Calcium acetylide

Endpoint summary

Description of key information

In contact with water calcium carbide instantly decomposes hydrolytically, yielding acetylene gas and calcium hydroxide. The reaction is completed within a few seconds. Accordingly, the hydrolysis half-life is significantly less than the REACH criterion for rapid hydrolysis of 12 hours. Therefore, the environmental fate assessment has to be based on the decomposition products instead of the parent substance itself.

Calcium hydroxide:

Calcium hydroxide is an inorganic substance hence biodegradation is not applicable to this compound.

In contact with water/moisture Ca(OH)2 instantly dissociates to Ca2+ and 2 OH-. OH- ions will be readily neutralised in the environment due to the buffering capacity of natural waters, sediments and soils, and due to the neutralising reaction with carbon dioxide. Ca2+ ions have a low tendency for adsorption to soil/sediments. Available Kd values range between 5.3 and 49.1 L/kg. Calcium is a ubiquitous integral part of almost all naturally occurring mineral matrices, in particular of soils and sediments. Also natural waters carry a significant level of calcium background concentrations. The calcium released from CaC2 is therefore of no environmental concern.

Also in the assessment of the bioaccumulation potential of Ca(OH)2, Ca2+ would be the species of interest (as opposed to OH–, which is quickly neutralised).

Calcium, a soft grey alkaline earth metal, is a ubiquitous substance: It is the fifth-most-abundant element by mass in the earth's crust and also the fifth-most-abundant dissolved ion in seawater both by molarity and mass.

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 in fish or a terrestrial species is not warranted. Calcium is obviously devoid of any bioaccumulation potential.

Acetylene:

Acetylene is a short-chain gaseous hydrocarbon. However, 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, although the vapour pressure and Henry’s Law constant are high.

QSAR estimates by means of BIOWIN v4.10 predict that acetylene is readily biodegradable. Based on the very short-chain, non-branched chemical structure of the substance, this prediction is considered appropriate and is hence used in chemical safety assessment.

Due to the ready biodegradability of the volatile gas acetylene, higher-tier studies on its biological degradation in surface water, sediment and soil do not have to be conducted (see REACH Annex IX, column 2, points 9.2.1.2, 9.2.1.3, and 9.2.1.4).

A significant potential for bioaccumulation and adsorption to soil/sediment for acetylene is can be safely excluded. On the one hand the substance is a gas which will not remain in the aqueous phase or soil pore water due to its high vapour pressure and Henry’s Law constant, on the other hand the log Kow is very low (0.37).

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. Accordingly, the hydrolysis half-life is significantly less than the REACH criterion for rapid hydrolysis of 12 hours. Therefore, the environmental fate assessment has to be based on the decomposition products instead of the parent substance itself.

Calcium hydroxide:

Calcium hydroxide is an inorganic substance hence biodegradation is not applicable to this compound.

In contact with water/moisture Ca(OH)2 instantly dissociates to Ca2+ and 2 OH-. OH- ions will be readily neutralised in the environment due to the buffering capacity of natural waters, sediments and soils, and due to the neutralising reaction with carbon dioxide. Ca2+ ions have a low tendency for adsorption to soil/sediments. Available Kd values range between 5.3 and 49.1 L/kg. Calcium is a ubiquitous integral part of almost all naturally occurring mineral matrices, in particular of soils and sediments. Also natural waters carry a significant level of calcium background concentrations. The calcium released from CaC2 is therefore of no environmental concern.

Also in the assessment of the bioaccumulation potential of Ca(OH)2, Ca2+ would be the species of interest (as opposed to OH–, which is quickly neutralised).

Calcium, a soft grey alkaline earth metal, is a ubiquitous substance: It is the fifth-most-abundant element by mass in the earth's crust and also the fifth-most-abundant dissolved ion in seawater both by molarity and mass.

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 in fish or a terrestrial species is not warranted. Calcium is obviously devoid of any bioaccumulation potential.

Acetylene:

Acetylene is a short-chain gaseous hydrocarbon. However, 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, although the vapour pressure and Henry’s Law constant are high.

QSAR estimates by means of BIOWIN v4.10 predict that acetylene is readily biodegradable. Based on the very short-chain, non-branched chemical structure of the substance, this prediction is considered appropriate and is hence used in chemical safety assessment.

Due to the ready biodegradability of the volatile gas acetylene, higher-tier studies on its biological degradation in surface water, sediment and soil do not have to be conducted (see REACH Annex IX, column 2, points 9.2.1.2, 9.2.1.3, and 9.2.1.4).

A significant potential for bioaccumulation and adsorption to soil/sediment for acetylene is can be safely excluded. On the one hand the substance is a gas which will not remain in the aqueous phase or soil pore water due to its high vapour pressure and Henry’s Law constant, on the other hand the log Kow is very low (0.37).