Soil, Site, and Management Factors Affecting Cadmium Concentrations in Cacao-Growing Soils

Abstract

Soil contamination by potentially toxic trace elements (PTEs) such as Cadmium (Cd), is a major environmental concern because of its potential implications to human health. Cacao-based products have been identified as food sources with relatively high Cd contents. Here, we assessed Cd concentrations of cacao-growing soils in four major agricultural regions with contrasting climates in Peru, one of the main exporters of cacao products worldwide. At each study site (n = 40) a broad range of potential factors affecting Cd concentration in soils, i.e., site, soil and management, were evaluated. Concentrations of Cd ranged between 1.1–3.2 mg kg−1. Mean values per region were below 2.7 mg kg−1, usually established as upper-limit for non-polluted soils. Cadmium concentrations were significantly (p < 0.001) higher in sites at higher elevations and in a temperate, drier climate. Cadmium correlated positively with pH (r = 0.57; p < 0.05) and was higher (p < 0.001) in alluvial sediments and Leptosols. Management factors (cacao variety, cultivation year, management practices) and agroecology did not affect Cd concentrations directly. Overall, this study highlights the importance of considering a broad range of both natural and anthropogenic factors to evaluate Cd concentrations in cacao-growing soils and contribute to effective and sustainable cacao production by improving land management and planning.

Cadmium in soil and cacao beans of Peruvian and South American origin

“…The geo-distribution (Figures 3 and 4) confirms that part of the Peruvian territory (central and northern zone) has beans with cadmium levels, which exceed the limits established by the EU, and similar to Peru, high levels have also been reported in parts of Ecuador (Mite et al, 2010;Chávez et al, 2015;Diaz et al, 2018;Argüello et al, 2019;Barraza et al, 2019), Venezuela (Sánchez et al, 2011;Lanza et al, 2016) , Colombia (Bravo et al, 2014;Jiménez, 2015;Rodríguez et al, 2019), Brazil (Oliveira et al, 2019) and Bolivia (Gramlich et al, 2017) . These countries contributed to world production with 12% in 2012 and 17% in 2019 (Morales et al, 2012;MINAGRI, 2016;Arvelo et al, 2017;Antolinez et al, 2020).…”

“…In addition, rock composition can elevate the cadmium levels in soil (Argüello et al, 2019); generally following the natural order of their evolution, with the lowest values being found in the most evolved soils, which have an acidic pH, low cation exchange capacity values and thick textures (Pérez and Azcona, 2012). Also, alluvial soil has been shown to have higher levels of available cadmium when compared with residual cadmium (Tantalean and Huauya, 2017;Scaccabarozzi et al, 2020); and the contribution of natural processes to the cadmium contamination of the soil is three to ten times less than in anthropogenic sources (He et al, 2015).…”

“…The higher the pH level of the soil, the greater the cadmium retention and the lower the cadmium contamination in cacao beans, according to the Kelley Directive (Acevedo et al, 2005). In addition, the cadmium concentration and mobility are influenced by the percentage of clay, the presence and type of organic matter (Bravo et al, 2014), the available cadmium (Sánchez et al, 2011;Gramlich et al, 2018), the cation exchange capacity, and the amount of mangnesium and zinc (Degryse et al, 2009;He et al, 2015;Arévalo-Hernández et al, 2017;Argüello et al, 2019;Zug et al, 2019). These authors suggest that the aforementioned indicators have a direct effect on the plant's absorption.…”

“…There are already successful experiences, including Florida et al (2019) in Padre Abad, Peru, who applied compost and NPK and found a significant reduction in cadmium levels of soil for cacao production, as well as the beans. Also, in Venezuela, Sánchez et al (2011) applied phosphorus doses and the amount of available cadmium decreased because of the phosphorus effect. The use of amendments from organic and mineral origin, together with efficient microorganisms, showed better results.…”

“…Soil generally has a low cadmium content (Kabata-Pendias, 2010), but regardless of the level and origin, the dynamics of the metal depend on its chemical form and the characteristics of the soil (Bravo et al, 2014;Díaz et al, 2018;Scaccabarozzi et al, 2020). This limits or contributes to the mobilization and uptake of cadmium from cacao plants (Gramlich et al 2017;Zug et al 2019); in some plant structures it is accumulative (Hernández-Baranda et al, 2017;Tantalean and Huauya, 2017;Casteblanco, 2018), and reaches concentrations that are higher than in the soil itself (Chávez et al, 2015;Díaz et al, 2018;Oliva et al, 2020).…”