Thiram

PBT assessment

PBT assessment: overall result

Reference

Reference 1

Name:

Thiram

Type of composition:

legal entity composition of the substance

State / form:

solid: particulate/powder

Reference substance:

Thiram

Reference 2

Name:

Thiram

Type of composition:

boundary composition of the substance

State / form:

solid: particulate/powder

Reference substance:

Thiram

PBT status:

the substance is not PBT / vPvB

Justification:

The PBT Assessment is based on the criteria set out in the “Guidance on information requirements and chemical safety assessment, Chapter R.11: PBT Assessment” (ECHA, 2017).

 

Persistence (P) Assessment

 

Tetramethylthiuram disulfide (CAS No. 137-26-8) is not readily biodegradable (30% after 28 d) according to the OECD criteria. Several higher tier studies investigating the degradation of the substance in water column, sediment/water and soil compartments are available.

 

The substance hydrolyses with specific half-lives of 68.5 days, 3.5 days and 6.9 hours under acidic, neutral and alkaline conditions, respectively. The major hydrolysis product was carbon disulfide (CS2).

 

Furthermore, simulation studies are available assessing the degradation of the substance in water, sediment and soil.

 

The key water simulation study (OECD 309) resulted into DT50 values in natural river water, treated with 2 and 10 µg/L, of 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 (n.d. after 62 d) and a maximum of 10.4% AR after 6 days (5.4% after 62 d). Since the recoveries were below the validity criteria of the study, one additional sample was connected to a catalytic converter in order to improve the system and minimize losses. The mass balance for this sample was 80.4% AR after 62 days and the 14CO2 accounted for 42.4% AR. In terms of mineralization, the sum of CO2 and CS2 rate was 58% after 62d. Unfortunately, if this data shows that mineralization occurs, it is not possible to know at which duration of the study the 50% of mineralization is met. Moreover, due to methodological deficiencies of the study (low recoveries), the study leaves doubts regarding the persistency behavior of the substance in freshwater and no unequivocal conclusion can be drawn regarding P criterion in water, as set out in the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT/vPvB assessment (2017).

 

The aerobic aquatic metabolism of the test substance in two different water/sediment systems (Abbey Lake and Swiss Lake, OECD 308) was investigated and resulted into total recoveries for both systems of > 90% at all sampling intervals. The best fit DT50 values based on test material analysis (calculated in a new kinetic assessment in compliance with FOCUS guideline 2006) were 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. Due to the low duration of the key and supporting studies (<120 d) and methodological deficiencies of further supporting studies (partly very low oxygen concentrations), the persistence of the substance in sediment cannot be fully assessed based on the criteria set out in the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT/vPvB assessment (2017).

 

Under aerobic conditions in soil (OECD 307), tetramethylthiuram disulfide (applied at 12.8 mg/kg soil dw) reached maximum mean mineralization (CO2 and CS2) 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 clearly > 50% of AR within 120 d. Thus, on the basis of the criteria set out in the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT/vPvB assessment (2017), the substance can be considered as not persistent or very persistent in soil since its presumed mineralization half-life was reached within 120 d (presumed mineralization DT50 < 120 days).

 

In conclusion based on simulation studies available for three compartments (water, sediment and soil) it can be concluded that the substance itself degrades rapidly in the environment through primary degradation. Mineralization behavior, in contrast, leaves some doubts regarding the P criterion evaluation. Indeed, if it can be clearly concluded that the substance is not P/vP in soil, however, even if primary degradation DT50 leads to a not P/vP conclusion in water and sediment compartments, unequivocal conclusion cannot be reached for these compartments regarding mineralisation.

  

Bioaccumulation (B) assessment

Tetramethylthiuram disulfide has a log Kow of 1.8 - 2.1 (OECD 117), which is below the trigger value of 3. The substance is not considered as ionizable or surface active.Thus, the substance does not meet the screening criterion for bioaccumulation and is not considered to be bioaccumulative (B) or very bioaccumulative (vB).

 

Toxicity (T) assessment

Long-term toxicity testing with Pimephales promelas resulted in a NOEC (33 d, survival and growth) of 4.6 µg a.i./L (mean measured, OECD 210) for tetramethylthiuram disulfide (CAS No. 137-26-8), which is below the trigger value of 0.01 mg/L for chronic results. Furthermore, tetramethylthiuram disulfide (CAS No. 137-26-8) is classified as STOT RE Cat. 2 according to Regulation (EC) No. 1272/2008. Thus, the criteria set out in Annex XIII of Regulation (EC) No. 1907/2006 are met and the substance is considered to meet the T criterion.

In conclusion based on the criteria set out in the “Guidance on information requirements and chemical safety assessment, Chapter R.11: PBT Assessment” (ECHA, 2017), the substance is not PBT / vPvB.

Likely routes of exposure:

Emission characterisation data is not required for Thiram (CAS No. 137-26-8) as this substance does not meet the criteria for a PBT or vPvB substance.