Carbamazepine and its transformation products in biosolids-amended soils: distribution in maize and transformation-product-dominated leaching

Purpose Municipal biosolid application at agronomic rates can introduce pharmaceuticals and their transformation products into soils, potentially affecting crop safety and environmental quality. Methods This two-year lysimeter study investigated the occurrence and distribution of carbamazepine (CBZ), carbamazepine-10,11-epoxide (CBZ-EP), and carbamazepine diol (CBZ-DiOH) in soil and maize tissues, their leaching below the root zone, and associated human health risk. We hypothesized that (1) crop nutrient requirement-based biosolid application would result in soil-profile distribution of target compounds and differential partitioning in maize, (2) soil type would influence plant uptake and leaching, and (3) grain occurrence could pose human health risks. Results The highest mean biosolid concentrations were 9.64, 10.74, and 65.56 ng/g dry weight for CBZ, CBZ-EP, and CBZ-DiOH, respectively. Post-harvest CBZ and CBZ-DiOH were below quantification limits in soil, whereas CBZ-EP occurred throughout the investigated profile to 70 cm, with significant Depth, Soil × Depth, and Soil × Year × Depth effects. Target compounds also occurred in maize tissues, collectively providing partial support for Hypothesis (1). Plant concentrations showed no consistent effect of soil texture. Soil texture significantly influenced CBZ-EP leaching and interacted with year; Year 2 CBZ-EP mass flux increased approximately 27-fold in clay and 47-fold in sandy clay loam, reaching 32,693.52 ng/m², partially supporting Hypothesis (2). Combined quantified drainage export represented 11.49% and 17.45% of the combined measured biosolids-derived input of the three target compounds in clay and sandy clay loam, respectively. Grain occurrence confirmed dietary exposure, but all CBZ and CBZ-EP hazard quotients were < 1 (maximum toddler HQ = 0.0561), partially supporting Hypothesis (3). Conclusion Overall, CBZ-EP showed the most consistent occurrence and greatest quantified leaching response. Longer-term field studies are required before broader biosolids-management implications can be established.