Medical waste management poses significant environmental and public health challenges in developing urban areas like Uyo metropolis, Nigeria, where inadequate disposal practices exacerbate contamination risks. This comparative study evaluates the generation, characterization, and environmental impacts of medical wastes from a secondary healthcare facility (St. Luke's Hospital, Anua) and a tertiary facility (University of Uyo Teaching Hospital), focusing on leachate composition, effects on plants and soil, groundwater quality, and air pollution. Employing a cross-sectional design, data were collected from June to December 2025, involving 240 samples (120 per facility) across waste streams, leachate, soil, plants, groundwater, and air. Waste characterization revealed the University of Uyo generating 3-4 times more waste (500-700 kg/day) with a higher hazardous fraction (48% against 35%), including elevated infectious (25% against 20%), sharps (8% against 5%), and pathological (10% against 5%) types. Leachate from the University of Uyo showed 1.5-3 times higher contaminants (BOD 400 mg/L against 250 mg/L; Pb 0.45 mg/L against 0.15 mg/L), exceeding World Health Organization (WHO) limits and indicating severe runoff risks in Uyo's rainy climate. Soil impacts were more pronounced at the University of Uyo, with higher metal accumulation (Pb 60 mg/kg against 25 mg/kg) leading to 30-40% plant growth inhibition (against 15-20%) and reduced microbial activity (8.0 × 10^5 CFU/g against 1.5 × 10^6 CFU/g). Groundwater contamination was 2-3 times greater at the University of Uyo (Pb 0.30 mg/L against 0.10 mg/L), yielding an unsuitable Water Quality Index (WQI) (300 against 150, poor). Air emissions from incineration were 1.5-2 times higher at the University of Uyo (PM2.5 65 µg/m³ against 40 µg/m³), contributing to urban air quality degradation. Statistical analyses (t-tests, p<0.05; large effect sizes, d>0.8) confirmed significant disparities, attributing them to the University of Uyo's scale and complexity. Findings underscore the need for enhanced waste segregation, treatment infrastructure, and regulatory enforcement at tertiary facilities to mitigate environmental hazards, promoting sustainable healthcare practices in Nigeria's urban south.