Phosphorus

Endpoint summary

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Additional information

Studies specifically on the absorption/distribution/metabolism/excretion (ADME) of this substance (Fe₃P) are not available. Their conduct was considered dispensable in view of the chemical inertness and extremely poor water solubility of the substance. However, data are currently available from in vivo toxicology studies performed with this substance, supporting the above conclusion on lack of bioavailability.

Fe₃P is an inorganic compound with a molecular weight of 198.5 g/mole. Its water solubility was verified to be below the limit of detection of the analytical method employed (≤ 1 mg/L). Fe₃P is used as an additive for powder metallurgy. It is a dark powder containing 31% w/w particles smaller than 10 μm (respirable particulate material). These physicochemical properties suggest that Fe₃P will not be readily absorbed across biological membranes.

Absorption

Oral route

The available data on the acute and repeated dose toxicity studies by the oral route does not indicate any systemic toxicity from Fe₃P; there were no obvious clinical signs specific to treatment with Fe₃P, the weights of examined organs after 28 days repeated oral administration were unaffected by treatment and no gross or microscopic changes were observed. This suggests that either the compound is absorbed and not toxic or it is not absorbed via the gastrointestinal tract. The abnormal colour (black) of the faeces recorded in the acute oral toxicity study in rats indeed suggests that Fe₃P is not absorbed, and instead is excreted via faeces.

 

Dermal route

Fe₃P did not show any potential to induce skin sensitization. No other data are available on absorption after dermal application. Therefore it is not possible to conclude whether Fe₃P can be absorbed through skin or not. However, the physicochemical properties of the compound suggest that it is very poorly absorbed through the skin.

 

Inhalation route

Effects seen in an acute inhaled toxicity study were limited to the lungs and tracheobronchial lymph nodes, suggesting the possibility of a local effect. The increased lung weights are consistent with the residual test material remaining in the lungs at the end of the 14‑day recovery period, and the enlarged lymph nodes are likely to be indicative of the on-going removal of exogenous material; neither effect is particularly indicative of a systemic toxic effect, and such findings could be expected for many powders of inhalable particle size. On this basis, it is concluded that Fe₃P is not readily absorbed via the lungs and that the treatment-related effects observed in the acute inhalation study are not specific to Fe₃P, but instead characteristic of inert particulate material of inhalable or near-inhalable size.

Distribution, Metabolism, Excretion

Data specifically from toxicokinetics studies with Fe₃P are not available. Likewise, no data are available on distribution and metabolism in the existing toxicity studies. However, there are clear indications to suggest that the substance is not readily absorbed by the gastrointestinal tract, through the lungs or the skin. Therefore it may be expected that Fe₃P will not be distributed systemically or metabolised to any relevant extent. Some metabolism may occur in the gastrointestinal tract, the lungs or the skin but the majority of the substance will be excreted/removed as such. The abnormal colour (black) of the faeces recorded in the acute oral toxicity study in rats suggests that the substance will be excreted via the faeces. When administered by inhalation, it is expected that the substance will be translocated from the respiratory tract by macrophages to the extrathoratic region from where it will be swallowed.

Conclusion

There is good evidence that the test substance is not readily absorbed by the gastro intestinal tract, the skin or the lungs. Since it is not absorbed, it is not expected to be distributed to internal body tissues/organs or metabolised. It seems to be excreted via the faeces when orally administered. When inhaled, there is evidence that it is removed from the lungs involving mucocilliary mechanisms.