Effects of Heavy Metal Stress on Germination and Growth of Selected Legumes

Abstract

Heavy metal contamination of agricultural soils has emerged as a serious global threat to food security, particularly in developing countries where irrigation with untreated wastewater, mining activities, and industrial effluents are widespread. Legumes are among the most important food and fodder crops, valued for their high protein content and their ability to improve soil fertility through biological nitrogen fixation. However, during seed germination and early seedling development, legumes remain highly vulnerable to environmental stressors, including heavy metals.

This study explores the effects of cadmium (Cd), lead (Pb), nickel (Ni), chromium (Cr), copper (Cu), and zinc (Zn) on the germination and early growth of chickpea (Cicer arietinum), lentil (Lens culinaris), mung bean (Vigna radiata), soybean (Glycine max), and pea (Pisum sativum). A synthesis of experimental findings indicates that Cd and Pb are the most toxic, significantly reducing germination percentage, seedling length, and biomass accumulation. Ni and Cr generally cause delayed germination and chlorosis in seedlings, while Zn and Cu show dual behavior—acting as essential micronutrients at low concentrations but becoming toxic when present in excess. Comparative tolerance ranking suggests that soybean and mung bean exhibit greater resilience under heavy metal stress, whereas chickpea and lentil are relatively more sensitive.

Physiological responses of legumes under heavy metal exposure include reduced chlorophyll content, membrane damage, and activation of antioxidant defense mechanisms such as superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD). The findings highlight the need for urgent soil remediation strategies, the development of tolerant legume varieties, and improved wastewater management policies. This research also contributes to the Sustainable Development Goals (SDGs), particularly SDG 2 (Zero Hunger), SDG 3 (Good Health and Well-being), SDG 6 (Clean Water and Sanitation), and SDG 15 (Life on Land), by addressing the intersections of food security, health, and environmental sustainability.