Microplastic pollution also threatens coastal lagoons around the planet

Coastal lagoons are transitional ecosystems between continental and marine aquatic systems. With great ecological and socioeconomic value, they are habitats also affected by the impact of human activities.

Coastal lagoons are of great importance for the conservation of biodiversity. In addition, they are the main providers of food and other ecosystem services to local populations -often vulnerable- who depend on them. 58% of these ecosystems have some national or international protection status (the Ramsar Convention on Wetlands of International Importance, biosphere reserves, areas of importance for wildlife conservation, or others).

On a global scale, the coastal lagoons of Lagos (Nigeria), Sakumo (Ghana) and Bizerte (Tunisia) —close to large urban centers and without waste or sewage treatment systems— are among the most affected aquatic ecosystems of this nature due to microplastic contamination. However, the highest concentrations of these microparticles have been detected in Barnes Sound and other small lagoons in a protected area north of Florida Bay (United States), a particular case that can be explained by the transport of microplastics that transport hurricanes from contaminated areas.

These are some of the conclusions of a study carried out by a team that includes the doctoral student Ostin Garcés-Ordóñez, led by Professor Miquel Canals, director of the Consolidated Research Group of Marine Geosciences of the Faculty of Earth Sciences of the University of Barcelona (UB). The study, which has the participation of experts from institutions in Colombia and Chile, reviews the progress of knowledge on microplastic contamination in coastal lagoons around the world and warns of the abundance of fibers and fragments of polyethylene, polyester and polypropylene. in some of these valuable ecosystems.

The study reviews the published scientific literature on microplastic pollution in 50 coastal lagoons in 20 countries on different continents, specifically Europe (32%), Asia (20%), Latin America and the Caribbean (18%), Africa (12 %), North America (10%) and Oceania (8%).

“In these natural habitats, the maximum levels of contamination by microplastics result from the combination of various factors. For example, the residence time and the renewal rate of the water in the lagoons, the presence of large urban and industrial developments with inadequate waste management, discharges from rivers and outfalls, seasonal climatic fluctuations, natural phenomena (hurricanes , typhoons, etc.) and the typology of microplastics”, details researcher Ostin Garcés-Ordóñez, member of the Consolidated Research Group in Marine Geosciences and first author of the study.

Accumulation of waste on the coast of the Ciénaga de La Virgen located in Cartagena, Colombia. (Photo: Ostin Garcés-Ordóñez (UB))

Coastal lagoons with slow —or very slow— water turnover rates are the most susceptible to high microplastic contamination. In the case of the Mosquito Lagoon in Florida (United States), the renewal of 50% of the water requires between 200 and 300 days and, therefore, the microplastics that reach this lagoon can remain in this ecosystem for considerable periods of time. .

«During the rainy season, the concentration of microplastics also increases in surface water compared to the dry season, a phenomenon that has been observed in the Río Lagarto lagoon (Mexico) and in the Ciénaga Grande de Santa Marta (Colombia). , with maximum levels in areas where the most intense human activities are recorded,” says Garcés-Ordóñez, also a member of the Colombian Institute of Marine and Coastal Research.

The fish fauna, of great commercial interest due to its exploitation for human consumption, is one of the best studied groups of organisms in relation to the impact of microplastics. In the study, which reviews the effects of pollution on 96 species, a maximum impact is detected on fish from the Bizerte and Ghar El Melh lagoons (Tunisia), especially the Liza aurata and Sarpa salpa species, with intakes of up to 65 microplastics per individual. Molluscs, with levels of up to 17 microplastics per individual, are another of the most affected groups, with maximum values ​​detected in the Virginia oyster (Crassostrea virginica) from the Mosquito Lagoon (United States).

The coastal lagoons of the Iberian Peninsula: data and perspectives

In the case of the Iberian Peninsula, the coastal lagoons are relatively few and small compared to other coastal lagoon systems in the world. Most of them are associated with the lower courses of rivers and their old mouths, as well as with the coastal drift of sediments, as is the case of the Empordà marshes, the Ebro delta, the Valencia lagoon or the Algarve lagoon system. Portuguese.

“The environmental state of these lagoons is variable and also changes over time. Some suffer the effects of pollution from urban, industrial and agricultural sources, such as the Valencia lagoon and also the Mar Menor in Murcia, where there have recently been massive fish deaths due to episodes of anoxia”, details Professor Miquel Canals, director of the Department of Earth and Ocean Dynamics at the UB and member of the research team.

«The Mar Menor, which is the largest coastal lagoon in Spain, has unique characteristics among the Iberian coastal lagoons, given the high salinity of its waters as a result of its permanent communication with the open sea and the presence of several volcanic islets. Drought episodes can have notable effects on some of these lacustrine systems, as is already happening in the Empordà or Doñana marshes,” says Canals.

The study reveals the presence of microplastics in the water column, sediments and fish in the coastal lagoons of the Mar Menor (Murcia), La Pletera (Catalonia) and in Ría Formosa and Aveiro (Portugal).

«In the Spanish lagoons, an average of 20.1±2.9 microplastics per kilogram of the digestive tract has been found in sea bream (Sparus aurata) from the Mar Menor, and an abundance of up to 2.5 microplastics per individual in the gambusia ( Gambusia holbrooki) from the restored lagoon of La Pletera, in Girona”, indicates Miquel Canals.

“In the Mar Menor – he continues – the average abundance would be 43.5 to 53.1 microplastics per kilogram of sediment according to two published studies, a value significantly lower than that found in the coastal lagoons of Venice and Sacca di Goro ( Italy), Anzali (Iran), Bizerte (Tunisia) and Lagos (Nigeria), but higher than that detected in the Ria Formosa (Portugal)».

Coastal lagoons, new sinks for microplastics?

In addition to accumulating in specific areas of lagoon ecosystems, microplastics can also end up in the sea and further aggravate the problem of ocean pollution.

“We can state with certainty that the different environmental matrices of coastal lagoons – that is, waters, sediments and organisms that live in these habitats – are recipients of microplastics and are affected by the pollution they cause. However, we still do not know to what extent coastal lagoons are final sinks for microplastics,” says Canals.

“This aspect is related to the characteristics and dynamics of each lagoon, as well as the quantities and properties of the incoming microplastics. Thus, certain lagoons could be true sinks while others could function as temporary sinks in the cycle of microplastics, facilitating, for example, their transfer from river systems to beaches and the marine environment. This type of criteria could be used to classify coastal lagoons according to the balance between incoming and, eventually, outgoing flows of microplastics.”

Objective: prevent the arrival of microplastics in the natural environment

The review is based on studies that have combined different methodological approaches—direct visual inspection, chemical digestion, density separation—to study different habitats that may include coral reefs, seagrass beds, beaches, and mangroves.

“Our study evidences the effort to improve microplastic sampling and identification methods: determine the optimal sample size and avoid possible contamination, apply staining techniques to optimize the identification of microplastics, and reduce the costs of the different methodologies for be able to apply them to long-term follow-up programmes”, points out Ostin Garcés-Ordóñez.

“In many parts of the planet, research is limited by the scarce availability of financial, human and infrastructure resources (for example, Raman or infrared spectrometers with Fourier Transform to characterize the composition of plastic polymers)”, explains Garcés- Ordonez. “Extensive application of both simple and more advanced methodologies will allow us to answer many open questions about the dynamics of microplastics in these environments or the role of lagoons as temporary or permanent sinks for microplastics,” she adds.

As detailed by Miquel Canals, “the best way to face and minimize the problem of contamination by microplastics in general and in coastal lagoons in particular is to stop their entry into natural systems at the root. It is necessary to act on the sources and the causes that favor its arrival in the coastal lagoons and the rest of the ecosystems».

“Achieving or at least approaching this objective —points out Canals—, would require a series of combined actions on a global, regional, national and local scale. To begin with, have an adequate regulatory framework and its effective implementation, and then promote actions to minimize the generation of plastic waste at all levels (for example, adequate management of waste and wastewater discharged into aquatic ecosystems, and strategies to eliminate the accumulation of large waste in the environment, which can generate secondary microplastics, among others).

“It is obvious that these examples are only some of the existing options, which should also be accompanied by environmental education and monitoring programs in order to objectively assess their effectiveness. Other options, such as the recovery of microplastics from the natural environment, are not, for now, viable”, concludes Miquel Canals.

The study is titled “A systematic review on microplastic pollution in water, sediments, and organisms from 50 coastal lagoons across the globe.” And it has been published in the academic journal Environmental Pollution. (Source: UB)