Plant metal concentrations in Theobroma cacao as affected by soil metal availability in different soil types

• Published in: Chemosphere (Oxford) 2021-01, Vol.262, p.127749-127749, Article 127749
• Main Authors: Lewis, Caleb, Lennon, Adrian M., Eudoxie, Gaius, Sivapatham, Paramasivam, Umaharan, Pathmanathan
• Format: Article
• Language: English
• Subjects: Bioaccumulation; Cocoa; Contaminants; Physicochemical characteristics; Soil extractants; Soil pedogenesis
• ISSN: 0045-6535; 1879-1298
• DOI: 10.1016/j.chemosphere.2020.127749

Beans of cacao (Theobroma cacaoL.) are used to produce a variety of chocolate products. Bioaccumulation of metals at toxic levels through the consumption of contaminated products has been identified as a health concern in humans. Both metal diversity and concentration as well as their interactions in the soil influence essential and non-essential metal uptake in plants; but the effects of these on bioaccumulation of metals in cacao is not understood across diverse soil types. In this study eight metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn) were investigated in 12 soil subgroups belonging to four soil orders across 15 locations in Trinidad, with the aim to investigate the effect of soil metal diversity and concentration on metal bioaccumulation in cacao. Soil metals were extracted using five methods (aqua regia, DTPA, Mehlich 3, nitric acid, and water). Cacao leaf metal concentrations were determined using the USEPA 3052 method. Metal extraction efficiency ranged between methods with aqua regia ≥ nitric acid > Mehlich 3 ≥ DTPA ≥ water across all metals. The soil extraction method that best predicted cacao leaf metal concentrations varied with the metal – Mehlich 3 or DTPA for Cd, Ni, Zn; aqua regia, Mehlich 3, or nitric acid for Pb, and water for Mn. A stepwise regression analysis showed that plant metal concentration can be predicted using soil physicochemical characteristics as well as the concentration of metals in the soil. The importance of soil type on cacao leaf metal bioaccumulation is discussed. [Display omitted] •Metal content from soil and cacao leaves across different soil types were correlated.•For each leaf metal, levels were influenced by soil content of multiple metals.•The DTPA and Mehlich 3 extractable soil Cd, Ni, and Zn predicted cacao leaf Cd.•The DTPA and aqua regia extractable soil Ni and Pb predicted cacao leaf Pb.•The water and DTPA extractable soil Mn and Zn predicted cacao leaf Mn.