The potential degradability of persistent organic pollutants (POPs) in soil: a perspective from soil aggregates

Aggregates are the fundamental units of soil structure. Clarifying the distribution characteristics of soil organic carbon (SOC), microbial properties (e.g. microbial abundance/diversity, soil enzyme composition/activity) and persistent organic pollutants (POPs) in soil aggregates, along with influencing factors such as aggregate size, specific surface area (SSA), and nutrient content, is crucial for grasping POPs degradation mechanisms in soil. This study reviewed existing literature and identified that SOC mainly accumulated in 0.25-2 mm aggregates, then >2 mm, 0.053-0.25 mm, and <0.053 mm ones. Meta-analysis revealed that microbial abundance and diversity were significantly lower in >2 mm aggregates (p < 0.05), with no difference in the other three. Soil enzyme activities did not show significant variations across different aggregates. Soil nutrients exerted the most pronounced influence on microbial communities within the 0.25-2 mm aggregates whereas the enzyme activities were prominent within the <0.053 mm and >2 mm aggregates, with a generally positive effect. PAHs are mainly distributed in <0.053 mm fractions. For different types of POPs, their distribution in the soil is closely related to their own species characteristics, while their content in aggregates shows a significant positive correlation with SOC and SSA. The heterogeneity in SOC, microbial properties, and POPs distribution increased POPs degradation complexity. Our study provides a basis for understanding POPs environmental behavior and insights for soil remediation. Future research should focus on the interaction mechanisms among nutrients, pollutants, and microbial properties at the aggregate scale to lay the foundation for soil remediation strategies.