based on the results of the 5-day Tier 1 preliminary test, the substance was determined to be hydrolytically stable and a full study is not required.

Based on the result of the source substances the target substance seems to be hydrolytically stable.