Microplastics biomonitoring in Australian urban wetlands using a common noxious fish (Gambusia holbrooki)
Graphical abstract
Introduction
Microplastics are considered an emerging pollution concern and global efforts are being made to account for their presence in environments (Browne et al., 2011; Cole et al., 2011; Mattsson et al., 2015). The ubiquitous existence of microplastics in aquatic ecosystems, as well as terrestrial systems, has been well documented over the past few decades (Dris et al., 2015; Horton et al., 2017). Understanding the interactions of microplastics with ecosystems is critical for assessments of its environmental risk (Galloway et al., 2017). The ingestion of microplastics, plus uptake of any associated chemicals by biota, is a serious concern because it potentially threatens the survival of wild populations. Threats include physical impacts such as entanglement and blockage of the digestive tract as well as toxicological effects from released chemicals (Wright et al., 2013). Moreover, microplastics that bioaccumulate into food webs may impact humans that consume the contaminated organisms (Seltenrich, 2015).
Monitoring the plastic debris in organisms has had a long history (Acampora et al., 2016; Fry et al., 1987). Reports of entanglement by, and ingestion of, plastic debris by marine biota initially caused concerns about the risks of plastic pollution in the 1980's (Laist, 1987; Ryan, 1987). Fishes are one of the most commonly used species in debris monitoring due to their wide distribution, ecological significance and (human) dietary importance (Miranda and de Carvalho-Souza, 2016; Wesch et al., 2016). Microplastic particles can be transported from freshwater to marine habitats and have been detected in more than 100 fish species around the world (Jabeen et al., 2017). Microplastics can enter the body of a fish via different pathways, which could prove hazardous to an individual's health and population development (Karami et al., 2017; Lu et al., 2016). Laboratory studies have revealed the negative impact of microplastics in fish; such as intestinal damage and inflammation from short to long term exposure (Jabeen et al., 2018; Rochman et al., 2013). Although ingestion is considered an important pathway in field conditions, several studies have shown that microplastics can enter internal organs after adhering to the gills and skin (Abbasi et al., 2018; Akhbarizadeh et al., 2018; Su et al., 2019). Such factors should be considered in microplastic risk assessments and in the design of monitoring protocols.
There is widespread recognition that wetlands provide valuable ecological services including habitat for species, protection against floods, water purification, amenities and recreational opportunities (Woodward and Wui, 2001). The health of wetland ecosystems is a significant concern in the field of environmental management (Euliss et al., 2008; Pettigrove and Hoffmann, 2005). In comparison with natural water bodies, some urban wetlands are specifically designed to treat urban runoff and to receive stormwater which makes them more vulnerable to environmental stress via anthropogenic influence and contamination (Wong and Geiger, 1997). Based on some preliminary studies, we know that microplastics can occur in natural wetland sediments, waters and birds (Lourenço et al., 2017). However, monitoring of plastic levels in urban wetlands and their inherent taxa is uncommon. Urban wetlands receive a considerable amount of material carried by surface run-off, and therefore constitute an important source of microplastic pollution (Dehghani et al., 2017). In addition, urban wetlands are typically small water bodies that are heavily influenced by surrounding catchment land use. The seriousness of microplastic pollution in small water bodies has been highlighted in some regional case studies (Hu et al., 2018; Nel et al., 2018; Zhang et al., 2015).
Gambusia holbrooki (Eastern mosquitofish) is invasive in most continents under a wide range of temperate climate conditions. Because of its widespread distribution, high abundance, ease of capture and ability to adapt to laboratory settings, Gambusia holbrooki is a common model fish for ecotoxicological testing and environmental monitoring (Pyke, 2005). The sex of adult individuals can be easily distinguished on the basis of externally visible characteristics (Leusch et al., 2006), which allows for gender-dependent investigations in pollution monitoring. The accumulation of metals and persistent organic pollutants has been observed in Gambusia holbrooki while few studies have investigated microplastic accumulation (Edwards et al., 2005; Nunes et al., 2005). As an invasive species in Australia, Gambusia holbrooki has a high level of biomass and dominance in some wetlands and small water bodies (Ayres et al., 2010). Furthermore, Gambusia holbrooki are a hardy species and are often found inhabiting polluted artificial ponds and wetlands where native species do not occur (Hopkins et al., 2003). Therefore, biomonitoring and routine investigations based on Gambusia holbrooki has limited impact on understanding pollutant effects on local, native fish populations, but does provide valuable information regarding impacts on resident species within polluted ponds and wetlands.
Given that microplastic research is substantially lacking for freshwater biota in the Southern Hemisphere, we conducted an investigation to determine the baseline pollution level of microplastics in Gambusia holbrooki. Fish size, weight and gender were examined in relation to microplastic uptake through the gills (head) and the gut (body). We aimed at attaining: 1) a snapshot of microplastic abundance in Gambusia holbrooki from wetlands close to urban areas; 2) the distribution and characteristics of microplastics in different parts of fish; 3) factors which may influence microplastic uptake in small fish (i.e. particle size/type).
Section snippets
Research area and sample collection
The greater Melbourne metropolitan area supports a population of approximately 4.5 million and encompasses a catchment area of approximately 12,800 km2 (Sharley et al., 2016). It contains a complex network of rivers, streams and constructed wetland systems. These wetlands are constructed for the interception and treatment of stormwater, to attenuate flows during storms and to treat water quality. Nine wetlands from urban and peri-urban areas were selected for this study (Fig. 1; Supplementary
Polymer identification in fish body and head
Of the 109 selected items from fish bodies and heads, 68 items were confirmed as plastic (62.4%). Eleven polymer types were identified: the most common polymers were polyester (25.7%), rayon (10.1%), polyamide (7.3%) and polypropylene (5.5%) (Supplementary tables Table S4). In particular, polyester and rayon occurred in more than 70% of sampling sites.
Sixty plastic items (72.3%) belonging to 11 polymer types were identified from body samples and 8 plastic items (30.8%) belonging to 5 polymer
The level and trend of microplastic pollution in Gambusia holbrooki from the Greater Melbourne Area
Our current work provides an initial snapshot of microplastic pollution levels in an Australian freshwater fish from the Greater Melbourne Area. Investigations into the microplastic pollution in freshwater organisms are few compared to similar studies of marine organisms. In addition, this is the first known field study to specifically target microplastics in Gambusia holbrooki. Based on the available literature, the average abundance of microplastics in freshwater fish, amphibians and
Conclusion
Microplastics were detected in the bodies, and to a lesser extent, the heads of Gambusia holbrooki individuals from urban wetlands located in the Greater Melbourne Area. Presuming that the body is representative of uptake via the gut and the head is representative of uptake via the gills, we conclude that the gut is the predominant route of microplastic uptake in this species. The overall prevalence of microplastics in these fish was 19.4% (body) and 7.2% (head), which is low relative to other
Notes
The authors declare no competing financial interest.
Acknowledgements
We thank Jessica French and Sarah McDonald for assistance with sample collection. This work was funded by a China Scholarship Council grant (201706140182) with support of the Centre of Aquatic Pollution Identification and Management (CAPIM), University of Melbourne. This work was partially funded by The Holsworth Wildlife Research Endowment & The Ecological Society of Australia (TA103146).
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