Microplastics ingestion by a common tropical freshwater fishing resource☆
Graphical abstract
Introduction
Plastic polymers are widely used by humans due to their versatility and durability. However, plastic material become an environmental problem when not properly disposed, because most plastic polymers have slow degradability and are easily transported when in the environment (Andrady, 2011, Browne et al., 2010). Several studies have shown the increasing accumulation of plastic debris in natural environments worldwide, which reflects the continuous expansion in production (PlasticsEurope, 2015), use and improper disposal of this material by humans (Gregory, 2009, Laist, 1997, Moore, 2008). When present in the environment, plastic debris become a risk to biodiversity as they can cause toxic and physical effects on the biota. Plastic debris are known to accumulate contaminants of various types in high concentration (Mato et al., 2001), such as organic pollutants (Ziccardi et al., 2016) and heavy metals (Holmes et al., 2012), and toxic effects can occur when these contaminants are released either in the environment where organisms are present or in the gut following ingestion (e.g. Browne et al., 2013, Gandara e Silva et al., 2016). However, the most studied impacts of plastic debris on biota are their physical effects, such as entanglement, ingestion and suffocation/asphyxia (Barnes et al., 2009, Ryan et al., 2009, Sigler, 2014).
Ingestion is probably the most common impact associated with plastic debris, having been reported for more than 270 taxa (Laist, 1997) from different trophic levels (Cole et al., 2011). Amongst the most affected taxa are fish, with several reports of ingestion of plastic debris for different species. For instance, the analysis of the stomach contents of fish collected in the North Pacific found that nearly 20% (Choy and Drazen, 2013) to 35% (Boerger et al., 2010) of the fish had debris inside the gut, especially plastics. Another study showed that 26%–52% of the fish collected in the English Channel had plastic debris in their gut (Lusher et al., 2013). It is thought that plastics and other types of debris may be intentionally or incidentally ingested by fish (Cole et al., 2011, Laist, 1997). Incidental ingestion occurs when items are swallowed along with natural food items (Peters and Bratton, 2016), or through trophic transfer, when fish consumes prey that has ingested plastic debris (Cedervall et al., 2012, Mattsson et al., 2015). On the other hand, intentional ingestion occurs when plastic material is mistaken for food, and the plastic particle is intentionally captured and ingested by the animal (Ivar do Sul and Costa, 2007). Evidence suggests that intentional ingestion of plastic is likely common in fish. For instance, marks left in large plastic debris suggest fish frequently attack and bite plastic items present in the environment (Carson, 2013), and laboratory experiments suggest fish larvae feed preferentially on plastic particles when exposed to both microplastics and natural food (Lönnstedt and Eklöv, 2016).
Little is known about the biological consequences of the ingestion of plastic debris for fish, but the few available studies on this issue suggest ingestion of plastic can be extremely harmful. Fish that ingested plastics debris may suffer from intestinal injury (Pedà et al., 2016) which in turn may reduce their ability to absorb nutrients. Also, ingested plastics may change fish behaviour and their ability to perceive predators (Lönnstedt and Eklöv, 2016, Mattsson et al., 2015). Ingestion of plastic debris also affects fish metabolic processes, such as fat metabolism (Cedervall et al., 2012, Mattsson et al., 2015), and interfere with fish immune system (Greven et al., 2016). Finally, contaminants released from ingested plastic can cause toxic effects such as hepatic stress in fish (Lu et al., 2016, Rochman et al., 2013).
A further impact of the ingestion of plastics by fish concerns the use of these organisms as a food resource by humans (Rochman et al., 2015) because both plastics and their associated contaminants can be accumulated in tissue. It has been demonstrated that microplastics can accumulate in tissue of seafood consumed by humans (e.g. Van Cauwenberghe and Janssen, 2014). Persistent organic pollutants, heavy metals and other contaminants such additives and plasticizers added to plastic, have the potential to bioaccumulate in fish (e.g. Rochman et al., 2013). These contaminants can be transferred either from the ingested plastic debris directly to fish, or from fish's prey that has ingested plastics. Humans are potentially exposed to these contaminants through bioaccumulation and biomagnification in the food web. Because there are several reports of plastic ingestion by fish species exploited by humans as food resource, plastic debris have been identified as a potential threat in commercial fisheries (Rochman et al., 2015) and in seafood originated from aquaculture (Van Cauwenberghe and Janssen, 2014). Nevertheless, the actual risk such processes pose to humans is yet unknown.
While reports of plastic debris ingestion by fish are frequent in the literature, most of the available information is for marine species. There is limited information on the ingestion of plastic debris by freshwater fishes, especially those used as food resource by humans. In this study, we assessed the ingestion of microplastics by Hoplosternum littorale, a common freshwater fish heavily consumed by humans in semi-arid regions of South America. We evaluated the spatial variation in gut content of fish caught by local fishermen in different sections of a river crossing a heavily urbanized area, and assessed the abundance and diversity of both plastic debris and other food items found in the gut of the fishes.
Section snippets
Study area
The study area was a section of the Pajeú river crossing the city of Serra Talhada, located in the semi-arid region of the Northeast of Brazil (Fig. 1). The Pajeú river basin is characterized mostly by a monotonous surface terrain with a smoothly undulating relief, primarily covered by hyperxerophilic vegetation of the Caatinga biome and stretches of deciduous forest. All water courses in the region show intermittent flow and are mainly regulated by irregular rainfall (Mascarenhas et al., 2005
Results
A total of 48 individuals of H. littoralle (40 males, 8 females) were obtained in our study. Individuals' total length ranged from 14.1 cm to 24.5 cm (average of 20.4 cm), weight from 46.8 g to 312.5 g (average of 188 g), gut weight from 2.6 to 26.6 g (average of 11 g), and condition factor (Fulton's K) from 1.19 to 9.4 (average of 2). Most of the fish were caught in station 2 (36 individuals, 75% of total) (Fig. 2).
Ingestion of microplastics by Hoplosternum littorale
We observed that 83% of the fish collected in our study had ingested plastic debris. This proportion of plastic debris ingestion is far above those reported for other freshwater and estuarine fish species, which lies between 5 and 45% (Table 3). Also, this proportion of plastic debris ingestion is above those observed for marine fish (e.g. Choy and Drazen, 2013, Lusher et al., 2013). We believe the interaction of H. littorale feeding behaviour and the high degree of environmental pollution at
Acknowledgments
This work was supported by CNPq (476241/2011-1) and FAPESP (2014/50711-3) grants. The first author is a fellow of the Tutorial Program of Education, Ministry of Education-Brazil. We thank two anonymous reviewers for their contributions to improve the manuscript.
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This paper has been recommended for acceptance by Eddy Y. Zeng.