## 4 Discussion  
The ingestion of various sizes of plastic debris by different aquatic organisms has been assessed in recent years. In fact, it is how these pollutants can affect biological systems and living organisms is the major issue under investigation of this topic [71,72]. It is known that plastic pollution can affect the natural environments and biota at all levels, in particular in terms of MPs and nanoplastics (NPs) [73,74]. Moreover, the influence of MPs on the biological, immunological and cellular functions is far from being completely understood in aquatic living organisms [75]. Microplastics ingestion was reported in many zooplankton organisms used as a model, such as _Daphnia magna_ for larger MPs debris [68,76], copepods [77,78] and _Artemia_ sp. [54,56] for smaller fractions (5-10 \(\upmu\)m). These results, in addition those obtained in this study, can help to comprehend the fate and behavior of MPs in natural environments and effects on biota. In this study, we investigated how the ingestion of 10 \(\upmu\)m of polystyrene microspheres in the first phases of life cycle can influence _A. salina_ larvae vitality, development and feeding behavior. The results obtained during the experimental phases highlighted that MPs can be easily internalized by brine shrimps through filtration. This feeding strategy is common in zooplankton organisms. This and other features make _A. salina_ an excellent model organism for the study of MPs pollution influence on zooplankton trophic webs, as already suggested by other authors [79,80]. Moreover, these organisms are involved in biomagnification phenomena [29,48]. In our study, we found that MPs are already ingested by _A. salina_ larvae 6 h post hatching in a dose-dependent manner, with the influence of exposure time reaching up to a maximum ingestible value after 48 h of exposure. These results are in accordance with other studies on MPs ingestion by zooplankton organisms that reported comparable ingestion times [55,81]. These values were maintained in the subsequent time points, highlighting that a threshold value for the ingestion of MPs under this condition was likely reached. The data reported in Table 2 show the differences found between the replicates with and without a food source. It is evident that in the presence of microalgae, the ingestion of MPs is lower, probably because during their non-selective filtration activity, brine shrimps encounter rarely and randomly the plastic debris in the experimental solutions filled of microalgal cells [55]. It is also interesting to note that in the presence of microalgae, no MPs was found at the lower tested concentrations (1, 10, 10\({}^{2}\) MPs/mL) during the  
Figure 8: _Artemia salina_ MPs filled area (%) at each concentration and experimental time. sampling steps. This represents important data if compared to the common environmental MPs concentrations reported by other authors [59, 60, 82, 83], which are usually not far from 1 MPs/mL, whose ingestion could hence be unusual by these organisms. However, as reported in Figure 2, we found evident traces of a few egested MPs at 10 and 100 MPs/mL concentrations in fecal pellets. This proves that the ingestion of MPs occurs even at these concentrations, although in a minimal percentage not detected inside the organisms. In accordance with [PERSON] [55, 56], this detection problem was probably due to the disproportion between MPs debris and microalgal cells in water. On the contrary, MPs contamination was detected at all the tested concentrations in absence of _D. salina_ food source from T24. This feature confirmed that in the absence of other suspended particles, brine shrimps encounter and actively filter 10 \(\upmu\)m of polystyrene microspheres, maintaining it inside the intestinal tract for a long time, as reported for other zooplankton organisms [84, 85, 86]. This also demonstrated the non-selective filtration activity of _A. salina_, in accordance with [PERSON] [55] and [PERSON] [65] that reported respectively for _A. parthenogenetic_ and _A.