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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Reliable studies for the toxicity of calcium to algae are lacking. Thus, a weight of evidence approach is applied to assess the potential of calcium for toxicity to algae. “Calcium is known as an essential nutrient for higher plants and one of the basic inorganic elements of algae. Calcium plays crucial roles in strengthening cell walls and plant tissues (OECD SIDS Initial Assessment Report “Calcium chloride”, 2002). The static exposure of freshwater green algae Pseudokirchneriella subcapitata to CaCl2 for 96 h resulted in EC10 and EC50 values for cell density of 291.6 and 561.1 mg Ca/L, respectively, that are above the OECD test limit of 100 mg/L (Simmons, 2012). An unbound EC50 of > 51.22 mg/L calcium was also reported for Chlorella vulgaris by De Jong (1965).

In European stream water, the median background concentration of calcium amounts to 40 mg Ca/L (Salminen et al. 2005). Since calcium is an essential macronutrient for algae and cyanobacteria, all media used for algae tests (e.g. OECD TG 201 medium, US. EPA AAP-medium) require the addition of calcium ranging from 1 to 5 mg Ca/L, moreover calcium contributes to the required water hardness.

As a constituent of calcareous skeletons, calcium is of essential importance for saltwater algae, including diatoms (Sverdrup et al. 1942). The HELCOM Red List Biotope Expert Group (2013, www.helcom.fi) defines the increasing acidification of oceans (due to rising atmospheric CO2 levels) as one of the future threats to marine organisms because it may lead to a degradation of calcium-carbonate skeletons. Thus, the toxicity of calcium to marine algae is expected to be low.

In sum, calcium as an essential element has a very low potential for toxicity to freshwater and saltwater algae.

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