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EC number: 260-135-8
CAS number: 56375-79-2
A substance can enter the body via the gastrointestinal tract, the
lungs, and through the skin. In general, a compound needs to be
dissolved before it can be taken up from the gastrointestinal tract
after oral administration (1). After oral intake, two characteristics of
MTBAC favor uptake via passive diffusion (passage of small water-soluble
molecules through aqueous pores or carriage of such molecules across
membranes with the bulk passage of water): (a) MTBAC is highly soluble
in water (> 1 * 103g/L), therefore the substance will
readily dissolve into the gastrointestinal fluids to allow direct
uptake; (b) MTBAC has a moderate molecular weight (approximately 236),
and small molecules can be taken up via diffusion. On the other hand,
MTBAC will not easily dissolve in lipids, as reflected in its log Pow
below 0 (log Pow = -2.0). Its lipophobic character will hamper
penetration through lipid membranes. Furthermore, MTBAC dissociates in
aqueous solution to render a chloride ion and a methyltributylammonium
ion. It is generally assumed that ionized substances do not readily
diffuse across biological membranes. Based on these two factors
hampering penetration (lipophobicity and ionicity), oral absorption of
MTBAC is set at 50% for risk assessment purposes (2). The oral toxicity
data do not provide reason to deviate from the proposed oral absorption
factor. Once absorbed, wide distribution of the test substance
throughout the body is expected based on its high water solubility and
moderate molecular weight. Absorbed MTBAC is most likely excreted via
urine (3). Based on the low partition coefficient, MTBAC is not expected
to bioaccumulate significantly in adipose tissue. The vapour pressure of
MTBAC was found to be low (7.0 * 10-3 Pa at 25°C), which indicates that
the substance is not available for inhalation as a vapour. However,
MTBAC is marketed in aqueous solution. This might lead to the formation
of aerosols, which may be inhaled and enter the respiratory tract. Once
MTBAC reaches the tracheobronchial region, the substance is likely to
dissolve within the mucus lining of the respiratory tract and to get
absorbed due to its high water solubility and moderate molecular weight.
Based on the above data, for risk assessment purposes the inhalation
absorption of MTBAC is set at 100%.Exposure to MTBAC will be considered
in aqueous solution. Dermal uptake is facilitated by this liquid form.
The first layer of the skin, the stratum corneum, is a barrier for
hydrophilic compounds. Based on its hydrophilic nature, crossing the
first layer of the skin, the stratum corneum, is expected to be
hampered. Moreover, its ionic state might influence penetration as the
quaternary ammonium ion can bind to skin components which would further
slow uptake (2). On the other hand, MTBAC is a skin irritant. This
implies that exposure of the skin will affect the skin integrity,
resulting in dermal uptake of MTBAC. The moderate molecular weight and
high water solubility of MTBAC are favourable for dermal absorption.
According to the criteria given in the REACH Guidance (2), 10% dermal
absorption will be considered in case MW >500 and log Pow <-1 or >4,
otherwise 100% dermal absorption should be used. As the
physical/chemical properties of MTBAC do not meet the criteria for
limited dermal absorption (MW 236; log Pow = -2), for risk assessment
purposes dermal absorption is set at 100%. This implies that dermal
absorption exceeds oral absorption, which is a direct consequence of the
skin irritating properties of MTBAC. Based on the above data, for risk
assessment purposes the dermal absorption of MTBAC is set at 100%. The
results of the toxicity studies do not provide reasons to deviate from
this proposed dermal absorption factor. 1. Martinez MN, Amidon GL.
Mechanistic approach to understanding the factors affecting drug
absorption: a review of fundamentals. J Clin Pharmacol 2002; 42: 620-43.
2. Guidance for the implementation of REACH. Guidance on information
requirements and chemical safety assessment. Chapter R.7c: Endpoint
specific guidance. European Chemical Agency, Version 2.0 November 2014.
3. Parkinson. In: Casarett and Doull’s Toxicology, The basic science of
poisons. Sixth edition. Ed. C.D. Klaassen. Chapter 6: Biotransformation
of xenobiotics. McGraw-Hill, New York, 2001.
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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