Pyrithione zinc

Biodegradation in soil

Administrative data

Endpoint:

biodegradation in soil

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2001

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

other: U.S. EPA Pesticide Assessment Guidelines, Subdivision N, §163-1, Chemistry: Environmental Fate

GLP compliance:

yes

Test type:

laboratory

Test material

Test material information

Constituent 1

Reference substance name:

Pyrithione zinc

EC Number:

236-671-3

EC Name:

Pyrithione zinc

Cas Number:

13463-41-7

Molecular formula:

C10H8N2O2S2Zn

IUPAC Name:

Bis [1-hydroxy-2(1H)-pyridinethionato-O,S](T-4)-zinc

Details on test material:

Purity: >95%
Spec ac: 157.63 mCi/mmol
Water solubility: 6ppm

Radiolabelling:

yes

Study design

Oxygen conditions:

not specified

Soil classification:

USDA (US Department of Agriculture)

Soil properties

Soil properties 1

Soil no.:

#1

Soil type:

sand

% Clay:

5

% Silt:

6

% Sand:

89

% Org. C:

1

pH:

7.5

CEC:

9.6

Bulk density (g/cm³):

1.29

Soil properties 2

Soil no.:

#2

Soil type:

loam

% Clay:

26

% Silt:

44

% Sand:

30

% Org. C:

5.4

pH:

6.9

CEC:

26.4

Bulk density (g/cm³):

1.07

Soil properties 3

Soil no.:

#3

Soil type:

clay loam

% Clay:

32

% Silt:

46

% Sand:

22

% Org. C:

4.4

pH:

6.9

CEC:

25.4

Bulk density (g/cm³):

1.07

Soil properties 4

Soil no.:

#4

Soil type:

sandy loam

% Clay:

6

% Silt:

26

% Sand:

68

% Org. C:

1

pH:

6.6

CEC:

5.6

Bulk density (g/cm³):

1.48

Parameter followed for biodegradation estimation:

radiochem. meas.

test mat. analysis

Details on experimental conditions:

Duplicate columns were prepared with each of four soil types using 3.7 cm internal diameter segmented glass columns. The bottom segment contained a stop-cock and a coarse porosity glass frit, above which was placed a 3.7-cm diameter glass-fiber filter. Joints between the column segments were wrapped with PTFE tape and held together with polyethylene tape. Soils were sifted through a 2-mm sieve before addition to the columns. To produce uniform packing and avoid the formation of channels in the column bed, a small amount of 0.01-M calcium chloride solution was added to the column followed by slow addition of the soil. Each column was filled with soil to a height of 30 centimeters, adding additional calcium chloride solution as necessary to keep the soil submerged to a depth of approximately two centimeters. After allowing the column to drain, a second glass-fiber filter was placed on top of the soil column to minimize disturbance of the soil surface during leaching.
Dosing solution was applied directly to a 1 to 2-cm layer of 0.01-M calcium chloride solution above the soil surface. The doses ranged from 15.38 μCi to 16.67 μCi and corresponded to an application rate of 2.9 - 3.1 μg/cm2 (0.29 - 0.31 kg/hectare).
The dose level was chosen to be high enough for measurement and identification of zinc pyrithione in the soil and leachate.
Two columns were also dosed with sandy loam soil to which zinc pyrithione had been added and allowed to age for 1-2 half-lives before addition to the soil column. Aging was done using 11 grams of sieved soil with a moisture content of 9.98% (75% of field moisture capacity) contained in 50 mL Nalgene polypropylene co-polymer Oak Ridge type (screw-cap) centrifuge tubes.
Ten grams of soil (dry weight) was added to individual centrifuge tubes. The appropriate amount of water was then mixed into the soil to raise the percent moisture to 9.98%. The soil was allowed to equilibrate at 25ºC for 3-4 days before dosing.
For each experiment with aged soil, two soil samples were dosed with 100 µL of zinc pyrithione in DMSO/ethanol 1:1 by adding the dose drop wise over the surface of the soil. One set was dosed with 16.42 μCi (3.0 mg/g) and the other set was dosed with 17.76 μCi (3.3 mg/g). After mixing the dosing solution into the soil and allowing the ethanol to evaporate, the tubes were capped and incubated in the dark for 25 hours at 25ºC. For one of the columns, a third undosed soil sample was prepared for measurement of the microbial activity in the soil.
After the incubation period, soil from one of the centrifuge tubes was applied to the layer of 0.01-M CaCl2 above a column of sandy loam soil prepared as described for the unaged soil. Two glass-fiber filters separated the aged soil from the remainder of the column. The centrifuge tube was rinsed with 5 mL of 0.01-M calcium chloride and the rinse was added to the soil column. After allowing the calcium chloride solution to drain to the soil surface, a glass-fiber filter was placed above the segment of aged soil. The height of the aged soil segment was 0.6 cm, resulting in a total height for the aged soil columns of 30.6 cm. The soil from the second incubated centrifuge tube was extracted to determine the total radioactive dose and to obtain the initial metabolic profile.
Each column was leached with 546 mL of 0.01-M calcium chloride (including the solution added during application of the dosing solution or aged soil), which corresponded to 20 inches (50.8 cm) times the cross-sectional area of the column. The leaching solution was delivered from an inverted 1-liter separatory funnel and was allowed to percolate through the soil column while maintaining a head of 1 to 2 cm of solution above the soil surface. The leachate was collected as a single fraction into a tared 1-liter amber bottle. Dosing and leaching were done at room temperature in the dark. The total leaching time was recorded for each column
Extraction: 1 x acetonitrile, 3 x 0.1M KOH

Results and discussion

Half-life / dissipation time of parent compound

DT50:

13 - 15.5 h

Type:

not specified

Transformation products:

yes

Identity of transformation products

Identity of transformation products 1

No.:

#1

Reference

Reference substance name:

Unnamed

IUPAC name:

pyrithione sulphinic acid

Identifier:

common name

Identity:

pyrithione sulphinic acid

Identity of transformation products 2

No.:

#2

Reference

Reference substance name:

Unnamed

IUPAC name:

2-pyridine-N-oxide sulphinic acid

Identifier:

common name

Identity:

2-pyridine-N-oxide sulphinic acid

Identity of transformation products 3

No.:

#3

Reference

Reference substance name:

Unnamed

IUPAC name:

pyrithione disulphide

Identifier:

common name

Identity:

pyrithione disulphide

Identity of transformation products 4

No.:

#4

Reference

Reference substance name:

Unnamed

IUPAC name:

2-pyridinesulphinic acid

Identifier:

common name

Identity:

2-pyridinesulphinic acid

Identity of transformation products 5

No.:

#5

Reference

Reference substance name:

Unnamed

IUPAC name:

2-pyridinesulphonic acid

Identifier:

common name

Identity:

2-pyridinesulphonic acid

Identity of transformation products 6

No.:

#6

Reference

Reference substance name:

Unnamed

IUPAC name:

'mixed' disulphide

Identifier:

common name

Identity:

'mixed' disulphide

Details on transformation products:

Base-extractable material, eluting as a broad peak associated with extracted organic material, was also found in the sandy loam soil and is discussed below. Because of the low concentrations of radioactivity below the top column segment, only the extracts of segment A were generally analyzed. Exceptions were columns #8 and #10 (loam), for which the acetonitrile extracts of segment B were also analyzed, and column #6 (sand) for which all five column segments were analyzed.
Pyrithione was present only in the KOH and acetonitrile extracts of segment A, and was identified by the retention times of its derivatives on HPLC system 1.
OMSiA was present in the leachate and the 0.1-M KOH soil extracts.
OMSA, PSA, and PSiA where present primarily in the leachate.
MxDS was present mainly in the KOH soil extracts.
OMDS was found mainly in the acetonitrile extracts of soil segments A, and was the only peak in the chromatograms of the acetonitrile extracts of segment B from columns #8 and #10 (loam). The extracts of all five segments of column #6 (sand) showed no discernable peaks, except traces of OMDS in some of the acetonitrile extracts. These were too small to integrate.
A later-eluting peak, seen only in the 0.1-M KOH extracts of sandy loam and representing 8.6% and 11.2% of the dose, was associated with a broad peak in the UV. It was observed that the KOH extracts of sandy loam were very dark brown, while the KOH extracts of the other soil types were clear to light yellow. Because of the dark color of the extract, the strong UV absorbance associated with the peak, and its presence only in the KOH extracts, the peak is characterized as base-soluble organic matter, most likely humic and fulvic acids, extracted from the soil. The radioactivity associated with this material may be tightly bound pyrithione and/or degradation products. However, any pyrithione associated with this material must be covalently bound to the soil fraction since it did not react with any derivatizing reagents.
The amount of pyrithione remaining in the aged soils after 25 hours at 25º represented 26.3% and 32.8% of the dose. This corresponds to a half-life of 13.0 and 15.5 hours. After further degradation on the soil columns during leaching (23.5 - 29.8 hours), the pyrithione was reduced to 16.8% and 17.9% of the dose, indicating that degradation occurs at approximately the same rate in moist and saturated soil.

Details on results:

The recovery of radioactivity (material balance) ranged from 97.1% to 104.8% of the dose, with an average value of 100.6%.
The leachate accounted for 3.3% – 25.9% of the dose, and contained only metabolites. The percentage of the dose in the leachate increased according to the extent to which zinc pyrithione was metabolized on the soil columns, which was proportional to the time required to leach the column. Most of the radioactivity remaining in the soil was present in the top six centimeters of the column (segment A). Sand showed the greatest permeation of radioactivity, although less than 10% of the dose was found in each segment below the top segment. It is likely that the coarse texture of the sand allowed some channeling of the leachate to occur. In one sand column (#7), which was assembled with six column segments instead of five, only 0.4% of the dose was recovered from the bottom segment.
Loam (columns #8 and #10) showed permeation of 9.2% and 12.2% of the dose into the second soil segment. The leaching time for these columns was short (0.17 and 0.19 days) and channeling may have been a factor. By comparison, a third more densely packed loam column (#9) required 1.51 days to leach and retained only 3.1% of the dose in the second segment.
Sandy loam and clay loam showed no significant permeation beyond the first soil segment. In the column dosed with aged sandy loam, most of the soil radioactivity remained in the 0.6-cm layer of aged soil.
Aging the soil prior to leaching did not produce a significant difference in the leaching behavior of the degradants since zinc pyrithione degraded significantly during leaching of the unaged columns. The metabolites formed during the aging period were identical to those formed during leaching.

Any other information on results incl. tables

Table 1: Dosing

Table 2: Leaching times 

Table 3: Metabolite distribution

Table 1: Dosing

Column ID#	Dose (kg/ha)
4	0.30
5	0.31
6	0.31
7	0.31
8	0.31
9	0.31
10	0.31
11	Control
12	0.29
13	0.29
14	0.31
15	0.33

Table 2: Leaching times

Column ID#	Soil Type	Leaching Time (days)	Rate (mL/hour)
4	Sandy loam	3.02	7.5
5	Sandy loam	2.31	9.8
6	Sand	0.03	758.3
7	Sand	0.04	568.8
8	Loam	0.19	119.7
9	Loam	1.51	15.1
10	Loam	0.14	162.5
11	Clay loam	0.17	133.8
12	Clay loam	0.50	45.5
13	Clay loam	0.32	71.1
14	Sandy loam (aged)	0.98	23.2
15	Sandy loam (aged)	1.24	18.3

Columns #1 - #3 were used to develop methods for preparation and analysis.

 

Table 3: Metabolite distribution

Column ID#	Soil type	OMDS	OMSiA	OMSA	PSiA	PSA	MxDS	ZPT	Humic
4	sandy loam	-	19.9	4.0	3.7	6.8	4.7	24.1	11.2
5	sandy loam	-	19.2	3.4	0.3	3.7	4.6	32.9	8.6
6	sand	2.2	9.7	0.0	-	0.3	7.4	31.2	-
7	sand	1.3	7.5	0.1	-	0.1	8.8	43.4	-
8	loam	8.6	19.8	2.6	-	1.1	4.1	19.2	-
9	loam	-	15.6	21.4	0.1	6.4	1.9	2.6	-
10	loam	5.7	22.8	1.3	-	1.9	3.7	23.3	-
12	clay loam	2.9	18.2	2.7	-	1.2	2.5	32.3	-
13	clay loam	2.5	15.5	2.7	-	0.8	1.1	29.9	-
14	sandy loam (aged)	0.2	18.8	2.6	-	2.3	2.8	16.8	15.4
15	sandy loam (aged)	0.3	15.5	3.5	-	2.8	3.6	17.9	15.1

 

 

Applicant's summary and conclusion

Conclusions:

The leaching behavior of zinc pyrithione in four soils shows pyrithione to be immobile, which is consistent with the results from the adsorption/desorption study in two soils and two sediments. Pyrithione degraded to varying extents during the leaching period. Only the degradants were found to be mobile in the soils. This was also observed to be true when leaching was done with a sample of aged soil. Based on this, the absorption coefficients from the adsorption/desorption study were probably on the low side since they were calculated based on radioactivity measurements, which included the more mobile degradation products. 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 Regulation EC 1907/2006.