Thiram

Endpoint summary

Additional information

Several studies testing the biodegradation of the substance tetramethylthiuram disulfide (CAS No. 137-26-8) in different systems are available.

 

Biodegradation of tetramethylthiuram disulfide in the screening test (OECD 310) reached 30% after 28 days and therefore, the substance is considered as not readily biodegradable. The results from the toxicity control showed that tetramethylthiuram disulfide was not inhibitory to the inoculated bacteria.

 

Furthermore, several simulation studies are available assessing the degradation of tetramethylthiuram disulfide (CAS No. 137-26-8) in water, sediment and soil.

 

The key water simulation study was performed according to the OECD guideline 309. The derived DT50 values in natural river water, treated with 2 and 10 µg/L, were 0.13 - 0.14 days and 0.14 – 0.16 days (0.28 – 0.3 and 0.3 – 0.34 days, recalculated to 12 °C), respectively. Mean recoveries of samples for the HPLC analysis were low and laid at 84.3 % AR (2 µg/L sample) and 64.3 % AR (10 µg/L) after 62 days. Direct volatile radioactivity (14CO2 and 14CS2) for the 2 µg/L and 10 µg/L treatments accounted for a maximum of 13% (AR) after 6 days (not detected after 62 d) and a maximum of 10.4% (AR) after 6 days (5.4% after 62 d). Since the recoveries were low, and in order to minimize the loss in recovery, one sample was connected to a catalytic converter in order to improve the system. The mass balance for this sample was 80.4% (AR) after 62 days and the 14CO2 accounting for 42.4% (AR). CS2 and CO2 were the major degradants (58% after 62d). Unfortunately, due to methodological deficiencies of the study (low recoveries), mineralization rate evaluation cannot be fully assessed.

 

In the second key study (2014), the aerobic aquatic metabolism of the test substance was investigated in two different water/sediment systems (Abbey Lake and Swiss Lake) according to the OECD guideline 308. The total recovery for both systems was > 90% at all sampling intervals. DMCS was the major metabolite identified for both systems. The DT50 values were calculated in a new kinetic assessment in compliance with FOCUS kinetic (2006). The study resulted into the best fit DT50 values based on test material analysis of 0.14 d at 20°C (FOMC kinetics, recalculated to 0.3 d for 12°C) and 0.129 d at °C (SFO kinetics, recalculated to 0.27 d for 12°C) for Abbey Lake and Swiss Lake, respectively. Mineralisation of the substance (CO2 and CS2) did not exceed 50% (24.42 and 37.67% of AR) by the end of the incubation period (60 d) in Abbey Lake and Swiss Lake, respectively.

 

Under aerobic conditions in soil (OECD 307), tetramethylthiuram disulfide (applied at 12.8 mg/kg soil dw) mineralization (CO2 and CS2) reached maximum mean amounts of 53.58% AR after 30 days, 54.28% AR after 39 days, 38.69% AR after 45 days and 49.58% AR after 120 days in four different soils. Further supporting simulation studies in soil also resulted into mineralization rates of > 50% of AR within 120 d.

 

In conclusion the substance is not readily biodegradable. Based on simulation studies available for three compartments (water, sediment and soil) the substance itself degrades rapidly in the environment through primary degradation. The mineralization DT50 in soil was < 120 d, based on the available data. Mineralization behavior in sediment and water compartments, in contrast, leaves some doubts regarding persistence, due to either methodological deficiencies or short duration of the available studies.