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Toxicity to aquatic algae and cyanobacteria

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Description of key information

No reduction of algal growth or yield could be determined up to a loading rate of 100 mg/L for ashes (residues), coal. The tested ashes (residues), coal with a higher content of free lime is harmful to algae (EC50 of 30 mg/L).

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Several studies with freshwater algae are available for different types of ashes (residues), coal. The most sensitive results are identified from a study with the ashes (residues), coal with a higher content of free lime. The GLP study according to OECD 201 showed a NOEL of 4.6 mg/L loading rate and a EL50 of 30 mg/L.

In further GLP studies according to OECD TG 201 toxicity of five different ashes (residues), coal to the freshwater algae Pseudokirchneriella subcapitata were tested (Migchielsen, 2010). Under static test conditions algae were exposed to a series of water accommodated fractions up to a loading rate of 100 mg/L. Algal growth was assessed by spectrophotometric measurements at 24 h intervals. No reduction of algal growth or inhibition of yield compared to the control could be observed during an exposure period of 72 h. The EL50 could not be determined as it was greater than the range tested, exceeding a loading rate of 100 mg/L. NOEL for all ashes (residues), coal equaled a loading rate of 100 mg/L. Based on these findings it can be concluded that the tested ashes (residues), coal are not harmful to algae.

Studies by Rejfkova (2008, 2009) and Nachtigallová (2009) on ashes (residues), coal confirm the findings of Migchielsen (2010). Both authors conducted limit tests under GLP according to OECD TG 201. After 72 hours no reduction in growth rate of Desmodesmus subspicatus could be observed. The EL50s were beyond 100 mg/L and NOELs equaled 100 mg/L.

Leachates corresponding to a loading rate of 100 g/L only showed effects on algal growth far greater than 100 mg/L (van Eijk, 2008; Vazelle, 1993).