Abstract
Microdebris are nowadays a new emerging threat to marine ecosystems. Estuarine systems are considered sinks of contaminants, retaining these in their sediments. Nevertheless, baseline studies are essential, especially in reference estuarine systems such as the Mira Estuary, in order to establish reference conditions for other ecosystem assessment studies. Microdebris were extracted by density separation with saturated NaCl from sediment samples collected at the bare intertidal area of the lower sector of the Mira Estuary. Sediment vertical profiles showed a high abundance of microdebris, dominated by spherical and fibre-like microdebris, but also presenting metallic and uncategorized items. It was possible to observe that microdebris accumulation had its maximum concentration at a depth of 10 cm, indicating a recent increase in its usage and prevalence on this estuarine system. Comparing the item density from this work with previous studies on other aquatic ecosystems, it was found that the sediments analysed here present a very high concentration of microdebris. Although the Mira Estuary has been considered as a reference condition for the classical chemical contaminant descriptors considered in the Water Framework Directive, the data here presented indicate that this concept should be revisited adding microdebris contamination.
Highlights
Microplastics (MP), plastics debris with a diameter smaller than 5 mm, are widely spread throughout the planet. They have been detected in all marine ecosystems, namely surface and deep waters of oceans, beaches and sediments [1,2,3,4,5], and in freshwater ecosystems, such as rivers and lakes [6,7]
Mira Estuary tidal ranges vary from 1.0 m at neap tide to 8.9 m at spring tide [31]
Sampling in only one site is a potential limitation of the present study, this choice was taken considering its location in the vicinity of the largest urban settlement in the estuarine system, in order understand its effect on the surrounding estuarine ecosystems
Summary
Microplastics (MP), plastics debris with a diameter smaller than 5 mm, are widely spread throughout the planet They have been detected in all marine ecosystems, namely surface and deep waters of oceans, beaches and sediments [1,2,3,4,5], and in freshwater ecosystems, such as rivers and lakes [6,7]. Microdebris are subjected to physical and chemical processes, leading to changes in their surfaces and making these particles suitable to adsorb contaminants, such as heavy metals, persistent organic pollutants, xenoestrogens and microbial pathogens [4,12,13,14,15] These microdebris can be ingested by aquatic organisms, with some studies showing that marine species can confuse MPs with food. The present work intents to be a first study regarding the vertical distribution of different types of microdebris in the intertidal sediments of a low-impacted estuary in order to establish a first baseline for this type of contaminant
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