Size Effects of Microplastics on Embryos and Observation of Toxicity Kinetics in Larvae of Grass Carp (Ctenopharyngodon idella)

Abstract

Microplastics have caused great concern in recent years. However, few studies have compared the toxicity of different sizes of microplastics in fishes, especially commercial fishes, which are more related to human health. In the present study, we revealed the effects of varying sizes of microplastics on grass carp embryos and larvae using scanning electron microscopy (SEM) and fluorescence imaging. Embryos were exposed to 80 nm and 8 μm microplastics at concentrations of 5, 15, and 45 mg/L. Toxicity kinetics of various sizes of fluorescent microplastics were analyzed through microscopic observation in the larvae. Results found that nanoplastics could not penetrate the embryo’s chorionic membrane, instead they conglutinated or aggregated on the chorion. Our results are the first to explore the defense mechanisms of commercial fish embryos against microplastics. Larvae were prone to ingesting their own excrement, resulting in microplastic flocculants winding around their mouth. For the first time, it was found that excreted microplastics could be reconsumed by fish and reaccumulated in the oral cavity. Microplastics of a certain size (1 μm) could be accumulated in the nasal cavity. We speculate that the presence of a special groove structure in the nasal cavity of grass carp larvae may manage to seize the microplastics with a particular size. As far as we know, this is the first report of microplastics being found in the nasal passages of fish. Fluorescence images clearly recorded the toxicity kinetics of microplastics in herbivorous fish.

Near-Infrared-II In Vivo Visualization and Quantitative Tracking of Micro/Nanoplastics in Fish

“…The most notable feature was that NIR-AIE-MNPs had strong emission at 1000 nm wavelength, which belonged to the second near-infrared (NIR-II) window (Figure D), thus enabling in vivo imaging at the NIR-II window. Usually, imaging in the visible range was accompanied by high tissue autofluorescence and background fluorescence, which led to observational artifacts in uptake and translocation studies of MNPs, as reported in fish and Daphnia . − In contrast, our results showed almost no autofluorescence of zebrafish in the NIR-II window and can obtain high signal-to-background ratios in NIR images (maximum over 39 for NIR-AIE-MPs and 28 for NIR-AIE-NPs in this study) (Figures H and I). By comparison, the imaging of other commercial fluorescent PS particles was accompanied by the interference of strong biological autofluorescence, making it difficult to calculate the signal-to-background ratio due to the inability to clearly identify the boundaries of signal and background (Figure S2).…”

Euryhaline fish larvae ingest more microplastic particles in seawater than in freshwater

“…Such differences in water uptake and osmoregulation may influence MP ingestion. However, previous studies of MPs in fish have investigated either FW or marine species only [14][15][16] , thus the difference of MP ingestion in the two media was not clear because no reports have compared MP uptake in FW and SW using the same species.Here, we employed medaka (Oryzias) fishes to demonstrate differences in MP uptake in the two different media. Medaka are an attractive model fish for ecotoxicology studies because of their low rearing cost, high fertility, ease in rearing of embryos, abundant developmental information, and availability of a complete genome sequence [17][18][19][20][21] .…”

“…Such differences in water uptake and osmoregulation may influence MP ingestion. However, previous studies of MPs in fish have investigated either FW or marine species only [14][15][16] , thus the difference of MP ingestion in the two media was not clear because no reports have compared MP uptake in FW and SW using the same species.…”

Editorial for the Special Issue “Microplastics in Aquatic Environments: Occurrence, Distribution and Effects”

“…The eight selected research papers can be grouped into three main themes: (1) the effects of microplastic exposure to aquatic biota (rotifers, mussels, fish larvae, and microalgae), encompassing 55% of the published papers in this SI [ 9 , 10 , 11 , 12 , 13 , 14 ]; (2) the distribution and seasonal variation of microplastics in aquatic environments [ 15 ]; and (3) the contaminants associated with microplastics in freshwater environments [ 16 ].…”

“…As Guest Editors of this Special Issue, we were pleased to receive several papers concerning the interaction between microplastics and biota; despite a large number of peer-reviewed papers published on this research topic, there are still several gaps that need to be filled [ 17 , 18 ]. Zhang et al (2022) [ 12 ], for instance, investigated the toxicity of fluorescent nano- and microplastics (80 nm and 8 μm) on grass carp embryos and larvae using scanning electron microscopy (SEM) and fluorescence imaging. Their results showed that nanoplastics accumulated in the chorion and did not penetrate the embryo’s chorionic membrane.…”