Environmental risk assessment of pharmaceuticals in low-infrastructure regions: a transferable framework demonstrated using praziquantel in Ethiopia

In sub-Saharan Africa, pharmaceutical release pathways to the environment differ substantially from the conventional wastewater-based assumptions underpinning international FDA and EMA guidelines. This study presents an integrated environmental risk assessment of praziquantel (PZQ) in Ethiopia, combining experimental and in silico hazard evaluations, soil exposure modelling appropriate to sub-Saharan Africa conditions, probabilistic uncertainty analysis, and spatially resolved risk mapping.PZQ exhibited moderate sorption potential (log Koc = 3.55), low bioaccumulation potential (BAF = 18.46 L kg⁻¹), negligible volatility, and limited biodegradability. A screening-level PNECsoil of 22,400 ng kg⁻¹ (95% CI: 16,137–28,662 ng kg⁻¹) was adopted using available experimental and in silico toxicity data.PECsoil estimates from prevalence- and consumption-based approaches were comparable. Combining prevalence-based human and veterinary exposure, yielded a probabilistic PECsoil of 1,576 ng kg⁻¹ (95% CI: 362–4,419 ng kg⁻¹), with veterinary use representing the dominant source of terrestrial PZQ loading. The resulting national soil risk quotient remained below the conventional threshold of concern (RQsoil = 0.074; 95% CI: 0.029–0.128). However, spatial refinement revealed substantial geographic heterogeneity: 3.47% of districts were classified as high or very high risk using total land area as the receiving compartment, increasing to 12.01% when agricultural land area was considered.These findings suggest limited ecological concern for PZQ at broader spatial scales, while highlighting the value of geographically explicit risk assessment for identifying localised hotspots overlooked by conventional assessments. The proposed framework provides a practical approach for context-specific pharmaceutical environmental risk assessment and prioritization of high-risk areas for targeted monitoring in heterogeneous, low infrastructure settings.