Disulfiram

Endpoint summary

Additional information

Data on the ready biodegradability of disulfiram are available. Simulation studies have been performed with the analogue substance tetramethylthiuram disulfide (CAS No. 137-26-8).

One study according to the OECD Guideline No. 301 B and GLP is available for disulfiram that investigates the ready biodegradability of the substance. The substance did not completely reach 60% biodegradation after the prolonged period of 60 d (58% after 60 d) and is therefore considered as not readily biodegradable. However, a plateau of biodegradation was not reached at the study period and it is therefore assumed that there is further potential for mineralization in the environment. The substance was not inhibitory to microorganisms, as shown by the toxicity control. 

Therefore, further higher tier biodegradation data from the analogue substance tetramethylthiuram disulfide (CAS No. 137-26-8) were taken into account in a weight of evidence approach for assessment of the biodegradation.

Under aerobic conditions in soil (OECD 307), mineralization (CO2 and CS2) of the analogue substance tetramethylthiuram disulfide (applied at 12.8 mg/kg soil dw), 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.

A water simulation study (2015) was performed according to the OECD guideline 309 with the analogue substance tetramethylthiuram disulfide (CAS No. 137-26-8). 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 a second study (2014), the aerobic aquatic metabolism of the test substance was investigated with the analogue substance tetramethylthiuram disulfide (CAS No. 137-26-8) 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) reached 24.42 and 37.67% of AR by the end of the incubation period (60 d) in Abbey Lake and Swiss Lake, respectively.

 

In conclusion the substance is not readily biodegradable but shows potential for mineralization as shown in the prolonged study according to OECD Guideline No. 301 (58% biodegradation after 60 d, no biodegradation plateau was reached). Based on simulation studies available for three compartments (water, sediment and soil) the substance is expected to degrade 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.