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Background: Green-synthesized Moringa oleifera silver nanoparticles (Mo-AgNPs) are being deployed for decentralized water treatment in rural Nigeria without any empirical risk framework. This study had one objective: to determine, through field-calibrated modeling, whether Mo-AgNP use in Doma LGA poses a seasonally dependent threat to drinking water safety, aquatic food chains, and human health or whether current practices can continue without modification. Methods: We first synthesized and fully characterized Mo-AgNPs (30 ± 5 nm; UV-Vis, FTIR, DLS, XRD) using locally sourced Moringa seeds. We then conducted dry- and wet-season field campaigns across six groundwater (GW1–GW6) and six surface water (SW1–SW6) sites in Doma, measuring flow velocities (0.3–1.0 m/s), pH, dissolved organic carbon (DOC), and turbidity. Using these data exclusively, we parameterized a coupled Advection-Dispersion-Reaction (ADR) transport model and a first-order bioaccumulation model. Laboratory batch experiments with local Tilapia spp., Chlorella vulgaris, and benthic snails (Bellamya spp.) provided species-specific uptake (kup) and elimination (kelim) rates under seasonally relevant temperatures (26–34°C) and DOC levels. Uncertainty was quantified via 10,000-iteration Monte Carlo simulations. Main Findings Specific Effect Sizes: The model reveals a stark seasonal dichotomy that any operational plan must address. (1) Wet season (v = 1.0 m/s, kd = 0.015 day–1): Tilapia tissue concentrations reach 15 mg/kg within 25 days 7.5 times the FAO/WHO safety limit of 2 mg/kg for human consumption. (2) Dry season (v = 0.3 m/s, kd = 0.002 day–1): Groundwater contamination persists beyond 200 days, with 60% of initial Mo-AgNPs remaining, creating a chronic exposure pathway ignored in previous assessments. (3) Bioaccumulation: Benthic snails achieve BCF = 400 (vs. BCF = 57 for tilapia), acting as long-term reservoirs (persistence >1 year) due to slow elimination (kelim = 0.005 day⁻¹). (4) Bioavailability modulation: DOC alters bio-uptake by ±40%, a factor of practical significance for risk mapping across different water bodies. (5) Human exposure: Estimated dietary intake via fish (0.03 mg/day for a 60 kg adult) exceeds the WHO tolerable daily intake (0.005 mg/kg-bw/day) by six-fold. (6) Uncertainty: Monte Carlo analysis identified kup (±35% variability) and kd (±30%) as dominant controls meaning that risk assessments using default literature values rather than locally measured kinetics will be systematically wrong. Conclusions: Current Mo-AgNP use in Doma presents a significant, season-dependent public health hazard that cannot be managed with a one-size-fits-all approach. Wet seasons demand immediate action on fish consumption advisories; dry seasons require groundwater monitoring and sediment management given the 200+ day persistence. The validated model is not an academic exercise it is an operational tool for policymakers aligning with Nigeria's water laws and SDGs 6 and 14. I recommend immediate seasonal monitoring protocols and redesigned nanoparticles with faster environmental degradation before wider deployment proceeds. Contributions: This work provides the first field-parameterized, seasonally explicit risk model for green AgNPs in a tropical savanna environment. The finding that benthic snails act as >1-year contaminant reservoirs introduces a chronic trophic transfer pathway previously undocumented for Moringa-derived AgNPs. The ±40% DOC modulation of bioavailability offers a practical, measurable water quality parameter for local risk mapping without additional laboratory capacity.
Abdul et al. (Sat,) studied this question.