Microplastic Detection in Lawaye River, San Juan, Batangas City,

Philippines Using Front-Face Fluorescence Spectroscopy

Jowi Rapha Cruz

1,2 a

, Jowi Tsidkenu Cruz

, Jejomar Bulan

, Aubrey Razon

Michaelina Smith

and

Galvez Maria Cecilia

1 b

Environment and RemoTe Sensing Research (EARTH) Laboratory, Department of Physics, College of Science,

De La Salle University, Manila 0922, Philippines

MS Fellow, Career Incentive Program, Department of Science, Science Education Institute, DOST Main Building,

General Santos Avenue, Brgy. Central Bicutan, Taguig, Metro Manila, Philippines

Keywords: Micro-Plastics (MP), Fluorescence Spectroscopy, Surface Water, Filtration.

Abstract: The Lawaye River in San Juan, Batangas plays a crucial role in sustaining the very complex local ecosystem

within the city. As it is utilized for irrigation for agricultural activities, household needs, fishing, and tourism.

However, increasing human activities pose significant threats to these vital bodies of water. Pollution,

particularly from microplastics, is a major concern due to its detrimental impacts on aquatic life and potential

human health risks. Studies have demonstrated the widespread presence of microplastics in various organisms

and their ability to accumulate in vital organs, including the brain. This study investigated the presence of

microplastics in the Lawaye River. Surface water samples (50 cm depth) were collected and subjected to

initial debris removal. Subsequently, samples were treated with a KOH solution to dissolve organic matter

and filtered through a 0.3 mm glass filter. Microscopic examination revealed the presence of microplastics in

various forms, including fragments, fibers, and films. Further fluorescence spectroscopy analysis, based on

known excitation-emission wavelengths of different plastics, suggested the potential presence of

microplastics, specifically Polypropylene (PP) and potentially Polystyrene (PS) which is commonly used on

single-use plastics.

1 INTRODUCTION

The Lawaye River is a freshwater class B type of

River located in San Juan, Batangas plays a crucial

role in sustaining the complex local ecosystem within

the city. As it is being utilized for irrigation for

agricultural activities from farming, rice paddies,

crop cultivation, household needs, fishing, and

tourism, it faces increasing pressure from human

activities such as agricultural runoff, pollution, being

near the town’s public market, and due to the growing

population in Batangas (Rochman, Hoh, Kurobe,,

Teh, & & Teh, 2023) This intensified human activity

has resulted in a steady increase in pollution, posing

a serious threat to the aquatic ecosystems and the

organisms that inhabit them. Recent studies, such as

that of Ziani on Microplastics have documented the

alarming presence of microplastics in various animal

https://orcid.org/0009-0003-2179-2756

https://orcid.org/0000-0001-5505-1778

species. These tiny plastic particles can accumulate in

vital organs, including the liver, spleen, heart, lungs,

and even brain, due to their ability to cross the blood-

brain barrier (Ziani, et al., 2023). Given the

persistence of plastics in the environment – taking

centuries to fully degrade while readily fragmenting

into smaller, more easily ingested microplastics

(Andrady, 2011) – this creates a pathway for

microplastics to enter and ascend the marine food

web.

Consequently, the presence of microplastics in

aquatic ecosystems poses a significant and ongoing

threat to the entire food chain. Addressing this

concern requires efficient and cost-effective

analytical techniques that can readily identify their

presence in the environment, such as fluorescence

spectroscopy. This technique offers a powerful yet

affordable alternative to methods in identifying the

Cruz, J. R., Cruz, J. T., Bulan, J., Razon, A., Smith, M. and Cecilia, G. M.

Microplastic Detection in Lawaye River, San Juan, Batangas City, Philippines Using Front-Face Fluorescence Spectroscopy.

DOI: 10.5220/0013444500003902

Paper published under CC license (CC BY-NC-ND 4.0)

In Proceedings of the 13th International Conference on Photonics, Optics and Laser Technology (PHOTOPTICS 2025), pages 173-177

ISBN: 978-989-758-736-8; ISSN: 2184-4364

173

presence of microplastic as well as characterizing

them like Scanning Electron Microscopy (SEM),

which can be costly and destructive to the sample.

Fluorescence spectroscopy works by sending off light

to the plastic particles with a specific wavelength of

light, causing them to excite and then emit a

fluorescent at a different, and usually longer

wavelength. The excitation, emission light, or

fluorescence is unique to each and different types of

plastic that can be used to differentiate them from one

another. By analyzing the fluorescence spectrum,

researchers can determine the types of plastics present

in a sample (Syed, Aisha, Murugesan, Hill, & Rozhin,

2024). This technique is particularly useful in

identifying and quantifying the number of

microplastics present in a sample due to its high

sensitivity and ability to detect even the smallest

particles (A. L. Lusher, N. A. Welden, P., & M.,

2016). To assess the extent of microplastic

contamination and to test the detection capacities of

fluorescence spectroscopy presence of microplastic

in filtered specimens in the Lawaye River, the study

employed fluorescence spectroscopy accompanied by

Microscopy to check for the presence of microplastic

and to identify and characterize the types of

microplastics present in surface water samples.

2 MATERIALS AND METHODS

The surface water samples were collected from the

bridge that connects 2 roads in Lawaye River near the

public city market in Batangas City, Philippines, with

the coordinates 13°49'20"N 121°23'48"E as indicated

in Figure 1.

2.1 Collection of Samples

The collection of water samples and sample

preparation follows the methodology described by

Gabriel, et al. (2023) with minimal changes. Water

samples were collected using a stainless-steel bucket,

taking a 10-liter sample at a depth of up to 50cm, and

subsequently filtered using a 0.3 mm metal sieve to

remove large debris before being transferred to amber

bottles for storage.

2.2 Sample Preparation

To prepare the sample for an initial investigation

using Olympus BX51 Microscope, the samples were

prepared by mixing them with a 2:1 sample ratio to a

20% concentration of KOH and water solution. KOH

* Coordinates: 13°49'20"N 121°23'48"E

Figure 1: Location of Lawaye River Samples.

is an effective chemical that digests organic matter

without damaging other components. The samples

were then stirred for an hour. Due to the uneven

heating capabilities of the magnetic stirrer present,

the samples were not heated and just maintained at

room temperature for 1 hour while stirring to prevent

the degradation of the physical and chemical

properties of the microplastic. The resulting mixture

containing the microplastics was then filtered using a

0.3 mm Whatman GF/C glass filter on a vacuum

filtration setup consisting of a Glass filter between the

Buchner funnel and the Buchner flask held together

by a clamp the vacuum is connected to the Buchner

Flask to create a negative pressure at the bottom of

the setup as shown in Figure 2. After the sample were

passed through the filter, the glass filter was carefully

removed using clean tongs placed in a clean petri

dish, and airdried inside a vacuum chamber for 2

days.

2.3 Microscopy

Using an Olympus BX51 with an eyepiece

magnification of 10x and an objective lens

magnification of 4x, giving us a total of 40X

magnification, each dried filter was visually

examined to identify and categorize the types of

microplastics present, such as fibers, fragments, and

others. The length and colors were also noted through

visual inspection using NIS ELEMENTS D 4.6.000

software of NIKON.

SpecSI 2025 - Special Session on Spectroscopy and Spectral Imaging

174

Figure 2: Water Filtration Setup.

2.4 Fluorescence Spectroscopy

Due to the limitations of access in the laboratory, the

next analysis was done after 2 weeks from the

digestion of organic matter within the sample.

Fluorescence spectroscopy was performed in the

filter sample. The filter sample is prepared by cutting

the filtered sample into a strip where the suspected

microplastic is located as shown in Figure 3 (left).

Figure 3: Cutting of the sample (Left) and Sample in the

Cuvette (Right).

A front-face-fluorescence spectroscopy (FFFS)

was performed on the air-dried filter. The block

diagram of the FFFS system is shown in Figure 4.

The light source is a broadband Xenon lamp with a

spectral range of 120 to 2000 nm. Light from the

lamp was guided by an optical fiber to a scanning

monochromator (MonoScan 2000) for wavelength

selection. From the monochromator, an optical fiber

directs the beam to the filter that was placed inside the

cuvette in such a way that the incident light is at a

right angle to the emitted light that goes through

another optical fiber that is connected to the

spectrometer, which is an Ocean Optics 2000+ XR1-

ES, to measure the fluorescence emission spectrum.

A fluorescence excitation-emission (FLE) map was

then obtained by following the known excitation-

emission peaks from Table 1 for the filter with known

microplastics.

Figure 4: Block diagram of the FFFS set-up.

Table 1: Plastic Fluorescence Excitation - Emission

Pairings (Syed, Aisha, Murugesan, Hill, & Rozhin, 2024).

Plastic

Excitation

(Peak)

Emission

(Peak)

Polystyrene

(PS)

300–400 nm

(360 nm)

350–450 nm

(380 & 405)

Polyethylene

terephthalate

(PET)

330 and 380nm

380 and 485 nm

(360nm)

370 and 510nm

400 to 530 nm

(390)

Polypropylene

(PP)

360 and 380 nm

385 and 430 nm

(370)

400 and 550

425 and 550

(455)

3 OBSERVATIONS

Microscopic examination of surface water samples

from the Lawaye River revealed the presence of

microplastics ranging in size from 0.5 µm to 1000

µm, consistent with the generally accepted definition

of microplastics as particles between 1 µm and 5000

µm (Syed, Aisha, Murugesan, Hill, & Rozhin, 2024).

The observed microplastics exhibited known

morphologies of microplastics, including fragments

and fibers, and a range of colors, with blue, red, and

green being the most common as illustrated in Figure

The sample underwent fluorescence spectroscopy

to identify the type of plastic detected within the film.

To identify the type of plastic, the excitation-emission

pairings were analyzed.

Microplastic Detection in Lawaye River, San Juan, Batangas City, Philippines Using Front-Face Fluorescence Spectroscopy

175

Legend: *500 px = 500 um

Figure 5: Sample Microphotograph.

Fluorescence analysis within the visible light

spectrum (400-420 nm) revealed a broad emission

peak between 490-550 nm. Figure 6. This emission

profile is characteristic of Polypropylene (PP) plastics

as it is compared with the emission-excitation peak of

PP plastic in Table 1, suggesting their presence within

the sample.

Figure 6: Visible Light Fluorescence Analysis.

UV fluorescence (300-320) Figure 7 Reveals a

broad peak between 370-420 nm. A prominent peak

is observed at an excitation wavelength of 310 nm,

with emission peaking around 373 nm. This spectral

profile strongly suggests the presence of Polystyrene

(PS), as it exhibits greater similarity to the

characteristic PS emission-excitation wavelengths

(Table 1) compared to Polyethylene Terephthalate

(PET), which typically displays a broader emission

spectrum from 370-510 nm with a peak at the UV

range.

The presence of microplastics, specifically

Polypropylene (PP) and potentially Polystyrene (PS),

in the Lawaye River highlights the significant impact

of human activity on aquatic ecosystems. These

plastic types, commonly found in household items

like diapers, napkins, and disposable food ware,

underscore the pervasive nature of plastic pollution

(Dayrit, 2019).

Figure 7: Ultraviolet Fluorescence Analysis.

As plastic consumption continues to rise, the

development of rapid, non-destructive, and label-free

methods for microplastic analysis across various

environments becomes crucial. This study

demonstrates the effectiveness of fluorescence

spectroscopy in characterizing microplastics, offering

a promising approach for future investigations into

the extent and impact of plastic pollution.

4 RECOMMENDATIONS AND

SUGGESTIONS

For future research, we recommend expanding the

use of Excitation-Emission Matrix (EEM)

spectroscopy to comprehensively map the excitation

and emission spectra of various microplastic

polymers. By establishing a robust spectral library of

common microplastic types, we can deconvolute

complex EEMs and accurately identify and quantify

the prevalent microplastic types within riverine

environments. Furthermore, incorporating an internal

standard and refining data processing methods to

minimize spectral interferences will enhance the

accuracy and reliability of these analyses.

ACKNOWLEDGEMENTS

The authors acknowledge the support from DOST-

SEI Career Incentive Program for the financial

support and the support from De La Salle University

RGMO Project “Fluorescence Detection of

Microplastics in Surface Waters” with Project no:

02 F R 1TAY23-1TAY24.

SpecSI 2025 - Special Session on Spectroscopy and Spectral Imaging

176

REFERENCES

A. L. Lusher, N. A. Welden, P., S., & M., C. (2016).

Sampling, isolating and identifying microplastics

ingested by fish and invertebrates. Analytical Methods,

1346-1360.

AAT Bioquest, Inc. (2025). Quest Graph™ Spectrum

[Polystyrene]. AAT Bioquest.

Andrady, A. L. (2011). Microplastics in the marine

environment. Marine Pollution Bulletin, 1596-1605.

Dayrit, F. (2019). Overview on Plastic Waste: The

Philippine Perspective. Transactions National

Academy of Science & Technology Philippines.

Gabriel, A. D., A. R., L. A., & &. B. (2023). Riverine

Microplastic Pollution: Insights from Cagayan de Oro

River, Philippines. International Journal of

Environmental Research and Public Health, 20(12),

6132.

Isuke Ouchi, Ryo Miyamura, Makoto Sakaguchi, Hosaka,

S., Kitagawa, M., & '. (1999). Excitation and Emission

Spectra of Polyethylene Terephthalate and

Polyethylene 2,6-Naphthalate Films. Polym. Adv.

Technol., 195-198.

Rochman, C. M., Hoh, E., K. T., Teh, S. J., & & Teh, F. C.

(2023). Global impacts of marine plastics debris on

ecosystem services. Proceedings of the National

Academy of Sciences, pp. 15434–15439.

Syed, A. I., Aisha, B., Murugesan, R. C., Hill, D., &

Rozhin, A. (2024). Excitation–Emission Fluorescence

Mapping Analysis of. Photochem, 488-500.

Ziani, K., Ioniță-Mîndrican, C. -B., Mititelu, M., Neacșu, S.

M., Negrei, C., Moroșan, E., . . . & Preda, O. -T. (2023).

Microplastics: A Real Global Threat for Environment

and Food Safety: A State of the Art Review. . Nutrients.

Microplastic Detection in Lawaye River, San Juan, Batangas City, Philippines Using Front-Face Fluorescence Spectroscopy

177