Calcium

Endpoint summary

Description of key information

Short description of key information on bioaccumulation potential result:
Calcium (Ca2+) is an essential element that is regulated by homeostasis in the human body. Calcium does not exhibit properties which would raise a concern for bioaccumulation potential.
Short description of key information on absorption rate:
Elemental calcium used in industrial processes may emit dust and fume and react with air to form calcium oxide and ultimately calcium dihydroxide, which both exert alkali effect upon first contact to external surfaces of the human body via release of hydroxyl ions.
Following the HERAG guidance for metals and inorganic metal compounds, the following conservative default values for dermal absorption are proposed:
0.1 % for dry (dust) exposure
1.0 % for exposure to liquid/wet media
These absorption rates are applicable to calcium present in hydrated lime as a worst case assumption although absorption of metallic calcium (or CaOH2) is not considered relevant based on qualitative assessment in section 9 of CSR. Since elemental calcium is reactive, dermal exposure has to be minimized as far as technically feasible. Based on the exposure assessment and qualitative risk characterisation of calcium metal, exposure potential is negligible and the qualitative assessment of risk indicates that risk is low, particularly as a result of the use of existing risk management measures in place (see chapter 9 and 10 in CSR). Thus, an absorption rate for dermal exposure is not considered relevant for the chemical safety assessment.

Key value for chemical safety assessment

Bioaccumulation potential:

no bioaccumulation potential

Additional information

Calcium (ionic form, Ca2+)is an essential element which is regulated by homeostasis in the human body and is considered in the Human health section.

Biological function: Calcium is an essential mineral nutrient for humans, with daily requirements ranging between 400 mg for infants, up to 1200 mg for pregnant women, as assessed by the Scientific Committee on Food. Calcium serves as a structural element in bone and tooth formation, mainly as hydroxyapatite, and is furthermore involved in a broad range of physiological processes: It plays a central role in blood coagulation, is involved in cell adhesion, hormone and neurotransmitter release, muscle contraction, cellular differentiation, several intracellular signalling pathways, and many others.

Absorption: From dietary sources and when ingested as a salt, calcium is absorbed in the intestine by, onaverage, 30 %, varying between 10 and 40 %, independent of the solubility of the salt. Calcium absorption is partly regulated (active transport), or may take place by passive diffusion over an electrochemical gradient. Absorption rates vary by age, reflecting the dietary needs of subjects in the various age classes, and are under genetic control. For metallic calcium absorption through skin and respiratory system can be considered negligible since on the first contact on external surfaces of the body will react with moisture and exert irritative effects.Given that dissolution is widely considered to be required prior to percutaneous absorption, this may be interpreted as a likely indication of low bioavailability via the dermal exposure route.

Distribution: More than 99 % of the calcium stores in the body are located in the bones and teeth. The soft tissues accordingly contain less than 1 % of total body calcium. In extracellular fluids calcium is tightly regulated at a concentration of approximately 2.5 mmol/L (10 mg/dL). In blood, calcium is available as freeCa2+by approximately 45 %, the remainder being complexed to citrate, phosphate, sulphate, and carbonate (ca. 10 %). Regulation ofCa2+levels is effected via three hormones, parathyroid hormone, 1,25-dihydroxycholecalciferol, and calcitonin. The extracellular calcium is involved in blood coagulation and cell adhesion, and serves as a source for bone metabolism. Intracellular calcium is primarily bound to membrane structures of the nucleus, mitochondria, endoplasmic reticulum, or stored in special vesicles. Also the intracellular concentration of freeCa2+is tightly regulated and is only 0.1 μmol/L, i. e. approximately 25,000 times below the extracellular level.

Excretion: Absorbed calcium is predominantly excreted via urine, but also via faeces and sweat. Renal calcium excretion is the result of glomerular filtration (about 8 to 10 g calcium per day in adults) and tubular reabsorption (normal more than 98 % of the filtered load), which is predominantly passive, taking place in the proximal tubules, and by 20 % active in the distal part of the convoluted tubules and connecting tubules. Active transport is under the control of parathyroid hormone, calcitonin and 1,25(OH)2D. Average 24-hour excretion of calcium amounts to 40 mg in young children, 80 mg in prepubertal children and reaches about 150-200 mg in adults, largely independent of dietary calcium intake in healthy persons.

Discussion on bioaccumulation potential result:

Due to its ubiquitous occurrence in the environment and its function as an essential mineral for human nutrition, calcium is among the most extensively investigated elements with respect to physiological behaviour. When evaluating the basic toxicokinetics of calcium, calcium (Ca2+) ionic form is considered in the Human Health Section. As an essential mineral nutrient, distribution of calcium is actively regulated according to the body's requirements.

Discussion on absorption rate:

Skin absorption is not considered a relevant parameter for metallic calcium since dissolution is widely considered to be required prior to percutaneous absorption, this may be interpreted as a likely indication of low bioavailability via the dermal exposure routed, and thus skin notation is not needed. Dermal exposure of metallic calcium from industrial processes is taken qualitatively account in the CSR section 9. An absorption rate for dermal exposure is not considered relevant for the chemical safety assessment.