Evaluation of soil amendments as a remediation alternative for cadmium-contaminated soils under cacao plantations

Abstract

Elevated plant-available cadmium (Cd) in soils results in contamination to cacao (Theobroma cacao L) beans. Effectiveness of vermicompost and zeolite in reducing available Cd in three cacao-growing soils was studied under laboratory conditions. Sorption-desorption experiments were conducted in soils and amendments. Cadmium was added at 0 or 5 mg kg(-1) (spiked), then, amendments were incorporated at 0, 0.5, or 2 %. Amended soils were incubated at room temperature for 28 days. Plant-available Cd was determined using 0.01 M CaCl2 (WSE) and Mehlich 3 (M3) extraction procedures in subsamples taken from individual bags at six time intervals. Soils and amendments displayed different sorption characteristics and a better fit was attained with Freundlich model (R (2) > 0.82). Amendments were ineffective in reducing extractable Cd in non-spiked soils. In Cd-spiked soils, vermicompost at 2 % significantly reduced WSE-Cd (P < 0.01) from 3.36, 0.54, and 0.38 mg kg(-1) to values lower that instrument's detection in all the three soils and significantly diminished M3-extractable Cd (P < 0.05) from 4.62 to 4.11 mg kg(-1) in only one soil. Vermicompost at 0.5 % significantly decreased WSE-Cd (P < 0.01) from 3.04 and 0.31 to 1.69 and 0.20 mg kg(-1), respectively, in two soils with low sorption capacity for Cd. In contrast, zeolite failed to reduce WSE- or M3-extractable Cd in all studied soils. A negative correlation occurred between soil pH and WSE-Cd (r > -0.89, P < 0.01). The decrease in WSE-Cd appears to be associated with the increase in pH of the vermicompost-amended soils.

Evolution, and functional analysis of Natural Resistance-Associated Macrophage Proteins (NRAMPs) from Theobroma cacao and their role in cadmium accumulation

“…Of specific relevance is the decision of the EU regulatory authorities to reduce from 2019 the permissible levels of dietary Cd 2+ (Commission Regulation (EU) no 488/2014). In an attempt to reduce the levels of Cd 2+ in crops, including cacao (the source of chocolate), a variety of research studies are underway to develop agronomic 3 , 4 or genetic 5 solutions to this problem.…”

Cd and Pb reduction in cocoa (Theobroma cacao) nib using two organic amendments.

“…Respect to soil pH, our results differ from those reported by Liu et al (2015) who mentions that in order to reduce the Cd absorption by plants, the soil pH need to increase with the increase of OM in the soil. Chavez et al (2016) reported the soil pH increase up to 60 days after application of vermicompost and zeolite on cocoa plantation soil, but on day 75 the soil pH decreased. In our study, we registered a slight soil pH change after 9 months of applying the organic amendments (compost and poultry manure).…”

“…However, most cocoa farmers in Peru, generally do not fertilise their parcels with OA, unlike Andean farmers who use OA, mainly livestock manure as fertilizer. In that sense, the presence, absorption and accumulation of heavy metals by cocoa plants may be related to soil characteristics such as pH, soil organic matter (OM) content, soil cation exchange capacity (CEC), among others (Chavez et al, 2016;Huamaní-Yupanqui et al, 2012), and these characteristics can be modified by OA application.…”

“…OA consist of humic substances (humina, humic and fulvic acids) and non-humic substances (cellulose, lignin and proteins), that can retain the heavy metals in soil (Chavez et al, 2016;Liu et al, 2009) and decrease their bioavailability for cocoa crops. OA application to cocoa trees could be an alternative to reduce Cd and Pb bioavailability from soil and uptake, lowering their content in cocoa nibs.…”

Effect of soil characteristics on cadmium absorption and plant growth of Theobroma cacao L. seedlings

“…It has been reported that pH and organic matter in soils are related to the absorption of Cd in cacao plants. 5,[48][49][50][51][52][53][54][55][56] Thus, several studies have used lime, 55,56 organic matter amendments 48 or biochar 20,24,[49][50][51]55 to manage Cd absorption by cacao plants. Lime acts mainly increasing soil pH, and it has been reported that the sorption of Cd in soils increases by a factor of 3 to 5 for each unit of increase in pH, 4 and organic matter causes Cd retention in soils by surface adsorption or by generating complexes with the Cd ions.…”