Here, upon acute (96 h) and chronic (14 days) exposure, ingestion of polystyrene NPs (100 nm) and physiological, biochemical, and cholinergic modulations were analyzed in the water flea Moina macrocopa exposed to different concentrations (0.001, 0.01, 0.1, 1, 5, 10, 50, 100, and 500 μg l-1). Exposed NPs were observed in the internal organs (e.g., digestive tract and foregut) of the water flea. Chronic exposure to the relatively high concentrations resulted in significant decreases in survival, body length, and the total number of molts, whereas reproduction parameter was not affected. Significant increase in oxidative stress biomarker (malondialdehyde) and decrease in the intracellular content of endogenous antioxidant (glutathione) and enzymatic activity of antioxidant enzymes (glutathione peroxidase, glutathione reductase, catalase, superoxide dismutase, and glutathione S-transferase) were detected in response to relatively high concentrations of NPs. Transcriptional expression of the hsp70 gene was increased in response to relatively high concentrations of NPs, whereas acetylcholinesterase activity was lowered by the same concentrations of NPs. Taken together, NPs exposure would be a significant modulator on physiological and biochemical metabolism of water flea.

Introduction
Materials and Methods
    1. Water flea culture
    2. Nanoplastics
    3. Chronic exposure
    4. Measurement of biochemical parameters
    5. Statistics
Results
    1. Nanoplastics ingestion
    2. Physiological responses to chronic exposure
    3. Biochemical responses
Discussion

• Md. Niamul Haque(Department of Marine Science, College of Natural Sciences, Incheon National University, Incheon 22012, Korea, Research Institute of Basic Sciences, Incheon National University, Incheon 22012, Korea)
• Jaehee Kim(Department of Marine Science, College of Natural Sciences, Incheon National University, Incheon 22012, Korea)
• Jae-Sung Rhee(Department of Marine Science, College of Natural Sciences, Incheon National University, Incheon 22012, Korea, Research Institute of Basic Sciences, Incheon National University, Incheon 22012, Korea, Yellow Sea Research Institute, Incheon 22012, Korea) Corresponding author