mancozeb (ISO); manganese ethylenebis(dithiocarbamate) (polymeric) complex with zinc salt  

Adsorption / desorption

Link to relevant study record(s)

Reference

Endpoint:

adsorption / desorption: screening

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1986

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Reliability 1

Qualifier:

according to guideline

Guideline:

other: EPA 163-1

Deviations:

no

GLP compliance:

yes

Remarks:

(incl. QA statement)

Type of method:

batch equilibrium method

Media:

soil

Radiolabelling:

yes

Remarks:

labelled at one ethylene carbon

Test temperature:

25.6 °C

Analytical monitoring:

yes

Remarks:

Liquid Scintillation Counting (LSC)

Details on sampling:

Advanced test
-Concentrations:
0.5, 1.0, 2.0 and 5.0 ppm
LOD 0.01 ppm per 50 g sample

Matrix no.:

#4

Matrix type:

clay loam

% Clay:

28

% Silt:

50

% Sand:

22

% Org. carbon:

1.5

pH:

7.4

CEC:

12.9 meq/100 g soil d.w.

Matrix no.:

#3

Matrix type:

silt loam

% Clay:

20

% Silt:

66

% Sand:

14

% Org. carbon:

2

pH:

6.4

CEC:

9.6 meq/100 g soil d.w.

Matrix no.:

#2

Matrix type:

sandy loam

% Clay:

12

% Silt:

10

% Sand:

78

% Org. carbon:

1.6

pH:

5.9

CEC:

5.7 meq/100 g soil d.w.

Matrix no.:

#1

Matrix type:

sand

% Clay:

4

% Silt:

8

% Sand:

88

% Org. carbon:

0.5

pH:

5.7

CEC:

3.5 meq/100 g soil d.w.

Details on matrix:

Matrix#1: Georgia, Log number 85E373
Matrix#2: Georgia, Log number 85E372
Matrix#3: Pennsylvania, Log number 85E655
Matrix#4: Mississippi, 85E416

Soil moisture content (% of wet soil):
Soil 1: 0.57
Soil 2: 0.96
Soil 3: 14.45
Soil 4: 8.85

Details on test conditions:

-Adsorption
All test vials were shaken by hand to assure good mixing of the soil and solution, and placed on an orbital shaker in horizontal position inside a dark incubator. Samples were shaken at approximately 225 RPM at a temperature of 25.6 °C. The adsorption phase of the experiment lasted 24 hours after which samples were removed from the shaker and were spun at 1000 RPM for 6 - 9 minutes. The supernatants were decanted, measured and two 100 µL aliquots taken for LSC counting. Supernatants were then stored frozen.

-Desorption:
Soil bound Dithane was desorbed 4 times into fresh 0.01M CaCl2 solution. After the adsorption supernatant was decanted, 30 mL 0.01M CaCl2 was dispensed into each test vial and the vials were placed back on the shaker. This was designated time 0 of the desorption phase. Desorption periods ended at 2, 4, 8 and 24 hours. At the end of each period, the samples were removed from the shaker, centrifuged, decanted, allquoted for LSC, fresh 0.01M CaCl2 dispensed to each test vial and returned to shaker as described. Note that during the time samples were off the shaker the "clock was stopped." After the final desorption supernatant was decanted, the test vials containing remaining wet soil were frozen along with the adsorption and desorption supernatants.

-Mass balance
Material balance was calculated for both the test vials without soil (blanks) and test vials containing soils. The material balance for the test compound In blanks, used to assess the compound's adsorption onto test vial walls, was computed for all concentrations.

Key result

Type:

Kd

Value:

9.74 L/kg

Temp.:

25.6 °C

Remarks on result:

other: mean Kd

Key result

Type:

Koc

Value:

771 L/kg

Temp.:

25.6 °C

Remarks on result:

other: mean Koc

Type:

Koc

Value:

675 L/kg

pH:

7.4

Temp.:

25.6 °C

Matrix:

#4

% Org. carbon:

1.5

Type:

Koc

Value:

363 L/kg

pH:

6.4

Temp.:

25.6 °C

Matrix:

#3

% Org. carbon:

2

Type:

Koc

Value:

618 L/kg

pH:

5.9

Temp.:

25.6 °C

Matrix:

#2

% Org. carbon:

1.6

Type:

Koc

Value:

2 334 L/kg

pH:

5.7

Temp.:

25.6 °C

Matrix:

#1

% Org. carbon:

0.5

Type:

Kd

Value:

10.13 L/kg

pH:

7.4

Temp.:

25.6 °C

Matrix:

#4

% Org. carbon:

1.5

Type:

Kd

Value:

7.26 L/kg

pH:

6.4

Temp.:

25.6 °C

Matrix:

#3

% Org. carbon:

2

Type:

Kd

Value:

9.89 L/kg

pH:

5.9

Temp.:

25.6 °C

Matrix:

#2

% Org. carbon:

1.6

Type:

Kd

Value:

11.67 L/kg

pH:

5.7

Temp.:

25.6 °C

Matrix:

#1

% Org. carbon:

0.5

Adsorption and desorption constants:

Adsorption Koc values ranged from 363 (medium mobility) for silt loam to 2334 (slight mobility) for sand; 1/n ranges from 0.686 to 0.777. Desorption Koc values ranged from 892 (low mobility) to 20726 (immobile); 1/n ranges from 0.608 to 917.

Recovery of test material:

Material balance for the different dosages were ranged from 93 to 106 %.

Transformation products:

not specified

Remarks:

Intermediate and final degradation products suggested by TLC are ethylenethiourea, ethyleneurea, ethylenebisisothiocyanate, Jaffe's base, and ethylenediamine.

Adsorption Koc values ranged from 363 (medium mobility) for silt loam to 2334 (slight mobility) for sand; 1/n ranges from 0.686 to 0.777. Desorption Koc values ranged from 892 (low mobility) to 20726 (immobile); 1/n ranges from 0.608 to 917.
The binding behaviour of mancozeb and its degradates does not correlate to % soil organic matter, soil cation exchange capacity, or soil pH.
The initial adsorption supernatant concentration, as mancozeb, was determined by LSC to be 4.64 ppm for the 5 ppm treated test samples. Analysis by GC revealed an average actual mancozeb concentration of 0.10 ppm in the adsorption supernatants of the 5 ppm treated test samples and an average of 1.01 ppm for soil samples measured after four desorptions. These data indicate nearly complete degradation of mancozeb by the end of the experimental period. The adsorption/desorption studies of this experiment were conducted in the 0.5 to 5.0 ppm range, where mancozeb may become solubilised and rapidly hydrolyse. Therefore, the adsorption/desorption behaviour described by radioanalysis is actually for mancozeb and its degradates, taken together.
Freundlich calculations approximate the actual soil behaviour of mancozeb and its degradates, as if they were equilibrated between soil and water in the field.
TLC analysis of the 5 ppm dosed soils after 24 hours equilibrium time showed mancozeb to be at least 45% degraded present at 17.0 – 44.9% of radioactivity on the TLC plates in the four soils (two replicates each) although this was a combination of mancozeb, EDA and Jaffe’s Basein the soil over the course of the experiment. Intermediate and final degradation products suggested by TLC are ethylenethiourea (ETU 5.8 – 16.7%, mean 4.6%), ethyleneurea (EU 11.8 – 39.7%, mean 26.6%), ethylenebisisothiocyanate (EBIS 5.7 – 22.4%, mean 14.0%), Jaffe's base (JB), and ethylenediamine (EDA). Material balance for the different dosages were ranged from 93 to 106 %.

Validity criteria fulfilled:

yes

Conclusions:

The geometric mean Koc value is calculated as 771 mL/g (Kom 447 mL/g). Average 1/n 0.741.

Executive summary:

¹⁴C- mancozeb at 0.5, 1.0, 2.0 and 5.0 ppm (formulated product) levels in water, containing 0.1M CaCl₂ was equilibrated with four types of soil: a sand, a sandy loam, a silt loam, and a clay loam. In individual experiments with each concentration and soil type, 30 ml of solution were added to vials containing 6 g of soil. Preliminary experiments indicated that 24 hours was sufficient time to reach adsorption equilibrium, as measured by radioactivity in the aqueous phase. Thus, the adsorption portion of the experiment was done for 24 hours; subsequently, four desorptions with fresh CaCl₂ solution were done over a second 24-hour period. The amount of radioactivity was quantitated in each adsorption or desorption supernatant by liquid scintillation counting and in soil after the final desorption by combustion radioassay.

Mancozeb is rapidly and strongly bound to soil. Adsorption K_oc values indicate for mancozeb and degradates a medium mobility potential in silt loam to slight mobility in sand. Desorption K_oc indicate a mobility potential from low mobility to immobile. TLC analysis indicate that approximately 45% of mancozeb degraded over the 24-hour test duration with ETU, EU, EBIS, Jaffe’s base and EDA (ethylediamine) as intermediate degradation products. Due to the lower K_OC of metabolites, the derived K_OC of Mancozeb can be considered as conservative.

Description of key information

The geometric mean Koc value is calculated as 771 mL/g (Kom 447 mL/g). Average 1/n 0.741.

Key value for chemical safety assessment

Koc at 20 °C:

771

Additional information

¹⁴C- mancozeb at 0.5, 1.0, 2.0 and 5.0 ppm (formulated product) levels in water, containing 0.1M CaCl₂ was equilibrated with four types of soil: a sand, a sandy loam, a silt loam, and a clay loam. In individual experiments with each concentration and soil type, 30 ml of solution were added to vials containing 6 g of soil. Preliminary experiments indicated that 24 hours was sufficient time to reach adsorption equilibrium, as measured by radioactivity in the aqueous phase. Thus, the adsorption portion of the experiment was done for 24 hours; subsequently, four desorptions with fresh CaCl₂ solution were done over a second 24-hour period. The amount of radioactivity was quantitated in each adsorption or desorption supernatant by liquid scintillation counting and in soil after the final desorption by combustion radioassay.

Mancozeb is rapidly and strongly bound to soil. Adsorption K_oc values indicate for mancozeb and degradates a medium mobility potential in silt loam to slight mobility in sand. Desorption K_oc indicate a mobility potential from low mobility to immobile. TLC analysis indicate that approximately 45% of mancozeb degraded over the 24-hour test duration with ETU, EU, EBIS, Jaffe’s base and EDA (ethylediamine) as intermediate degradation products. Due to the lower K_OC of metabolites, the derived K_OC of Mancozeb can be considered as conservative.