Selection of an extraction method for the determination of Cadmium in soils and cacao

Long-term consumption of foods with elevated levels of cadmium (Cd) is harmful to health. This study aimed to identify an efficient method for Cd extraction in sandy loam soils and extrapolate it to cacao beans for determination by atomic absorption spectrophotometry (AAS). Three extraction methods (microwave irradiation, aqua regia digestion and ultrasonic cavitation) were compared in terms of recovery, precision and applicability. Ultrasound-assisted extraction proved to be the most robust method, achieving recoveries between 97.5% and 101.8% and a %RSD as low as 2.79%, outperforming microwave and aqua regia methods, which showed higher variability and longer processing times. Optimal conditions were established as 30 min of sonication with 37% HCl, using 5 mL of acid per 0.50 g of soil. The method was further validated in fortified cacao beans and a certified reference material, with no significant differences observed compared with soil matrices. The technique reduces acid consumption and analysis time, thus aligning with the principles of green analytical chemistry. These findings demonstrate the potential of ultrasound-assisted extraction as a cost-effective, environmentally friendly and reliable method for monitoring Cd levels in soils and cacao, with direct relevance for food safety and compliance with international regulations.