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Environmental fate & pathways

Biodegradation in soil

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Reference
Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Comparable to guideline study with acceptable restrictions.
Qualifier:
no guideline available
Principles of method if other than guideline:
The degradation of dimethylamine was monitored in three Saskatchewan soils at 85 % of field capacity under laboratory conditions at 20 °C using [14C] dimethylamine at rates of 0.5-100 µg/g.
GLP compliance:
not specified
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
other: Clay from Indian Head
% Clay:
48
% Silt:
30
% Sand:
22
% Org. C:
3.7
pH:
7.3
Soil no.:
#2
Soil type:
other: Clay from Regina
% Clay:
62
% Silt:
36
% Sand:
2
% Org. C:
3.3
pH:
7.6
Soil no.:
#3
Soil type:
other: Loamy sand from White City
% Clay:
11
% Silt:
9
% Sand:
80
% Org. C:
1.6
pH:
7.8
Details on soil characteristics:
The soils were collected in September 1991 from the 5 cm top horizon.
Soil No.:
#1
Duration:
7 d
Soil No.:
#2
Duration:
7 d
Soil No.:
#3
Duration:
7 d
Parameter followed for biodegradation estimation:
radiochem. meas.
Details on experimental conditions:
Soil samples were moistened to 85 % of their field capacity moistures and incubated in the dark for 7 days at 20 +/- 1 °C. Water was added if
necessary.
Samples were taken and weighed into polystyrene foam cartons and plased in jars fitted with spring-clip lids. The jars were placed into the incubatofor 7 days in the dark at 20 +/- 1 °C to allow soil equilibrium.
Each soil was then treated with [14C]dimethylamine solution (25 µL, 3.7 µg) and sufficient aqueous nonradioactive dimethylamine solution so that
treatments were prepared containing 0.5, 10, 50, and 100 µg of dimethylamine / g of moist soil.
In each jar was placed a 50 mL beaker inside which was a 20 mL glass vial containing 15 mL of 0.2 M aqueous sodium hydroxide to trap any
[14C]carbon dioxide evolved as [14C]carbonate. The samples were reincubate at 20 +/- 1°C.
Samples (1mL) of the sodium hydroxide solution were analyzed for radioactivity after 2,4 and 7 days.
After 7 days incubation time the levels of radioactivity into to soil microbial biomass were determined using a chloroform fumigation-incubation
technique. (Chlorform disrupts microbial cell membranes, releasing internal 14C-labeled constituents, whereby a portion is liberated as a flush of
[14C]-Carbon dioxide. This flush is measured using a mineralization factor (Kc) of 0.41, the levels of radioactivity incorparated into the biomass
were calculated.

Nine samples of WLhite City laomy sand were treated in the same way, but after incubation these were removed for analysis after 5 min, 3 days and 6 days. Three air - dried soils were analyzed only after 7 days.
Soil No.:
#1
% Degr.:
> 40
Parameter:
radiochem. meas.
Sampling time:
2 d
Soil No.:
#2
% Degr.:
> 40
Parameter:
radiochem. meas.
Sampling time:
2 d
Soil No.:
#3
% Degr.:
> 40
Parameter:
radiochem. meas.
Sampling time:
2 d
Soil No.:
#1
% Degr.:
69 - 89
Parameter:
radiochem. meas.
Sampling time:
7 d
Soil No.:
#2
% Degr.:
69 - 89
Parameter:
radiochem. meas.
Sampling time:
7 d
Soil No.:
#3
% Degr.:
69 - 89
Parameter:
radiochem. meas.
Sampling time:
7 d
Transformation products:
not measured
Evaporation of parent compound:
not measured
Volatile metabolites:
yes
Residues:
no
Details on results:
At all concentrations in soils at 85 % Field Capacity (FC) and at 20 °C there was a very rapid release of the labeled dimethyamine carbon atoms as
[14C]carbon dioxide with over 40 % of the applied 14C being so released after 2 days and 69 - 89 % after 7 days.
The percentage of the applied radioactivity incorporated into the soil biomass for 7 days with 0.5, 10 and 100 µg/g [14c]dimethylamine ranged
from 10 - 16 %.
Measurement of dimethylamine and radioactivity in the loamy sand incubated with 25 µg/g [14C]dimethylamine indicated that after 5 min, all of the radioactivity recovered using calcium chloride as extractant was idenfitiable colorimetrically as dimethylamine.

At all concentrations in soils at 85 % Field Capacity (FC) and at 20 °C there was a very rapid release of the labeled dimethyamine carbon atoms as [14C]carbon dioxide with over 40 % of the applied 14C being so released after 2 days and 69 - 89 % after 7 days. The percentage of the applied radioactivity incorporated into the soil biomass for 7 days with 0.5, 10 and 100 µg/g [14c]dimethylamine ranged from 10 - 16 %. Measurement of dimethylamine and radioactivity in the loamy sand incubated with 25 µg/g [14C]dimethylamine indicated that after 5 min, all of the radioactivity recovered using calcium chloride as extractant was idenfitiable colorimetrically as dimethylamine.

Conclusions:
It can be concluded that in agricultural soils there will be rapid metabolism of dimethylamine resulting from application of herbicide formulations with no likelihood of any buildup of residues.
Executive summary:

The degradation of dimethylamine was monitored in three Saskatchewan soils at 85 % of field capacity under laboratory conditions at 20 °C using [14C] dimethylamine at rates of 0.5-100 µg/g.

It can be concluded that in agricultural soils there will be rapid metabolism of dimethylamine resulting from application of herbicide formulations with no likelihood of any buildup of residues.

Description of key information

Key value for chemical safety assessment

Additional information

Three Saskatchewan soils (clay from Indian Head, clay from Regina, and loamy sand from White City) were used to detect the degradation of dimethylamine under laboratory conditions (20 °C, [14C]-label, 0.5 -100 µg/g). The soils were collected from the 5 cm top horizon. After allowing to reach soil equilibrium in the laboratory jars, dimethylamine was added in concentrations of 0.5, 10, 50, and 100 µg. After 7 days incubation time the levels of radioactivity into to soil microbial biomass were determined using a chloroform fumigation-incubation technique. At all concentrations there was a very rapid release of the labeled substance as [14C]carbon dioxide with over 40 % of the applied with over 40 % of the applied 14C being so released after 2 days and 69 - 89 % after 7 days. The percentage of the applied radioactivity incorporated into the soil biomass for 7 days with 0.5, 10, and 100 µg/g [14C]dimethylamine ranged from 10 - 16 %. It can be concluded that in agricultural soils there will be rapid metabolism of dimethylamine resulting from application of herbicide formulations with no likelihood of any buildup of residues.