Microplastic Size-Dependent Toxicity, Oxidative Stress Induction, and p-JNK and p-p38 Activation in the Monogonont Rotifer (Brachionus koreanus)

Abstract

In this study, we evaluated accumulation and adverse effects of ingestion of microplastics in the monogonont rotifer (Brachionus koreanus). The dependence of microplastic toxicity on particle size was investigated by measuring several in vivo end points and studying the ingestion and egestion using 0.05-, 0.5-, and 6-μm nonfunctionalized polystyrene microbeads. To identify the defense mechanisms activated in response to microplastic exposure, the activities of several antioxidant-related enzymes and the phosphorylation status of mitogen-activated protein kinases (MAPKs) were determined. Exposure to polystyrene microbeads of all sizes led to significant sizedependent effects, including reduced growth rate, reduced fecundity, decreased lifespan and longer reproduction time. Rotifers exposed to 6-μm fluorescently labeled microbeads exhibited almost no fluorescence after 24 h, while rotifers exposed to 0.05-and 0.5-μm fluorescently labeled microbeads displayed fluorescence until 48 h, suggesting that 6-μm microbeads are more effectively egested from B. koreanus than 0.05-or 0.5-μm microbeads. This observation provides a potential explanation for our findings that microbead toxicity was sizedependent and smaller microbeads were more toxic. In vitro tests revealed that antioxidant-related enzymes and MAPK signaling pathways were significantly activated in response to microplastic exposure in a size-dependent manner.

Adverse effects of microplastics and oxidative stress-induced MAPK/Nrf2 pathway-mediated defense mechanisms in the marine copepod Paracyclopina nana

“…In this study, 0.05-μm microbeads-exposed P. nana showed prolonged retention time in the body 24 h after ingestion compared to 0.5- and 6-μm microbeads, suggesting that larger microbeads are more easily egested compared to smaller microbeads. In the case of 0.05-μm microbeads, the dispersed fluorescence was seen througout the body of P. nana after 24-h exposure as seen in the rotifer B. koreanus 12. In B. koreanus , 0.05-μm polystyrene microbeads were retained for a longer time periods in the digestive organs compared to that with 0.5- and 6-μm microbeads, causing more negative effects on lifespan, growth time, fecundity, and reproduction time.…”

“…Several studies also supported the toxicity of nano-sized microbeads compared to larger microbeads in aquatic invertebrates. For example, in the rotifer B. koreanus, different sizes of polystyrene microbeads (0.05, 0.5, and 6 μm) caused a significant size-dependent decrease in growth rate, reproduction, lifespan, and body size12. In the copepod T. japonicus , growth and survival rates were also decreased according to size13.…”

“…In the case of GSH content, it was controversial as shown in the microplastic-exposed rotifer B. koreanus . In B. koreanus , GSH contents had a slightly decreased pattern, while the activity of GPx, GR, SOD, and GST was increased in a microbead size-dependent manner12. However, considering the multifunctional roles of GSH molecules in various biological processes such as DNA synthesis, microtubular-related processes, and immune function, GSH content may vary depending on the species or other experimental conditions575859.…”

“…The size of the plastic particle is considered as the most significant factor, causing adverse effects on marine invertebrates. For example, the size-dependent toxicity of microplastics has been observed in the rotifer Brachionus koreanus 12. In the copepod Tigriopus japonicus 13, exposure to 0.05- and 0.5-μm polystyrene microbeads led to significant retardation of developmental time and decreased survival rate, while 6-μm polystyrene microbeads exposure did not lead to significant growth retardation.…”

“…the whales Megaptera novaeangliae and Mesoplodon mirus 1516, and the zebrafish Danio rerio , the Japanese medaka Oryzias latipes and several species of pelagic and demersal fish171819. Zooplankton also ingest microplastics as primary consumers including the copepod T. japonicus 13202122, the water flea Daphnia 23, and the rotifers1224 which can have negative effects on survival and reproduction.…”