Effect of biochar amendment on Pb-polluted agricultural soils in a mid-term experiment.

BLANCO, A.; BARBERO, MEDINA G.P.; MEDINA, R.; ARIAS, R. A.; WANNAZ, E.D.; SALAZAR M.J.

Montevideo

Congreso; SETAC Latin America 15th Biennial Meeting; 2023

Society of Environmental Toxicology and Chemistry

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 preventthe migration of contaminants to crops. BC is a carbon-rich product obtained from biomass by pyrolysis. Itseffects depend on the starting organic matter, pyrolysis temperature, soil characteristics, and thecontaminant. 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 peanutindustry 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 distributedamong 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 theirwater-holding capacity) for 18 months, with sampling every 9 months. They were then subjected toagricultural use, soybean crop, for two cycles, with soil samples taken after each harvest. Sequentialextraction 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 mostfractions. The 3 BCs caused an increase in fraction (i) and a decrease in fractions (ii) and (iii), BC300 andBC400 also caused a decrease in fraction (v). It is important to note that the decrease in fraction (ii) wassmaller than the increase in fraction (i), so that, in contrast to what was expected, the bioavailability of Pbwas increased with the amendment. The Pb distribution in soil fractions evolved over time, with sustainedincreases observed in fraction (i) for treatments BC300 and BC400, in fraction (v) for all experiments, and infraction (iii) during incubation for all treatments. Fraction (ii) showed a gradual reduction over time for alltreatments.In conclusion, the application of BC produced from peanut shells modified the distribution of Pb in the soilfractions, but these changes are not optimal to reduce the Pb bioavailability for the crops grown there.