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Phytoremediation of tailings from a Chilean copper mine



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Department of Forest and Conservation Sciences, University of British Columbia, ʷməθkʷəy̓əm Territory

My doctoral study was able to shed light on the application of phytoremediation as an additional stabilization technique for tailings from a Chilean Copper mine.

Firstly, I was able to assess growth, survival and metal accumulation in locally available and native woody plants established on tailings, with or without additional treatments. This phytoremediation project was a result of a long dispute between a local community and the mine. There were several benefits to working on this site: the establishment was already in place and comprised several native woody tree species, the company accepted my research placement in their facilities and provided support, the entire site was fenced, and the plants were drip fertigated. Some plants appeared to be better equipped than others in dealing with the site conditions. Although all species showed signs of photoinhibition, algarrobo, romero and espino had the highest survival, and were the tallest and largest. Although quillay was not one of the most productive plants on the site, it was one of the greenest species, and may do better if soil is provided. Algarrrobo and espino are N-fixers, which can account for their better growth in the field (i.e., differences in growth were not significant in the greenhouse, where resources were not limiting). Quillay accumulated similar amounts of Cu in roots as other species but its translocation factor was very low, maintaining very low foliar concentrations of Cu. Furthermore, quillay was resistant to hare damage. Even though quillay is an endemic species, it was very abundant in the surrounding area of the phytostabilization site.

More information: Milla-Moreno E, Guy RD (2020) Growth response, uptake and mobilization of metals in native plant species on tailings at a Chilean copper mine. International Journal of Phytoremediation 23:539–547; DOI: 10.1080/15226514.2020.1838435.

A photo gallery with the plants used in this study, stating their uses and geographical distributions, is available in Pabellón Arauco at the Faculty of Forestry (University of Chile), as well as in the Office of the Association of Forest Engineers pro-Native Forest.

 

Secondly, I followed up on my field study in a controlled environment experiment. Two Chilean native hardwood species, quillay and espino, were grown under three increasing Cu levels for 6 months in a greenhouse setting. I measured growth, photosynthetic performance and elemental concentrations of leaves and roots to further evaluate their potential for phytoremediation. Both quillay and espino demonstrated high tolerance to the provision of excess Cu. Indeed, espino may require considerably more Cu than normal to support optimal growth, as also evidenced by its improved photosynthetic performance with increased Cu in the media. Excess Cu was mostly restricted to the roots of both species and showed some tendency to accumulate in tissue layers outside the periderm. Foliar Cu concentrations remained below toxicity levels in both species, in contrast to our previous study of older plants growing on tailings in the field, where this threshold was exceeded in espino. These observations suggest that differences in age and/or other soil conditions (i.e., multi-metal stress) may affect experimental outcomes. This study allowed us to confirm the potential of quillay in phytostabilization projects and provided a pilot experience in the use of XRF imaging for the screening of plants with potential for phytoremediation. This technique allows a rapid and fine screening of elemental distributions in plants, that can help understand differences and similarities in the accumulation of heavy metals as well as the roles that other elements may play in metal tolerance (e.g., the apparent association of Ni with calcium oxalate crystals).

More information: Milla-Moreno E, Guy RD, Soolanayakanahally RY (2022) Enlightening the pathway of phytoremediation: Ecophysiology and X-ray fluorescence visualization of two Chilean hardwoods exposed to excess copper. Toxics 10:237; DOI: 10.3390/toxics10050237. (Open Access & Editor‘s choice article).

Additionally, I have created a Borealis Dataverse Repository where images related to this work can be downloaded for educational purposes with proper copyright use.

 

Lastly, I found a cross-sector consensus on the need to do better when it comes to tailings management in Chile. Currently, the damage caused by mining is not reversible and, with increased activity following on the nascent energy transition, more innovation is required. Though more research is desirable, professionals clearly consider phytoremediation to be a feasible supplementary approach to tackle this situation. Phytoremediation with native plants may be particularly useful for restoration of abandoned sites, some of which are many decades old, and projects that meaningfully involve local communities are more likely to lead to success. (Manuscript submitted)

 

Throughout this doctoral thesis, but particularly when analyzing the data from the survey, I realized that the challenge of tailing management in Chile should not be siloed within either industry, non-governmental organizations, government or academia. A problem with so many implications must include an interdisciplinary approach and science-based solutions that account for power imbalances and social and environmental disparities.