Arsenic (As) is a hazardous, non-essential semi-metal that poses significant health risks to animals, humans, and plants. Its environmental levels have risen globally due to increased mining, industrial activities, vehicle emissions, and other human actions, creating significant environmental and health concerns. The remediation of As-contaminated soils is therefore an urgent priority to ensure the provision of safe and healthy food. A critical review published in Ecotoxicology and Environmental Safety by Fei He, Fukang Liu, Shehong Li, Jen-How Huang, Xiaomin Mu, Qiao Han, Lian Song, explores the sources of soil As pollution, its environmental ramifications, the complex dynamics of As contamination, and contemporary advancements in remediation methods.

Arsenic can infiltrate soil from multiple sources, including both natural occurrences and human activities. Natural sources include volcanic activity, geothermal fluids, and the weathering and dissolution of rocks and minerals. Anthropogenic activities, such as agricultural practices involving arsenic-based pesticides and herbicides, and industrial uses in ceramics, mirrors, and glassware manufacturing, are also significant contributors. As production peaked in recent years, reaching 60,000 metric tons annually from 2020 to 2023.

The presence of arsenic in soil poses serious health hazards to human populations through contaminated water supplies and the food chain. For instance, countries like Bangladesh and India face alarming levels of arsenic in their soil and groundwater, far exceeding the World Health Organization (WHO) recommended limit of 10 µg/L. This contamination can lead to stunted plant growth, reduced crop yields, and, in severe cases, crop mortality, causing financial losses for farmers and food insecurity for affected communities. Long-term ingestion of arsenic-contaminated food or water can result in severe health issues, including skin lesions, cardiovascular disorders, anemia, diabetes, and an increased risk of various cancers.

Understanding the factors that influence arsenic transmission in soil is crucial for effective remediation. Soil pHpH is a measure of how acidic or alkaline a substance is. A pH of 7 is neutral, while lower pH values indicate acidity and higher values indicate alkalinity. Biochars are normally alkaline and can influence soil pH, often increasing it, which can be beneficial More plays a critical role; arsenic is more mobile in acidic conditions, while higher pH levels promote arsenic adsorption onto soil particles, reducing its bioavailability. Redox potential affects arsenic speciation, with arsenate (As(V)) being more stable in oxidizing conditions and arsenite (As(III)) more mobile under reducing conditions. Soil texture also impacts transmission, as finer soils like clay tend to retain arsenic, whereas sandy soils allow for easier movement due to lower adsorption capacity. Organic matter, iron and aluminum oxides, phosphate levels, and microbial activities all influence arsenic’s solubility and transport.

Various techniques are employed globally to remediate As-contaminated soils, categorized into physical, chemical, biological, and other innovative strategies. Physical methods include soil washing, excavation and replacement, containment and encapsulation, vitrification, and soil blending. While effective, some of these methods can be costly, disruptive, or generate contaminated wastewater. Chemical treatments involve applying chemical agents to stabilize or remove arsenic. Common approaches include lime application to increase soil pH , phosphate amendments to compete with arsenic for adsorption sites , adding iron oxides or iron-based compounds to enhance arsenic adsorption , and redox manipulation to transform arsenic into less toxic forms.

BiocharBiochar is a carbon-rich material created from biomass decomposition in low-oxygen conditions. It has important applications in environmental remediation, soil improvement, agriculture, carbon sequestration, energy storage, and sustainable materials, promoting efficiency and reducing waste in various contexts while addressing climate change challenges. More and activated carbonActivated carbon is a form of carbon that has been processed to create a vast network of tiny pores, increasing its surface area significantly. This extensive surface area makes activated carbon exceptionally effective at trapping and holding impurities, like a molecular sponge. It is commonly More have emerged as cost-effective and sustainable chemical treatment materials for arsenic remediation. These materials possess a substantial surface area, allowing them to adsorb arsenic efficiently. Their porous structure makes them ideal for trapping arsenic, thus lowering its concentration in the soil and preventing it from contaminating groundwater or being taken up by plants. Biochar, produced from organic materials, is an environmentally friendly option that can improve soil health. Biological strategies harness living organisms to detoxify or stabilize contaminants. These include phytoremediationThis is a technique that uses plants to clean up contaminated soil or water. Biochar can enhance phytoremediation by improving soil conditions and promoting plant growth, allowing plants to absorb and break down pollutants more effectively.   More (using plants to absorb or stabilize arsenic) , mycoremediation (employing fungi) , bioaugmentation (introducing specific microbial strains) , and rhizoremediation (a synergistic approach combining plants and microorganisms). These methods are eco-friendly and can improve soil quality. Other innovative techniques include underground permeable reactive barriers to treat contaminated groundwater and electrokinetic remediation, which uses an electric field to mobilize contaminants towards electrodes for removal.

Addressing arsenic contamination requires a diversified and comprehensive strategy. While remediation techniques can be time-consuming and susceptible to external factors , ongoing research into innovative approaches like nanotechnology , genetically modified plants , and the integrated use of biochar, compost, and other organic additions holds significant promise. Effective long-term solutions require collaborative research concentrating on comprehending the interactions between different remediation technologies and the soil-plant-microbe continuum. This comprehensive strategy that integrates technological innovation, community engagement, and regulatory frameworks is essential to mitigate arsenic contamination and safeguard human wellness and the surroundings.

Source: He, F., Liu, F., Li, S., Huang, J., Mu, X., Han, Q., Song, L. (2025). A critical review of soil pollution sources and advances in the remediation of arsenic-contaminated soil. Ecotoxicology and Environmental Safety, 302, 118504.