Market-Based Pesticide Residue Surveillance in Nepal: Temporal Trends, Commodity Profiles, and Geographic Traceback Analysis from the Kalimati Fruits and Vegetable Market

Abstract

In Nepal, commercial vegetable production relies heavily on chemical pesticides; yet long-term market-level residue data remain scarce. This study presents a 12-year (FY 2014/15-FY 2025/26) analysis of pesticide residue screening at the Kalimati Fruits and Vegetable Market using the Rapid Bioassay for Pesticide Residue (RBPR), a method that detects organophosphate and carbamate residues through acetylcholinesterase (AChE) inhibition. Of 25,799 samples screened, 98.76% showed AChE inhibition below the RBPR action threshold, While 0.47% and 0.78% were classified as Yellow (quarantine) and Red (non-compliant), respectively. Red-category detection rates varied considerably among years, peaking in FY 2022/23 (1.6004; 16.0 per 1,000 samples), FY 2024/25 (1.43%), and FY 2016/17 (1.08%), but Mann-Kendall trend analysis indicated no statistically significant long-term monotonic trend (τ = 0.309, p =  0213). Trace-back of 154 Red-category samples (2021—Feb 2026) identified pronounced commodity and location-specific concentration, With broadleaf mustard (n = 36; 23.4%) and cauliflower (n = 21; 13.6%) most frequently disposed. Geographic risk was concentrated in Bhaktapur, Sarlahi, and Dhading districts (50.6% of detections), While Lalbandi, Madhyapur Thimi, and Dhunibesi Municipalities emerged as critical production hotspots. Imported produce from India accounted for 7.8% (n = 12) of traced detections. A moderate, statistically significant positive correlation (r = 0.61 , p = 0.048, n = 11) was observed between annual national insecticide imports and combined Yellow and Red-category detections, although the exploratory nature of this analysis (11 annual observations) warranted cautious interpretation. These findings highlight the continued value of RBPR-based market surveillance and traceback investigations, while underscoring the need for commodity and location-specific extension interventions and complementary confirmatory testing (e.g., GC—MS, LC MS/MS) to address pesticide residue risks not captured by RBPR screening.