Spatiotemporal and seasonal surveillance with risk assessment and multimarket analysis of aflatoxin contamination in Citrullus lanatus melon seeds across six Nigerian states

Aflatoxin contamination of food crops remains a critical public health challenge in tropical regions, requiring robust risk management and data-driven surveillance. This study assessed the seasonal prevalence and spatial distribution of aflatoxins in melon seeds ( Citrullus lanatus var. colocynthis ) across eight Nigerian states (Oyo, Ekiti, Nasarawa, Kogi, Kwara, Lagos, Ogun, and the Federal Capital Territory). Composite samples (n = 41) were collected from formal and informal markets during wet and dry seasons. Fungal taxa were identified using culture-based methods, while aflatoxins B₁, B₂, G₁, and G₂ were quantified using thin-layer chromatography (TLC) coupled with densitometric scanning. Statistical, spatial, and risk analyses including chi-square tests, Mann–Whitney U test, Global Moran’s I, Getis-Ord Gi*, Monte Carlo simulation (10,000 iterations), and generalized linear modeling were applied. Rhizopus oryzae (42.3%) and Aspergillus flavus (38.6%) were the most prevalent fungal isolates (χ 2 test, p < 0.001). Total aflatoxin concentrations were significantly higher during the wet season (mean: 207.5 µg/kg) compared to the dry season (mean: 25.55 µg/kg; Mann–Whitney U = 12.0, p < 0.004), with 50% of wet-season samples exceeding the European Union regulatory limit of 5 µg/kg. Spatial analysis revealed significant clustering of contamination (Global Moran’s I = 0.41, p = 0.02), with Getis-Ord Gi* identifying high-intensity hotspots in Ekiti (Z = 3.12) and Oyo (Z = 2.87). A 10,000-iteration Monte Carlo simulation projected elevated potential lifetime cancer risks, particularly among children, with estimated intakes reaching 5.21 ng/kg bw/day (95% UI: 3.87–6.98). Generalized linear modeling identified relative humidity and informal market storage as key determinants of contamination heterogeneity. The co-occurrence of high aflatoxin levels and toxigenic Aspergillus flavus highlights a significant food safety risk driven by environmental and post-harvest handling conditions, particularly during the wet season. These findings provide a quantitative basis for prioritizing targeted risk management interventions, including improved storage practices and humidity control, and underscore the importance of evidence-based surveillance systems to mitigate aflatoxin exposure in Nigerian food systems.