Interaction and Cotransport of λ-Cyhalothrin and Chitosan in Saturated Quartz Sand: Sorption Mechanisms and Remediation Implications

The λ-Cyhalothrin is a type II synthetic pyrethroid and a widely applied hydrophobic insecticide. Its accumulation in subsurface environments raises environmental and public health concerns due to its persistence and toxicity. Chitosan, a biodegradable polymer with notable physicochemical and adsorptive properties, is increasingly explored for environmental remediation. This study investigates the interaction and cotransport behavior of λ-cyhalothrin and colloidal chitosan in water-saturated quartz sand under static, batch and column flow conditions at 25°C. Sorption kinetics followed a pseudo-second-order model, while transport behavior was simulated using the advection–dispersion equation, incorporating two-site attachment mechanisms both linear and nonlinear, with ripening effects. The results indicate that λ-cyhalothrin undergoes chemisorption onto both chitosan and quartz sand. Cotransport experiments revealed significant bidirectional interactions: chitosan–λ-cyhalothrin aggregates enhanced chitosan retention while concurrently reducing λ-cyhalothrin attachment. These findings demonstrate that chitosan increases λ-cyhalothrin mobility in porous media, while also increasing its own immobilization through aggregate formation. The developed model effectively captured these dynamics, suggesting chitosan’s promising role as a dual-function agent for pesticide mitigation and nanoparticle delivery in groundwater remediation applications.