Occurrence and amount of microplastic ingested by fishes in watersheds of the Gulf of Mexico

Highlights

• 8% of the freshwater fishes and 10% of marine fishes had microplastic in their gut tract.

• Fishes from freshwater and marine environments in Texas ingest microplastics ubiquitously across habitat and trophic guilds.

• Significantly more fishes taken from one of the urbanized streams had ingested microplastic.

• A subsample of plastic fragments, filaments and film was analyzed using FT-IR spectroscopy.

Abstract

Ingestion of microplastics by fishes could be an emerging environmental crisis because of the proliferation of plastic pollution in aquatic environments. Microplastics in marine ecosystems are well documented, however only one study has reported percent occurrence of microplastics in freshwater fishes. The purpose of this study was to quantify the occurrences and types of microplastics ingested by fishes within several freshwater drainages of the Gulf of Mexico and an estuary of the Gulf of Mexico. Among 535 fishes examined in this study, 8% of the freshwater fishes and 10% of the marine fishes had microplastics in their gut tract. Percentage occurrence of microplastics ingested by fishes in non-urbanized streams (5%) was less than that of one of the urbanized streams (Neches River; 29%). Percent occurrence of microplastics by habitat (i.e., benthic, pelagic) and trophic guilds (herbivore/omnivore, invertivore, carnivore) were similar. Low but widespread occurrences among drainages, habitat guilds, and trophic guilds indicate proliferation of plastic pollution within watersheds of the Gulf of Mexico, but consequences to fish health are unknown at this time.

Introduction

Globally, plastic pollution is ubiquitous on land and in water and is increasing. Plastic production continues to accelerate with developed and developing countries adopting the use-and-dispose culture. Annual plastic production has increased from 1.5 million tonnes in the 1950s to 288 million tonnes in 2012 (PlasticsEurope, 2013) with only 9% of plastics being currently recycled in the USA (EPA, 2014). Non-recycled plastics are disposed in landfills (Barnes et al., 2009) or in the environment as a pollutant (Cole et al., 2011). Marine plastic pollution has been of concern since the 1970s, when the first reports of microplastic ingestion in fishes were published (Carpenter et al., 1972). Plastic is prolific throughout the marine environment with as much as 80% of marine debris being plastic because of its durable nature (Barnes et al., 2009).

Plastic accounts for 92% of all encounters between organisms and marine debris, the effects of large plastic items (i.e., macroplastic), such as entanglement, ingestion and death, being widely reported in fish and wildlife (Gall and Thompson, 2015). However, a greater proportion of plastic pollution is microscopic (< 5 mm; Arthur et al., 2009). Some microplastics, for instance microbeads, are manufactured to be of a microscopic size, typically polyethylene and polypropylene and used in skin exfoliators and cosmetics and in air-blasting technology (Derraik, 2002, Fendall and Sewell, 2009, Gregory, 2009). Additionally, microplastics are derived from macroplastic fragmenting and disintegrating into smaller particles through a process of photo-degradation caused by the ultraviolet rays of the sun, mechanical forces, and weather (Andrady, 2011, Cole et al., 2011, Derraik, 2002). These macroplastics are made of a variety of plastics; more abundant forms are polyolefins (polyethylene and polypropylene), which are primarily used for single-use packaging (Browne et al., 2010a, Browne et al., 2010b). A large proportion of the plastic fragments are lost from the surface due to hydrodynamic processes (Eriksen et al., 2014). Other sources of microplastics are acrylic, polyester, and polyamide fibers from textiles (Browne et al., 2011). Densities of plastic vary considerably, depending on the type of polymer and the manufacturing process. Size and density of plastic determine its position in the water column (Browne et al., 2011) and potentially its environmental effects including ingestion by fishes.

Occurrence of microplastics in the stomachs of fish poses several environmental concerns. Ingested microplastics are passed through in the feces, retained in the digestive tract, or translocated from the gut into body tissues via the epithelial lining (M. A. Browne et al., 2010a, Browne et al., 2010b). Negative effects on fish health are due to the toxic nature of the plastic itself and to other pollutants in the environment absorbed by plastic. Microplastics consist of synthetic organic polymers that are transport medium for persistent organic pollutants (POPs). Polymers act as a sponge and absorb toxins, such as polychlorinated biphenyls (PCBs), dioxins, pesticides, flame-retardants and carcinogens from the marine environment (Rochman, 2013). Toxic substances pass from microplastics to the carrier and accumulate in tissues, causing liver toxicity and lesions (Rochman et al., 2013).

Since the 1970s, occurrence of microplastic ingestion in marine environments has been well documented with a surge in research since 2000. Percent occurrences of plastics in the stomach contents of marine fishes range from 2.6% in the North Sea (Foekema et al., 2013) to 37% in the English Channel (Lusher et al., 2013). Reports from other areas include Brazilian estuaries (Possatto et al., 2011, Dantas et al., 2012) and North Pacific Gyre (Boerger et al., 2010). Reports of microplastic ingestion are limited for freshwater fishes with one study reporting 12% in urbanized streams of France (Sanchez et al., 2014).

Freshwater environments, like marine environments, are susceptible to microplastic pollution with rivers serving as major pathways of plastic transport from terrestrial environments to marine environments (Lechner et al., 2014). Microplastics occur in Laurentian Great Lakes of North America (Eriksen et al., 2013), freshwater inflows into Jade Bay, Germany (Dubaish and Liebezeit, 2013) and the remote Lake Hovsgol, Mongolia (Free et al., 2014) at amounts comparable to those in marine systems. Abundances of microplastic pollution and urban population density are directly related with microplastics coming from wastewater treatment effluents (Browne et al., 2011, Free et al., 2014). Concerns and subsequent effects of incidental ingestion by freshwater and marine aquatic animals are emerging environmental issues. Bioavailability of the smaller-sized microplastics is more likely than macroplastics, especially to fishes that mistakenly or incidentally ingest microplastic while feeding in the water column or along the benthos (Browne et al., 2010a, Browne et al., 2010b).

The objective of this study was to document occurrence, frequency, amount, and types of plastic ingested by fishes in freshwater drainages of the Gulf of Mexico and by marine fishes within a large bay system of the Gulf of Mexico. To further illustrate the link between highly human-altered areas and plastic pollution, this study compared ingestion amounts in fishes from urbanized and non-urbanized streams. Predictions were that percent occurrence of microplastics ingested by fish will be similar to the range of ingestion amounts reported in marine studies conducted in estuaries (8 to 33%; Possatto et al., 2011, Dantas et al., 2012) and freshwater (12%; Sanchez et al., 2014), will be greater in urbanized streams than in non-urbanized streams, and will differ among trophic and habitat guilds of fishes (e.g., benthic omnivore, pelagic piscivore), depending on the location of plastics within aquatic environments (i.e., benthic, pelagic, surface). Within the large bay system, Laguna Madre is naturally a hypersaline bay because of limited freshwater inflows. As such, microplastic availability might be lower than in other bay and estuary systems where plastic ingestion has been reported and therefore has lower incidents of microplastic ingestion among bay and offshore fishes.