Influence of roadways on heavy metal content in soils and yerba mate tissue in southern Brazil

PurposeVehicular road traffic may represent an important soil and plant contamination source. In this context, the concentration of heavy metals (Cd, Pb, As, Sb, Ni, Cu, Fe, Al, Mn and Zn) and macronutrients (Ca, Mg, K and P) was evaluated in yerba mate (Ilex paraguariensis St. Hil.) cultivations and in soils adjacent to highways.Design/methodology/approachThe investigated yerba mate cultivations were located in southern Brazil. Plant tissue (young and old leaves and branches) and soil (0–10 cm) samples were collected at five distances from the highway (0–10, 10–20, 20–30, 30–40 and 40–50 m). Plant tissue was analyzed with and without washing to evaluate contributions from particulate deposition.FindingsAlthough increases in soil pseudo-total concentrations of Cd, Cu, Ni, Zn, Fe, Mn, Ca and Mg were observed only at the Erechim site, geoaccumulation indices and enrichment factors (EFs) did not indicate any heavy metal pollution. These results indicate the existence of natural variation in soil. Cadmium was more concentrated in branches than in leaves, while the opposite was observed for Pb. High levels of Mn and Al were found in foliar tissue. In summary, highway proximity did not lead to heavy metal contamination of yerba mate under the evaluated conditions.Originality/valueThis research explores the possibility of heavy metal pollution in plantations of yerba mate adjacent to highways and indicates natural concentrations of toxic elements that exceed current legislation, which was an important discovery regarding the yerba mate production chain.