Fitorremediação em associação com o uso de biossólido em solo impactado por rejeito de mineração de cobre

Abstract

In Brazil, mining activity is the main source of copper (Cu) soil contamination. In Rio Grande do Sul, Cu mining activities have occurred for over a century in the Minas do Camaquã region, leaving an extensive area impacted by tailings disposal. Even after the cessation of activities, the area still exhibits high Cu levels, resulting in limited or absent vegetative cover and heightening the risk of environmental contamination. Phytoremediation combined with the use of organic amendments is a technique that can be used successfully in remediating these areas. The objective of the study was to assess the efficiency of biosolids from a domestic wastewater treatment plant combined with black oat (Avena strigosa Schreb.) and jack bean (Canavalia ensiformis (L.) D.C.) as a phytoremediation strategy for an area impacted by copper mining tailing. The soil was collected in the area impacted by copper mining tailing in Minas do Camaquã/RS, and plant cultivation was conducted in a randomized complete block design in a greenhouse. In Article I, increasing doses of biosolids (0, 90, 180, 360, 720, and 1440 kg ha-1 of N) were added to the soil for black oat cultivation. In Article II, after black oat cultivation, jack bean cultivation was carried out in the same soil without additional biosolid applications. The availability of Cu and other nutrients in the solid phase and in solution was assessed in the soil after each cropping season. In the plants, the accumulation of Cu and other nutrients in the aboveground and root parts, plant growthnd Cu phytotoxicity were assessed, including photochemical efficiency, concentration of photosynthetic pigments, and the activity of oxidative stress enzymes. The results show that biosolids reduce soil pH and increase nutrient concentration in solution. At intermediate doses applied to the soil (180 and 360 kg ha-1 of N), excess of Cu is reduced in solution. In black oat cultivation, biosolids enhanced the plant's phytostabilization potential. In this case, the 360 kg ha-1 of N dose promoted the highest plant growth with a reduction in phytotoxicity caused by this element. Jack bean exhibited greater growth at higher doses (720 and 1440 kg ha-1 of N) with a decrease in the phytotoxic effects of Cu. Meanwhile, intermediate doses (180 and 360 kg ha-1 of N) showed a behavior similar to the higher doses, with increased accumulation of Cu in the aboveground parts. Therefore, biosolids increase the growth of black oats and jack beans in a sandy soil impacted by Cu mining tailings and promote greater accumulation of nutrients, reduction of pH and Cu concentration in solution when added at doses 180 and 360 kg ha-1 of N.