Factors influencing heavy metal contamination in black pepper fields: a randomized study of the traditional chemical fertilized black pepper fields of South India concerning soil types

Despite the prevalence of heavy metal contamination in crop fields, targeted studies examining how factors like soil type affect contamination in chemically fertilized fields are scarce. This study assessed heavy metal contamination in Kerala's traditional black pepper fields, focusing on soil types-both soil order and series-and cultivation practices. We collected 266 soil samples from 70 diverse black pepper fields across five districts, which were categorized into 39 composite samples representing 13 soil series from two soil orders based on standard previous studies. Using Inductively Coupled Plasma-Mass Spectrometry, we quantitatively measured nine heavy metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) along with macronutrients (Mg and Ca). We analyzed heavy metal indices, including contamination factor, geo-accumulation index, pollution load index (PLI), and human health risk assessment, and explored correlations between heavy metals and soil nutrient parameters. It indicated that Cd, Zn, Cr, Pb, and Cu were the contaminants in the region's black pepper soils, while Fe and Mn levels were within natural limits. The PLI > 1 indicated significant contamination across both soil orders and most soil series. Mg levels were significantly higher (p > 0.05) in chemicalized fields, but Ca was undetectable in most samples, except from the Paippara series. Notable correlations were found between heavy metals and soil fertility parameters. This study underscores the extent of heavy metal contamination in black pepper fields relative to soil types and emphasizes the need for tailored soil fertility amendments and pesticide applications to promote sustainable agricultural practices.