Effect of Biochar Amendment on Pb-Polluted Agricultural Soils in a Mid-Term Experiment

DR. ANDRÉS BLANCO; ING. GONZALO P. BARBERO; ING. ROCIO MEDINA; DR. EDUARDO E. WANNAZ; DRA. M. J. SALAZAR

Montevideo

Congreso; SETAC Latin America 15th Biennial Meeting; 2023

SETAC

Heavy metal contamination of soils is one of the most serious environmental problems today. Recently, numerous studies have focused on the use of biochar (BC) as an amendment of polluted soils to prevent the migration of contaminants to crops. BC is a carbon-rich product obtained from biomass by pyrolysis. Its effects depend on the starting organic matter, pyrolysis temperature, soil characteristics, and the contaminant. In addition, these effects may vary over time with BC aging. This work aimed to study the effect of BC application, produced at different temperatures from peanut industry residues, in an Pb polluted agricultural soil, following its evolution for 36 months. For this purpose, the soil was collected from a polluted site in Córdoba province. It was dried, homogenized, and distributed among 4 treatments: polluted soil without amendment (Pb); polluted soil with BC produced at 300 °C (BC300); at 400 °C (BC400); and at 500 °C (BC500). The soils were incubated (darkness and 70% of their water-holding capacity) for 18 months, with sampling every 9 months. They were then subjected to agricultural use, soybean crop, for two cycles, with soil samples taken after each harvest. Sequential extraction was performed on the samples to determine the concentration of Pb in different soil fractions: (i) exchangeable; (ii) bound to carbonates; (iii) bound to Fe and Mn oxides; (iv) bound to organic matter; (v) pseudo-residual. Fractions (i) and (ii) are interpreted as bioavailable. Regardless of the time course, BC application produced significant effects on the Pb concentration in most fractions. The 3 BCs caused an increase in fraction (i) and a decrease in fractions (ii) and (iii), BC300 and BC400 also caused a decrease in fraction (v). It is important to note that the decrease in fraction (ii) was smaller than the increase in fraction (i), so that, in contrast to what was expected, the bioavailability of Pb was increased with the amendment. The Pb distribution in soil fractions evolved over time, with sustained increases observed in fraction (i) for treatments BC300 and BC400, in fraction (v) for all experiments, and in fraction (iii) during incubation for all treatments. Fraction (ii) showed a gradual reduction over time for all treatments. In conclusion, the application of BC produced from peanut shells modified the distribution of Pb in the soil fractions, but these changes are not optimal to reduce the Pb bioavailability for the crops grown there.