Seasonal Dynamics of Heavy Metal Bioaccumulation Potential in Nymphaea Nouchali and Lemna Minor from the Penna River, Nellore, Andhra Pradesh, India

Abstract

Background: Anthropogenic heavy metal pollution in lotic ecosystems represents a severe global threat to biodiversity and public health due to elemental toxicity and food chain biomagnification. Objective: This study investigates the spatiotemporal dynamics of toxic metal contamination and evaluates the comparative bioconcentration efficiencies of two native aquatic macrophytes, Nymphaea nouchali (rooted floating) and Lemna minor (free-floating), along the River Penna at Nellore, Andhra Pradesh, India. Methods: Surface water and macrophyte samples were collected across three seasons (Pre-monsoon, Monsoon, and Post-monsoon) from two distinct locations: Sangam Barrage (agricultural influence) and Penna Bridge (urban sewage influence). Elements—Arsenic (As), Cadmium (Cd), Lead (Pb), and Mercury (Hg)—were quantified using optimized Flame Atomic Absorption Spectrometry (FAAS) following specialized acid and dry ash digestions. Results: The results revealed a distinct spatial gradient, with the urbanized Penna Bridge station consistently exhibiting elevated elemental loads. Surface water concentrations of Pb reached an absolute peak of 0.160 ± 0.015 mg/L during the monsoon at Penna Bridge, more than doubling the levels observed at Sangam Barrage (0.070 ± 0.017 mg/L). Temporally, dissolved metal levels peaked during the monsoon, showing that regional precipitation drives surface runoff kinetics and catchment scouring rather than simple volumetric dilution. Ecotoxicological tissue profiling demonstrated species-specific extraction efficiencies. The free-floating Lemna minor functioned as a superior sink for Pb and Hg, maintaining a Pb Bioconcentration Factor (BCF) up to 0.800 and an Hg BCF up to 1.667. This high capacity is facilitated by full-surface vegetative immersion which maximizes passive biosorption. Conversely, the foliar structures of Nymphaea nouchali exhibited a highly efficient pathway for Cadmium translocation, achieving a maximum BCF of 5.000 during both monsoon and pre-monsoon stress phases. Analysis of Variance (ANOVA) indicated that environmental shifts were statistically non-significant (p > 0.05), reflecting the highly dynamic, pulse-fed nature of open open-channel river ecosystems. Conclusion: Ultimately, both macrophytes serve as sensitive continuous bio-indicators. Managed populations can be strategically deployed as low-cost, sustainable phytoremediation tools to protect the ecological equilibrium of the River Penna basin.