Between the Manta Net Sampling Method and Neuston Net Sampling Method, Which Has More Precision in Sampling Microplastic Particles in Marine Environments?

Abstract

The purpose of this research is to compare the two popular marine microplastic sampling methods: Manta net method and the Neuston net method. Specifically, the precision in the data that each method collected is compared, and a conclusion is deduced. This will be done using various viewpoints including a histogram, a world map microplastic density diagram, and a box-and-whisker plot consisting of count of density measurements vs. density measurements, pure density measurements, and time vs. density measurements respectively. The comparison of precision is done for each viewpoints, and the method that has a higher precision in the data it collected is concluded in the conclusion section.

1. Introduction

Since the worldwide commercialization of plastic products, microplastic particles have been mixed into our drinking water. These microplastic particles are small plastic particles which their diameters are less or equal to 5 millimetres. These microplastic particles can possibly be hazardous to human body when consumed, although there are some debates about the specific effects, including lipid metabolism, induce oxidative stress, and include neurotoxic responses. In order to avoid these harmful effects, there is a need to filter out the microplastic particles from our drinking water. 

However, as microplastic particles are distributed around the globe differently by region, there is a need to use different filtering plans depending on the distribution. And in order to formulate specific plans by region, there is a need to apprehend the specific densities in marine environments by region. Since it is realistically impossible to observe microplastic particles in every ocean, samples have to be used to determine the approximate densities of microplastic particles in the oceans. 

Two useful methods for sampling of microplastic densities are using a Manta net and using a Neuston net. These two sampling methods have different properties, and the selection of which method is going to be used should be determined by evaluating these two methods critically, and concluding which method has more reliability in the measurements. This paper will compare the data collected by using these two sampling methods, and determine which sampling method has higher precision in their measurements.

1.1 Background Research

1.1.1 Manta Net Method

The Manta Net’s name comes from Manta Rays, a sea animal that feeds from small sea organisms at the ocean’s surface. As this name indicates, the Manta Net’s original function was to collect small sea organisms from the surface of the ocean. But as the Manta Net is capable of collecting micro-sized objects, it was started to be used as a microplastic density sampling tool from oceans. 

The specifics of the properties of the Manta Net’s structure are the following:

• The opening of the net has varying dimensions, the width varying from 30 cm to 120 cm, and the height varying from 10 cm to 75 cm. The most common values for these dimensions are 60 cm for width and 15 cm for height according to various researches. 
• Following the dimensions of the opening, the net’s length varies from 200 cm to 300 cm
• The mesh size the of the manta net vary from 300 μm to 350 μm, and the most common mesh size is 330 μm. 

1.1.2 Neuston Net Method

The Neuston net is named after the species “Neustons,” aquatic organisms that stays mostly on the surface of water that originates from planktons. As can be known for the origin of the name, Neuston nets are used for surface sampling of water surface organisms such as zooplankton, but it also used to sample marine microplastic on the surface of water used for research. 

The specifics of the properties of the Neuston nets vary significantly by its function, usage, and design, but the most common properties are the following:

• The opening of the net has varying dimensions, the opening area varying from 0.5 to 1 square meters 
• Following the dimensions of the opening, the net’s length varies from 3 to 8 meters.
• The mesh size the of the neuston nets are usually 333 μm and 335 μm, 

1.1.3 Properties of microplastics in the ocean

A crucial piece information that is essential for the filteration of microplastic is their properties. Microplastic particles are plastic pieces that consists of dimensions shorter than 5 mm, which are part of beads, fragments, pellets, film, foam, and fiber. These microplastic particles are made from different types of polymer chains, the most abundant and dominant type of polymers being polyethylene and polypropylene. 

Polyethylene microplastic particles come from plastic bottles, water tanks, and bags. A reason for these applications is because of its hydrophobic property. As the molecular structure of the polyethylene is non-polar, water, or other liquid with polar structures, is repelled and as a result is water-proof. And as polyethylene has relatively low density, it tends to float on the surface of water, which can be sampled using Manta net or Neuston net.

Polypropylene microplastic particles come from food packaging, automobiles, and electronics. Polypropylene is water-proof, as its water absorption rate is 0.01% after 24 hours in water. Also, polypropylene has a very low density, which makes it capable of being sampled by Manta net or Neuston net.

1.2 Data and Method

1.2.1 Data Base used for Data Collection

The data base used in this research is from “National Centers for Environmental Information” (NCEI), which is based on various sampling methods of microplastic particles in the ocean surface. The sampling methods that are going to be examined are Manta net method and the Neuston net method. 

The data base consists of the date the data was collected, the Latitude of the collection position, the longitude of the collection position, the ocean that the data was collected, region of collection (including subregions), measurement of the density of the particles (pieces/m³), density class range, concentration class, sampling method, references, organization of collection, and accession numbers. The database can be accessed through an article published by the NCEI which has a title “Marine Microplastics,” which will be cited below in the Work Cited section (section 4).

1.2.2 Software used for Data Analysis

In this research, the Tableau Public 2024.2 software was used to analyze and organize the data. Using this software, the pieces of data in the data base was organized into different diagrams in order to explore the different aspects of the effectiveness of the Manta net and the Neuston net method in the sampling of microplastic in marine environments.

2. Research Question

Between the Manta net sampling method and Neuston net sampling method, which method has more precision in sampling microplastic particles in marine environments?

3. Data Collection and Analysis

3.1 Measurement vs. Count of Measurement

The histogram shows the count of measurements for each measurement values according to the two sampling methods, Manta Net method and Neuston Net method represented as blue and orange respectfully. The range of values for the count of measurements are set to be larger or equal to 1, zeros in the y axis will create many holes in the histogram, which will make the data be difficult to compare. Also, for the difference to be shown clearly shown in the model, the upper maximum value for the measurement values has been set to 0.1, since the values of the count of measurement for the two models above the measurement values of 0.1 were consistently 1, which is insignificant for the comparison of the data to conclude which sampling method has higher precision than another. 

This histogram has several implications, first showing the significant difference in count of measurements by sampling method. The highest count of measurement for all measurements is 6 for Manta Net method, and 536 to the third significant figures for the Neuston Net method. The big difference in the number of values gives a portion of the indication that the Neuston Net method has a higher precision than the Neuston Net method, as the higher number of the count of measurement may show the measurements not varying in a large amount throughout repeated trials. However, the distribution of the measurements, specifically the range of the count of measurements has to be analyzed in order to conclude that the Manta Net method has a higher precision than the Neuston Net method.

The range of the count of measurement for the two marine microplastic sampling methods is a strong indication of their precision, as a larger range indicates that the values measured were more consistent throughout the measurement process, especially for the measurement value that the maximum value for the count of measurements is associated with. The range values can be deduced by the following:

As the count of measurement values for the histogram is set to have values of larger or equal to 1, the lowest count of measurement that is shown in the histogram is 1. The Manta Net method’s range of the count of measurement values can be calculated by subtracting the minimum value from the maximum, which gives 6-1=5. Therefore, the Manta Net method’s range of the count of measurement is 5. The Neuston Net method’s range of the count of measurement values can be calculated by subtracting the minimum value from the maximum, which gives 536-1=535. Therefore, the Neuston Net method’s range of the count of measurement is 535. In terms of the whole distribution of values, the range of 5 for the Manta Net method and the range of 535 for the Neuston Net method is a significant difference. And as the Neuston Net method has a larger range than the Manta Net method, it can be deduced that the Neuston Net method had consistent measurements, specifically for the measurement value of 0.00216 which the 536 count of measurements is associated with, and therefore it can be pre-concluded that the Neuston Net method has higher precision than the Manta Net method in terms of sampling marine microplastic densities.

However, there are limitations in this model. First, the region that these measurements were taken are not considered in the histogram. As precision is defined as the consistency of the measurements of microplastic densities in water within a certain region, the region that the values were taken from has to be analyzed in order to accurately conclude which sampling method has higher precision. For the conclusion made above using the histogram, the region that the measurement value of 0.00216 was measured has to be considered, and if they are taken from different regions, the conclusion will vary according to the portion of values that were taken from the different regions. Secondly, the amount of time that each sampling method used to collect the measurement values are not considered. Longer time taken for the collection of the data may result in larger counts of measurements, which can contaminate the data. The time taken for the measurements should also be taken into account in order to make an accurate conclusion for the precision of the two sampling methods.

3.2 World Map Microplastic Density Diagram Analysis

The world microplastic density diagrams show the density measurements for each measurement values according to the two sampling methods, Manta Net method and Neuston Net method represented as blue and orange respectfully. The range of values for the measurements are set to be larger or equal to 0.0007 pieces/m³, as the density is measured in this case so the values can be measured lower than 1, but has to be higher than 0. The lowest value found in the set was 0.0007 pieces/m³, which is applied to the filter in the software. Also, for the difference to be shown clearly shown in the model, the upper maximum value for the measurement values has been set to 1 pieces/m³, since the values above 1 pieces/m³ are not many in count but much higher in value, which makes the majority of the values not significantly seen as visuals as this diagram’s features higher density values as larger area of the color in respect to the sampling methods. The data base as a whole has most of the measurements done in the Pacific and Atlantic Ocean, and the other oceans’ measurements has insignificant difference between the two sampling methods. Therefore, the other regions will be neglected from the discussion for the reason of concision and significance. 

As this world map diagram shows the microplastic density in terms of regions, it can be used to evaluate the consistency of data collection in specific regions. First, to examine the Pacific Ocean region, there is not a very notable difference in the orange and blue regions shown in Figure 2 and Figure 3 respectively. However, there is a difference in area of the colored region. Figure 2 shows a variety of size of area of the colored region, consisting of many smaller areas and relatively fewer larger areas. Conversely, Figure 3 shows relatively higher consistency in the size of blue colored areas, mostly larger colored areas, also in a more compacted region in the Pacific Ocean. Therefore, it can be pre-concluded that in the Pacific Ocean region, the Manta net method has a higher precision than the Neuston net Method, as it has less random errors in the measurement in the same region.

The Atlantic Ocean region has a very significance in the measurement regions between the Manta net and Neuston net sampling methods. In figure 2, the Neuston net method shows a relatively consistent measurement in a compacted area near North America and Central America, while almost no measurement was done with the Manta net method in Figure 3. In this region, the Neuston net method shows high precision as the size of the colored areas are relatively consistent, and the region of measurement is compacted. In the European region of the Atlantic Ocean, there are relatively more measurements done using Manta net method than the Neuston net Method. In this region, the measurements made using the Manta net method has a variety of size of the colored region, having more small colored areas compared to the Neuston net method’s sampling near the North and Central America. Also, the region the measurements were made is relatively larger, which also impacts the amount of data collected by decreasing the consistency of the measured regions. Therefore, in the Atlantic Ocean region, it can be pre-concluded that the Neuston net method has higher precision than the Manta net method in marine microplastic sampling.

However, there are limitations in this model. First, the total amount of measurements done for each method was not taken account. The number of trials is crucial to deducing the precision of a sampling method, as difference in the number of trials can impact the data set to have higher or lower precision than the other method. Therefore, the conclusions made were under the assumption that the number of trials of the sampling using Manta net and the Neuston net does not have a large difference, which will allow a conclusion to be deduced from this diagram. Also, the duration of the data collection has not been considered in this diagram. If the duration of the measurement is very long, the measurement of the microplastic density for both sampling method is capable of varying as time passes, which will impact the precision for both methods as the values themselves change during the trials. Therefore, the conclusion is under the assumption that the values changed not in a large amount between trials.

3.3 Box-and-Whisker Diagram by Time vs. Measurement

The box-and-whisker diagrams show the density measurements for each measurement values according to the two sampling methods, Manta Net method and Neuston, both according to the year that the data was collected. The range of values for the count of measurements are set to be larger or equal to 0.0007 pieces/m³, as the density is measured in this case so the values can be measured lower than 1, but has to be higher than 0. The lowest value found in the set was 0.0007 pieces/m³, which is applied to the filter in the software. Also, for the time of measurement, the years that both methods commonly had been used for the convenience of comparison between the data of two sampling methods. 

To analyze the box-and-whisker plot to compare the precision of the two sampling methods, the number of outliers is the factor. As precision is defined as the consistency of measuring the values between trials of the same condition, in this case, the year that the measurement was done, the higher number of outliers shows that the method has a low precision. In order to calculate the number of outliers, the upper and lower whiskers of the box-and-whisker diagrams have to be calculated, since the values that are higher or lower respectively are outliers of the data. The calculation for the minimum value, or the lower whisker, is done as: 

Minimum Value = Q1 – 1.5(IQR)

where Q1 is the 25^th percentile of the data and IQR is the interquartile range of the data. For the upper The calculation for the maximum value, or the lower whisker, is done as:  

Minimum Value = Q3 + 1.5(IQR)

where Q3 is the 75^th percentile of the data. The values for these maximum and minimums are calculated for each year for figure 4 and 5, which is shown in the table below:

	Neuston Net	Manta Net
1987	0.0012	0.0110
1999	0.0017	0.0060
2000	0.0014	0.0240
2006	0.0013	0.0050
2009	0.0022	0.0090
2010	0.0022	0.0080
2011	0.0015	0.0097
2012	0.0015	0.0053
2013	0.0060	0.0137
2014	0.0017	0.0181
2015	0.0041	0.0040
2016	0.0031	0.0022
2017	0.0024	0.0039
2018	0.0047	0.0028
2019	0.0036	0.0033
2020	0.0084	0.0033
2021	0.0071	0.0035

	Neuston Net	Manta Net
1987	0.1188	0.0440
1999	0.2090	0.0190
2000	0.2030	0.0440
2006	0.0911	0.0190
2009	0.9774	0.9600
2010	0.7563	0.4790
2011	0.6234	0.9920
2012	0.4327	0.1590
2013	0.9961	0.9964
2014	0.2507	0.9941
2015	0.1381	0.9950
2016	0.1519	0.1605
2017	0.0862	0.6935
2018	0.3722	0.4032
2019	0.1469	0.9700
2020	0.1161	0.9101
2021	0.1568	0.9678

The count of the number of outliers for each year for the two sampling methods is shown in the table below:

	Neuston Net (#)	Manta Net (#)	Method with more outliers
1987	6	1	Neuston Net
1999	11	1	Neuston Net
2000	9	1	Neuston Net
2006	6	0	Neuston Net
2009	0	0	Neuston Net
2010	7	1	Neuston Net
2011	0	0	Neuston Net
2012	24	21	Neuston Net
2013	0	0	Neuston Net
2014	20	0	Neuston Net
2015	0	0	Neuston Net
2016	4	12	Manta Net
2017	4	0	Neuston Net
2018	7	23	Manta Net
2019	10	2	Neuston Net
2020	1	0	Neuston Net
2021	4	0

As can be seen in Table 3, the box-and-whisker diagram for the Manta net method (Figure 4) has much less years that has more outliers than the Nueston net method, which shows that the precision for each year is dependent on the consistency of the values measured in each trials in the same condition, which means that the outliers reflect an inconsistency in the measurements. Therefore, in the box-and-whisker diagram aspect in respect to the time the measurement was done, it can be pre-concluded that the Manta net method has a higher precision than the Neuston net method.

4. Conclusion

By examining the three diagrams, it could be known that Manta net method and Neuston net method has higher precision when viewed in certain aspects but lower in another; specifically, the histogram viewpoint shows that the Neuston net method has higher precision than the Manta net method, the world map view shows varying results for different regions of ocean that the measurement took place, and the box-and-whisker diagram shows that the Manta net method has higher precision than the Neuston net method. Therefore, it can be concluded that the two method has similar precision in general. However, as the world map showed more significant results in the Atlantic Ocean region where Neuston net method is shown to be more precise, it can also be concluded that the Neuston net sampling method has higher precision than the Manta net method in sampling marine microplastic. 

Works Cited

Author links open overlay panelGabriel Erni-Cassola a, et al. “Distribution of Plastic Polymer Types in the Marine Environment; a Meta-Analysis.” Journal of Hazardous Materials, Elsevier, 21 Feb. 2019, www.sciencedirect.com/science/article/pii/S0304389419301979. 

 “Marine Microplastics.” National Centers for Environmental Information (NCEI), 18 Nov. 2024, www.ncei.noaa.gov/products/microplastics. 

“Neuston.” Neuston – an Overview | ScienceDirect Topics, www.sciencedirect.com/topics/earth-and-planetary-sciences/neuston. Accessed 26 Nov. 2024. 

Nyadjro, Ebenezer S., et al. “The NOAA NCEI Marine Microplastics Database.” Nature News, Nature Publishing Group, 20 Oct. 2023, www.nature.com/articles/s41597-023-02632-y. 

Pasquier, Gabriel, et al. “Manta Net: The Golden Method for Sampling Surface Water Microplastics in Aquatic Environments.” Frontiers, Frontiers, 21 Feb. 2022, www.frontiersin.org/journals/environmental-science/articles/10.3389/fenvs.2022.811112/full. 

Sharma, Kabita. “Polyethylene: Structure, Properties, Types, Uses.” Science Info, 3 Apr. 2024, scienceinfo.com/polyethylene-structure-properties-types-uses/. 

Useon. “Polypropylene (PP) Plastic: Types, Uses and Processing.” USEON, 18 Nov. 2024, www.useon.com/polypropylene/. 

US Department of Commerce, National Oceanic and Atmospheric Administration. “NOAA National Ocean Service Education: Coastal Pollution Tutorial.” NOAA’s National Ocean Service, 22 Oct. 2019, oceanservice.noaa.gov/education/tutorial-coastal/marine-debris/md04.html. 

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