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Description of key information

A toxicokinetic assessment was performed based on the available data of the substance.

Key value for chemical safety assessment

Bioaccumulation potential:
low bioaccumulation potential
Absorption rate - oral (%):
50
Absorption rate - dermal (%):
50
Absorption rate - inhalation (%):
100

Additional information

A substance can enter the body via the lungs, the gastrointestinal tract, or the skin, depending on the exposure route. To determine the rate of absorption, the different routes are assessed individually.

After oral administration, in general, a compound needs to be dissolved before it can be taken up from the gastro-intestinal tract. Two characteristics of guanidinium phosphate (1:1) 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) Guanidinium phosphate (1:1) is highly soluble in water (> 10000 mg/L); therefore the substance will dissolve into the gastrointestinal fluids. (b) Guanidinium phosphate (1:1) has a low molecular weight (approximately 157), which allows easy diffusion. Since guanidinium phosphate (1:1) has a log Pow below 0 (< -3.48), the compound is hydrophilic. This characteristic will hamper penetration through lipid membranes. As soon as guanidinium phosphate (1:1) dissolves in the fluids of the gastro-intestinal tract, it will dissociate into a phosphate-ion and a guanidinium-ion. It is generally assumed that ionized substances do not readily diffuse across biological membranes, but the absorption of ionic substances (i.e. acids and bases) is influenced by the varying pH of the GI tract.

Taking all information together, for risk assessment purposes oral absorption of guanidinium phosphate (1:1) is set at 50%. 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 low molecular weight. Absorbed guanidinium phosphate (1:1) is most likely excreted via urine. Based on its low partition coefficient (< -3.48), it is very unlikely that guanidinium phosphate (1:1) will accumulate in adipose tissue.

The low vapour pressure (<0.015 Pa) indicates that it is not likely that guanidinium phosphate (1:1) will reach the nasopharyncheal region or subsequently the tracheo/bronchial/pulmonary region via inhalation of vapour. If guanidinium phosphate (1:1) reaches the tracheobronchial region, it is likely to dissolve within the mucus lining the respiratory tract and to get absorbed due to its high water solubility and low molecular weight.

Based on the above data, for risk assessment purposes the inhalation absorption of guanidinium phosphate (1:1) is set at 100%.

Guanidinium phosphate (1:1) is a white crystalline powder. When it comes in contact with the skin without additional water, uptake will be limited. However, given the fact that guanidinium phosphate (1:1) has a high water solubility, it will dissolve into the surface moisture of the skin. The first layer of the skin, the stratum corneum, is a barrier for hydrophilic compounds. Guanidinium phosphate (1:1) has a log Pow <–1, suggesting that the substance is not likely to be sufficiently lipophilic to cross the stratum corneum, therefore dermal absorption is likely to be low. Furthermore, it can be assumed that the ions formed after guanidinium phosphate (1:1) has dissolved can influence its adsorption. According to the criteria given in the REACH Guidance, 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 guanidinium phosphate (1:1) do not meet the criteria for limited dermal absorption (MW 157), for risk assessment purposes dermal absorption should be set at 100%. However, in parallel with the motivation for the oral adsorption rate, the substance will dissociate into a phosphate-ion and a guanidinium-ion. It is generally assumed that ionized substances do not readily diffuse across biological membranes. Furthermore, guanidinium phosphate (1:1) has a log Pow below 0 (< -3.48), which will limit crossing of biological barriers.

Based on the above data, for risk assessment purposes the dermal absorption of guanidinium phosphate (1:1) is set at 50%. The results of the toxicity studies do not provide reasons to deviate from this proposed dermal absorption factor.