Ecological strategy for soil contaminated with mercury

Plant Soil Ecological strategy for soil contaminated with mercury M. Pogrzeba 0 D. Ciszek 0 R. Galimska-Stypa 0 B. Nowak 0 A. Sas-Nowosielska 0 Responsible Editor: Juan Barcelo. 0 0 R. Galimska-Stypa University of Silesia , 12 Bankowa Str, Katowice , Poland 1 Institute for Ecology of Industrial Areas , 6 Kossutha Str, 40-844 Katowice , Poland Aims The paper presents results from plot experiments aimed at the development of an ecological strategy for soil contaminated with mercury. Meadow grass (Poa pratensis) was tested on mercury contaminated soil in a former chlor-alkali plant (CAP) in southern Poland for its phytoremediation potential. Methods The stabilisation potential of the plants was investigated on plots without additives and after the addition of granular sulphur. Biomass production, uptake and distribution of mercury by plants, as well as leachates and rhizosphere microorganisms were investigated, along with the growth and vitality of plants during one growing season. Results The analysed plants grew easily on mercury contaminated soil, accumulating lower amounts of mercury, especially in the roots, from soil with additive of granular sulphur (0.5 % w/w) and sustained a rich microbial population in the rhizosphere. After amendment application the reduction of Hg evaporation was observed. Conclusions The obtained results demonstrate the potential of using Poa pratensis and sulphur for remediation of mercury contaminated soil and reduction of the Hg evaporation from soil. In the presented study, methods of Hg reduction on Bhot spots^ were proposed, with a special focus on environmental protection. This approach provides a simple remediation tool for large areas heavily contaminated with mercury. Hg uptake; Rhizosphere area; Soil evaporation; Microbial population; Phytoremediation Introduction Mercury and its compounds are considered to be potentially hazardous to all biological organisms (Asztalos et al. 2012; Boening 2000; Chen and Yang 2012) . Mercury cannot be destroyed biologically but only transformed into volatile metallic mercury, HgO (Hobman and Brown 1997) or biomethylated by a number of bacterial species to gaseous methyl mercury (De et al. 2008) or dimethyl mercury (Rodriguez et al. 2005) . In soil the element is mostly associated with humic acids forming strong complexes with sulphur-containing functional groups (Hooda 2010; Zuo et al. 2013) . Mercury occurs naturally at trace levels in the earth’s crust, however, potentially toxic concentrations of mercury are continuously released into the environment from anthropogenic sources. For several decades chemical plant facilities in Poland (e.g. chlor-alkali production processes) as well as in other countries (Zagury et al. 2006; Dufault et al. 2009; Esbrí et al. 2014) have been using mercury and its compounds in manufacturing processes, which resulted in high concentrations of mercury in nearby soils. This poses potential health and environmental risk over a much wider area (Cachada et al. 2009; Pereira et al. 2009) . The most popular remediation technologies for mercury contaminated soils are: liquid extraction, thermal treatment, electrolytic methods, mercury flotation or immobilisation and solidification/stabilisation (S/S). Some of the S/S technologies are based on Hg stabilisation and solidification with sulphur polymer cement, thiolfunctionalised zeolite compounds and alkali sulphide (Fuhrmann et al. 2002; Piao and Bishop 2006; Bower et al. 2008; Zhang et al. 2009) . These technologies are expensive, complex processes that are destructive for soil organisms and of limited application in soil treatment (Wang et al. 2012; Randall and Chattopadhyay 2013) . The less disruptive and more affordable alternatives based on phytoremediation approach use the physiological and biochemical possibilities of plants and the appropriate modification of soil compartment properties. Such an approach, based on the reduction of Hg bioavailable fractions, was investigated in the contaminated areas of the chlor-alkali plant in southern Poland. Poa pratensis was tested for its potential for aided phytostabilisation. Granular sulphur in concentration of 0.5 % w/w was used as a soil additive. The beneficial effect of sulphur on the retention of Hg in soil was first suggested by Lagerwerff (1967) and continued by Maclean (1974) . According to Outridge et al. (2001) the direct interaction between Hg and S leads to the formation of metacinnabar or cinnabar. The environmental impact of sulphur addition to the Hg contaminated soil was tested via analysis of soil leachates for Hg, SO4+2 and total organic carbon (TOC) concentrations as well as soil microorganisms. Materials and methods Experimental site The experimental site was located inside the former chemical facility (southern Poland) that has been operating for over 50 years. For several decades the facility had been using mercury and its compounds in its manufacturing processe (...truncated)