## 4 Discussion
### Physical and Biochemical Drivers for the Distribution of Soil Cd
It also suggests a Cd presence in cacao beans due to specific conditions that may vary at the farm level (ranging from 0.02 to 1.3 \(\pm\) 0.4 mg\(\cdot\)kg\({}^{-1}\) Cd). In this study, Fe was determined to be higher at all farms where the Cd content was higher as well, e.g., 8.80 \(\pm\) 0.7 and 11.50 \(\pm\) 0.2 mg\(\cdot\)kg\({}^{-1}\) Fe at farms in Muzo and San Vicente de Chucuri, respectively. At farms in San Vicente de Chucuri, less acidic pH values (5.4 on average) were found with a higher level of soil Cd (2.76 \(\pm\) 0.2 mg\(\cdot\)kg\({}^{-1}\)) and higher content of Fe (836 \(\pm\) 4.4 mg\(\cdot\)kg\({}^{-1}\)). Soil pH could also influence the distribution of Cd in the subsoil of cacao systems. Soil-solution pH greatly influences diffusion rates because of the strong pH effect on Cd solubility in soil [34], generating a reciprocity between the pH and Cd/resistivity ratio. In farms in Arauquita, Muzo, and SanVicente de Chucuri (Figure 8A-C) similar patterns of distribution were described. Such reciprocity between pH and soil Cd content has also been observed in previous studies [35]. Soils assessed in this study have pH ranging from 3.5 to 7. Acidic pH is associated with lower Ca and P content (<1 and <15 mg\(\cdot\)kg\({}^{-1}\), respectively), and higher Fe and Cd content, as also observed in other studies [36]. Figure 8: Vertical distribution of Cd, pH, and resistivity in soils. (**A**) Representative comparison of farms in Arauquita; (**B**) Muzo; and (**C**) San Vicente de Chucuri. In each case, the comparison shows an inverse relationship between pH (black dots), Cd (red inverted triangles), and resistivity (grey triangles), whereas a positive relationship is observed between Cd and resistivity. The values are given as mean of replicates and vertical bars represents the standard deviation (\(n=3\)). Critical non-biotic factors influencing Cd debris, according to the literature, includes soil pH, clay content, carbonates, and SOM content [37]. Factors directly controlling Cd mobility, as reported in literature, are pH and soil type [21]. In the present survey of cacao soils, the order of factors related to soil Cd were resistivity \(>\) P \(>\) SOM \(>\) Fe \(>\) pH \(>\) Ca, as shown on the PCA plot in Figure 9.  
Acidic soil pH was observed in Muzo (3.5), followed by San Vicente de Chucuri and Arauquita (4 and 4.6, respectively). Interestingly, farms in these municipalities have medium to high soil Cd content (0.54, 0.84, and 1.3 mg\(\cdot\)kg\({}^{-1}\) at Arauquita, Muzo, and San Vicente de Chucuri, respectively). At the same boundaries where acidic pH was found, a higher Fe content was also found (i.e., 16.54, 76, and 200 mg\(\cdot\)kg\({}^{-1}\) in Arauquita, Muzo and San Vicente de Chucuri, respectively). Calcium, as shown in Figure 9, is the least significant nutrient related to Cd distribution in soils of farms assessed in this study. However, its presence was enriched at the same boundaries where the level of Cd was found to be high. Thus, the flux of calcium and its role in Cd distribution should be addressed in further studies.