Calcium acetylide

Endpoint summary

Link to relevant study record(s)

Reference

Endpoint:

basic toxicokinetics in vivo

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Justification for type of information:

As calcium carbide instantly hydrolyses to Ca(OH)2 and C2H2 upon contact with water/moisture the assessment is based on the degradation products. For details please refer to the read across report in section 13.

Reason / purpose for cross-reference:

read-across source

Type:

absorption

Results:

99%

Key result

Test no.:

#1

Transfer type:

other: transfer to bones

Observation:

distinct transfer

Remarks:

bones

Details on excretion:

1.2 % Ca was excreted in urin

Conclusions:

Ca2+ applied by gavage is almost completely resorbed and built into the bones. 1.2 % of the dose was excreted in urine

Executive summary:

In a metabolism study, 45-Calcium bis(2 ,3,4,5,6)-pentahydroxyhexanoate was administered to rats daily by oral gavage at a dose level of 30 mg/kg bw/day for 12 days.

The test material was almost completely resorbed and built into the bones. 1.2 % of the dose was excreted in urine.

This information is used in a read-across approach in the assessment of the target substance. For justification of read-across please refer to the read-across report attached to IUCLID section 13.

Description of key information

Ca2+ applied by gavage is almost completely resorbed and built into the bones. 1.2 % of the dose was excreted in urine

Key value for chemical safety assessment

Bioaccumulation potential:

low bioaccumulation potential

Absorption rate - oral (%):

99

Additional information

In contact with water calcium carbide instantly decomposes hydrolytically, yielding acetylene gas and calcium hydroxide. The reaction is completed within a few seconds. Calcium hydroxide dissociates into calcium and hydroxyl ions. Due to the release of hydroxyl ions the risk assessment is driven by local irritant effects on the skin, eyes and respiratory tract. As hydroxyl ions are readily buffered in biological fluids/tissue, only calcium ions and gaseous acetylene needs to be taken into account for the assessment of systemic effects.

Calcium:

For humans, calcium is an important component of a healthy diet as the mineral is necessary for life. Calcium has particular importance in cell physiology, as Ca2+ transport from and into the cytoplasm acts as a signal for numerous cellular processes. Moreover, Ca is stored in bones and teeth of humans and animals, and is an integral part of mollusc shells. Thus, calcium is the most abundant metal by mass in many animals.

In humans, approximately 99 % of the body's calcium is stored in the bones and teeth, while the rest is important for the functioning of processes like exocytosis, neurotransmitter release or muscle contraction, with special importance for the heart muscle.

Calcium levels in blood serum are subject to homoeostatic regulation. However, long-term calcium deficiency may cause rickets and impairment of blood clotting as well as osteoporosis in menopausal women. While a lifelong deficit can affect bone and tooth formation hypercalcaemia (elevated levels of calcium in the blood), impaired kidney function including kidney stone formation and decreased absorption of other minerals may be caused by over-retention of calcium. Moreover, the following potential adverse effects of excessive calcium intake have been proposed: the milk-alkali syndrome (MAS), vascular calcification, increased risk of cardiovascular disease and increased risk of prostate cancer (EFSA, 2012).

In 2003, the Upper Intake Level (UL) was thus set at 2,500 mg calcium/day for adults and for pregnant and lactating women by the Scientific Committee on Food (SCF). Following a request from the European Commission, the Panel on Dietetic Products, Nutrition and Allergies was asked to re-evaluate the safety in use of calcium and to provide, if necessary, revised Tolerable Upper Intake Levels (ULs) of calcium for all relevant population groups. The Panel comes to the conclusion that no new data have become available which would require a revision of the UL for calcium for adults, including pregnant and lactating women, i.e. 2500 mg/day.

Thus, in the light of the fact that calcium is a ubiquitous, essential mineral nutrient and the high UL of 2500 mg/d, a study investigating the bioaccumulation behaviour of calcium ions is not warranted.

Acetylene:

Acetylene is a short-chain gaseous hydrocarbon. The water solubility for acetylene (1200 mg/L at 20 °C, CRC Handbook, see IUCLID section 4.8) is relatively high. Thus, residues of acetylene in the water phase cannot be excluded. However, the vapour pressure and Henry’s Law constant of acetylene are high. The low log Kow of 0,37 does not indicate a significant transfer from body fluids into fatty tissue. Thus, bioaccumulation of acetylene is not considered relevant.