Accumulation of Cadmium in Soils, Litter and Leaves in Cacao Farms in the North Sierra Nevada De Santa Marta, Colombia
58 Pages Posted: 3 Nov 2023
Abstract
Cadmium (Cd) accumulation in cacao has become a concern for cacao growers due to its potential adverse human health effects. European Union legislation regulating Cd content in chocolate products that are manufactured using cacao beans, has increased the need to understand its accumulation dynamics in soils and plants. In Colombia, cacao plays a significant role as an agricultural commodity and a tool for illegal crop replacement, yet our understanding of Cd dynamics in Colombian cacao cultivation is still limited. This research provides the first comprehensive investigation of cadmium biogeochemistry in cacao agroecosystems in Colombia's Sierra Nevada de Santa Marta. This study aims at characterizing the interactions between subsurface soils, topsoil, rock fragments, a permanent litter layer, and cacao leaf Cd concentrations from 30 farms. Our results reveal that total soil Cd concentrations in the study area are generally low. The mean Cd concentration for topsoil and subsurface soil is 0.12 mg kg-1 and 0.05 mg kg-1, respectively. Leaf and litter Cd concentrations are significantly higher than soil Cd concentrations, with a mean of 0.42 and 0.4 mg kg-1, respectively. Our results suggest that age dependent surface-level processes such as the bioaccumulation and biocycling of Cd over time through the leaves, litter, and topsoil, govern Cd in the topsoil, leading to older cultivars and trees exhibiting higher Cd concentrations in leaves, litter, and soils. These surface biocycling processes may be affected by additional surface Cd deposition as a trace element in some fertilizers or irrigation waters and suspended Cd bearing sediments. Subsurface soil Cd is primarily driven by geogenic Cd and its interactions with other soil properties with a hypothesized contribution from pedogenic Cd being translocated to deeper soil horizons from the topsoil via clay and oxide illuviation. Our research provides insights into the accumulation of Cd in cacao plants and soils, which can lead to long-term preferential accumulation of cadmium on soil layers and thus increase plant uptake through roots. The overall concentration of Cd in soils and plants in the study area is low and within regulatory limits, which is favorable for current and future farmers.
Keywords: Theobroma cacao, Cadmium, Cd biocycling, Cd bioaccumulation, Geogenic Cd, Anthropogenic Cd
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