Plastic waste poses a serious threat to ecosystems and human health. Similarly, the increasing use of automobiles has led to a rise in discarded tires, exacerbating environmental concerns. However, repurposing this waste into new materials promotes sustainability and supports the concept of a circular economy. In this study, we explored the combination of reclaimed ground tire rubber (rGTR) and additive manufacturing technology (3D printing) for the development of novel conductive filaments. For this purpose, a filament composed of 25% rGTR, 25% carbon black (CB), and 50% low-density polyethylene (LDPE) was formulated for constructing additively manufactured electrodes. The produced filament exhibited excellent flexibility, with successful incorporation of rGTR into the matrix, as confirmed by TGA, SEM and AFM data. 3D printed working electrodes using rGTR, CB, and LDPE subjected to atmospheric air plasma pen (3D-CB/rGTR/LDPE-PT) were applied for detecting a hazardous fungicide, carbendazim (CBZ). Thus, under optimized differential pulse voltammetry (DPV) conditions, the sensor demonstrated a linear response ranging from 1.0 to 40.0 µmol L⁻¹ CBZ, with limits of detection (LOD) and quantification (LOQ) of 79 nmol L⁻¹ and 262 nmol L⁻¹, respectively. The proposed 3D-CB/rGTR/LDPE-PT sensor was successfully applied for detecting CBZ in drinking water and effluent samples, achieving recovery rates between 95–105%, highlighting its excellent analytical performance. This work demonstrates that recycled raw materials from the automotive industry can be repurposed to develop innovative devices for detecting environmental contamination caused by indiscriminate pesticide use, while also simultaneously promoting sustainability through reuse and recycling of waste tire rubber.