Long-Term Toxicity of 50-nm and 1-μm Surface-Charged Polystyrene Microbeads in the Brine Shrimp Artemia parthenogenetica and Role of Food Availability

Micro and nanoplastics (MNPs) as emerging contaminants have become a global environmental issue due to their small size and high bioavailability. However, very little information is available regarding their impact on zooplankton, especially when food availability is a limiting factor. Therefore, the present study aims at evaluating the long-term effects of two different sizes (50 nm and 1 μm) of amnio-modified polystyrene (PS-NH₂) particles on brine shrimp, <i>Artemia parthenogenetica,</i> by providing different levels of food (microalgae) supply. Larvae were exposed to three environmentally relevant concentrations (5.5, 55, and 550 μg/L) of MNPs over a 14-days of exposure with two food levels, high (3 × 10⁵~1 × 10⁷ cells/mL), and low (1 × 10⁵ cells/mL) food conditions. When exposed to high food levels, the survival, growth, and development of <i>A. parthenogenetica</i> were not negatively affected at the studied exposure concentrations. By comparison, when exposed to a low food level, a U shape trend was observed for the three measured effects (survival rate, body length, and instar). Significant interactions between food level and exposure concentration were found for all three measured effects (three-way ANOVA, <i>p</i> < 0.05). The activities of additives extracted from 50 nm PS-NH₂ suspensions were below toxic levels, while those from 1-μm PS-NH₂ showed an impact on <i>artemia</i> growth and development. Our results demonstrate the long-term risks posed by MNPs when zooplankton have low levels of food intake.