Remediation of metalliferous mines, revegetation challenges and emerging prospects in semi-arid and arid conditions

Abstract

Understanding plant behaviour in polluted soils is critical for the sustainable remediation of metal-polluted sites including abandoned mines. Post-operational and abandoned metal mines particularly in semi-arid and arid zones are one of the major sources of pollution by soil erosion or plant hyperaccumulation bringing ecological impacts. We have selected from the literature 157 species belonging to 50 families to present a global overview of 'plants under action' against heavy metal pollution. Generally, all species of plants that are drought, salt and metal tolerant are candidates of interest to deal with harsh environmental conditions, particularly at semi-arid and arid mine sites. Pioneer metallophytes namely Atriplex nummularia, Atriplex semibaccata, Salsola kali, Phragmites australis and Medicago sativa, representing the taxonomic orders Caryophyllales, Poales and Fabales are evaluated in terms of phytoremediation in this review. Phytoremediation processes, microbial and algal bioremediation, the use and implication of tissue culture and biotechnology are critically examined. Overall, an integration of available remediation plant-based technologies, referred to here as 'integrated remediation technology,' is proposed to be one of the possible ways ahead to effectively address problems of toxic heavy metal pollution. Graphical abstract Integrated remediation technology (IRT) in metal-contaminated semi-arid and arid conditions. The hexagonal red line represents an IRT concept based on remediation decisions by combination of plants and microbial processes.

Progresses in restoration of post-mining landscape in Africa

“…On the global scale, research output in phytoremediation has been increasing at a faster rate than other restoration techniques over the past decade, particularly in Southeast Asia (Koelmel et al 2015). This large and spatially scattered body of knowledge has been systematically reviewed, covering a range of issues from ecological impacts , concepts and applications (Ali et al 2013), to restoration challenges (Pietrzykowski 2015;Mahar et al 2016;Nirola et al 2016) and potential restoration techniques (Rajkumar et al 2012;Paz-Ferreiro et al 2014;Sarwar et al 2017). National reviews of ecological restoration of mine wasteland are also available, e.g., for China (Li 2006) and Ghana (Mensah 2015).…”

Role of microorganisms in rehabilitation of mining sites, focus on Sub Saharan African countries

“…The vegetative cover and the plant roots also contribute to the reduction of wind and water erosion. It also enables the sequestration of carbon, and contributes to maintain the food chain (Tordoff et al, 2000;Nirola et al, 2016). Phytostabilization is thus a technically sustainable and economically viable option for large areas affected by metals and metalloids pollution, like tailings (Doumas et al, 2016).…”

“…physical, chemical and microbiological properties of soils, as well as evolution in drainage and in hydrological properties of these soils. However, as seen in many reviews, there is accumulating evidence that promising outcomes are possible (Mendez and Maier, 2008;Lamb et al, 2015;Nirola et al, 2016;Thavamani et al, 2017;Karaca et al, 2018;Novo et al, 2018). However, more researches are needed on the effect of PGP microorganisms in mine soils and mine tailings in long term in field experiments.…”

“…Particularly a better knowledge about plant microbiome interactions is required to optimize the rate of phytostabilisation and provide a sustainable plant establishment (Garris et al, 2016;Ma et al, 2016;Thavamani et al, 2017;Valentin-Vargas et al, 2018). The long term monitoring of mining sites (more than 2 years) treated with phytoremediation is also scarce, but this is a necessity to test the effectiveness and robustness of this technique, study the decomposition of amendments and evaluate the evolution of metallic contaminants in terms of mobility and speciation, (Tordoff et al, 2000;Pond et al 2005;Mains et al 2006;Nirola et al, 2016;Venkateswarlu et al, 2016). Different parameters must be also monitored on the long term as the capacity of plants to self propagate successfully with no additional inputs or the non toxicity of plants for domestic and wild animals required to prevent further contamination of the ecosystem.…”

“…In arid and semi arid climates, erosion of tailings will be mainly done through a combination of wind and water erosion with strong winds and heavy rainfalls. In contrast, in temperate or tropical and equatorial environments, the tailing will be more subjected to leaching leading to formation of acid mine drainage (Mendez and Mayer, 2008;Nirola et al, 2016). Furthermore, a vegetative cover could limit the infiltration of water inside tailing like see in arid and semi arid region, where evapotranspiration can limit mine drainage formation (Robinson et al, 2006).…”