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Diss Factsheets

Administrative data

Link to relevant study record(s)

Description of key information

Key value for chemical safety assessment

Additional information

Assessment of the Toxicokinetic Behaviour

 

Naphthalene-2 -sulfonic acid (CAS-No. 120 -18 -3)

 

There were no studies available in which the toxicokinetic properties of naphthalen-2 -esulfonic acid were investigated. However, a dermal absorption study is available for the sodium salt of naphthalenesulfonic acids.  

Naphthalenesulfonic acids are a mixture of naphthalene-1-sulfonic acid, naphthalene-2-sulfonic acid and multiple sulfonic naphthalene acids. The following assessment is refereeing to the both single sulfonic naphthalene acids.

Both substances have a molecular weight of 208.28 g/mol is a brown solid, which is highly soluble in water (calculated water solubility: 254 g/l at 20 °C (EPIWIN v1.41). The experimental log Po/w for naphthalene-1-sulfonic acid is -0.944 at 23 °C (BASF 1995, see chapter “Partition Coefficient”), indicating that a general accumulation of naphthalenesulfonic acids in the adipose tissue is improbable.

 

Absorption

In acute oral toxicity studies, rats were administered naphthalenesulfonic acids by gavage. Exact levels of the LD50 were reported; partly, clinical signs of toxicity were observed. Additionally, a high water solubility and a moderate log Po/w are considered; therefore bioavailability of naphthalenesulfonic acids after oral administration is indicated (BASF AG 1972; see chapter “Acute Oral Toxicity”).

In a well documented study, the potential of naphthalenesulfonic acid, sodium salt for dermal absorption was studied in pig skin ex vivo (Goldwell 1997). In total eight dissections of pig skin (thickness 2-3 mm, available surface 1.13 cm2) were placed in diffusion chambers with 339 µL of an aqueous solution containing 1mg test substance/mL in the donor chamber for 24 h and incubated at 37°C. The concentration of the permeated test substance was measured via UV- absorption. The permeation constants for two comparable trials were 2.47-2.48*10e-4 cm/h, indicating a very low potential of naphthalenesulfonic acid, sodium salt for dermal absorption. Under the conditions of the test, 1% of the test substance did permeate pig skin within 24 h. Considerations on local effects of the naphthalenesulfonic acids (the substance has to be considered as corrosive) the barrier function of the skin layers is affected, depending on the concentration of the test substance. On the other hand, considerations on physical-chemical properties (regarding the high water solubility (> 10 g/l) and the low log P value (< 0)) lead to the assumption that the substance may be too hydrophilic to cross the lipid rich environment of the stratum corneum. Taken together the very low measured potential for dermal absorption in skin pig as reliable model for human skin and the considerations on local effects and physical-chemical properties, dermal uptake of naphthalenesulfonic acids in humans – and, subsequently, the risk for systemic toxicity after dermal exposure - is considered as improbable in low concentrations; with increasing local concentrations, the corrosive potential of naphthalenesulfonic acids come to the fore.

Naphthalenesulfonic acids have a very low calculated vapour pressure of 3.01 µPa at 25°C (MPBPWIN v1.43, 2009); subsequently, the calculated vapour saturation threshold is < 0.01 mg/L. Even with a measured vapour pressure of 0.053 Pa at 24.5°C of the sodium salt, the vapour saturation threshold is very low. Additionally, the calculated Henry constant of < 0.01 Pa*m3/mole indicates that the substance would slowly evaporate from water surface into the atmosphere and that an exposure and absorption via atmosphere is negligible.

 

Metabolism

No potential metabolites were calculated by OECD toolbox 1.00 for liver, gastrointestinal tract and skin.

Studies on genotoxicity (Ames-Test, gene mutation in mammalian cells in-vitro, micronucleus assay in-vivo) were negative, i.e. there is no indication of a reactivity of naphthalenesulfonic acids or its metabolites under the test conditions.  

 

Excretion

Possible metabolites should be considered as water soluble and should have a molecular weight lower than 500 u. Therefore, parental naphthalenesulfonic acids and their metabolites are expected to be excreted predominantly via the urine.

Read across justification:

 

The registration item contains ca. 78.89% of naphthalene-2-sulphonic acid (CAS # 120-18-3) and ca. 6.5 % of naphthalene-1-sulphonic acid (CAS # 85-47-2). These two substances have the same molecular weight and are structurally almost identical. Therefore naphthalene-2-sulphonic acid and naphthalene-1-sulphonic acid and their respective salts are suitable for read across in order to fulfill the data requirements.