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Evaluating sublethal effects of long-term exposure of Daphnia magna to nanoplastics at a low concentration
Summary
Lab experiments exposed Daphnia magna — a water flea that links primary producers to larger predators — to nanoplastics at low concentrations over multiple generations. The nanoplastics caused sublethal reproductive effects that became more pronounced over successive generations, suggesting that long-term, low-level nanoplastic exposure in the environment could gradually impair aquatic invertebrate population health.
Plastic production is increasing every year and with it the amount of plastic debris found in the aquatic environment. These debris can be of different sizes including micro- and nano-sized particles. The latter have been found to be more toxic than bigger particles, in special particles smaller than 53 nm of diameter. This is because their small size allows them to pass biological barriers like the cellular membrane. In the ecosystem, the nanoplastic particles can be ingested by filter-feeder organisms like Daphnia magna that is a direct link between primary producers and higher trophic level consumers in freshwater ecosystems. Thus, nanoplastic particles could find their way into the food-chain and with it, being a possible risk to human health. So, it is of great importance to study the effects that these particles may have on aquatic organisms like D. magna and an important way of studying these effects is by evaluating the sub-lethal effects as physiological changes or behavioral changes in the organism after being exposed to sub-lethal concentrations, because these may show the first effects of the pollutant in the environment and also represents closer conditions to the ones found in the environment. Therefore, in this study I aimed to evaluate the sub-lethal effects of two different sizes of nanoplastics (45 and 180 nm) after a long-term exposure of 14 days in three different aspects of D. magna behavior and physiology, being: the predator avoidance behavior, the grazing rate, and the population development. These particle sizes were used aiming to compare the effects of smaller particles than 53 nm and bigger particles that should not be as toxic as the first ones. Furthermore, for evaluating these sub-lethal effects, a sub-lethal concentration of 0.032 mg/L was used based on the lethal concentration found of ten times higher (0.32 mg/L) for particles ranging 53 nm and smaller. However, no effects were found on any of the characteristics evaluated on D. magna after being exposed to nanoplastic particles for a period of 14 days. This may be due to the low concentration used comparing this study to previous ones where significant effects of nanoplastics were found. Or it could be a matter of time exposure where more exposure time was needed. In conclusion, this study shows the importance of evaluating sub-lethal effects of a persistent pollutant like nanoplastic in an aquatic organism like D. magna and, even though no effects were found, significant effects could potentially be expected using a longer exposure time or a higher concentration. (Less)
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