[Influences of Acidification on the Allocation and Availability of Lead and Cadmium within Soil Aggregates].

Abstract

Soil aggregates, the fundamental units of soil structure, crucially regulate soil physicochemical properties. Acidification alters soil aggregation, impacting heavy metal distribution and availability within aggregates. This study explores aggregate composition in differently acidified yellow and purple soils, along with the variation in the distribution and availability of cadmium （Cd） and lead （Pb） in different-sized aggregates. Acidification reduced the mass fraction of large aggregates （>2 mm）, with non-acidified soil being 5%-15% higher. In both soils, large aggregates contributed most to the total amount of Cd and Pb （contribution factors 0.31-0.47）. Yellow soil showed the highest Cd and Pb contents in small （1-0.25 mm） and micro-aggregates （<0.25 mm）, while the highest contents were observed in large aggregates in acidified purple soil. The mass fractions determined the distribution of external Pb and Cd in aggregates when entered into soils. In highly acidified soil, smaller aggregates posed a higher heavy metal release risk, while in non-acidified soil, the large aggregates showed higher Cd and Pb contents and thus a higher release risk. The alterations in the transformation and availability of Cd and Pb were attributed to the variations in soil aggregate composition and their properties driven by acidification, including mineral weathering, iron oxide leaching, organic matter loss, etc. These results provide the basis for the co-remediation of soil acidification and heavy metal pollution.