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Soil contamination is a global environmental concern, with toxic metals and metalloids from industrial activities persisting as long-term pollutants. Arsenic (As), although naturally occurring, becomes widespread when mobilized by mining. Abandoned gold mines are major sources, releasing arsenic-rich minerals into surrounding environments through erosion and leaching. Forest soils, essential for ecosystem health and biodiversity, are particularly vulnerable. Despite arsenic's mobility under specific soil conditions and known toxicity, its behavior in forest soils and impacts on soil organisms remain poorly understood.

In a recent study, a research team led by Professor Yun-Sik Lee from Pusan National University, Korea, investigated how arsenic interacts with different forest soils and how these interactions influence its toxicity to soil-dwelling organisms.

As Prof. Lee explains, "Our goal was to determine how soil properties affect arsenic binding, mobility, and bioavailability, and how these factors in turn impact the survival and reproduction of the springtail Allonychiurus kimi (A. kimi), an important indicator species for soil health." The findings were published in the on 5 October, 2025.

The study collected four uncontaminated forest soils and characterized their physicochemical properties, including pH, cation exchange capacity (CEC), phosphorus content, organic matter, metal oxides, clay content, and total arsenic. Soil samples were spiked with arsenic at 20–100 mg/kg and aged under wet-dry cycles to simulate environmental contamination.

Using the Wenzel sequential extraction method, arsenic was fractionated into F1 and F2 (weakly bound, highly mobile), F3 (bound to amorphous Fe/Al oxides, potentially bioavailable), F4 (bound to crystalline Fe/Al oxides), and F5 (residual, strongly bound). Adult and juvenile A. kimi were exposed to these soils for 28 days to assess arsenic accumulation, survival, and reproduction.

Results showed that newly introduced arsenic primarily accumulated in mobile fractions (F1–F3), making it bioavailable to soil organisms. Prof. Lee notes, "Even at the same total arsenic concentration, contamination levels and biotoxicity varied markedly depending on soil properties. CEC, phosphorus, and aluminum oxides strongly influenced arsenic binding and mobility."

Life stage strongly affected toxicity: adults accumulated arsenic without significant impacts on survival, with body burdens correlating more with F3 and total arsenic levels. Juveniles were highly sensitive, with reproduction strongly reduced by mobile arsenic fractions, highlighting vulnerability during early development.

This research improves understanding of arsenic bioavailability and toxicity in forest soils. "The findings support the development of more accurate ecotoxicological assessments that account for differential sensitivity between juveniles and adults," explains Prof. Lee.

"Moreover, the study emphasizes the need for soil-specific risk evaluations based on bioavailable arsenic fractions rather than total concentrations, providing a stronger foundation for targeted ecosystem management and remediation strategies."

In conclusion, the study demonstrates that arsenic behavior in forest soils is controlled by soil properties and that toxicity varies according to chemical fraction and life stage. These insights provide a basis for soil-specific management and remediation strategies to protect ecosystems from arsenic contamination.