Sodium nitrate

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics, other

Remarks:

expert statement

Type of information:

other: expert statement

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Based on the current knowledge the statement has been written.

Objective of study:

absorption

Principles of method if other than guideline:

no guideline as it is an expert statement

GLP compliance:

no

Radiolabelling:

no

Type:

absorption

Results:

50% absorption is taken for oral, dermal and inhalation exposure.

Details on absorption:

Based on low MW, high water solubility, assumed low logPow high absorption is expected. However, the ion formation of the substance inmediately when in contact with a fluid decreases the absorption. The guidance has also been taken into consideration. Therefore, 50% absorption is taken for oral, dermal and inhalation exposure.

In general, a compound needs to be dissolved before it can be taken up from the gastro-intestinal tract after oral administration (1). Based on the relatively high water solubility (>10 g/L) nitrate compounds are expected to have the potential to be absorbed by passive diffusion and may pass through aqueous pores or be carried through the epithelial barriers by the bulk passage of water. While calcium nitrate double salt (CN-Nitcal) has a high molecular weight (900) which is not favourable for absorption, the relatively low molecular weight of most nitrate compounds (for calcium nitrate, potassium nitrate, magnesium nitrate and sodium nitrate, all below 200) is favourable for absorption.On the other hand, calcium nitrate, magnesium nitrate, potassium nitrate, sodium nitrate and CN-Nitcal being all water soluble salts, will dissociate into the calcium/magnesium/potassium/sodium cation and the nitrate anion, which will impair the passage of the gastrointestinal wall (1). Although a partition coefficient cannot be determined for these nitrate substances, it is considered to be low, due to the chemical properties, and not favourable for uptake from the gastrointestinal tract. For risk assessment purposes, the oral absorption is set at 50%. The results of the toxicity studies do not provide reason to deviate from this proposed oral absorption.

Once absorbed, widely distribution of all nitrate substances throughout the body, by means its dissociation products, is expected based on its relatively low molecular weight and high water solubility. Based on its hydrophilic character and ion formation, the extracellular concentration is expected to be higher than intracellular concentration. It is expected that the ions will be excreted mainly via the urine (low molecular weight compounds).

The high melting point (above 100˚C) and boiling point and low vapour pressure (both expected to be high based on the lack of melting at temperatures up to 300˚C), indicate that it is not likely that vapours of the nitrate substances will reach the nasopharyngeal region or subsequently the tracheobronchial or pulmonary region. In addition, the particle size of these substances is much higher than 100μm with only a negligible fraction below 100μm, and thus having no or limited potential to be inhaled.Particles between 100 and 10μm will deposit in the nasopharyngeal region and subsequently be coughed or sneezed out of the body or swallowed. However, particles below 10μm might reach the tracheobronchial or pulmonary regions (2), and then absorption through aqueous pores will be likely taking the molecular weight of <200 into account (although less for the high molecular weight compound CN-Nitcal). The high water solubility of all nitrate substances (> 10 g/L) is favourable for dissolution of the substance in the mucus lining of the respiratory tract.The assumed low partition coefficient of the nitrate substances is, however, indicative for low potential of absorption directly across the respiratory tract epithelium. Overall, it is concluded that when calcium nitrate, magnesium nitrate, potassium nitrate, sodium nitrate or CN-Nitcal is inhaled (particles <10μm only), absorption of these substances is to be expected, and for risk assessment purposes the inhalation absorption for these substances is set at 50%.

Calcium nitrate, magnesium nitrate, potassium nitrate, sodium nitrate and CN-Nitcal are being very well water soluble substances and thus have the potential to be absorbed dermally as the surface moisture of the skin will not limit the availablility. The low molecular weights and high water solubility of these substances are favourable for dermal uptake, although the higher molecular weight of CN-Nitcal is less favourable for dermal uptake. Although a partition coefficient cannot be determined for these substances, it is considered to be low. The criteria for reduced dermal absorption (10%) as given in the REACH guidance, Chapter R7c. (2) (MW>500 and log Pow is smaller than -1 or higher than 4) are not met, and therefore 100% dermal absorption should be considered for risk assessment purposes. Since it is assumed that dermal absorption will not exceed oral absorption, the oral absorption of 50% may be considered as a more realistic value for dermal absorption of calcium nitrate, magnesium nitrate, potassium nitrate, sodium nitrate and CN-Nitcal.

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 (%):

50

Additional information

In aqueous environments, such as the body the sodium nitrate is completely dissociated into the sodium (Na+) and the nitrate (NO3-) ions.

Nitrate is reduced to nitrite by the enzyme nitrate reductase. This enzyme is found in plants, certain bacterial species, and mammalian gastric tissues. After ingestion, nitrates are reduced to nitrites by bacteria in the lower intestine of the adult. However, in babies, which have a physiological gastric achlorhydria (lack of HCl in the stomach), the reduction occurs in the stomach and duodenum from which the nitrites are readily absorbed into the blood stream. Furthermore, methemoglobin-reductase (NADH-cytochrome b5 reductase) in infants has not yet reached full activity. After absorption, nitrites convert oxyhemoglobin into methemoglobin and thus interfere with oxygen transport in the blood, resulting in methemoglobineamia (“blue baby syndrome”). Nitrites can also cause vasodilation, which, like methemoglobineamia, is dose-related.

The sodium cation is an essential ion, and is present in the blood and various body fluids, playing an important role in sustaining health. The Dutch Voedingscentrum does not set an acceptable daily intake, but does state to a maximum of sodium intake of 2.4 g/day.

Based on low MW, high water solubility, assumed low logPow high absorption is expected. However, the ion formation of the substance inmediately when in contact with a fluid decreases the absorption. Therefore, 50% absorption is taken for oral, dermal and inhalation exposure.