Phytoremediation of cadmium-contaminated Coffea arabica coffee-growing soils using Moringa oleifera in the Peruvian Andes

Abstract

Cadmium contamination in coffee-growing soils affects soil quality, food safety and the sustainability of Andean coffee systems. In this study, we evaluated changes in total recoverable Cd within a planted, non-draining pot system containing Moringa oleifera and Coffea arabica coffee-growing soil from Chirinos, Cajamarca, Peru. A 4 × 4 factorial pot experiment was conducted under a randomized complete block design with four blocks. The factors were initial soil Cd, 1.9, 2.4, 2.8 and 3.5 mg kg-1, and development time, 30, 45, 60 and 75 days after transplanting. Residual soil Cd was determined by US EPA 3050B acid digestion and ICP-OES, under US EPA 6010B. Cd removal, Cd removed from soil, plant height, stem thickness, root length and total dry biomass were also evaluated. All initial Cd levels exceeded the Peruvian agricultural soil standard of 1.4 mg kg-1. Residual Cd declined with development time, from 1.603 ± 0.207 mg kg-1 at 30 days to 0.496 ± 0.326 mg kg-1 at 60 days and 0.472 ± 0.192 mg kg-1 at 75 days. The strongest operational response occurred at 3.5 mg kg-1 initial Cd and 60 days, with residual Cd <0.12 mg kg-1, removal ≥96.6% and Cd removed ≥3.380 mg kg-1. Time was the dominant factor in the ANOVA, F = 81.53 and p < 0.001, while initial Cd was also significant, F = 3.56 and p = 0.020. The Moringa oleifera maintained growth under Cd exposure, with total dry biomass increasing from 0.668 ± 0.087 to 2.945 ± 0.527 g plant-1 between 30 and 75 days. The results obtained support controlled validation of this low-input Moringa-soil system for reducing recoverable Cd. The interpretation remains operational because the trial did not include an unplanted contaminated control and Cd was not quantified in plant organs.