Naphthalenesulfonic acid, di-C9-rich C8-10-branched alkyl derivs., barium salts

Basic toxicokinetics

Administrative data

Endpoint:

basic toxicokinetics

Type of information:

other: Expert Statement

Adequacy of study:

key study

Study period:

May 5 2013 to May 20 2013

Reliability:

2 (reliable with restrictions)

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

2013

Report date:

2013

Materials and methods

Test guideline

Qualifier:

no guideline followed

GLP compliance:

no

Test material

Test material information

Constituent 1

Reference substance name:

barium bis(di C8-C10, branched, C9 rich, alkylnaphthalenesulphonate)

EC Number:

939-718-2

Cas Number:

1474044-80-8

Molecular formula:

C28H44O3S.1/2Ba

IUPAC Name:

barium bis(di C8-C10, branched, C9 rich, alkylnaphthalenesulphonate)

Test material form:

solid: particulate/powder

Remarks:

migrated information: powder

Applicant's summary and conclusion

Conclusions:

Interpretation of results (migrated information): other: low bioaccumulation based on QSAR
Barium bis( di C8-C10, branched, C9 rich, alkylnaphthalene sulphonate) will not bioaccumulate or be widely distributed in the body. Its high molecular weight and low solubility will reduce absorption and distribution. For risk assessment, absoption is set at 10% for oral, dermal and inhalation exposure.

Executive summary:

Toxicokinetic Assessment for Barium bis( di C8-C10, branched, C9 rich, alkylnaphthalene sulphonate

A substance can enter the body via the lungs, the gastrointestinal tract, and the skin. To determine the absorption rate, the different routes need to be assessed individually.

 

In general, a compound needs to be dissolved before it can be taken up from the gastro-intestinal tract after oral administration (1). Barium bis( di C8-C10, branched, C9 rich, alkylnaphthalene sulphonate; hereafter, Barium DNNSA) has a low water solubility (0.213 mg/l), therefore it is expected to dissolve to a small extent into the gastrointestinal fluids. Uptake by passive diffusion is thus limited, but it will occur. Barium DNNSA is a UVCB substance. Its approximate molecular weight is moderate (MW = 1056), absorption is thus expected to be low. Barium DNNSA has a high log Pow (> 6.7 at 20°C), which makes the compound very hydrophobic. This characteristic will enable micellular solubilisation by bile salts in the gastro-intestinal tract which allows crossing of lipid biomembranes. The structure contains an ionizable group (SO3H), which might hamper diffusion across biological membranes.

 

The effects seen on the kidney after 28 days repeated exposure by gavage (tubular crystals in the kidney) indicates that the substance has poor solubility in bodily fluids, is excreted via urine and is unlikely to be widely distributed and absorbed in most tissues. The additional observation in the 28 day study of the congestion and discoloration in the mesenteric lymph nodes suggests the filtering action of the lymph nodes of some of Barium DNNSA that passes through the intestinal wall. This may be also act to reduce bioavailability and systemic exposure.

 

The metabolism of barium-DNNSA is mainly contingent on both the nature of the alkyl groups and the nature and extent of naphthalene ring substitutions. There are currently no metabolism studies of barium-DNNSA, however, the US EPA has evaluated the metabolism of analogs in in the sodium alkyl naphthalenesulfonate cluster (SANS), a group of sodium salts of naphthalenesulfonic acids.[1] In a US EPA final rule for SANS, it was stated that “the1- or 2-sulfonic acid sodium salt moieties on the naphthalene ring may provide a handle by which these compounds can be readily conjugated and eliminated.” In addition, the Agency's August 1998 Toxicological Review of Naphthalene (CAS Reg. No. 91-20-3) states that the “in vivo and in vitro

metabolism of the parent unsubstituted naphthalene has been studied extensively in mammalian systems. Without a functional group for conjugation, it is expected that the majority of absorbed unsubstituted naphthalene is eliminated and will proceed through microsome cytochrome P-450 oxygenases to 1- and 2-napthols.” [1] Though the available information

is not definitive for barium-DNNSA, it is expected that the metabolism of substance will be factor enhancing elimination.

For risk assessment purposes, the high log Pow, low water solubility and the high molecular weight of Barium DNNSA do not favor absorption via the oral exposure route. However, absorption of Barium DNNSA by the oral route is set at 10%, based on the evidence for some systemic toxicity as seen in the 28 days subacute study.

 

Once absorbed, wide distribution of the test substance throughout the body is not expected based on its low water solubility. Barium DNNSA has an approximate molecular weight of 1056. In general, molecules of this size do not pass readily through cell membranes thus limiting wide distribution. Based on its size and its low water solubility, distribution is expected to be limited. Excretion of Barium DNNSA will occur via the bile (high molecular weight) or the urine (low molecular weight). Based on its high partition coefficient (>6.7 measured at 20°C; 22.4 based on EPIWIN calculation), it might initially be assumed that Barium DNNSA will distribute into cells and accumulate in adipose tissue. However, for highly hydrophobic substances, e.g. with log Kow > 6, experimental data now demonstrate that bioaccumulation factor (BCF) values tend to decrease with increasing log Kow above 6 (2). The bioaccumulation factor (calculated applying the BCFWIN/BCFBAF model) was found to be 3.14L/kg wet-wt(based on log Pow 22.4). Taken all data together, it is concluded that the bioaccumulation potential is low.

 

The low vapor pressure (<6.4 × 10^-12Pa at 20°C) indicates that Barium DNNSA has a very low volatility and is not expected to evaporate and be available via inhalation. Moreover, aerosols are not expected from the current uses which would reach the respiratory tract. If Barium DNNSA reaches the tracheobronchial region, it is not likely to dissolve within the mucus lining the respiratory tract due to its low water solubility. Based on its high log Pow, micellular solubilisation can occur which will enable some uptake of the substance by crossing of biomembranes.

 

Based on the above data, for risk assessment purposes the inhalation absorption of Barium DNNSA is set at 10% (3).

 

When Barium DNNSA comes in contact with the skin, the first layer of the skin, the stratum corneum, forms a barrier for hydrophilic compounds. Barium DNNSA has a log Pow > 6.7, suggesting that the substance can be taken up in the stratum corneum. However, due to its low water solubility (0.213 mg/l), the transfer between the stratum corneum and the epidermis will be limited.

The structure contains a ionisable group (-SO3H), since it is generally thought that ionized substances do not readily diffuse across biological membranes, penetration of the substance is hampered. A rabbit skin irritation study showed that Barium DNNSA was moderately irritating to skin but the study does not report any skin corrosion which might enhance dermal absorption. 

 

According to the criteria given in the REACH Guidance (3), 10% dermal absorption will be considered in cases where the MW >500 and log Pow <-1 or >4. The weight of evidence of the following factors indicates that Barium DNNSA can be assumed to have a dermal absorption of 10%: 1) the molecular weight (1056) greatly exceeds the criterion 2) the log P is considerably outside the stated range (22.4) and 3) skin irritation testing did not report any corrosive effects which would enhance absorption.

 

In conclusion, the dermal absorption for risk assessment purposes of Barium DNNSA is set at 10%.

 

[1]Sodium Alkyl Naphthalenesulfonate; Exemption from the Requirement of a Tolerance. 40 CFR 180.Federal Register Number:E9-18702. August 5, 2009.