Microplastics in Water: Multi-Factor Experimental Assessment of Aqueous Leachate Toxicity and a Framework for Human Health Risk Screening

Abstract

The effects of polymer type, particle size, leaching temperature, and duration on leachate bioactivity from polypropylene (PP), polyethylene (PE), and polyethylene terephthalate (PET) were examined with a framework for screening human-health implications. Fractions spanning 0.175–3.0 mm were leached for 30 days. Phytotoxicity was assessed in wheat and lentil with leachates prepared at 25 °C, 37 °C, and 60 °C; sperm motility and dermal irritation were assessed at 40 °C using bull semen and rabbits. Higher temperature significantly inhibited germination parameters (p < 0.001), and 0.175–0.3 mm fractions produced the strongest effects. Phytotoxicity ranked PP > PET > PE, whereas spermatotoxicity ranked PET > PP > PE. The lowest scenario-specific Germination Index (GI) dropped to 38.20%, sperm-motility deviation reached 29.1%, and the responses were inversely correlated (Pearson’s r = −0.547, df = 13, p = 0.035). Compared with previous 1-day data, 30-day leaching increased mean sperm-motility deviation 2.5–4.1-fold. One dermal application caused no visible irritation (index = 0). Across 45 scenarios, the Total Risk Index ranged from 0.012 to 0.400, whereas limiting-factor assessment assigned high-risk classes where endpoint-specific responses were diluted by averaging. The framework supports conservative hazard screening but does not establish human toxicity or exposure thresholds.