Heavy Metal Accumulation in Agricultural Soils and its Consequences for Crop Plants and Food Safety

The accumulation of heavy metals and metalloids in agricultural soils is a permanent threat to soil health, crop productivity and food safety. Cadmium, lead, arsenic, mercury, chromium, nickel and copper enter agricultural land from geogenic weathering, atmospheric deposition, mining, industrial activities, phosphate fertilisers, pesticides, livestock manures, sewage sludge and irrigation with wastewater. Being non-biodegradable elements, repeated inputs can increase soil concentrations over time, both total and bioavailable. Their impact on crops is highly dependent on soil pH, organic matter, redox conditions, texture, microbial activity and crop species. Excess metals affect seed germination, root growth, nutrient uptake, photosynthesis, water relations and enzyme function, usually through oxidative stress and disruption of essential metal homeostasis. Different crops have different capacities to absorb and translocate metals. Leafy vegetables, rice and some root crops can accumulate worrying levels of cadmium, arsenic or lead. Dietary exposure to contaminated crops is associated with nephrotoxicity, neurotoxicity, cardiovascular effects, developmental toxicity and cancer risk. Good management includes source control, routine testing of soil and crops, pH and organic-matter management, safe irrigation water, low-accumulating cultivars, and site-specific remediation. This review summarises sources, soil processes, plant responses, food chain transfer, health risks and mitigation methods of heavy metals in agricultural systems.