Disulfiram

Biodegradation in soil

Description of key information

-         DT50 of parent substance in soil: 4.7 – 45.1 days at 20 °C based on test material analysis (recalculated to 9.98 – 98.75 d at 12 °C, aerobic, OECD 307 and FOCUS 2006, soil).

-         38.69 - 54.28% of AR mineralization (CO2 and CS2) after 30 to 120 days in key study and clearly > 50% of AR in supporting studies.

Additional information

No higher tier studies on biodegradation are available for disulfiram. The degradation of the analogue substance tetramethylthiuram disulfide (thiram) (CAS No. 137-26-8) in soil was investigated in several simulation studies under aerobic and anaerobic conditions.

 

In the study (2016), conducted according to OECD guideline 307 and GLP, the formation and identity of metabolite P8 (chromatographic region around 29 minutes) after application of the analogue substance thiram to soil was investigated. In parallel, the degradation rate of the substance was investigated in four european soils at 20°C for 30 to 120 days (depending on the soil) under aerobic test conditions. The recoveries for the duration of the study were 100.4 % of AR (EFS546), 94.9 % of AR (EFS558), 98.2 % of AR (EFS559) and 102.2 % of AR (EFS567). The test substance degraded rapidly in all four soils based on test material analysis. Mineralization to 14CO2 reached a maximum average of 51.8, 53.0, 40.7 and 35.1% AR for the Bologna (EFS546), Bologna (EFS558), Parma (EFS559) and Bologna (EFS567) soils, respectively, by the end of the soil incubations. Mineralization to 14CS2, reached a maximum of 1.8, 1.3, 8.9 and 3.6% AR for the Bologna (EFS546), Bologna (EFS558), Parma (EFS559) and Bologna (EFS567) soils, respectively, by the end of the soil incubations. The P8 metabolite was not detected in the soil extracts analyzed by HPLC. Therefore, it could be concluded that the P8 metabolite detected in old studies was an artifact peak due to poor chromatography and not a true metabolite. Data from this study were retrospectively used to calculate DT50 values for thiram based on the FOCUS guideline (2006). The normalized test item DT50 value obtained based on the SFO kinetic model were between 4.7 and 45.1 d at 20°C (9.98 – 98.75 d, recalculated to 12°C) depending on the soil. 

 

In the study (2000), which was conducted according to the EU Method C.23 (Aerobic and Anaerobic Transformation in Soil) and GLP the degradation behaviour of the analogue substance thiram in three European soils was investigated at 20 ± 2 °C and 10 ± 2 °C (one soil). 14C-volatiles steadily increased to a maximum between 60.9 and 73.9 % of AR during the incubation period showing a high mineralization of the test substance. DMCS was a main metabolite with > 10 % of AR. A non-polar metabolite (P8) was observed although it was only found at a significant level in one soil, reaching a maximum of 11.41 %. This metabolite was further investigated in the key study described above. The DT50 values based on test material analysis ranged between 3.7 and 6.8 d at 20°C and 9.8 d at 10°C.

 

In the study (1995), according to US-EPA 540/9-82-021 and GLP the DT50 values based on test material analysis was 2 d at 20°C (recalculated to 4.25 d at 12°C). Mineralisation exceeded 50% on Day 21 and reached 74.9% after 205 d. The recovery of the radiolabeled test substance was always > 90% of AR. A retrospective kinetic analysis according to the FOCUS guideline (2006), resulted in a geom. mean DT50 value for degradation of 4.89 d.

 

The leaching characteristics of the analogue substance 14C-thiram and its degradates was studied in a sandy soil following aerobic incubation for ~3 days according to Commission Directive 95/36/EC (1995). Thiram was aged in the sandy soil to its approximate half-life and added to the top of two replicate soil columns containing the identical soil. Simulated rainfall (0.01 M calcium chloride; 200 mm) was added to each column dropwise over a two-day period. Overall, 14C-thiram showed no mobility in the soil at an artificial rainfall of about 200 mm over a period of approximately 2 days.

 

Finally, a study is available evaluating the degradation potential of the analogue substance under anaerobic conditions and 20°C in one soil. The test resulted in a maximum mineralization of 6.01% CO2 at test termination (42 d). The test material DT50 was 3.91 d at 20°C (recalculated to 8.3 d at 12°C).

 

In view of these results and the high mineralization rates (mostly > 50%), it can be expected that the analogue substance tetramethylthiuram disulfide will not persist in the soil compartment so does disulfiram.