# Degradation of Low-Molecular-Weight Diesel Fractions (C10−C16 Alkane) Drives Cd Stabilization and Pb Activation in Calcareous Soils from Karst Areas

## TL;DR

Diesel fuel breakdown in calcareous soils affects how cadmium and lead behave, with low-molecular-weight diesel fractions stabilizing Cd but making Pb more available.

## Contribution

This study reveals how diesel fraction degradation influences Cd and Pb speciation in calcareous karst soils through physicochemical and microbial mechanisms.

## Key findings

- C10−C16 diesel fractions degradation promotes Cd stabilization via electrostatic attraction and speciation changes.
- Degradation of C10−C16 fractions increases Pb bioavailability by altering its speciation through microbial activity.
- DOM and CaCO3 in soils reduce metal interactions with diesel fractions, weakening their mobility predictions.

## Abstract

The influence of petroleum hydrocarbons (PHCs) on the transport and transformation of heavy metals may limit bioremediation efficiency. The mechanisms by which PHC degradation intermediates control heavy metal distribution in calcareous soils from karst areas require further exploration. This study systematically investigated how compositional changes in diesel fuel during aging regulated the fate of Cd and Pb in calcareous soils. The results demonstrated that the low-molecular-weight fractions of diesel fuel (C10−C16) were preferentially degraded. This degradation process altered zeta potential, cation exchange capacity (CEC), and pH, thereby promoting Cd stabilization through electrostatic attraction and speciation transformation. Particularly, reducible Cd content showed a strong positive correlation with C16 content (r = 0.88, p < 0.05). Furthermore, the degradation of C10−C16 fractions caused Pb transformation from residual to bioavailable fractions by stimulating microbial activity. Residual Pb content was positively correlated with C10−C16 fractions (r = 0.55, p < 0.05). Notably, dissolved organic matter (DOM) and CaCO3 content in calcareous soils enhanced Cd and Pb adsorption, thereby weakening the interactions between these metals and C10−C16 fractions. Consequently, multiple linear regression (MLR) models relying exclusively on C10−C16 degradation parameters showed poor fitting coefficients for Cd/Pb mobility. The present work provides scientific guidance for heavy metal bioremediation in calcareous soils.