Growth of selected plant species in biosolids-amended mine tailings

• Biosolids contain Hg while Au mine tailings contain residual Au.
• The growth of selected plants on biosolids-Au mine tailings substrates was studied.
• Plants were selected for their ability to phytoextract Hg and/or Au.
• Brassica juncea and Daucus carota were found to thrive on the substrates studied.
• The best substrate contained 75% biosolids and 25% Au mine tailings.

Biosolids stockpiles from sewage treatment plants are a valuable source of organic matter which could be utilized to improve the nutritional status and physical properties of Au mine tailings and support the growth of vegetation planted in the tailings. However, biosolids often contain elevated concentrations of heavy metals including Hg while Au mine tailings would usually contain residual Au. Therefore, it would be beneficial to select plants capable of both tolerating and phytoextracting Hg and/or Au.This paper reports on a glasshouse-based screening study which examined the growth of plant species known for their ability to phytoextract Hg and/or Au which can grow on substrates consisting of biosolids, Au mine tailings, or different combinations of both. The germination and establishment of plants over 8–12 weeks were monitored for Brassica juncea (Indian mustard), Daucus carota (carrot), Lupinus albus (white lupin), Beta vulgaris (sugar beet), Solanum tuberosum (potato), and Manihot esculenta (cassava).Each plant species exhibited differential responses in terms of germination, seedling quality, leaf area, specific leaf area, root and shoot biomass, and percentage dry matter partitioning to the roots. Both the Indian mustard and carrot grew successfully in the biosolids-mine tailings substrate combinations while white lupin, sugar beet, cassava, and potato failed to grow in most of the substrate combinations. The most suitable biosolids-mine tailings combination was determined to be 75% biosolids – 25% mine tailings, wherein most of the abovementioned growth parameters did not differ significantly from those of the plants grown in the control potting mix.