Effects of Low-Molecular-Weight Organic Acids on Soil Micropores and Implication for Organic Contaminant Availability

Experiments were conducted to study the effects of low-molecular-weight organic acids (LMWOAs) on micropore properties of black soil, red soil, lignin, and humin. Black soil and red soil were treated with four LMWOAs including malic, citric, succinic, and tartaric acids, whereas lignin and humin were treated with malic and citric acids. The results indicated that soil micropore distribution was changed by LMWOAs. Citric and malic acids reduced soil micropore surface area and volume significantly, but lignin micropores were not changed significantly by these two acids. Therefore, clogging may not be a main reason for the surface area and micropore volume reduction of soil organic matter. The release of metal ions from humin and soils was enhanced by LMWOAs, indicating the dissolution of soil mineral particles. Therefore, soil micropore reduction may result from the destruction of soil aggregates due to dissolution of mineral particles and extraction of metals from bridging sites.