Lead fractionation and availability in contaminated soils: a comparative study of organic wastes and zeolite as...

Lead (Pb) contamination in soils is a major environmental concern due to its persistence, toxicity, and bioaccumulation. This study evaluated the effects of organic amendments (sewage sludge, cattle manure, and poultry manure) and zeolite with different particle sizes (< 0.4, 2-8, and > 8 mm) applied at 1, 5, and 10% (v/v) on Pb mobility and availability in soil contaminated with Pb-rich mine tailings. Soil pH and acid-labile Pb extracted with Mehlich-1 were monitored for 30 days, and Pb fractions were assessed by sequential extraction at the end of the experiment. Mine tailings increased soil pH from 5.5 to 7.3 and stabilized acid-labile Pb at 223 mg kg^-1 by day 8. Organic amendments altered pH and Pb availability, with stabilization occurring within 5-15 days depending on amendment type and dose. Poultry manure increased soil pH and reduced acid-labile Pb by 17 and 32% at 5 and 10%, respectively, whereas sewage sludge caused initial acidification followed by stabilization near neutral pH. All organic amendments promoted Pb redistribution toward more stable organic matter- and oxide-associated fractions. Zeolite significantly reduced acid-labile Pb across all particle sizes, with the fine fraction (< 0.4 mm) at 10% achieving the greatest immobilization (61%). Sequential extraction indicated Pb stabilization through increased association with crystalline Fe/Al oxides. Overall, poultry manure and fine zeolite effectively immobilized Pb, highlighting their potential as low-cost amendments for mitigating Pb contamination in mining-impacted soils.