Calcined Oyster Shell-Humic Complex as Soil Amendment to Remediate Cd- and As-Contaminated Soil

Abstract

Soil acidification in the subtropical region reduces soil productivity and increases the bioavailability of heavy metal(loid)s in soil. Here 800 °C-calcined oyster shell and leonardite-derived humic substance were combined to form a Ca-humic complex to remediate an acidic soil contaminated by cadmium (Cd) and arsenic (As) for safe vegetable production. In the pot experiment, the complex was added to soil as a soil amendment at 0%, 0.5%, 1.0%, 2.0%, and 5.0%. A 2.0% dose reduced Cd and As contents of the vegetable bok choy by 98% and 71%, respectively, alleviating the human health risk of Cd and As from the food chain. The unified bio-accessibility method (UBM) was followed to estimate the bio-accessibility of Cd and As. The complex at a 2.0% dose lowered soil Cd and As bio-accessibility in simulated gastric (BioG) and intestine (BioGI) compartments by 15.5% for BioG-Cd, 39.2% for BioGI-Cd, 28.8% for BioG-As, and 45.0% for BioGI-As, thus reducing the human health risk of Cd and As from soil ingestion. The use of oyster shell waste to produce Ca-humic complex as a soil amendment is a practical means of achieving dual agronomic and environmental benefits, from the remediation of soil contamination to the safe disposal of shell waste.