Contamination of soil by DDT remains a significant concern globally. Researchers from Chalmers University of Technology in Sweden have found an innovative way to mitigate the environmental dangers posed by this toxin by combining it with biochar. Their experiments at a former tree nursery demonstrated that incorporating biochar into contaminated soil halved the amount of DDT absorbed by earthworms. This technique could allow for the cultivation of specific crops on land that is presently deemed unusable due to pollution risks.
The remnants of DDT usage by past generations continue to impact us. In the 1950s and 60s, this insecticide was widely employed to manage pests in agriculture and forestry. Though it has been prohibited for over 50 years, numerous sites in Sweden still show signs of DDT contamination. This issue is prevalent in various other countries as well.
The toxin is associated with numerous adverse health effects for both humans and wildlife and is known for its slow degradation. It represents an ecological threat as it can be ingested by land-based organisms like earthworms. When these creatures are consumed by birds and other animals, DDT accumulates within the food chain, significantly impacting top predators with higher toxin levels.
For three years, the researchers at Chalmers University have been exploring a novel approach to minimize the ecological risks of DDT at a contaminated former tree nursery in southern Sweden.
“During our field trials, we blended biochar into the soil and cultivated various plants. We discovered that biochar effectively binds DDT, preventing its absorption by soil-dwelling organisms,” explains Paul Drenning, a postdoctoral researcher in the Department of Architecture and Civil Engineering and lead author of the study.
Affordable and Eco-Friendly Solution In-Situ
Biochar, which resembles charcoal, is both an affordable and eco-friendly material. It captures pollutants and promotes soil health when added to existing soil. Additionally, this measure can assist in climate change mitigation through the long-term retention of carbon in the soil.
The study revealed that earthworms’ absorption of DDT in the soil fell by approximately 50% with the addition of biochar. This suggests a lowered bioavailability of DDT to soil organisms, indicating that the soil became less toxic with a reduced likelihood of DDT transferring through animal food chains or leaching into water sources.
This decrease in environmental hazards could enable landowners to resume farming on parcels of land that are currently non-productive due to the need for remediation of contaminated soil.
“Handling large amounts of contaminated soil can be expensive and complex. Typically, the solution involves excavating the soil and transporting it to a hazardous waste landfill, which results in the loss of quality soil and is impractical for vast contaminated regions,” Paul Drenning notes. “Using biochar treatment on-site could revitalize the land, making it viable for use rather than leaving it barren or degrading, all while being significantly less costly for both property owners and the environment.”
Anticipated Long-Term Benefits
Potential crops that could thrive in the treated areas include pine and spruce saplings, hay for animal forage, or bioenergy crops like willow trees (Salix). Biochar treatment also suggests that plants may uptake less DDT from the soil, although they accumulate minimal amounts even without this treatment.
“The reason the contaminated land remains unused today is not due to health risks from crops but rather that landowners are required by law to address the ecological risks associated with DDT. As they await investigations and decisions on remediation, the land sits idle,” states Jenny Norrman, a Professor at the Department of Architecture and Civil Engineering and project leader.
Biochar has a slow decomposition rate in soil, and researchers foresee the positive effects of this treatment lasting long-term — potentially for decades. They plan to continue sampling at the site for many years to monitor the ongoing development in the area. Additionally, they will investigate methods to scale the experiment up, enabling the mixing of biochar into the soil without the need for extensive excavation.
Significant Potential for This Method
Though the use of biochar for soil remediation is not yet common, the researchers believe that this technique has not been previously explored at forest nurseries in Sweden or anywhere with the same soil and climate conditions internationally.
“There is considerable interest in deploying biochar for stabilizing DDT and various other soil contaminants such as metals and polycyclic aromatic hydrocarbons. Thus, it is encouraging to observe its effectiveness in our study,” remarks Paul Drenning.
Soil is a crucial resource that regenerates at a slow pace — forming just one centimeter of soil can take centuries. In the European Union, a significant portion of soil (60-70%) is regarded as unhealthy due to degradation, with soil pollution being a primary contributor. The EU is actively working to enhance soil pollution control efforts. The upcoming Soil Monitoring Law from the European Commission aims to implement stricter regulations for sustainable land management and remediation of polluted areas, emphasizing soil health.
The Chalmers team has also researched additional factors affecting soil health—like how various treatments influence functions such as nutrient cycling, water management, and carbon storage—yielding positive results in conjunction with the impact of biochar on DDT. Their field experiment exemplifies a general methodology that they have crafted to assess the impacts of gentle remediation strategies on soil health, designed for accessibility by practitioners and decision-makers such as landowners.
Further Information: Scientific Study
The three-year research was conducted on a 23-hectare site contaminated with DDT at a former tree nursery in southern Sweden. The researchers excavated soil from a 50 x 5-meter area, separated it into piles, and mixed biochar into half of the samples. They established 24 experimental plots and randomly allocated the soils to these, with half featuring biochar-enhanced soil. Various plants were then introduced to the plots, including pumpkins, grasses, legumes, and willows. They utilized physical, chemical, and biological measurements to evaluate soil health and analyze the effects of both the plants and biochar.
Further Information: Biochar
Biochar is a soil enhancement material with vast application potential. While it resembles charcoal and BBQ coals, it is specifically produced for incorporation into farmland, possessing unique properties that make it effective for stabilizing pollutants in soil. This material is generated through pyrolysis, where organic waste, such as leftovers from agriculture and forestry, is burned in an oxygen-free environment.
Like activated carbon, which is used for water purification and treating certain toxins in humans, biochar also has a strong affinity for binding pollutants.
Thanks to its porous structure, biochar assists in retaining moisture, air, and nutrients in the soil. The synergistic effect of using charcoal to enhance soil fertility has been practiced for thousands of years across various cultures, such as in slash-and-burn agriculture.
Further Information: DDT
Dichlorodiphenyltrichloroethane (DDT) is an insecticide introduced in 1942 and has been banned for over five decades. However, it continues to persist in substantial quantities across global soils. In the 50s and 60s, its application in Sweden included immersing cuttings in DDT, often used in conjunction with surface applications.
DDT is a harmful environmental toxin recognized for its endocrine-disrupting properties, linked to health risks such as cancer, heart disease, and reproductive issues in both humans and wildlife. Due to its slow decomposition rate, DDT tends to accumulate within animal food chains, adversely affecting apex predators, which can include humans.
Further Information: The EU Soil Monitoring Law, Expected in 2025
Europe is estimated to have around 2.8 million potentially contaminated sites. To confront the pollution legacies from previous activities, the Proposal for a Directive on Soil Monitoring and Resilience (Soil Monitoring Law) urges EU member states to:
- Identify all potentially contaminated sites
- Generate a public registry of these sites
- Conduct investigations of the sites
- Address any substantial threats to human health and the environment.
The ultimate goal is to ensure that all soils remain healthy by 2050, aligning with the EU’s Zero Pollution initiative. To meet these objectives, the Directive will also include:
- A standardized definition of soil health
- A detailed monitoring framework
- Principles of sustainable soil management to direct practices for soil management and remediation of contaminated areas.
