Sodium methanethiolate

Endpoint summary

Description of key information

The LD50 of sodium methylmercaptide administered by oral  route in the male rat was 116 (75-161) or  109 (84-146) mg/kg using the pure test substance. The test substance  toxicity in the females was similar to that of the males. 
The LD0 of sodium methylmercaptide when administered by dermal route in rats was > 400 mg/kg using the formulated  test substance (21.2% in water).

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

LD50

Value:

116 mg/kg bw

Acute toxicity: via dermal route

Endpoint conclusion

Dose descriptor:

discriminating dose

Value:

85 mg/kg bw

Additional information

Oral route:

In a study conducted according to OECD Test Guideline 401 (Clouzeau, 1989), 5 male Sprague-Dawley rats/dose were given sodium methanethiolate via oral gavage (supplied as a 19.9% solution in water; diluted further in water and dosed at 10 ml/kg except for the high dose (which was administered at 2.05 ml/kg of the 19.9% solution); the doses were equivalent to 400, 620, 950, 1400 and 2000 mg/kg bw of the 19.9% solution or 80, 123, 189, 279, and 398 mg active ingredient (a.i.)/kg bw. Five female rats/group were dosed at 620, 950 and 2000 mg/kg bw (equivalent to 123, 189 and 398 mg a.i./kg bw). Animals were observed for 14 days after dosing. Mortality in the males was 1/5 and 2/5 at 400 and 620 mg/kg bw, respectively, and 5/5 at higher doses. Mortality was recorded within minutes of dosing. The mortality in the females was 3/5, 5/5, and 4/5 at 620, 950, and 2000 mg/kg bw, respectively. In males, a significant decrease in spontaneous activity and dyspnea at 400 and 620 mg/kg bw, tonic-clonic convulsions at the dose levels of 950 and 1400 mg/kg bw before death of the rats, and ataxia and coma at 2000 mg/kg bw were the main clinical signs recorded. Also in males, abnormal red coloration of the stomach was observed during the macroscopic examination of all animals from all dose levels found dead during the study. The necropsy performed on animals sacrificed at the end of the study revealed no macroscopic abnormalities. The toxicity in the females was similar to that of the males. The LD50 of the formulation (19.9% sodium methanethiolate solution) was 581 mg/kg bw, equivalent to 116 mg a.i./kg bw. 

Dermal route

Sodium methanethiolate (21.2% solution in water) was applied directly to the skin of one male and one female rat at 2000 mg/kg body weight (424 mg active ingredient (a.i.) /kg bw) in an OECD TG 402 study (Clouzeau, 1994). After occlusion for 24 hours, tissue lesions on the whole depth of the skin were noted and these animals were euthanized for humane reasons. Eight additional rats (4/sex) were dosed with 400 mg/kg bw test solution in water (84.8 mg a.i. /kg bw). The dose site was wrapped with a semi-occlusive dressing for 24 hours. Two females exhibited reversible body weight loss and clinical signs that included hypoactivity and tremors between days 1 and 5. No cutaneous reactions or deaths were observed for any of the animals over the 14-day observation period, resulting in LD₅₀of >400 mg/kg bw for the 21.2% water solution and > 84.8 mg/kg bw for the active ingredient.

Justification for classification or non-classification

According to REGULATION (EC) No 1272/2008:

Pure sodium methylmercaptide and water solutions [C >= 38%] should be classified as toxic if swallowed (category 3) and water solutions [C < 38%] should be classified as harmful if swallowed (category 4).

According to DIRECTIVE 67/548/EEC

Pure sodium methylmercaptide and water solutions [C >= 58%] should be classified as toxic if swallowed (T, R25) and water solutions [C < 58%] should be classified as harmful if swallowed (Xn, R22).