Microplastic Contamination of Urban and Bushland Dominated Beaches of the Shoalhaven

Microplastic Contamination of Urban and Bushland Dominated Beaches of the Shoalhaven

Megan Jeffers – Ulladulla High School

Microplastics in the marine environment represent a form of pollution of increasing concern. This investigation examined two beaches in the Shoalhaven for microplastic abundance. A total of eight samples, four from Ulladulla Harbour and four from Termeil Beach, were collected and analysed using visual microscopy. Microplastic occurrence was detected in all samples, with Ulladulla harbour having an average of 66.75 plastic pieces per sample and Termeil Beach having and average 21.25 plastic pieces per sample. The results suggest that urban dominated beaches, as represented by Ulladulla Harbour, have a higher risk of microplastic occurrence. The most common items were fibres <630μm.

Key words: microplastic; urban; bushland; marine pollution.

Introduction

Marine anthropogenic litter is recognized as an emerging global pollutant. Plastic production is increasing each year, with 348 million tonnes being produced in 2017 worldwide (Garside, 2019). This plastic is dispersed by currents and winds, and persistent plastics rarely degrade, but instead become fragmented over time (Löder & Gerdts, 2015). Much of this plastic ends up in the oceans, with an estimated 5 trillion pieces weighing roughly 250 million tonnes in the global seas (Glaser, 2015). The distribution of microplastics in the ocean has effects, both direct and indirect, on marine fauna and local economies. The most abundant and problematic form of anthropogenic litter are buoyant and persistent plastics (Frias, et al., 2018). These most often occur in the form of microplastics, being defined as between 1μm and 5mm

(Masura, et al., 2015). They can be either primary (produced to be of microscopic size) or secondary (resulting from fragmentation) (Löder & Gerdts, 2015). Microplastics tend to present themselves as beach litter, floating litter, seafloor litter or biota litter (Joint Research Centre of the European Commission, 2013). The distribution of microplastics is largely dependent on density, and as most plastics have densities lower than seawater, they float on the water surface. However, some plastics can be suspended in the water column or sink into the sediment. Beaches, as intermediate environments, can accumulate floating, buoyant and sinking plastics (Löder & Gerdts, 2015).

Microplastics can have effects on marine life when ingested, by causing blockages throughout the digestive system (Löder & Gerdts, 2015). In addition, microplastics contain a mixture of chemicals added during manufacture and efficiently absorb Persistent, Bioaccumulative and Toxic contaminants (PBTs) from the environment. The ingestion of microplastics by aquatic organisms and the accumulation of PBTs have been central to the perceived hazard and risk of microplastics in the marine environment (Lusher, et al., 2017). This can also pose risks as toxic chemicals are propagated throughout the food web, with potential for entering human food sources.

While the risk of microplastics being consumed from fish by humans is minimal (as the gastrointestinal track is most often removed), microplastic pollution continues to increase thus, increasing the risk of microplastic ingestion and increasing the risk of negative effects from exposure to PBTs in humans (Cheung, et al., 2018). As there are no standardised methods for monitoring microplastic occurrence, there are significant gaps in knowledge, particularly with smaller sized microplastics (<150μm) (Löder & Gerdts, 2015). This research assesses microplastic contamination (occurrence and physical qualities) on urban and bushland dominated beaches in the Shoalhaven.

Literature review

Increased environmental awareness has led to a large amount of research into plastics in the environment. It is estimated that plastic pollution is composed of more than 5 trillion plastics pieces equal to roughly 250,000 tons in the global seas (Glaser, 2015). An increasing number of reports have been published concerning micro-plastic pollution in aquatic environments, however, these studies continue to be updated and lack standardisation (Mai, et al., 2018). In an effort to standardise the methods for researching micro-plastic pollution, several papers have also been published reviewing common methods. These include methods for sampling, separation, identification and quantitation. Microplastics are commonly researched within water samples, sand samples, sediment and biota within the literature. For the purpose of this review, sand samples will be focussed upon. While the definition for microplastics is still under debate, the majority agree that microplastics are plastics from 1μm to 5mm (Löder & Gerdts, 2015) (Frias, et al., 2018) (Masura, et al., 2015). Microplastics contain a mixture of chemicals, and also effectively absorb persistent, bio-accumulative toxic contaminants (PBTs) from the environment (Lusher, et al., 2017). Microplastic contamination within the environment will continue to increase as plastic production increases and ineffective methods are used for rubbish disposal. Currently, there are no standardised methods (Löder & Gerdts, 2015) and significant gaps in knowledge when it comes to smaller plastics and nanoplastics, and their possible effects on seafood safety (Lusher, et al., 2017).

Methods are broken up into three main sections, sampling, extraction and identification. The methods for sampling beach sediment is similar throughout the literature, however details differ between papers. Generally, sampling beach sediments requires non-plastics sampling and storage tools (Löder & Gerdts, 2015). However, the amount and nature of the samples differs. Sample amounts range from less than 500g to 10kg (Löder & Gerdts, 2015). Sampling tools include grab samplers, core samplers, dredge samplers, remotely operated vehicles (Frias, et al., 2018) and manual collection (spoon, trowel, shovel) (Löder & Gerdts, 2015). Generally the high tide line is sampled (Löder & Gerdts, 2015) (Sul, et al., 2017), from depths of 2cm (Sul, et al., 2017) to 30cm (Löder & Gerdts, 2015). The units of microplastic abundance depends on sampling approach, thus abundance is normalised to sampling area, sediment weight or volume (Löder & Gerdts, 2015).

Once sampled, extraction of the microplastics is then conducted. Once again, there is no standard protocol for the extraction of microplastics from samples, although two main methods are used, density separation (Löder & Gerdts, 2015) (Masura, et al., 2015) (Frias, et al., 2018) and dry sieving (Sul, et al., 2017). The density separation method uses sediment purification using hydrogen peroxide(H2O2) at 6-10% (Frias, et al., 2018) up to 30% (Löder & Gerdts, 2015) (Masura, et al., 2015). This can be carried out prior to separation (Frias, et al., 2018) or afterwards (Löder & Gerdts, 2015) (Masura, et al., 2015). Other ways to purify include rinsing with pure water or ultrasonic cleaning (Löder & Gerdts, 2015). However, purification should be carefully considered as brittle plastics can be degraded (Löder & Gerdts, 2015). Density separation includes adding a saturated salt solution of high density and agitating (by stirring, shaking, aeration etc.) for a certain amount of time, before allowing plastic particles to float to the surface or stay in suspension whilst the heavier sediments settle (Löder & Gerdts, 2015) (Masura, et al., 2015) (Frias, et al., 2018). The supernatant is then decanted and filtered to remove microplastics (Frias, et al., 2018) (Löder & Gerdts,

2015) (Masura, et al., 2015). The alternative method is dry sieving. Sand samples are dried and sieved through a series of sieves (Sul, et al., 2017) (Löder & Gerdts, 2015), and then sorted into size class before microplastics are identified (Sul, et al., 2017). Alternatively, plastics >500μm can be sorted manually under a microscope, with the smaller samples being purified and filtered (Löder & Gerdts, 2015).

Once extracted, the next step is identification of microplastics. This section is the most standardised section, with plastics being sorted into size and colour (Frias, et al., 2018) (Löder & Gerdts, 2015) (Masura, et al., 2015) as well as source, shape and degradation stage (Löder & Gerdts, 2015). As well as this, type (Frias, et al., 2018) (Löder & Gerdts, 2015) (Sul, et al., 2017) and chemical analysis can also be carried out (Frias, et al., 2018) (Löder & Gerdts, 2015). Once identified, results can be expressed as: no. Microplastics per area, no. Microplastics per volume, no. Microplastics per mass, mass of Microplastics per area or mass of Microplastics per volume (Frias, et al., 2018).

Most of the literature analysed are reviews of the various methods used by research papers. These have advantages as they mention a variety of methods, however, they do not review the results from these various methods. This means that there is a limited ability to compare results to other published papers. In addition, the majority of literature is based in Europe, including summaries of methods which are produced by European institutions. While the results from this research can give implications into microplastic pollution, further research is required to examine the extent of microplastic pollution in Australia.

Research question and hypothesis

The research question that will be investigated in this report is ‘Is there a higher rate of microplastic occurrence on urban dominated beaches than bushland dominated beaches in the Shoalhaven?’

The Hypothesis states ‘Bushland dominated beaches will have a lower rate of microplastic occurrence than urban dominated beaches in the Shoalhaven’.

Therefore, the null hypothesis states that ‘There is no difference in microplastic occurrence between bushland dominated and urban dominated beaches in the Shoalhaven.’ The alternate hypothesis states ‘There is a difference in microplastic occurrence between urban dominated and bushland dominated beaches in the Shoalhaven.’

Method

Sampling

Sand was collected from two beaches in the Shoalhaven, the urban dominated beach being Ulladulla Harbour and the bushland dominated beach being Termeil beach.

Location, Length, Grain Size, Direction, Slope

Ulladulla Harbour, 1500m, Fine, East, 6°

Termeil Beach, 600m, Medium-fine, East, 7°

A total of eight samples were collected, four samples from each beach, spaced in equal increments so that there was one sample collected from each end and two in the middle (See figure 1) whilst practicing caution towards any hazards on the beach. The sand was sampled by excavating the top two centimeters of sand from 250cm2 quadrants. Non-plastic collection and storage tools were used to prevent plastic contamination.

Figure 1: Sample sites from Ulladulla

Statistical Analysis

The collected data was analysed using Microsoft Excel. Because this data has a difference in variance, a one-tailed unpaired and un-equal variance t-test was used to demonstrate the difference in bushland and urban dominated beaches in the Shoalhaven in terms of number of microplastic pieces that occurred. Data collected was also demonstrated by number of plastic items per weight. In addition, descriptive statistics were also displayed in this study, including mean values alongside median values and standard deviation. A 0.05 level of significance was adopted.

Results

Abundance of particles

The physical characteristics of each beach sampled are shown in tables. In this study, the presence of microplastics on beaches in the Shoalhaven was confirmed. A total of 352 microplastic pieces were identified with 75.85% being from Ulladulla Harbour Beach and 24.15% being from Termeil beach. Each of the four samples from both beaches were contaminated. The recorded results were adjusted using the number of microplastics that occurred on blank petri dishes that were analysed parallel to each sand sample.

The mean number of microplastic items was significantly higher in the urban dominated beach than the bushland dominated beach (p=0.0039, a=0.05). On average, 66.75 microplastic pieces were found in each 500g sample from Ulladulla Harbour, while only an average of 21.25 was found in each 500g sample from Termeil beach.

Types, colours and sizes of plastics

A total of 204 fibres were observed in Ulladulla samples, which accounted for 76.4% of the plastics from Ulladulla Harbour. A further 56 fragments were found making up 20.97%, and 7 beads which constituted the last 2.62% of plastics from Ulladulla Harbour. Fibres were also the most common microplastic from Termeil beach, which constituted 62 fibres which made up 72.94% of the plastic pieces found at Termeil, followed by 23 fragments which made up the last 27.06%. Overall, fibres were the most common microplastic (75.57%), followed by fragments (22.44%) and beads (1.44%). Ten different colours of plastics were observed, with the most common colour being clear, making up 35.51% of the total microplastic pieces. Other plastic items were black, pink, blue, purple, white, orange, green, brown and yellow. There was a higher variety of colours on Ulladulla Harbour beach than Termeil Beach, in which only seven colours were observed.

Figure 2: a) Examples of fragments b) Example of bead

Figure 3: Examples of fibres

The mean number of microplastic items was significantly higher in the urban dominated beach than the bushland dominated beach (p=0.0039, a=0.05). On average, 66.75 microplastic pieces were found in each 500g sample from Ulladulla Harbour, while only an average of 21.25 was found in each 500g sample from Termeil beach.

Discussion

This study aimed to determine whether or not there is a significant difference in the abundance of microplastics on urban dominated or bushland dominated beaches in the Shoalhaven. Visual identification was used to determine the rate of occurrence of microplastics in four 500g samples from two beaches, Ulladulla Harbour representing an urban dominated beach and Termeil Beach representing a bushland dominated beach. Ulladulla Harbour was chosen as the urban dominated beach in this study as it is situated in the most populated local area, as well as being influenced by industrial fishing and having Millards creek empty into the harbour, acting as storm water runoff. Termeil Beach was chosen to represent the bushland dominated beach as it is surrounded by bushland, having the nearest settlement 3km away. In addition, it is only accessible by 4wd, meaning it experiences a low level of human interaction.

In this study, it was found that the mean number of plastic particles was significantly higher in Ulladulla harbour (urban) than Termeil Beach (bushland). On average, 66.75 microplastic pieces were found in each 500g sample from Ulladulla Harbour, while only an average of 21.25 was found in each 500g sample from Termeil beach.

The higher abundance of microplastics on Ulladulla Harbour beach may be related to the difference in environment, and the different uses of the areas. Microplastics can be introduced into the environment through land-based sources including sewage discharge, illegal dumping, storm-water runoff, industrial activities and accidental spillage during transportation (Cheung, et al., 2018).

In this study, fibres were found to be the most common type of microplastic for both sample sites. Fibres were also the most common microplastic in previous studies of microplastics in the marine environment (Cheung, et al., 2018). Other studies did not find any fibres (Sul, et al., 2017). However, this study only analysed samples >1mm, meaning that fibres may have been present in smaller size categories.

In this study, the two beaches that were examined had fine sand, with Ulladulla Harbour also having some medium grain sand, as well as some pebbles. The microplastics observed were most predominant in size categories that had the largest mass of the sand sample. Due to this, data cannot be accurately compared to studies such as conducted by (Sul et al). that only examine samples of in larger size categories. In the above mentioned study, the majority of beaches examined had fine grain size, meaning that analysing only categories of >1mm reduces the accuracy of their results as it is likely that the majority of microplastics reside in the smaller size categories that match the grain size of the beaches.

Currently, the reliability and comparability of the literature surrounding microplastics in the marine environment is hampered by the huge variety of methodologies applied. Thus, one basic aim must be the standardization of methodologies for identification and quantification of microplastics in the marine environment, and the subsequent formulation of standard operating procedures (SOPs) (Löder & Gerdts, 2015). This should include the whole cycle of the assessment of microplastics in the marine environment, including sampling procedures, purification, and microplastic identification. Due to variety of methodologies used in the literature, there are complications when comparing data from this study with others.

In this study, the method of visual identification was employed. While this method has benefits, it also has limitations. If identifying by first using a density separation, some microplastics may not be counted depending of the density of the salt solution used. This can be impractical as salts of higher densities often have high costs and therefore are not economically efficient. The method of visual microscopy eliminates most costs, however, it relies heavily on the ability of the researcher to identify plastics. In this study, if there was any doubt about the nature of a particle, it was not counted as a plastic particle (Munno, n.d.). This means that the rate of microplastic occurrence may be lower than the actual abundance. However, while criteria for identifying plastic pieces was followed, without a chemical analysis, there is still the possibility that some particles identified as plastic pieces were misidentified, and were in actuality pieces of organic matter.

Another limitation with this method is that there is risk of contamination from airborne microplastic. To limit the risk of contamination, all materials used were not made of plastics. In addition, analysis was conducted in a low-dust room with minimal movements being made by the researcher to limit the movement of plastic fibres which may become airborne from clothing or other items in the room. Further actions taken to limit this risk include keeping samples covered for the maximum amount of time possible and running blanks parallel to the sand samples. These blanks were empty petri dishes that were treated the same as sand samples and analysed by visual microscopy. Blank petri dishes returned abundances of microplastics between 0 and 3, creating a degree of uncertainty.

In addition, 500g samples were analysed due to time restrictions. However, while the results from these samples give a reliable indication into the abundance of microplastics from their respective beaches, a larger sample size is required.

Recent research shows that the commonly applied method of visual inspection of samples alone is insufficient to identify microplastic particles in environmental samples, especially for particle sizes <500μm (Löder & Gerdts, 2015). It is suggested that micro-Ramen or micro-STIR spectroscopy is essential to accurately identify microplastic pieces, and has been successfully applied to analyzing marine samples. Spectroscopic techniques would also add value to research as it provides data on polymer composition. A future standardised method for Spectroscopic techniques would allow a generation of valid data that includes concentration, particle size distribution, involved polymers and distribution among different environments and marine biota (Löder & Gerdts, 2015). This will essentially lead to accurate comparability of different data sets. Furthermore, this data is crucial for a reliable evaluation and assessment of potential impacts and risks of microplastics in the world’s oceans (Löder & Gerdts, 2015).

This study provided evidence that microplastics exist on sandy beaches in the Shoalhaven, indicating the presence of microplastics in the oceans of the east coast of Australia. While this researcher provides indication of microplastics in the ocean, the effect of these plastics on human life and the risks they provide requires further research into the presence of microplastics in fish (Cheung, et al., 2018) and other foods such as sea salt (Thiele & Hudson, 2018). Although there is still uncertainty about the safety of microplastic ingestion by humans, it is known that microplastics are subject to the bioaccumulation of marine pollutants (Löder & Gerdts, 2015).

Conclusion

This study highlights the occurrence of microplastics in the marine environment. It aimed to investigate the question ‘Is there a higher rate of microplastic occurrence on urban dominated beaches than bushland dominated beaches in the Shoalhaven?’ A p-value of 0.0039 was returned, thus, rejecting the null hypothesis.

The results indicate that urban dominated beaches are more likely to have a higher rate of microplastic contamination than bushland dominated beaches. This may be due to the Urban dominated beach (Ulladulla Harbour) having a large amount of microplastics introduced from landbased sources, compared to the bushland dominated beach (Termeil Beach) which has minimal influence from obvious plastic debris sources. However, other factors must also be considered such as current patterns, waves action and wind exposure of the beaches.

Beyond effects of ingestion, chemical leaching and contaminant absorption; microplastics may also change the physical properties of beaches by increasing permeability and lowering subsurface temperatures, having subsequent impacts of marine life (Sul, et al., 2017).

International government and academic efforts are needed to establish universal protocols to further investigate microplastic contamination, both in sediment types and biota, and assess the risks of microplastics on human and wildlife health.

Acknowledgements

The author would like to thank their mentor, Dr. Scott Wilson (Senior Lecturer in Environmental Science, Department of Environmental Sciences, Macquarie University, Sydney, Australia) for his invaluable advice and assistance with method development, the supply of literature and guidance throughout the development of this research.

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