Heavy metals such as lead (Pb) accumulated in soil may become a problem for plant growth and human health. An alternative is to grow nonfood crops in these contaminated areas. A pot experiment was carried out in order to investigate the effect of increasing doses (900, 1,800, 3,600, 7,200, and 9,000 mg kg⁻¹) of Pb on the yield and chemical composition of essential oil and phytoaccumulation of garden mint (Mentha crispa L., Lamiaceae). It was observed that the length of the root and aerial parts of this species was not significantly affected in different assayed experiments when compared to the control. However, the leaf number, budding, and green mass were very influenced by the presence of Pb in the soil, showing a significant resistance. Regarding Pb phytoaccumulation, it was verified an accumulation of this metal in roots and aerial parts. Although M. crispa is a species that tolerates high concentrations of Pb, it is not considered a Pb hyperaccumulator species. Considering the production of essential oil, a high amount of Pb affected significantly its yield, and it was 10 times higher under extreme contamination conditions than the amount of oil produced by the control. The chemical composition of M. crispa essential oil was also affected by high Pb doses, and its major component (carvone) concentration varied from 39.3% for cultivation in noncontaminated soil (control) to 90% for all cultivations in Pb-contaminated soils.

The present paper focuses on improving chromium (III) uptake capacity of sugarcane bagasse through its chemical modification with citric acid and/or sodium hydroxide. The chemical modifications were confirmed by infrared spectroscopy, with an evident peak observed at 1730 cm-1, attributed to carbonyl groups. Equilibrium was reached after 24 h, and the kinetics followed the pseudo-second-order model. The highest chromium (III) maximum adsorption capacity (MAC) value was found when using sugarcane bagasse modified with sodium hydroxide and citric acid (58.00 mg g-1) giving a MAC value about three times greater (20.34 mg g-1) than for raw sugarcane bagasse.