Texture and Contamination-Level Dependent Effects of Calcium-Rich Deinking Paper Sludge Biochar on Soil Cd Availability, Enzymatic Activity, and Plant Stress Mitigation

Abstract

The study evaluated calcium-rich deinking paper sludge (DPS) biochar's capability as a viable alternative method to mitigate soil cadmium (Cd) availability. Our analysis of 68 recent studies showed that 75% of the studies focused on contamination levels below 10 mg kg-1. However, mining and smelting areas exhibit higher levels of Cd contamination (mean value of 57.5 mg kg-1 with a CV of 128%), necessitating a contamination rate-dependent approach.Clay loam (CL) and sandy loam (SL) soils were artificially contaminated with Cd to mimic polluted areas (20, 40, 80 mg kg-1). Soils were aged for six months and then treated with DPS biochar doses of 0%, 1%, and 3% (w/w) for a month. Cd extractability and toxicity were gauged using diethylenetriaminepentaacetic acid extraction and plant physiology tests. Supplementarily, machine learning algorithms were tested to predict plant physiological parameters and biomass production, leveraging variables from principal component analysis and design parameters.Biochar application (3%, w/w) reduced soil Cd availability (20.1% in SL, 8.4% in CL; p < .05), attributed to increased soil pH, enhanced microbial activity, and expanded soil surface area. The plants grown in treated soils displayed increased dry matter content, chlorophyll, relative water content, and decreased malondialdehyde levels. The impact varied, being more pronounced in SL soils with high Cd contamination.This study presents the first report on the use of DPS biochar in Cd-contaminated soils and sets expectations for its outcomes regarding plant physiology and soil microbial activity in a diversified experimental design. DPS biochar appeared as a tool for mitigating soil Cd availability and alleviating plant stress particularly in SL soils. The biochar's efficiency was influenced by its dose, the level of contamination, and the soil type, highlighting the importance of tailored application strategies.