Can microplastic pollution be affected by beach nourishment? Assessment in intertidal sediment and bivalves

Introduction

Coastal regions are naturally dynamic and subject to erosion and sediment deposition cycles. The imbalance between these cycles can compromise the coastline, leading to erosion. Coastal erosion is a natural process associated with sediment loss that occurs whenever the transport of sediments away from the coastline is higher than the volume of sediment deposited on the coastline. Coastal vulnerability to erosion is caused by natural causes such as waves, currents, and winds, especially during storms, but is also highly affected by anthropogenic changes in the development of cities and infrastructure along the coast (Ferreira et al., 2021).

Different methods can be used to mitigate coastal erosion. One of the leading solutions is a standard practice in developed countries known as beach nourishment (BN), sand replenishment, or sand filling, which involves the use of dredged material for nourishment, adding sand to extend an eroding beach and its shallow coastal zone towards the sea, creating a barrier to protect the beach from erosion processes (Stronkhorst et al., 2018; de Schipper et al., 2020; Saengsupavanich et al., 2023; McGill et al., 2024). BN has gained popularity in recent decades because it conserves beach resources and provides recreational value, protection of shoreline structures, reducing damaging impacts of coastal erosion, and cultural ecosystem services (Luo et al., 2015; de Schipper et al., 2020).

However, there remain many uncertainties and important questions regarding the environmental effects of BN (Peterson and Bishop, 2005; Staudt et al., 2021). One of the main disadvantages is the impact on the environment: beach and nearshore habitats are highly disturbed and can be degraded from the dredging process, which can negatively affect marine organisms through entrainment, habitat degradation, noise, sedimentation, and increased suspended sediment concentrations through remobilization of contaminants (Todd et al., 2014). Other adverse environmental effects of BN include the direct burial of benthic organisms. Burial can reduce the presence of benthic organisms in the nourished area, also causing the loss of prey to predators (Speybroeck et al., 2006; Peterson et al., 2014; Herman et al., 2021). Although BN is considered a sustainable and effective solution to contain beach erosion (Hanley et al., 2014), several studies show that BN can potentially affect the entire marine ecosystem and the environmental impacts of feeding are often underestimated or overlooked (Hernandez-Delgado et al., 2011; Manning et al., 2013; Peterson et al., 2014; Hernández-Delgado and Rosado-Matías, 2017).

Another major concern regarding BN is the quality of the dredged material since the seabed sediments from port regions are generally highly polluted and commonly used in BN (Rippy et al., 2013; Li et al., 2020). Sediments from these regions are considered reservoirs of various pollutants, including heavy metals, which pose risks to coastal ecosystems and are problematic in dredging activities (Albarano et al., 2020; Marrugo-Negrete et al., 2024).

Meanwhile, the effects of BN on nearshore remain poorly known regarding plastic waste pollution. Plastic compounds are currently one of the most used and essential materials in the world, as they possess properties that have enabled great technology in recent decades, such as their low density, high resistance, and affordable price, properties that promote their use in various activities (Abayomi et al., 2017; Amobonye et al., 2021). Due to the above characteristics, the production of plastic polymers has increased exponentially and on a large scale since the 1950s (Geyer et al., 2017). Different types of plastics are available on the market, with some polymers making up >80 % of the total plastic demand (Razeghi et al., 2021). Among these polymers, polypropylene (PP) and Low- and High-Density Polyethylene (LDPE and HDPE) can be highlighted as the three most common types, followed by polyvinyl chloride (PVC), polyurethane (PUR), and polyvinyl terephthalate ethylene (PET) (Plastics Europe, 2021). After a single use, some of these plastic materials are released into the environment, where they become microplastics ranging in size from 1 μm to 5 mm (da Costa et al., 2017) through the degradation and breakdown of larger plastic debris, as a result of physical and abiotic processes such as temperature, light, and salinity (da Costa et al., 2017; Dimassi et al., 2022).

Currently, research on MPs on bathing beaches is still in a basic stage (Bissen and Chawchai, 2020; Wu et al., 2020; Zuo et al., 2024), and most studies provide only baseline data on accumulation. In Brazil, the studies of the presence of MPs on beaches have been growing (e.g. Santana et al., 2016, Santana et al., 2017; da Costa et al., 2021; Carvalho and Baptista Neto, 2016; da Costa et al., 2023; Schuab et al., 2023a, Schuab et al., 2023b; Otegui et al., 2023 and Otegui et al., 2024).

Mussels are benthic organisms that have been widely used for environmental biomonitoring studies in marine environments, mainly due to their selective mechanism of suspension feeding, which leads to the accumulation of MPs and chemical pollutants (Van Cauwenberghe et al., 2013; Paul-Pont et al., 2016). They have a wide geographical distribution, are sedentary or have low mobility, easy accessibility and sampling, a well-known life cycle, and great importance as a food resource for local communities (von Moos et al., 2012; De Witte et al., 2014; Avio et al., 2015; Li et al., 2015).

Camburi Beach, in Vitória, is about 6 km long, and due to many structural interventions and the construction of the Port of Tubarão, it has been subject to erosion processes and successive nourishments since the 1960s. Curva da Jurema Beach, located approximately 2.5 km from Camburi Beach, is a small beach created by the BN in 1920, situated in a highly urbanized and economically valued region. This beach also undergoes periodic interventions to correct the coastline and control erosion using BN. The last BN process on these two beaches was carried out in 2020, during which sediment extracted from two offshore quarries in a region allegedly contaminated by untreated domestic effluent was used (Fig. 1).

Immediately prior to this last BN, da Costa et al. (2023) assessed microplastic pollution in sediment samples as a function of the elevation of the coastline on these beaches and the abundance/frequency MPs in four (4) different species of mussels, Crassostrea brasiliana (Lamarck, 1819), Mytella strigata (Hanley, 1843), Perna perna (Linnaeus, 1758) and Tivela mactroides (Born, 1778). Therefore, in order to verify the possible influence of BN on microplastic pollution in the sediment of these beaches and in the same species of bivalves, the study by da Costa et al. (2023) was repeated 10 months after the occurrence of BN, using the same methodology, sampling points, and species.

Considering that the environmental impacts on beach quality after a BN process are still little known and that the impact of BN on plastic pollution in all its forms has not yet been investigated, we consider it important to carry out this comparative study. We hypothesize that the BN process can increase MPs pollution, generating new impacts in the nourished and adjacent areas for sediments and biota.

Section snippets

Study area

Sediment samples were collected at five sampling points in March 2021 in the high, mid, and low tide zones at Camburi and Curva da Jurema beach, located in the northern part of Vitoria, a metropolitan region of Espírito Santo.

The last BN on these beaches was carried out between May and June 2020 through dredging and a hydraulic dam, using 188,000 m³ of sediment removed from two offshore quarries approximately 5 km from the center of the nourishment area (Fig. 1).

Species

Similarly to the study by da

Results

A total of 9057 items were classified in the present study as potential MPs, of which 1960 were present in the sediment samples collected at the five sampling points, 6272 were present in individual mollusk tissue samples, and 825 were present in the pool of bivalves analyzed. All analyzed samples, both sediments and mollusk tissues, presented MPs, configuring a frequency of occurrence of 100 %.

Furthermore, the individual analyses of the specimens showed a higher amount of MPs than those

Discussion

Similar to the study of da Costa et al. (2023), which evaluated MPs before BN, all analyzed sampling points in this study were contaminated by MPs, with 100 % of occurrence in both sediment samples and tissue samples of the four species of bivalves, Crassostrea brasiliana, Perna perna, Mytella strigata, and Tivela mactroides.

The results of the present work suggest that a greater variety of particles is present in the sampled sites compared to the type of polymers observed in a previous study by

Conclusion and recommendations

There are many and varied benefits of NB, as long as they are carried out with the necessary care, especially with the quality of the sediments in the donor area, which must include studies that demonstrate the absence of contaminants, allowing the fattened area to present the benefits of the intervention without causing major impacts on local fauna, even avoiding compromising the quality of organisms such as bivalves, widely used in the human diet.

Our study assessed the presence and

Environmental implication

The beach nourishment (BN) technique is widely used to mitigate beach and coastal erosion in urban areas, and their impacts on the local fauna have been poorly investigated. The transference of sand quarries to the surface for BN can disturb the biota by discharging a large quantity of chemical pollutants deposited on the seafloor, and among them, microplastic (MP) particles sunk into the sediment. Our study, the first of its kind, shows a significant influence of BN on the density of MP

CRediT authorship contribution statementMidiã Silva de Paula:

Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Formal analysis, Data curation. João Marcos Schuab: Writing – original draft, Visualization, Validation, Supervision, Methodology, Investigation, Formal analysis, Data curation. Émilien Pelletier: Writing – original draft, Visualization, Validation, Supervision, Methodology, Formal analysis, Data curation. Youssouf D. Soubaneh: Writing – original draft, Visualization, Validation,

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

Midia Silva de Paula reports financial support was provided by Coordination of Higher Education Personnel Improvement. Mercia Barcellos da Costa reports financial support was provided by Foundation for Research Support of Espírito Santo. If there are other authors, they declare that they have no known competing financial interests or personal relationships that

Acknowledgments

We want to thank the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) for funding a scholarship during the 24 months of the master’s degree period of Midiã S. de Paula. We would also like to thank the Center for Competency in Petroleum Chemistry (NCQP/LabPetro – UFES) and the Foundation for Support of Research and Technology of Espírito Santo (FAPES/Vale – n° 01/2015) for all the funding and availability of equipment. We want to extend this thanks to Guilherme Januário de

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