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Toxicity to soil macroorganisms except arthropods

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Description of key information

The most sensitive NOEC of ashes (residues), coal is 32 g/kg soil d. w.

Key value for chemical safety assessment

Additional information

On behalf of the VGB PowerTech e. V. the toxicity of ashes (residues), coal to earthworm was assessed by Roembke (2008) according to the ISO guideline 11268-1 (Effects of Pollutants on Earthworms. 1, Determination of Acute Toxicity Using Artificial Soil Substrate, 1997). Different ashes (residues), coal types originated from combustion of hard coal or lignite with and without co-combustion, respectively, were tested.

During an exposure period of 14 days the earthworm species Eisenia fetida was exposed to different concentrations of ashes (residues), coal in soil, ranging from an ash to soil ratio of 1/32 (3.1% ash, 96.9% soil) up to a substrate consisting only of ash (100% ash). The test was conducted in covered glass vessels containing 500 g of substrate and 10 adult earthworms per concentration. After 7 days as well as at the end of the experiment on day 14 the number of earthworms alive and their weight was determined.

The most sensitive study is the one performed with a ashes (residues), coal with a higher content of free lime (FA 6). Under the conditions of this study no mortality was observed at a test substance concentration of 32 g/kg soil d. w. (NOEC). Meanwhile at a concentration of 67 g/kg soil d. w. all animals were dead after an exposure period of 14 days. LC50 was not calculated but must be between 32 and 67 g/kg soil d. w. Other studies with ashes (residues), coal with a higher content of free lime revealed EC50 values between 66 and greater than 1000 g/kg.

In general ashes (residues), coal without a higher content of free lime only caused mortality in earthworms at very high test concentrations. At concentrations up to 143 g ash/kg soil no mortality was observed. The most critical ash was found to be a fly ash originated from combustion of hard coal and secondary fuels (FA5). At a concentration of 333 g/kg of this ash (FA5) 95% of the earthworms were dead at the end of the test. Other ashes (residues), coal - fly ashes showed 100% mortality at the significant higher concentration of 1000 g/kg (FA1, FA2, FA3). In general bottom ashes seemed to be less toxic than ashes (residues), coal - fly ashes. Both bottom ashes tested (KS1 and KS2) caused no or only very low mortality at a concentration of 1000 g/kg.