Advances in Understanding Environmental Risks of Red Mud After the Ajka Spill, Hungary

In the 5 years since the 2010 Ajka red mud spill (Hungary), there have been 46 scientific studies assessing the key risks and impacts associated with the largest single release of bauxite-processing residue (red mud) to the environment. These studies have provided insight into the main environmental concerns, as well as the effectiveness of remedial efforts that can inform future management of red mud elsewhere. The key immediate risks after the spill were associated with the highly caustic nature of the red mud slurry and fine particle size, which once desiccated, could generate fugitive dust. Studies on affected populations showed no major hazards identified beyond caustic exposure, while red mud dust risks were considered equal to or lesser than those provided by urban dusts of similar particle size distribution. The longer-term environmental risks were related to the saline nature of the spill material (salinization of inundated soils) and the release and the potential cycling of oxyanion-forming metals and metalloids (e.g., Al, As, Cr, Mo, and V) in the soil–water environment. Of these, those that are soluble at high pH, inefficiently removed from solution during dilution and likely to be exchangeable at ambient pH are of chief concern (e.g., Mo and V). Various ecotoxicological studies have identified negative impacts of red mud-amended soils and sediments at high volumes (typically [5 %) on different test organisms, with some evidence of molecularlevel impacts at high dose (e.g., genotoxic effects on plants and mice). These data provide a valuable database to inform future toxicological studies for red mud. However, extensive management efforts in the aftermath of the spill greatly limited these exposure risks through leachate neutralization and red mud recovery from the affected land. Monitoring of affected soils, stream sediments, waters and aquatic biota (fungi, invertebrates and fish) have all shown a very rapid recovery toward prespill conditions. The accident also prompted research that has also highlighted potential benefits of red mud use for critical raw material recovery (e.g., Ga, Co, V, rare earths, inform), carbon sequestration, biofuel crop production, and use as a soil ameliorant

Relations between soil properties and the 1 M NH4NO3 soluble mobile element fraction

The aim of the present study was to establish whether the 1 M NH4NO3 extraction is a suitable method for determining the background concentrations of mobile element fractions in soils and for describing the relations among mobile element fractions and soil properties. The 1 M NH4NO3 extraction resulted As, Cr and Pb concentrations below the detection limit in 90% of the investigated soils. This shows that the mobile element content determined simply in 1 M NH4NO3 solution is probably inadequate for the determination of the mobile background concentrations of these elements. Therefore, in the risk assessment of soil contamination other soil properties and element fractions – like “total” (cc. HNO3+H2O2 soluble) – should also be taken into consideration. The mobile Al concentration increased exponentially below pH 4. No correlation was found among 1 M NH4NO3 soluble mobile As, Cr, Cu and Pb element concentrations and any investigated soil property. Mobile Co, Mn, Al, Ni and Zn concentrations were determined mainly by soil pH. Soil colloid content correlated particularly with mobile Sr and B contents

A progressive shift alternative to evaluate nonparametric tests for skewed data

When the power of different nonparametric tests is evaluated by simulation, the alternative hypothesis should be carefully designed to ensure validity of the results in the specific research field. In the paper, we propose a probit-based progressive shift alternative that is more realistic than the simple shift alternative for skewed non-negative data that occur in many research areas. Our motivation comes from parasitology. The progressive shift alternative is used to compare the power of 6 location-scale tests and 7 commonly used location tests for several skewed theoretical and empirical parasite distributions. It is shown that location-scale tests are more powerful than location tests. The results are relevant also in other fields where skewed distributions are common, e.g. in the analysis of financial, health care, or treatment cost data. The methods studied in the paper are available in a free and user friendly web tool