Evaluation of the Affinity of a Nanocarbon-Based Product for Soils in Agricultural Applications

Carbon-based nanomaterials (CBNMs) are promising agricultural amendments, yet predicting their transport and retention in heterogeneous soils remains challenging. In this study, we evaluated the colloidal stability and heteroaggregation of a commercial oxidized carbon nanoparticle (BPGP) across complex pore water conditions and representative North American agricultural soil matrices. Utilizing a high-throughput batch test functional assay, we systematically decoupled the physical influence of collector abundance (B) from the intrinsic physicochemical attachment efficiency (αβ) across fractionated and bulk soils. While BPGP remained stable in monovalent electrolytes, it rapidly destabilized in the presence of divalent cations (Ca²⁺ critical coagulation concentration ∼ 1 mM). This study isolated the intrinsic affinity (αβ) from the overall attachment behavior (αβB), revealed the high retention observed in fine-textured soils is predominantly caused by high surface area instead of higher physicochemical affinity. The intrinsic chemical affinity is suppressed by soil organic matter (SOM), which caused a steric masking effect that overrides the localized coagulating influence of coaccumulated cations. Furthermore, a physically blended Mesocosm soil demonstrated a nonadditive enhancement in intrinsic attachment (α = 0.167), highlighting the impact of synergistic physicochemical heterogeneities (e.g., charge patchiness). This work validates a semiquantitative method for assessing CBNM mobility and offers actionable application guidance, notably demonstrating that coapplication with calcium-rich fertilizers should be avoided to prevent premature immobilization.