Análises químicas, bioquímicas e ecofisiológicas em plantas de alface (Lactuca sativa L.) cultivadas em rejeitos de minério de ferro da barragem de Fundão

Abstract

The rupture of the Fundão Dam, owned by Samarco/Vale/BHP companies, in the municipality of Mariana, MG, caused immeasurable socio-environmental and economic impacts, releasing a large amount of tailings into the Doce River. These residues significantly altered the normal concentrations of total solids and heavy metals in terrestrial and aquatic environments. Consequently, without proper support, the affected population continues to produce food in areas affected by the tailings deposition. Therefore, the aim of this study was to assess the effects of different concentrations of iron ore tailings from the Fundão Dam on some ecophysiological parameters and the biochemical and nutritional composition of lettuce plants (Lactuca sativa L.). Plants were obtained from seed germination and, when reaching uniform size, transplanted into 2.8-liter pots containing concentrations of 0, 25, 50, 75, and 100% of Fundão Dam iron ore tailings. The 0% concentration (fertile substrate) corresponded to the control treatment, and 100% to the tailings treatment. After 40-50 days of cultivation under controlled conditions, plant samples were analyzed for the presence of heavy metals and essential elements. Additionally, total soluble protein levels, specific enzymatic activities of SOD, CAT, and POD, gas exchange, chlorophyll a fluorescence, and plant antioxidant activity (DPPH) were evaluated. Other biochemical parameters, such as the composition of photosynthetic pigments and certain metabolites (carbohydrates and proline), as well as nutritional analyses (Vitamins A and C), were also determined. The experimental design used was a completely randomized design (CRD), with three replicates per treatment. The results were subjected to analysis of variance (ANOVA) by the F-test (P ≤ 0.05), and means were compared using the Scott-Knott test (P ≤ 0.05). In the treatment containing 25% tailings, there were no significant differences in terms of growth, development, mineral composition, and vitamins. This suggests that, up to this proportion, iron ore tailings did not cause severe/significant adverse impacts on lettuce productivity and nutritional composition. In the 50% tailings treatment, detrimental effects on seedlings were observed in some parameters, but with minor impacts that could potentially be mitigated with fertilization and substrate correction. At proportions of 75% and 100%, significant impacts were observed, particularly in terms of development (fresh and dry mass). However, no elements were found in the plants that posed risks of toxicity to human health through consumption. On the contrary, a nutritional deficiency was observed as a result of reduced translocation of essential elements to the leaves (aerial part). The results are satisfactory when considering the food and nutritional security of the population that lives in and consumes food produced in areas affected by iron ore tailings. No risks or damages to human health were found. Additionally, the findings indicate the possibility of maintaining family farming in affected areas, which plays a crucial economic role in food production.