Registration Dossier

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Administrative data

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:
PNEC aqua (freshwater)
PNEC value:
4.62 µg/L
Assessment factor:
1 000
Extrapolation method:
assessment factor
PNEC freshwater (intermittent releases):
46.2 µg/L

Marine water

Hazard assessment conclusion:
PNEC aqua (marine water)
PNEC value:
0.462 µg/L
Assessment factor:
10 000
Extrapolation method:
assessment factor

STP

Hazard assessment conclusion:
no emission to STP expected

Sediment (freshwater)

Hazard assessment conclusion:
no exposure of sediment expected

Sediment (marine water)

Hazard assessment conclusion:
no exposure of sediment expected

Hazard for air

Air

Hazard assessment conclusion:
no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:
no exposure of soil expected

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:
no potential for bioaccumulation

Additional information

The PNECs of calcium carbide for the aquatic environment are based on acute aquatic toxicity tests conducted with calcium carbide of technical grade. Assessment factors in agreement with pertinent guidance documents by ECHA were applied. PNECs for sediment and terrestrial compartments were not derived for the following reasons: Calcium carbide decomposes rapidly in contact with moisture, forming acetylene and calcium hydroxide. Calcium hydroxide is alkaline, and therefore has the capacity to change the pH of environmental media. Aquatic ecosystems are characterised by pH, among other factors; the organisms inhabiting any ecosystem are adapted to the prevailing conditions. The pH of aquatic habitats can range from 6 in poorly buffered ‘soft’ waters to 9 in well buffered ‘hard’ waters. The tolerance of aquatic ecosystems against natural variations in pH is well understood and has been quantified and reported extensively in ecological publications and handbooks (e.g. OECD SIDS for CAS No. 7647-01-0). The buffering capacity of the environment will neutralise calcium hydroxide formed from calcium carbide. Ca2+ (from Ca(OH)2) is a ubiquitous substance with no toxicological relevance in the concentrations released from CaC2. Moreover, Ca2+ is an essential mineral nutrient for humans and animals that is homoeostatically regulated in the body. Acetylene has a high tendency to volatilise and will not remain in the aqueous phase. Furthermore, acetylene has a very low potential to adsorb to soil or sediment due to its low partitioning coefficient (log Pow = 0.37). Thus, exposure of sediments to acetylene based on the release of CaC2 to surface water is not expected.

Due to the identified uses of CaC2 direct release of the substance to soil and/or surface waters can be excluded. Indirect exposure (deposition via air) is negligible as CaC2 is released in the form of fine particles with very high surface area, that are transformed into Ca(OH)2 and C2H2. C2H2 is a gas and will remain in the gaseous phase. Due to the very high particle surface Ca(OH)2 is highly reactive and will undergo quick transformation to CaCO3 upon contact with CO2 (within hours to few days). Thus, only CaCO3 will be deposited in soil. CaCO3 is of no toxicological or environmental concern as the substance is a constituent of the soil matrix anyway.

Furthermore, neither calcium carbide nor its degradation products calcium hydroxide and acetylene have a tendency to accumulate in the food chain (for details please refer to the endpoint bioaccumulation in IUCLID section 5.3). Therefore, a risk for secondary poisoning in the food chain by calcium carbide can be excluded.

Conclusion on classification

Calcium carbide instantly decomposes hydrolytically upon contact with water/moisture, yielding calcium hydroxide and acetylene. Studies on the acute toxicity to aquatic invertebrates, algae and fish are available that were conducted with technical calcium carbide. Therefore, effects reported in these studies can be attributed to the entirety of the decomposition products of technical calcium carbide, i.e. calcium hydroxide and acetylene, including any impurities of the technical material. The lowest acute effect concentration of technical calcium carbide among the three aquatic species could be observed in Daphnia magna. The reported effect level (EC50) after 48-hr exposure is 4.62 mg CaC2/L. As long-term toxicity studies with technical calcium carbide are not available the classification of the substance is based on the available acute aquatic toxicity data. As the lowest acute effect level is 4.62 mg/L in Daphnia magna, classification for Category Acute 1 is not warranted. Furthermore, classification for Category Chronic 2 is not warranted either as this category does only apply to substances with effect levels in the range 1 to 10 mg/L that are moreover not rapidly biodegradable and/or that have a BCF value ≥ 500 (or a log Pow ≥ 4). The biodegradability criterion neither applies to calcium carbide nor to its decomposition product calcium hydroxide since they are inorganic substances. The second degradation product acetylene is considered to be readily biodegradable. Regarding the bioaccumulation potential, calcium is an essential mineral nutrient for animals and humans that is homoeostatically regulated in the body. Calcium hence is devoid of any bioaccumulation potential. Acetylene has a very low log Kow (0.37) and is thus not expected to have a significant bioaccumulation potential.