In a laboratory experiment [thiocarbonyl-14C]thiram was incubated in aquatic systems of river water and sediment (Rhine) and pond water and sediment (Judenweiher) in the dark at 20°C under aerobic conditions for 101 days (Wyss-Benz, 1992). The system was continuously supplied with humidified air; evolved volatile compounds were trapped. The initial thiram levels in the water were 1.2 - 1.4 mg ai/l in the two experimental runs. The pH of the waters was 7.5-8.0. The organic carbon content of the river sediment, a loamy sand, was 0.62% and the pond sediment, a loam, 3.2%.
The decrease of thiram and the appearance of two identified products are shown in Table 21. The initial half-life of thiram was about 2 days with more than 90% disappearance within 7 days. Thiram itself was not detectable in solvent extracts of the sediments. Methyl dimethyldithiocarbamate (DMDTC-Me), CS2 and CO2 were identified as products. A number of other compounds were detected by HPLC, but were generally at low levels and could not be identified with any of the reference materials.
About half of the total 14C disappeared from the water in 14 days. The 14C in the sediments increased to a maximum of about 30% of that applied by days 14-30 and thereafter declined to 16-24% by day 101.
Table 21. Thiram and identified degradation products in the water phase of aquatic systems incubated with [14C]thiram at 20°C in the dark under aerobic conditions (Wyss-Benz, 1992).
|
Days |
14C as thiram, mg/l |
|||||
|
River |
Pond |
|||||
|
Thiram |
DMDTC-Me |
CS2 |
Thiram |
DMDTC-Me |
CS2 |
|
|
0 |
1.3 |
n |
n |
1.3 |
n |
n |
|
0.25 |
1.2 |
n |
n |
1.2 |
n |
n |
|
1 |
0.73 |
0.021 |
0.063 |
0.90 |
0.043 |
0.046 |
|
2 |
0.73 |
0.022 |
0.022 |
0.75 |
0.014 |
0.015 |
|
4 |
0.32 |
0.076 |
0.073 |
0.30 |
0.066 |
0.086 |
|
7 |
0.096 |
0.058 |
0.049 |
0.030 |
0.045 |
0.10 |
|
14 |
n |
0.059 |
n |
n |
0.044 |
n |
|
30 |
n |
0.034 |
n |
n |
0.025 |
n |
|
57 |
n |
n |
n |
n |
n |
n |
|
101 |
n |
n |
n |
n |
n |
n |
n: no detectable residue
DMDTC-Me: methyl dimethyldithiocarbamate
The degradation pathways of thiram in water/sedimant systems are shown in Figure 4.
Figure 4. Degradation of thiram in aerobic water/sediment systems.
