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Description of key information

Short description of key information on bioaccumulation potential result:
Whereas MBTS is absorbed rapidly after oral administration, dermal absorption is slight. The test substance is metabolized rapidly and eliminated in the urine, and to a lesser extent in the feces. Metabolism to MBT seems likely, since glucuronic acid derivatives of MBT have been detected in urine.

Key value for chemical safety assessment

Additional information

Analogue read-across approach

MBTS consists of two molecules MBT; as discussed by El Dareer (1989) MBT and MBTS have remarkable similarities in their kinetics and extent of absorption, distribution, excretion, and metabolism and since the identified metabolites of both derivates of MBT, it is apparent that MBTS is readily converted to MBT.

A read-across approach with data from MBT (benzothiazole-2 -thiol) was performed.

The available physico-chemical data and mammalian toxicity data from MBTS were compared with data from MBT (see table data matrix). Similarities in mammalian toxicity were noted in MBT and MBTS treated animals. Both substances showed a non skin- and eye irritating potential in rabbits. For both substances a moderate skin sensitizing potential was revealed. The oral and dermal acute toxicity of MBTS and MBT is very low, indicated by oral LD50 values of >= 3800 mg/kg bw rat and dermal LD50 values > 7940 mg/kg bw. Overall, no mutagenic potential was indicated for MBTS and MBT in bacterial mutation assays.

Data Matrix, analogue approach

   Target Chemical (MBTS)  Source Chemical (MBT)
 CAS # 120 -78 -5  149-30-4
Chemical Name di(benzothiazol-2-yl) disulphide  benzothiazole-2-thiol
Physico-Chemical Data    
Physical state at 20°C and 101.3 kPa solid (needles)

solid (crystalline)

Appearance Colour: pale yellow

colour: yellow

Molecular weight range 332.4867  167.2513
Melting point >= 164 — <= 179 °C  180 - 182°C. (NIOSH 2004)
Relative density 1.5 g/cm3 at 19°C  1.42 g/cm³ at 20°C. (Lide 2002)
Mammalian Toxicity    
Dermal irritation/corrosion  not irritating rabbit (Monsanto Co. 1973) not irritating rabbit (Monsanto Co. 1975)
Eye irritation   not irritating rabbit (New Zealand White) (Monsanto Co. 1973)  not irritating rabbit (New Zealand White) (Monsanto Co. 1975)
Dermal sensitization   moderate skin sensitizing modified LLNA (De Jong 2002) moderate skin sensitizing Guinea pig maximisation test (Bayer AG 1999)
Mutagenicity (bacteria) overall: negative in Ames assay Ames assay: negative (CMA 1984)
Acute toxicity (oral) LD50: > 7940 mg/kg bw (Monsanto Co. 1973) LD50: 3800 mg/kg bw rat (Monsanto Co.1975)
Acute toxicity (inhalation)   no data available no data available
Acute toxicity (dermal)   LD50: > 7940 mg/kg bw (Monsanto Co.1973) LD50: > 7940 mg/kg bw (Monsanto Co.1975)

Discussion on bioaccumulation potential result:

Metabolism, Toxicokinetics (cited in BUA 1995):

After a single oral dose of 0.438 or 51.1 mg 14C-MBTS/kg bw to male and female F-344 rats, maximum 14C radioactivity was reached in the total blood and plasma within 8 hours. After 96 hours 0.4% to 2% of the 14C radioactivity was still detectable in erythrocytes; this also explained the relatively slight decline of the 14C radioactivity in the total blood compared to the plasma. Due to the relatively high 14C concentration in the total blood and plasma in animals in the low dose group, the authors concluded that the reaction was saturated. The elimination from total blood and plasma was biphasic, with a rapid alpha-phase and slower beta-phase. More than 50% of the absorbed 14C radioactivity had already been excreted in the urine after 24 hours, and after 96 hours the excretion was considerably >80%. In comparison, excretion in the feces was relatively slight (>18%). The 8-hour urine revealed 2 main and 5 metabolites (not identified), but no 14C-MBTS (CMA 1986).

El Dareer (1989) obtained comparable results in a follow-up study with F-344 rats (males and females) and Hartley guinea pigs (females). After daily oral doses of 0.547 mg/kg bw for 14 days and a subsequent single oral dose of 0.73 mg 14C-MBTS/ kg bw to rats, the substance was distributed rapidly in the organism. After 8 hours the highest 14C radioactivity was measured in the kidneys, thyroid gland, liver, total blood and plasma; after 96 hours only the 14C radioactivity in the thyroid gland and total blood was still elevated compared to the other tissues. According to the authors the substance was probably bound covalently to the erythrocyte membrane (after 96 hours 1.2 to 1.7% of the 14C radioactivity was still detectable in the erythrocytes); the elimination was also biphasic (single oral dose 0.73 mg/kg bw: males: alpha/beta phase 4.32/102 h; females: 3.91/138 h). Within 96 hours the excretion in the urine was about 61% for male animals and about 82% for females; the amount of administered 14C radioactivity eliminated in the feces was 7% and 3% respectively.

No MBTS was detected in the 8-hour urine. Since two MBT metabolites (a thioglucuronide and probably a sulfonic acid derivate) were detected, which also occurred after oral MBT administration, the authors (El Dareer et al. 1989) concluded that MBTS is metabolized to MBT in the organism.

After a single intravenous dose of 0.571 mg 14C-MBTS/kg bw, rats again showed a binding to the erythrocyte membrane (after 96 hours 1.5 to 2% of the 14C radioactivity was still detectable in the erythrocytes), as well as biphasic elimination (males alpha/beta phase: 1.29/18.9 h; females: 0.64/13.2 h). Within 72 hours the elimination in the urine was about 93% for male animals and about 101% in females; excretion of the administered 14C radioactivity in the feces amounted to about 10 and 5% respectively (El Dareer, 1989).

After 96-hours dermal application of 0.0336 mg 14C-MBTS/animal (application surface: rat 2 cm2, guinea pig 5 cm2) 6-8% of the administered dose was absorbed by male and female F-344 rats and 12% by female Hartley guinea pigs. In this experiment most of the absorbed 14C radioactivity was again eliminated within 96 hours in the urine (88% to 92% for rats; 97% for guinea pigs) and only a very small amount (4 to 9 % and 1 to 2%, respectively) in the feces (El Dareer 1989).