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Administrative data

Link to relevant study record(s)

Description of key information

Short description of key information on bioaccumulation potential result: 
There are no toxicokinetic data available for SMBT. A read-across approach (systemic effects) was done with toxicokinetic data from MBT (see discussion endpoint summary toxicokinetics).
The toxicokinetic of MBT was evaluated in several studies in rats and guinea pigs (CMA 1986, CMA 1987, Nagamatsu 1979). Orally administered MBT was readily absorbed and excreted, whereas excretion was primarily in the urine, and small amounts in faeces (CMA 1986, 1987). Recovery data, after oral or intravenously administered of MBT, did not indicate that appreciable amounts of radioactivity from 14C-labeled MBT were retained in tissues other than blood. Metabolism studies revealed a glucuronide, a glutathione conjugate, the mercapturic acid as well as a sulphate and dibenzothiazyl disulfide as metabolites of MBT in urine.

Key value for chemical safety assessment

Additional information

SMBT is a sodium salt of MBT (mass content SMBT: MBT 88%, sodium: 12%). SMBT is a strong base (pH 10, as discussed in chapter 1.3) and is classified as corrosive (R34/category 1C). The corrosive character of SMBT is the predominant local effect and determines the local DNEL. According to ECHA Guidance Document Part E: Risk Characterisation, substances with R-phrases R34 (causes burs), R41 (risk of serious damage to the eyes), which relate to corrosive or severe irritant effects to the eye or irritant effects to the eyes are allocated to the moderate hazard category.

Read across approach (systemic effects)

There are no toxicokinetic data, no valid repeated dose study data and reproduction toxicity data available for SMBT. A read-across approach with systemic toxicity data from MBT (benzothiazole-2 -thiol) was performed. In addition, the second component the sodium ion Na+ is briefly discussed.

The available systemic mammalian toxicity data from SMBT were compared with data from MBT (see table data matrix). Similarities in mammalian systemic toxicity were noted in SMBT and MBT treated animals. The oral and dermal toxicity of SMBT and MBT is very low, indicated by oral LD50 values > 2000 mg/kg bw and dermal LD50 values >7940 mg/kg bw. No mutagenic potential or even a weak response was indicated for SMBT and MBT in bacteria.

Data Matrix, analogue approach

   Target Chemical (SMBT)  Source Chemical (MBT)
 CAS # 2492-26-4  149-30-4
Chemical Name sodium benzothiazol-2-yl sulphide  benzothiazole-2-thiol
Structure    
Physico-Chemical Data    
Physical state at 20°C and 101.3 kPa liquid (aqueous solution) solid (crystalline)

Appearance Colour: yellowish-brown

colour: yellow

Molecular weight range 189.2331 g/mol  167.2513 g/mol
Relative density 1.26 kg/l (20°C) was reported by Lanxess 50% solution and 1.14 kg/l (20°C) for 30% solution  1.42 g/cm³ at 20°C. (Lide 2002)
Water solubility liquid (aqueous solution) 118 mg/l at 25°C and pH 7. (Monsanto 1980)
Mammalian Toxicity    
Dermal irritation/corrosion corrosive not irritating rabbit (Monsanto Co. 1975)
Eye irritation  corrosive  not irritating rabbit (New Zealand White) (Monsanto Co. 1975)
Dermal sensitization  corrosive(no in vivo skin sensitzing data availabe) moderate skin sensitizing Guinea pig maximisation test (Bayer AG 1999)
Mutagenicity (bacteria)  Ames assay: negative (Monsanto Co. 1976, Goodyear 1979)Ames assay: weak positive (NTP 1984) Ames assay: negative (CMA 1984)
Mutagenicity in vivo assays no data Genotoxicity: negative micronucleus assay (CMA 1984)
Acute toxicity (oral) LD50: 2100 mg/kg bw (Bayer AG 1978) LD50: 3800 mg/kg bw rat (Monsanto Co.1975)
Acute toxicity (inhalation)  no valid data available no data available
Acute toxicity (dermal)  LD50:> 7940 mg/kg bw (Monsanto Co. 1974) LD50: > 7940 mg/kg bw (Monsanto Co.1975)

Sodium

Sodium is the quantitative main cation of the extracellular room. In combination with other electrolytes as chloride and potassium, the sodium ion is involved in several essential functions in the human body. The main function is the maintenance of the extracellular volumes, the regulation of the osmotic pressure, the regulation of the acid-base homeostasis, production of gastric acid, activation of enzymes and the trans-membrane potential (e.g. transmitting signals in neurons and muscle cells). The recommended daily intake is in the range of 575 to 3500 mg Na+/day (SCF 2003).

Discussion on bioaccumulation potential result:

There are no toxicokinetic data available for SMBT.

A read-across approach (systemic effects) was done with toxicokinetic data from MBT (see discussion endpoint summary toxicokinetics). Read across with MBT (systemic effects) Several toxicokinetic studies were conducted to evaluate absorption, metabolism, distribution and elimination of MBT.

The oral absorption and distribution of MBT was evaluated in male and female Fischer 344 rats (CMA 1987). Male and female rats were dosed orally for 14 days with unlabeled MBT prior to dosing with 14C-labeled MBT. The average dose of the unlabeled compound was 0.510 mg/kg/day; the dose of the labeled compound was 0.503 mg/kg (0.0586 mCi/kg). Groups of four rats of each sex were dosed with 14C-MBT and sacrificed at each selected time point (8, 24, 48, 72 and 96 h). Whole blood, plasma various tissues, urine, and faeces were collected and analyzed for radioactivity. Male rats orally dosed with the 14C-MBT excreted 90.7% and the females 101% in urine 96 hours after application. Similarly, 9.99% and 5.22% of the dose, respectively, is excreted in the faeces in 96 hours. A small portion of the administered radioactivity (1.20 to 1.53 % of the dose) remains associated with the erythrocytes at 96 hours after dosing. Most of this radioactivity was bound to the erythrocyte membranes. Half-lives of elimination from the plasma have been calculated to be 4.7 to 8.56 h and 5780 to 6000 h for the alpha and beta phases, respectively. At 96 hours after dosing, only trace amounts of radioactivity remain in other tissues. Of these tissues, thyroid contained the highest concentration. No intact MBT was seen in the urine. Only two metabolites were detected in the urine 8 hours after sample administration. The major one was a glucuronide derivate of MBT. The other metabolite was not subject to hydrolysis by acid, beta-glucuronidase, or sulfatase, and thus the author concluded that this metabolite was not a conjugate.

In another toxicokinetic study, male and female Fischer 344 rats were dosed once orally with a low or high dose (0.592 or 55.5 mg/kg) of 14C-labeled MBT (CMA 1986). Groups of four rats of each sex were dosed and sacrificed at each selected time point (8, 24, 48, 72, and 96 hours). Whole blood, plasma, urine and faeces were collected and analyzed for radioactivity, and a profile of urinary metabolites was obtained. Rats dosed with 14C-labeled MBT excreted 72.1 % to 106 % of the radioactivity administered in the urine in 96 hours; whereas in faeces 4.03% to 10.3% of the radioactivity was excreted in this time. A small portion of the administered radioactivity (0.423 to 2.04% of the dose) remains associated with the erythrocytes at 96 hours after dosing; and for rats given low doses of MBT, there were greater values for percent of the dose in whole blood and plasma, relative to the high dose, indicating that a saturable process is operative at the high dose. Although tissues, except blood, were not examined in this study, the recovery data did not indicate that appreciable amounts of radioactivity from 14C-labled MBT were retained in tissues other than blood. In a preliminary analysis of the urine a total of seven metabolites of MBT were detected. The authors concluded that MBT was readily absorbed and excreted, primarily in the urine and only small amounts in the faeces.

In addition, male and female Fischer 344 rats were dosed intravenously with 14C-labeled MBT. The animals were treated with 0.602 mg/kg 14C-MBT (CMA 1986). Groups of four rats of each sex were dosed and sacrificed at each selected time point (5min, 15 min, 1 h, 2 h, 24 h and 72 h). Whole blood, plasma, urine, and faeces were collected and analyzed for radioactivity; and a profile of urinary metabolites was obtained. The treated rats excreted 90.9 to 101% of the radioactivity administered in the urine in 72 hours; 3.79 % to 15.1% of the radioactivity was excreted in the faeces in this time. A small amount of the administered radioactivity (1.52 to 1.96 % of the dose) remains associated with the erythrocytes at 72 hours after dosing. Although tissues, except blood and tail, were not examined in this study, the recovery data did not indicate that appreciable amounts of radioactivity from 14C-labeled MBT were retained in tissues other than blood. A total of four metabolites of 14C-MBT were detected in urine two were major metabolites and two minor metabolites.

In an early study with guinea pigs (Nagamatsu 1979) two metabolites glucuronide and sulphate of MBT, were identified in urine by thin layer chromatography; 7.62% of MBT and 90% of conjugates were determined in the sampled urine six hours after treatment. Metabolism studies revealed that metabolic transformation of MBT takes place exclusively at SH-group of the molecule. A glucuronide, a glutathione conjugate and the mercapturic acid formed from this as well as a sulphate and dibenzothiazyl disulfide have been detected as metabolites (Fukuoka 1987, 1995).