Proactive solutions for reducing heavy metals from soil

In an era of heightened industrialization, the improper disposal of industrial waste has led to the accumulation of toxic metals such as lead, cadmium, mercury, and arsenic in soils. Using an integrated approach, geotechnical engineering is answering the call to consider effective soil management solutions and ensure safe and sustainable environments and communities.   

Understanding heavy metal contamination 

Heavy metals are naturally occurring elements with high atomic weights and densities. While some heavy metals are necessary for biological processes in trace amounts, excessive concentrations can be harmful. Contaminated soils can cause these metals to be absorbed by plants, entering the food chain and posing health risks to humans and animals. Traditional remediation methods such as soil excavation and landfilling can be costly and environmentally disruptive. 

Fortunately, innovative and sustainable geotechnical solutions are making progress in reducing contaminated soils. 

Phytoremediation: Harnessing the power of plants 

Phytoremediation utilizes plants to remove, stabilize, or degrade contaminants from soil and water. This method is considered cost-effective and environmentally friendly and also has aesthetic attributes. Certain plants, referred to as hyperaccumulators, have the capability to absorb and concentrate heavy metals in their tissues; Indian mustard and sunflowers, for instance, can effectively accumulate lead and cadmium. 

Phytoremediation involves several process mechanisms: 

• Phytoextraction: Plants absorb contaminants through their roots and translocate them to above-ground parts. 
• Phytostabilization: Plants immobilize contaminants in the soil, reducing their bioavailability. 
• Phytodegradation: Plants degrade organic contaminants through metabolic processes. 
• Rhizofiltration: Plant roots absorb contaminants from aqueous solutions. 

Bioremediation: Leveraging microbial activity 

Bioremediation uses microorganisms to degrade or transform contaminants into less toxic forms. Soil microorganisms, including bacteria and fungi, play an essential role in the natural attenuation of heavy metals. Recent studies have focused on improving the remediation potential of soils through the combined application of microbial inoculants and plants. For example, the combination of the Serratia marcescens WZ14 strain of bacteria with leguminous plants like black locust has shown effective results in reducing cadmium and lead levels in contaminated soils. 

Key mechanisms in bioremediation include: 

• Bioaugmentation: Introducing specific strains of microorganisms to enhance degradation. 
• Biostimulation: Adding nutrients to stimulate the activity of indigenous microorganisms. 
• Biosorption: Microorganisms adsorb and concentrate heavy metals on their cell surfaces. 
• Bioaccumulation: Microorganisms uptake and accumulate heavy metals within their cells. 

Electrokinetic remediation: Applying electric fields 

Electrokinetic remediation involves using electric fields to mobilize and remove heavy metals from soils. Electrodes are inserted into the contaminated soil, and a low-voltage electric current is applied. This process causes heavy metal ions to migrate towards the electrodes, where they can be collected and removed. Electrokinetic remediation is suitable for soils with low permeability and high clay content. 

Soil washing and chemical leaching 

Soil washing uses water or chemicals to remove heavy metals from contaminated soils. It can be combined with chemical leaching, where agents are added to increase metal solubility and mobility. Extracted metals are separated from the solution by precipitation, adsorption, or ion exchange. These methods need careful management to avoid secondary contamination. 

Nanotechnology: A cutting-edge approach 

Nanotechnology provides innovative soil remediation solutions using nanoparticles. These particles, with their high surface area and reactivity, effectively absorb and degrade contaminants. For instance, zero-valent iron nanoparticles reduce and immobilize heavy metals like arsenic and chromium in soils. Though still in its early stages, nanotechnology holds great promise for future soil remediation advancements. 

What’s next? 

An integrated approach ensures that construction activities won’t exacerbate existing contamination and that the environment remains protected. To do this, geotechnical engineers must work closely with environmental agencies to ensure remediation efforts comply with local and federal regulations and that construction projects meet environmental standards for public health protection. 

At Hatch we develop innovative geotechnical solutions for remediating heavy metal-contaminated soils to protect human health and the environment. Phytoremediation, bioremediation, electrokinetic remediation, soil washing, and nanotechnology are means used to offer diverse and effective approaches to address this challenge. We continue to both monitor and participate in continued research and development in these areas to pave the way for safer and more sustainable land use. As we strive toward a healthier and more resilient planet, we continue to integrate and assess such solutions into comprehensive soil management strategies for our clients. 

Contact us to learn how we’re powering positive change in our infrastructure projects, or browse our related content: 
 
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