Evidence of microplastics in samples of zooplankton from Portuguese coastal waters
Graphical abstract
Introduction
In recent years, the presence and impacts of plastic marine debris (PMD) have been documented throughout the world in all oceans. Plastic debris, which may be unintentionally lost or deliberately discarded, tend to accumulate in coastal areas, posing a direct threat to marine fauna through ingestion and/or entanglement (Crimmins et al., 2002, Allen et al., 2012, Cole et al., 2013; Wright et al., 2013).
It is estimated that 80% of PMD derive from land sources (Allsopp et al., 2006), being transported by water courses (river streams, drainage systems, ocean currents) (Corcoran et al., 2009, Furness, 1983, Laist, 1987, Laist, 1997, Gregory and Andrady, 2003) and/or migratory animals (birds, turtles, dolphins, seals, among others) (Ryan et al., 2009, Teuten et al., 2009, Franeker et al., 2011), enabling PMD to travel great distances, being found in remote regions, far away from any known source (Ivar do Sul and Costa, 2007, Barnes et al., 2009, Martins and Sobral, 2011, Heskett et al., 2012).
PMD concentration increase in the oceans is linked to human consumption behaviour, industrial activities and poor waste management. Buoyancy contributes to the wide dispersion of PMD in the open ocean, as plastics float and are transported by surface currents. High concentrations of plastics and microplastics accumulate in convergence zones known as ocean gyres (Pichel et al., 2007).
Reports of the high incidence of PMD in the North Pacific Central Gyre (Moore et al., 2001, Moore et al., 2002, Moore, 2008, Goldstein et al., 2012), and in other places of the world, have raised concern and an unprecedented interest for research on the topic in the areas of marine sciences (Derraik, 2002, Arthur et al., 2008, Thompson et al., 2004) as well as in social sciences (Thiel et al. 2003; Bravo et al. 2009; Hinojosa and Thiel, 2009; Luís and Spínola, 2010).
Microplastics, defined as plastic materials or fragments with diameter below 5 mm (Arthur et al., 2008), have also the tendency to increase concentration over time as result of plastic degradation. Factors like solar radiation, abrasion, water and wind movements cause PMD to break into progressively smaller pieces without substantial chemical degradation (Moore, 2008; Barnes et al., 2009). These are ingested by marine animals (Browne et al., 2008) and are potentially transferred through the trophic chain, and therefore constitute a main problem for the world's oceans (Barnes et al., 2009, Hirai et al., 2011).
Microplastics are a particular threat not only due to their size but also for their capacity to adsorb persistent organic pollutants (POP) (Takada et al., 2005, Teuten et al., 2007, Ogata et al., 2009, Frias et al., 2010, Martins and Sobral, 2011), which varies according to different polymers.
Studies concerning POP adsorbed to microplastics (Mato et al., 2001, Moore, 2008; Takada et al., 2005) and adsorption rates of POP in microplastics (Bakir et al., 2012) report important concentration values of contaminants in plastic debris, however their potential effects on the food web (Teuten et al. 2007; Browne et al., 2008) are still uncertain. Recent studies have shown the ability for filter feeders and zooplankton to ingest plastic particles ranging from 1.7 to 30.6 μm (Crimmins et al., 2002, Browne et al., 2008, Cole et al., 2013), which may eventually increase the risk for toxic effects due to accumulation of persistent toxic chemicals in lipid reserves. Accumulated toxic chemicals may transfer along the food chain into human diets (Ryan et al., 1988, Zarfl and Matthies, 2010).
While dense varieties of plastics such as commonly used nylons, polyvinyl chloride (PVC) and polyethylene terephthalate (PET) tend to sink in the water column and reach the coastal sediment (Andrady, 2011), most microplastic debris from the widely used polymers, polyethylene (PE), polypropylene (PP) and polystyrene (PS) will float (Vianello et al., 2013) and may be collected using plankton nets. This technique underestimates the amount of plastics and microplastics in the oceans, as well as those in sediment and mid-water. Several size ranges of zooplankton may incorporate the tiny pieces of plastic in their diet, potentially causing a large scale accumulation problem in the lower levels of the food chain, with unpredictable consequences (Cole et al., 2013).
In order to estimate the effects of PMD on marine organisms and clarify the magnitude of the problem it is essential to obtain more data on the size of plastic debris in the oceans, especially the smaller size classes and different polymers. Plankton surveys which are regularly performed for monitoring fish stocks may provide data on microplastics in the oceans without further cost of days at sea, and contribute to the marine litter evaluation as included in the Marine Strategy Framework Directive (2008/56/EC) (MSFD) for the European seas. Therefore, the main goals of this exploratory work were to (1) detect and quantify microplastic debris in zooplankton samples and assess variations among sites; (2) identify the plastic polymers present, using a spectroscopy technique – the Fourier Transform Infrared Spectroscopy (μ-FTIR).
Section snippets
Sample collection and processing
Zooplankton samples were collected between 2002 and 2008, in four areas of Portuguese coastal waters – Aveiro (Av), Lisboa (Lx), Costa Vicentina (Cv) and Algarve (Al) (Fig. 1) – as part of annual surveys performed by the Instituto Português do Mar e da Atmosfera (IPMA) to assess fish stocks. Samples were collected using three different sampling methods, W (WP2 net), N (Neuston net) and L (Longhurst Hardy Plankton Recorder, Pro-LHPR).
Sampling methods differ in mesh size (W – 180 μm; N – 280 μm;
Microplastics collected
The non-standardized, number of microplastics collected in all processed samples was 684 and the total volume of microplastics totalled 113.01 cm3, which corresponds to 61% of all samples. Table 1 summarizes standardized microplastic and zooplankton volumes (cm3 m−3, mean ± sd); microplastic: zooplankton ratio and microplastic concentration (n°. m−3, mean ± sd) for each sampling site.
Microplastic: zooplankton ratios were determined for each site (Table 1) and for each sampling method – 0.02 for
Discussion
Results confirm the presence of microplastics in samples of zooplankton from Portuguese coastal waters, with different concentrations and abundances among sites (Table 1, Figs. 3 and 4). As expected, sampling method L (LHPR) collected low concentrations of microplastics, as it is deployed at a depth range of 25 m in the water column. As consequence, sampling method L had lower microplastic: zooplankton ratios. Floating plastics and microplastics are more likely to be collected by N (Neuston
Conclusions
This work identified several types of commonly used plastic polymers in Portuguese coastal waters. Sixty one per cent of all zooplankton samples had microplastics. The total number of microplastics identified was 684 in 93 samples, corresponding to a volume of 113.01 cm3. Costa Vicentina and Lisboa, were the regions with the highest microplastic concentrations, abundances and microplastic: zooplankton ratios. In the case of Costa Vicentina these values are probably related to the proximity to
Acknowledgements
We would kindly like to acknowledge Doctor Maria João Melo (Department of Conservation and Restoration, FCT-UNL) for her support and supervision on the FTIR analysis. This work would not have been possible without the support of Dr. Antonina dos Santos (IPMA), who kindly provided us the plankton samples. Finally, we would like to acknowledge Fundação para a Ciência e Tecnologia for their financial support through the fellowship reference number SFRH/BD/74772/2010, project reference number
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