Morpholinium sulphamate

Endpoint summary

Description of key information

Based on physico-chemical characteristics, particularly water solubility and octanol-water partition coefficient and experimental data absorption via oral route and to a less extent via inhalation route is likely to occur. However, bioavailability after dermal exposure is low. Extracellular concentration is likely to be higher than intracellular due to the hydrophilicity of morpholinium sulphamate. As morpholinium sulphamate is already a small, highly water soluble molecule, no metabolic conversion is expected. Based on the molecular weight and the high water solubility morpholinium sulphamate is excreted via the urine. Bioaccumulation of the test substance is not likely to occur based on their physico-chemical properties.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Toxicological profile of Morpholinium Sulphamate

An acute oral toxicity study conducted with morpholinium sulphamate using male and female rats revealed a LD50-value of greater than 2000 mg/kg bw (Toxi Coop, 2012). No mortality was observed. Conspicuous yellow coloured urine was noted in a few animals on day 1 and 2. The animals were free of symptoms from day 3 to day 14. No pathological changes were found during necropsy. In an acute dermal toxicity study with rats a LD50 of greater than 2000 mg/kg bw was determined for morpholinium sulphamate (Toxi Coop, 2012). The test item did not cause dermal irritation symptoms and no macroscopic alterations of organs and tissues were seen during necropsy. As inhalation exposure is an unlikely route of exposure due to the physico-chemical properties of Morpholinium sulphamate, no information on acute inhalation toxicity is available.

In an in vitro skin irritation test on reconstructed human epidermis (Toxi Coop, 2012), Morpholinium sulphamate had no impact on the viability of the skin model and is therefore considered as non-irritant to the skin. The potential of morpholinium sulphamate to induce severe eye damage was assessed in an in vitro Isolated Chicken Eye Test (Toxi Coop, 2012). As no ocular corrosion was observed an in vivo study on rabbits was performed (Toxi Coop, 2012). Morpholinium sulphamate caused only slight effects on the rabbit’s eye and was not considered to be an eye irritant. Based on the toxicity data from skin and mucosa, no respiratory irritation is expected. A LLNA study revealed that morpholinium sulphamate has no skin sensitizing potential (Toxi Coop, 2013).

Morpholinium sulphamate did not induce reverse mutations in a bacterial reverse mutation test (Ames test) with five Salmonella typhimurium strains and one Escherichia coli strain in the absence and in the presence of a metabolic activation system (Toxi Coop, 2012). The mutagenic potential was further evaluated in several in vitro mutation assays with morpholine and sulphamidic acid (read-across approach). Genetic toxicity testing of these analogous substances revealed negative findings except one in vitro mouse lymphoma gene mutation assay with morpholine (Huntsman, 1979) in the absence of metabolic activity which produced an ambiguous result. As all further in vitro gene mutation assays as well as the available in vivo study with morpholine were clearly negative, morpholine and subsequent morpholinium sulphamate are considered to be non-mutagenic.

A 14 day dose range finding study (Toxi Coop, 2012) using oral administration of morpholinium sulphamate was performed in male and female Wistar rats in order to obtain first information on the toxic potential of the test item after long-term administration to allow a dose-setting for a reproduction/developmental toxicity screening test. The chemical was administered orally (by gavage) once a day for a total of 14 days at 0 (vehicle control), 100, 300 and 1000 mg/kg bw/day. No mortality was observed through this study. Test item related salivation appeared in male and female animals dosed with 1000 mg/kg bw/day. There were no test item-related effects on the body weight although the body weight gain was slightly less in male and female animals at 1000 mg/kg bw/day with respect to the control group during the first week. The mean daily food consumption was less than in the control in female animals dosed with 1000 mg/kg bw/day during week 1. The mean blood coagulation parameters (activated partial thromboplastin time and prothrombin time) were slightly but significantly lower in the male animals dosed with 1000 mg/kg bw/day with respect to the control group. However, as this slight reduction was only observed in the male species with no further dose dependency observable, it was not considered to be of toxicological relevance. Furthermore, there were no test item related changes in the remaining hematological parameters. Clinical chemistry examinations revealed significantly higher mean concentrations of serum bile acids in female animals at 1000 mg/kg bw/day. Specific macroscopic alterations related to the test item were not found during the necropsy. There were no test item related changes in the examined organ weights. Based on these results the following three doses were selected for the aforementioned reproduction/developmental toxicity screening study: 100, 300 and 1000 mg/kg bw/day.

The main study (Toxi Coop, 2012) revealed no mortality of male and female animals/dams exposed to Morpholinium sulphamate. Under the conditions of this study the test item did not cause toxic changes and did not influence male and female reproductive performance (gonad function, mating behavior, conception, pregnancy, parturition) in parental male and female Hsd.Brl.Han: Wistar rats or development of the F1 offspring from conception to day 4 post-partum after repeated dose oral administration at 100, 300 or 1000 mg/kg bw/day. Based on these observations the No Observed Adverse Effect Levels (NOAEL) were determined to be 1000 mg/kg bw/day for male and female animals as well as for the offspring.

Oral toxicity after repeated administration of morpholinium sulphamate was further assessed by two repeated dose toxicity studies conducted with morpholine and ammonium sulphamate.

In a repeated dose toxicity study (Sander & Bürkle, 1969) morpholine was administered on female Sprague-Dawley rats orally by feed for eight weeks. The daily uptake average was 500 mg/kg bw. This dosage did not cause mortality within the entire study period. After 270 days moderate adiposis of the liver was observed. No further macroscopic or microscopic alterations were noted. Therefore, the LOAEL was determined to be 500 mg/kg bw/day.

In a 90 day repeated dose study with ammonium sulphamate on rats up to a dose level of 500 mg/kg bw/day (Gupta et al., 1979) no mortality occurred and no adverse effects were observed. Dissociation of the test item into the ammonium cation and the sulphamidic anion is expected, as ammonium sulphamate was dissolved in distilled water before oral administration. The NOAEL was determined to be 500 mg/kg bw/day.

In conclusion, the oral toxicity study with morpholine was considered as a worst-case approach for the assessment of oral toxicity of morpholinium sulphamate after repeated administration. The LOAEL of 500 mg morpholine/kg bw/day was considered as the appropriate LOAEL for morpholinium sulphamate.

 

Developmental toxicity was further assessed by a prenatal developmental toxicity study with morpholinium hydrochloride (97 % w/v) on Wistar rats (BASF 2009). The oral administration of the test item up to 750 mg/kg bw/day had no influence on gestational parameters. Morpholine hydrochloride showed no direct and specific effect on the respective morphological structures. Fetal findings in this study were primarily limited to a slight increase in delayed ossification in the mid- and high-dose groups. These specific skeletal variations mirror common minor effects on fetal morphology which are considered to be transient in nature, being obviously secondary to maternal toxicity. Thus, these findings were regarded to be of no toxicological relevance and are not classified as adverse events. The developmental NOAEL is 750 mg/kg bw/day.

 

Toxicokinetic analysis of Morpholinium Sulphamate

Morpholinium sulphamate is a colourless solid at room temperature with a molecular weight of 184.2141 g/mol. The substance is soluble in water (984.5 g/L at 20°C). The log Pow of morpholinium sulphamate was measured and determined to be -0.07 at 20°C. The melting point of test item is approximately 118-121 °C. In an aqueous solution, Morpholinium sulphamate dissociates into morpholinium cation and sulphamidic anion. Morpholinium sulphamate is manufactured as 50 % (w/v) solution. Therefore, assessment of toxicokinetic properties was based on the aqueous solution.

Absorption

Generally, oral absorption is favoured for molecular weights below 500 g/mol. This characteristic combined with a log Pow value between -1 and 0 and a high water solubility allow dissolution of Morpholinium sulphamate in the gastro-intestinal fluids and contact with the mucosal surface. However, diffusion through biological membranes might be limited by the ionic properties of the substance. Due to its low pKa value (1.0) sulphamidic acid is estimated to be absorbed in the acidic milieu of the stomach (~ pH 1.4 to 4.5). Based on its pKs value (8.4) morpholine might be absorbed in the small intestine due to the present basic milieu (~ pH 5 to 8). Passage through aqueous pores or carriage through the epithelial barrier by the bulk passage of water is assumed to be an alternative pathway of absorption for small, water soluble substances like the test substance. Oral administration of morpholinium sulphamate revealed no adverse effects. However, increased mean concentrations of serum bile acids in female animals and decreased activated partial thromboplastin time and prothrombin time in male animals at 1000 mg/kg bw/day might be associated with the bioavailability of the test item. This assumption is in line with experimental data of Tanaka et al. (1978) who have shown bioavailability of 14C labelled morpholine after oral administration in rats.

Inhalation exposure of vapour was considered to be not relevant as morpholinium sulphamate is manufactured in an aqueous solution (50 %, w/v) and evaporation of the dissociated test substance can be excluded. However, the substance might reach the respiratory tract in form of mist and might dissolve in the mucous. As passive diffusion of ionic substance through the respiratory tract epithelium is limited carriage through aqueous pores is assumed to be an entry route to systemic circulation.

Dermal penetration of morpholinium sulphamate is estimated to be low due to its high water solubility (> 900 g/L) and low log Pow value (< 0). It is general accepted that if a compound’s water solubility is higher than 10 g/L and the log Pow value is below 0 absorption can be anticipated to be low. The ionic properties of morpholinium sulphamate in aqueous solution further limit uptake through the skin. No enhanced dermal penetration is expected as morpholinium sulphamate has no skin irritation properties.

Taken together, physico-chemical properties and experimental data indicate bioavailability of morpholinium sulphamate via oral route and to a less extent via inhalation route. Dermal uptake is estimated to be low.

Distribution

Assuming that morpholinium sulphamate is absorbed into the organism following oral intake, it may be widely distributed via the blood stream due to its hydrophilic properties and in turn the extracellular concentration may be higher than the intracellular one. In a toxicokinetic study with 14C labelled morpholine palmitate (Tanaka et al., 1978) the highest tissue concentration of morpholine after oral administration was found in the muscle and in the intestine. Intravenous administration of radio labelled morpholine (Stee et al., 1981) revealed a high tissue concentration in the kidney.

Particularly, due to the high water solubility and low log Pow value a long biological half-life in tissues is not expected. This assumption is supported by experimental data of Tanaka et al. (1978) and Sohn et al. (1982). 90 % of the original dose was found in the urine after 3 days and 0.08 to 0.14 % was found in the faeces after oral administration of morpholine salts (200 mg/kg bw) on rats (Tanaka et al., 1978). After intraperitoneal administration of 125 mg/kg bw 14C Morpholine (Sohn et al., 1982) the blood plasma half-lives in the rat, hamster and guinea pig were 115, 120 and 300 min, respectively. In all three species, approximately 80 % of the radioactivity was excreted in the urine in 24 hours.

Metabolism

Generally, the function of xenobiotic metabolism is to increase water solubility of highly lipophilic substances to facilitate their excretion from the organism. As morpholinium sulphamate is already a small, highly water soluble molecule, no metabolic conversion is expected. This assumption is in line with excretion data of morpholine published by Sohn et al. (1982). While non-metabolized 14C Morpholine constituted up to 99 % of the urinary radioactivity in the rat and hamster, a significant portion of the dose (approximately 20 %) appeared as N-methylmorpholine-N-oxide in the urine of guinea pigs after i.p. administration of morpholine. As no or only minor metabolite formation is expected for morpholinium sulphamate, there is no indication for metabolic activation of the test substance.

Excretion

Based on the high water solubility, morpholinium sulphamate is expected to be excreted via urine. This assumption is supported by Tanaka et al. (1978), Sohn et al. (1982) and van Stee et al. (1981) who have shown that 90 to 99% of administered morpholine was renal excreted. Less than 1 % was found in faeces.

Summary

Based on physico-chemical characteristics, particularly water solubility and octanol-water partition coefficient and experimental data absorption via oral route and to a less extent via inhalation route is likely to occur. However, bioavailability after dermal exposure is low.

Extracellular concentration is likely to be higher than intracellular due to the hydrophilicity of morpholinium sulphamate. As morpholinium sulphamate is already a small, highly water soluble molecule, no metabolic conversion is expected. Based on the molecular weight and the high water solubility morpholinium sulphamate is excreted via the urine. Bioaccumulation of the test substance is not likely to occur based on their physico-chemical properties.

References

ECHA (2008), Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance.

 

Marquardt H., Schäfer S. (2004). Toxicology. Academic Press, San Diego, USA, 2nd Edition 688-689.

 

Sohn OS, Fiala ES, Conaway CC & Weisburger JH (1982) Metabolism and Disposition of Morpholine in the Rat, Hamster and Guinea Pig. Toxicol. Appl. Pharmacol. 64: 486-491.

 

Tanaka A, Tokieda T, Nambaru S, Osawa M & Yamaha T (1978) Excretion and Distribution of Morpholine Salts in Rats. J. Food Hygienic Soc. 19: 329-334.

 

Van Stee EW, Wynns PC & Moorman MP (1981) Distribution and disposition of Morpholine in the rabbit. Toxicology 20: 53-60.