Slags, ferrochromium-manufg.

Endpoint summary

Description of key information

Short description of key information on absorption rate: 
The percutaneous penetration of chromium metal powder has been studied in in vitro models in synthetic sweat at pH 4.5. The penetration through the skin was very low; about 99% of the Cr was detected in the skin.

Key value for chemical safety assessment

Absorption rate - dermal (%):

1

Additional information

No toxicokinetic studies have been performed with FeCr-slag.

The amorphous glass phase of FeCr-slag consists of practically insoluble silicates, and therefore

silicates and amorphous silica were used for read-across purposes. Data on chromium were also presented. There is no need to generate specific data related to FeCr slag.

The dissolution tests have shown that the levels of elements (Fe, Cr, Cr(VI),Pb, Mn,Pb,Ni, Cd, Al and As) as well as SiO2 are below the detection limit in transformation/ dissolution tests. Co was detected but its concentration was close to the detection limit. The detection limit of silicon is, however, high when compared with others.

Silicon in different forms is ubiquitous in the environment, various foods, drinking water and beverages contain silicon. Our normal dietary intake of silicon is between 20-50 mg Si/day and the silicon in diet seems to be in highly bioavailable form as shown as a high proportion of dietary silicon excreted in the urine. The differences in dietary intake are likely to explain the variability in urine levels of silicon between different individuals.

After ingestion, amorphous silicon dioxide seems to have insignificant effects on tissue or urinary silicon levels. Since silicon in different forms is ubiquitous in the environment, various foods, drinking water and beverages contain silicon. Our normal dietary intake of silicon is between 20-50 mg Si/day and the silicon in diet seems to be in highly bioavailable form as shown as a high proportion of dietary silicon excreted in the urine. The differences in dietary intake are likely to explain the variability in urine levels of silicon between different individuals. Although in neutral solutions elemental silicon and amorphous silicon dioxide is slowly dissolved, in acidic solutions the dissolution of silicon and amorphous silicon dioxide is significantly impaired. Thus, e. g. in stomach, the release of silicon from silicon particles is likely to be low, which is likely to affect the absorption from gastrointestinal tract.

After inhalation of synthetic amorphous silicon dioxide, the lung silicon content reaches a plateau level at which elimination equates with deposition. After the cessation of exposure amorphous silica is rapidly eliminated from the lung tissue.

No significant deposition into the lymph nodes has been seen in prolonged rat exposure during the first 40 days, but after 120 days the retention was about 31% of total deposited (and 1.5 - 2% of theoretically deposited) silica. This suggests that the involvement of lymphatic elimination is not relevant at short exposure periods/lower body burdens.

Absorption of chromium in the body is largely dependent on chromium species. Intratracheal studies on chromium(III)oxide and chromite show that lung clearance of these insoluble chromium compounds is slow. The elimination half-life was 11 days in sheep administered chromium(III) oxide and 6 months in rats after intratracheal administration of chromite particles. No studies on gastrointestinal absorption is available on poorly soluble chromium(III))species, but even soluble chromium(III)chloride is absorbed only at the levels of <2% from the GI-tract.Thus, the oral absorption of chromium metal is likely to be very low, due to the practically insoluble nature of the substance. The dermal absorption of chromium metal has been tested by in vitro models, and has been shown to be very low.

In the blood plasma most of the chromium is bound to large molecular mass proteins (e. g. transferrin). Chromium associates also with the oligopeptide low-molecular-weight chromium-binding substance (chromodulin). In blood, chromium is mostly (about 95%) bound to large molecular weight plasma proteins and only a minor part of the chromium can be found in erythrocytes.

The administered Cr is mainly distributed into the liver, kidneys, spleen and bone. Many of these toxicokinetic studies were done with CrCl₃, which is much more soluble than chromium metal. Therefore, the absorption of this substance is much higher that of the practically insoluble chromium metal and the systemic distribution of chromium is likely to be significantly lower.

The excretion of absorbed chromium(III) occurs mainly in the faeces, and to a low extent in the urine.

 

 

Discussion on absorption rate:

The percutaneous penetration of chromium metal powder has been studied in in vitro models in synthetic sweat at pH 4.5. Franz diffusion cells with intact and damaged human skin were used for the tests. About 99% of the Cr was detected in the skin, indicating that penetration of chromium through the skin is very low.