Using native plants to evaluate urban metal pollution and appoint emission sources in the Brazilian Steel Valley region.

In southeastern Brazil, the city of Ipatinga is inserted in the Steel Valley Metropolitan Region, which hosts the largest industrial complex for flat-steel production in Latin America, while also having one of the largest vehicle fleets in the entire country. Since potentially toxic elements (PTEs) are not emitted solely by industries, yet also by vehicular activity, the predominant emission source can be determined by evaluating the ratio between different elements, which are called technogenic tracers. We performed a biomonitoring assay using two tropical legumes, Paubrasilia echinata and Libidibia ferrea var. leiostachya, aiming to assess chemical markers for the origin of emissions in the region, distinguishing between different anthropogenic sources. Plants were exposed for 90 days in four urban sites and in a neighboring park which served as reference. After the experimental period, plants were evaluated for trace-metal accumulation. L. ferrea var. leiostachya retained lower amounts of metals associated with vehicular and industrial emission. The opposite was found with P. echinata, a species which should be recommended for biomonitoring of air pollution as a bioaccumulator. Plants of P. echinata were enriched with Fe, Al, Ni, Cr, and Ba, whereas plants of L. ferrea var. leiostachya were enriched with Fe, Cu, and Co. In both species, Fe was the element with which plants were enriched the most. Plants showed highest iron enrichment at Bom Retiro, the site downwind to the steel industry, which has shown to be the main particle emission source in the region.

Leaf surface traits related to differential particle adsorption - A case study of two tropical legumes.

We aimed to test a set of epidermal traits in two legume species with contrasting chemical, physical, and micromorphological leaf-surface features to assess which ones would determine higher PM retention. For that, we performed a biomonitoring study in southeastern Brazil at the Steel Valley Metropolitan Region, where there is predominance of steel industry and one of the largest vehicle fleets in the country. A reference station was installed at a neighboring park. We evaluated leaf-surface roughness at two hierarchical levels, leaf wettability, epidermal-cell anticlinal-wall undulation, epidermal-cell perimeter, and the micromorphology and chemical composition of epicuticular waxes. Particle retention was significantly higher in Paubrasilia echinata than in Libidibia ferrea var. leiostachya, the former of which has lower roughness given by both the epidermal tissue (macro-roughness; 0.6 vs 2.6 µm) and epicuticular waxes (micro-roughness; 68 vs 220 nm), higher leaf wettability (82° vs 143°), lower epidermal-cell undulation index (1.2 vs 1.8), lower epidermal-cell perimeter (93 vs 146 µm), wax deposition in the form of a smooth layer (as opposed to densely aggregated rosettes of vertical platelets), and more polar wax chemical constitution (68% vs 47% of polar compounds). While all of the assessed traits contributed to particle retention, canonical loadings revealed that macro-roughness was the trait that contributed the most to the retention of PM2.5 (ca = 1.47; r = -0.56), PM10 (ca = 1.08; r = -0.61), PM100 (ca = -4.95; r = -0.39) and TSP (ca = 0.98; r = -0.62), although this trait was shown by factor analysis to be secondary in distinguishing between species (0.92 contribution to the second axis). Our findings shed new light on the criteria that should be considered when selecting species for green infrastructure aiming to reduce urban air pollution, as well as on novel possibilities for PM biomonitoring in the tropics.

Leaf morphoanatomy of species tolerant to excess iron and evaluation of their phytoextraction potential.

Setaria parviflora (Poir.) Kerguélen and Paspalum urvillei Steudel are grasses that grow naturally in a soil with high iron contents. This study aimed to characterize morphoanatomically and histochemically the iron phytotoxicity on leaves and evaluate the phytoextraction potential of these grasses. Saplings were cultivated in hydroponic solution with and without excess Fe-EDTA. Regarding measurements taken on leaves, reduction was observed among treatments of Fe-EDTA on height values of abaxial epidermis and bundle sheath in both species. As for iron histolocalization, stronger reaction was observed in leaves of S. parviflora, in comparison with P. urvillei. Anatomical damage, such as protoplast retraction, irregular xylem, changes in cell volume, and cell collapse, and visual symptoms, like leaf bronzing, chlorosis, and necrosis, were similar in both species when exposed to excess iron; however, P. urvillei showed more severe damage. This species accumulated more iron in shoots than S. parviflora and therefore is more favorable for use in phytoextraction. The root system of both species accumulated higher iron concentrations in relation to shoots.