Histological Analysis of the Effects of Plastic Particles (nano-micro size) following Ingestion in Early Life Stages of Zebrafish (Danio rerio)

Plastic has become a prominent environmental pollutant and the potential for negative effects on marine ecosystems are a global concern. Within the environment, pieces of plastic can fragment into nano and micro-sized particles, and these particles readily transport throughout the oceans leading to organism exposure by physical contact or ingestion. Ingestion of plastic particles may lead to many negative effects that include mortality, reduced feeding activity, disruption of digestive system physiology, nutritional deficiency, and inhibited growth and development. Investigation of these effects requires a suitable laboratory fish model, and zebrafish Danio rerio has emerged as a particularly good surrogate for toxicology studies representing both marine and freshwater fishes. Previous studies have indicated that particle size affects likelihood of ingestion and that ingested size of plastic particles is consistent with the size of target prey items. Although information about the toxic effects of micro-particles is abundant, more research is needed concerning the harmful effects of nano-plastics. Research shows that the best route for uptake is through oral exposure, in previous research has shown the maximum size taken up at larval stages should be 50 nm (Van Pomeren et al., 2016; Bisesi et al., 2014; Manabe et al., 2011), our research shows otherwise, demonstrating that polystyrene particles of up to 500 nm can be absorbed across the gastrointestinal tract at 5 days post fertilization. Research by Karami et al. (2017) showed that non-uniformly shaped low density polyethylene, 90% of which were of sizes of below 17.6 μm did not gather in the other organs of the fish throughout the larval stage. In the case of adult zebrafish, studies show that 5 μm particles were able to accumulate in the gills, gut and liver while 20 μm particles were only seen in the gills and gut (Lu et al., 2016). A study conducted by Yang et al. (2014) showed bisphenol AF affected the heaptocytes at a higher concentration of 1 mg/L but not at lower concentrations. They also found differences in the results between male and female fish, finding males to be more affected, indicating that gender plays a role in the extent of toxicity The aim of this review is to collect literature that summarizes the effect nano and microplastics have on the uptake, accumulation and histopathology of zebrafish (Danio rerio).