Assessment of Storage-Induced Microplastic Generation, Polymer Characteristics, and Human Exposure Risks in Bottled and Sachet Drinking Water Under Different Environmental Conditions in Port Harcourt, Nigeria

Microplastic contamination of drinking water is an emerging environmental and public health concern, especially in tropical regions where packaged water is often exposed to high temperatures and sunlight. This study investigated the effects of storage conditions and duration on microplastic generation in bottled and sachet drinking water commonly consumed in Port Harcourt Metropolis, Rivers State, Nigeria. Ten popular brands (five bottled and five sachet) were subjected to four storage conditions: indoor control (25 ± 2°C), ambient market storage (28–32°C), direct sunlight exposure (30–40°C), and elevated temperature (45 ± 2°C). Samples were analysed at 0, 30, 60, and 90 days using membrane filtration, stereomicroscopy, and FTIR spectroscopy. Data were analysed using descriptive statistics, t-test, Pearson correlation, one-way ANOVA, two-way ANOVA, and multiple regression at p < 0.05. Results showed a progressive and significant increase in microplastic concentrations with storage duration and harsher conditions. At 90 days, the highest concentrations were recorded under elevated temperature storage (58.7 ± 18.2 particles/L in bottled water and 78.5 ± 22.7 particles/L in sachet water), while the lowest levels occurred under indoor control conditions (11.8 ± 3.2 particles/L in bottled water and 15.0 ± 5.8 particles/L in sachet water). One-way ANOVA revealed significant differences among storage conditions (F = 58.42, p < 0.001). Sachet water exhibited higher microplastic levels than bottled water, though the difference was not statistically significant at Day 90 (p = 0.085). Fragments (40.3%) and fibers (34.4%) dominated the microplastics, with over 72% of particles smaller than 500 μm. FTIR analysis identified PET (38.0%), PE (27.6%), and PP (20.6%) as the predominant polymers. Strong positive correlations were observed between storage temperature and microplastic concentration (r = 0.842, p < 0.001) and storage duration (r = 0.791, p < 0.001). Multiple regression confirmed temperature and duration as significant predictors (R² = 0.998). The study concludes that prolonged storage under elevated temperatures and direct sunlight significantly accelerates microplastic release from packaging materials into drinking water, with sachet water being more vulnerable. These findings highlight the urgent need for improved storage practices, better packaging standards, and regulatory guidelines to reduce human exposure to microplastics in tropical environments.