If harmful effect was measured, please, specify what was measured, which method was used, who did the measurement, and what was the result
The Environmental Microbiology and Biotechnology research group of BME-ABÉT have conducted biological-ecotoxicity tests with red-mud flooded soils of various pH. The tests include aerobic heterotrophic cell counts, substrate utilization with BIOLOG Ecoplate, Aliivibrio fischeri bioluminescence inhibition tests, Sinapis alba seed germination test.
10-20% red mud mixed into the soil had stimulating effect on fungi and bacteria after 3 months. The red mud proved to be toxic in the Aliivibrio fischeri bioluminescence inhibition test only at 100% red mud proportion after 5 months. According to the Sinapis alba test seed germination inhibition decreased by the 5th months and the inhibition exceeded 50% only in the microcoms containing 100% red mud.
The ecotoxicity tests performed by Ujaczki et al, 2016 on leachate and soil showed that 20% w/w RMSM had no adverse effect on the following testorganisms: S. alba, T. aestivum, A. fischeri and F. candida during the experiments (10 months).
Assessing all the environmental toxicity test results Ujaczki et al, 2016 concluded that 20% RMSM application did not have any harmful effect on the subsoil (LQS).
Suspected harmful effects
According to the Bayer technology, applied also by the Ajka plant, the aluminium content of the bauxite was separated by NaOH, for which reason the remaining red mud residue was highly alkaline. The spilled alkaline red mud (pH: 12) removed from the soil surface together with the soil, resulted a red mud-soil mixture with a lower pH (Ujaczki et al, 2016). However due to its NAOH content, the Na ion concentration was still high, therefore the suspected harmful effect is soil salinisation. The As, Cr, Hg and Ni content of the studied Ajka red mud-soil mixture exceeds the limit values set by the Hungarian regulation (Government Decree No. 50/2001 IV. 3. on the rules and handling of wastes and sludge in agriculture). However, when adding this red mud-soil mixture to soil the toxic effect and the limit value exeedance does not occur (Ujaczki et al, 2016).