4-(cyclohexylamino)butane-1-sulfonic acid

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics, other

Remarks:

theoretical assessment

Type of information:

other: expert statement

Adequacy of study:

key study

Study period:

2020

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: see 'Remark'

Remarks:

Theoretical assessment taking all currrently available relevant information into account, based on the REACH Guidance: Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.7c Endpoint specific guidance. Since this is a theoretical assessment, the Klimisch value cannot be 1.

GLP compliance:

no

Type:

absorption

Results:

Based on the physical/chemical properties of the substance, absorption factors for this substance are derived to be 50% (oral), 50% (inhalation) and 50% (dermal) for risk assessment purposes.

After exposure, a substance can enter the body via the gastrointestinal tract (GI), the lungs, and the skin. Since different parameters are relevant for absorption via the different routes of exposure, the uptake via these three routes will be addressed individually. After oral administration, in general, a substance needs to be dissolved before it can be taken up from the gastrointestinal tract. Since the water solubility of 4-(cyclohexylamino)butane-1-sulfonic acid is high at 475 g/L at 20°C, the substance is expected to dissolve completely into the gastrointestinal fluids and become available for uptake. The high water solubility and low molecular weight (MW = 235.34 g/mol) enables passive uptake through aqueous pores which facilitate transport of small water-soluble substances across the epithelial barrier. The partitioning coefficient value (log Pow = -2.0) indicates that 4-(cyclohexylamino)butane-1-sulfonic acid has a high affinity for the aqueous phase. Absorption of very hydrophilic substances by passive diffusion is limited by the rate at which the substance will partition out of the gastrointestinal fluid. Moreover, the sulfonic acid group will dissociate in aqueous medium and thus 4-(cyclohexylamino)butane-1-sulfonic acid will be negatively charged at the pH levels (4 - 8) found within the GI tract. Generally passive diffusion across lipid membranes for ionized substances is hampered. Since the ionization and negative log Pow limit uptake via passive diffusion through lipid membranes but the small molecular size and high water solubility favor uptake through aqueous pores the oral absorption of the substance is set at 50% for risk assessment purposes.

The substance is a solid with a low vapor pressure (5.5 x 10^-8Pa at 25°C), which indicates that exposure via inhalation as a vapor is negligible. However, based on the average particle size of 4-(cyclohexylamino)butane-1-sulfonic acid (MMAD = 83.9 µm)some particles are of an inhalable size.If the substance is aspired, the high water solubility will enable the substance to dissolve in the mucus lining the respiratory tract. The small molecular size favors uptake as the substance can be absorbed via passive diffusion through the intercellular junction pores. However, as the substance is very hydrophilic, the mucus may retain the substance and subsequently clear the lungs of the substance by cilia transporting mucus towards the pharynx where it can be swallowed. Based on these considerations above for risk assessment purposes, the inhalation absorption of the substance is set at 50%.

As the substance is a solid it first needs to dissolve into surface moisture before uptake can take place. According to the criteria given in the REACH Guidance, a default value of 100% dermal absorption should be used unless the MW >500 and log Pow is <-1 or >4, in which case a value of 10% skin absorption should be chosen. The substance has a low molecular weight (MW = 235.34) which favors uptake and therefore, the criteria for 10% absorption are not met and 100% absorption should be considered. However, as the substance has a high water solubility and is hydrophilic the uptake through the stratum corneum will be limited. Based on these considerationsand as it is generally accepted that dermal absorption will not be higher than oral absorption, for risk assessment purposes the dermal absorption of the substance is set at 50%.

Once absorbed, distribution of 4-(cyclohexylamino)butane-1-sulfonic acid throughout the body is expected based on its high water solubility and low molecular weight. Orally absorbed the substance may be metabolized in the GI tract or the liver. The substance is hydrophilic (log Pow = 2.0) and therefore the substance is considered not to accumulate in adipose tissue under normal repeated intermittent exposure. The major routes of excretion of substances from systemic circulation are the urine and/or the feces. Based on its low molecular weight and water solubility 4-(cyclohexylamino)butane-1-sulfonic acid is favorable for urinary excretion. Based on the information above the bioaccumulation potential of the substance is considered low.

Conclusions:

A toxicokinetic assessment was performed based on the available data of 4-(cyclohexylamino)butane-1-sulfonic acid. Based on the physical/chemical properties of the substance, absorption factors for this substance are derived to be 50% (oral), 50% (inhalation) and 50% (dermal) for risk assessment purposes. The bioaccumulation potential is considered low.

Description of key information

A toxicokinetic assessment was performed based on the available data of 4-(cyclohexylamino)butane-1-sulfonic acid. Based on the physical/chemical properties of the substance, absorption factors for this substance are derived to be 50% (oral), 50% (inhalation) and 50% (dermal) for risk assessment purposes. The bioaccumulation potential is considered low.

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

50

Absorption rate - dermal (%):

50

Absorption rate - inhalation (%):

50

Additional information

After exposure, a substance can enter the body via the gastrointestinal tract (GI), the lungs, and the skin. Since different parameters are relevant for absorption via the different routes of exposure, the uptake via these three routes will be addressed individually. After oral administration, in general, a substance needs to be dissolved before it can be taken up from the gastrointestinal tract. Since the water solubility of 4-(cyclohexylamino)butane-1-sulfonic acid is high at 475 g/L at 20°C, the substance is expected to dissolve completely into the gastrointestinal fluids and become available for uptake. The high water solubility and low molecular weight (MW = 235.34 g/mol) enables passive uptake through aqueous pores which facilitate transport of small water-soluble substances across the epithelial barrier. The partitioning coefficient value (log Pow = -2.0) indicates that 4-(cyclohexylamino)butane-1-sulfonic acid has a high affinity for the aqueous phase. Absorption of very hydrophilic substances by passive diffusion is limited by the rate at which the substance will partition out of the gastrointestinal fluid. Moreover, the sulfonic acid group will dissociate in aqueous medium and thus 4-(cyclohexylamino)butane-1-sulfonic acid will be negatively charged at the pH levels (4 - 8) found within the GI tract. Generally passive diffusion across lipid membranes for ionized substances is hampered. Since the ionization and negative log Pow limit uptake via passive diffusion through lipid membranes but the small molecular size and high water solubility favor uptake through aqueous pores the oral absorption of the substance is set at 50% for risk assessment purposes.

The substance is a solid with a low vapor pressure (5.5 x 10^-8 Pa at 25°C), which indicates that exposure via inhalation as a vapor is negligible. However, based on the average particle size of 4-(cyclohexylamino)butane-1-sulfonic acid (MMAD = 83.9 µm)some particles are of an inhalable size.If the substance is aspired, the high water solubility will enable the substance to dissolve in the mucus lining the respiratory tract. The small molecular size favors uptake as the substance can be absorbed via passive diffusion through the intercellular junction pores. However, as the substance is very hydrophilic, the mucus may retain the substance and subsequently clear the lungs of the substance by cilia transporting mucus towards the pharynx where it can be swallowed. Based on these considerations above for risk assessment purposes, the inhalation absorption of the substance is set at 50%.

As the substance is a solid it first needs to dissolve into surface moisture before uptake can take place. According to the criteria given in the REACH Guidance, a default value of 100% dermal absorption should be used unless the MW >500 and log Pow is <-1 or >4, in which case a value of 10% skin absorption should be chosen. The substance has a low molecular weight (MW = 235.34) which favors uptake and therefore, the criteria for 10% absorption are not met and 100% absorption should be considered. However, as the substance has a high water solubility and is hydrophilic the uptake through the stratum corneum will be limited. Based on these considerationsand as it is generally accepted that dermal absorption will not be higher than oral absorption, for risk assessment purposes the dermal absorption of the substance is set at 50%.

Once absorbed, distribution of 4-(cyclohexylamino)butane-1-sulfonic acid throughout the body is expected based on its high water solubility and low molecular weight. Orally absorbed the substance may be metabolized in the GI tract or the liver. The substance is hydrophilic (log Pow = 2.0) and therefore the substance is considered not to accumulate in adipose tissue under normal repeated intermittent exposure. The major routes of excretion of substances from systemic circulation are the urine and/or the feces. Based on its low molecular weight and water solubility 4-(cyclohexylamino)butane-1-sulfonic acid is favorable for urinary excretion. Based on the information above the bioaccumulation potential of the substance is considered low.