Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Hydrolysis

In a guideline study NaPT was found to be hydrolytically stable (Table 5.1.1).

In a GLP study conducted according to US guideline Federal Register Vol. 50, No. 188 (Friday 27 1985) Rules and Regulations, p. 39252.(similar to OECD 111) (5.1.2.001) at a concentration of 140 mg/L, no DT50for hydrolysis could be determined even after 28 days in pH 3, 7, and 11 buffer.

 

Photolysis

Photodegradation in water

A study of the photolysis rate of sodium pyrithione has been carried out.

In a GLP study conducted according to US guideline US FDA Technical Assistance Document, Guideline 3.10 Photodegradation. 1987.) (5.1.3.001, EZPTF 7011-121) at a concentration of 10 mg/L, DT50for photolysis were determined to be <10 minutes at pH 5 and 7 and <15 minutes at pH 9. Degradants were not identified in this study.

A further study of the aqueous photolysis rate of pyrithione has also been conducted (refer to Table 5.1.2).

Study (5.1.3.003, EZPTF 7011-123) was conducted to determine the influence of concentration on photolysis rates. Photolysis was done in deionized water with zinc pyrithione concentrations of 0.1-1 μg/L, which are much closer to predicted environmental concentrations than those of the other two studies. Exposure to natural sunlight (42° N latitude) was done in quartz tubes at noon during the months of July through October. ZnPT was shown to have considerable absorptivity in the range of 290-400 nm, where photoactive solar radiation is available and photolysis in natural sunlight was very rapid. Measured photolysis half-lives ranged from 1.1 to 1.4 minutes in deionized water. Simultaneous exposure of the actinometer (o‑nitrobenzaldehyde) solutions allowed the calculation of photolysis disappearance quantum yields. Reproducibility at the very low concentrations used in this study required that several exposure experiments be run for each test compound and the results averaged. The quantum yield for ZnPT at 3.15 x 10-9M and 3.15 x 10-10M was 0.17 ± 0.06 (n = 4). This study also demonstrated that three metallic complexes of pyrithione (Zinc, Copper and Sodium) all exhibited the same photolysis rate at environmentally relevant concentrations.

 

Photodegradation in air

This point is regarded not to be relevant because:

-         the vapour pressure of NaPT is very low, resulting in negligible exposure to the atmosphere.

-         the calculation according to the Atkinson calculation method (5.1.1.001, ESPTF 7031-001) indicates a short half-life (53.8 hours) of sodium pyrithione in the atmosphere.

Summary of degradation

-         Sodium pyrithione is hydrolytically stable.

-         Sodium pyrithione passes the ready biodegradability test according to OECD 301B and biodegradation is rapid in soil, water-sediment, and STP. The degradation profile is well identified passing through several transient degradants to a final somewhat persistent degradant 2‑pyridine sulphonic acid (PSA).

-         Photolysis is extremely rapid—again leading to the final somewhat persistent degradant 2‑pyridine sulphonic acid (PSA).

-         The final degradant, PSA, passes the ready biodegradability test according to OECD 301B.

Table 5.1.1 Hydrolysis

Guideline /
Test method

pH

Temperature
[°C]

Initial TS concentration, C0
[mg/L]

Reaction rate constant, Kh

Half-life, DT50

Coefficient of correlation, r2

Reference

Federal Register Vol. 50, No. 188 (Friday 27 1985) Rules and Regulations, p. 39252. (similar to OECD 111)

pH 3; 7; and 11

25 ± 1°C(pH 5, 7 and 9 fw)

25 ± 1°C(pH 8.2 sw)

140 mg/L

0.0

No detectable degradation

 

n.a.

5.1.2.001

ESPTF 7011-111

Stanley et al (1996)

 

Table 5.1.2 Photolysis

Guideline /
Test method

Initial molar TS concen­tration

Total recovery of test substance
[% of appl. a.s.]

Photolysis rate constant (kcp)

Direct photolysis sunlight rate constant (kpE)

Reaction quantum yield (fcE)

Half-life (t1/2E)

Reference

US FDA Technical Assistance Document, Guideline 3.10 Photodegradation. 1987.

10 mg/L

 

not determined

pH 5 buffer:
0.12 to 0.18 min-1

pH 7 buffer:
0.15 to 0.19 min-1

 

pH 9 buffer:

n.a.

 

 

Not reported, not applicable to the testing guideline.

Not reported, not applicable to the testing guideline.

Half lives under the conditions of this study were <10 minutes in pH 5 and 7 buffer and

<15 minutes in pH 9 buffer.

5.1.3.001

ESPTF 7011-121

Croudace, Gilbert, Woods (1996)

Methods used are similar to the requirements of OPPTS 835.2210 and OPPTS 830.7050

1x10-3μg/mL,
1
x10-4μg/mL

(3.15x10-9M, 3.15x10-10M)

Not applicable

Non-radiolabelled test substance.

0.483 min-1to 0.631 min.-1(depending on the weather conditions)

0.2201 to 0.2869min-1

0.17 ± 0.06

3.0 /10.6 min (latitude 40 summer/ winter)

3.1 /22.2 min (latitude 50 summer /winter)

Key Study

5.1.3.003

EZPTF 7011-123

Fenn (2005)

  The information contained within this robust summary document comes from studies which are in the ownership of Arch Chemicals Inc. and which are protected in several regions globally. This information may not be used for any purpose other than in support of the Chemical safety Report submitted by Arch Chemicals Inc. under RegulationEC 1907/2006.