Microplastics assessment in Arabian Sea fishes: accumulation, characterization, and method development

Riaz, S.; Nasreen, S.; Burhan, Z.; Shafique, S.; Alvi, S. A.; Khan, M. A.

doi:10.1590/1519-6984.270694

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Original Article • Braz. J. Biol. 84 • 2024 • https://doi.org/10.1590/1519-6984.270694 linkcopy

Microplastics assessment in Arabian Sea fishes: accumulation, characterization, and method development

Avaliação de microplásticos em peixes do mar arábico: acumulação, caracterização e desenvolvimento de métodos

Authorship SCIMAGO INSTITUTIONS RANKINGS

Abstract

Around the globe, plastic has been entering the aquatic system and is ingested by organisms. Identification, optimal digestion method, and characterization of the polymers to trace sources are of growing importance. Hence, the present work investigated microplastics accumulation, digestion protocol efficiency, and characterization of polymers with FTIR analysis in the guts of five fishes (Lethrinus nebulosus, Rastrelliger kanagurta, Acanthopagrus arabicus, Otolithes ruber, and Euryglossa orientalis) from the Karachi coastal area, Arabian Sea. A total of 1154 microplastics (MPs) were ingested by 29 out of 33 fish species (87%). The highest average MP/fish was recorded in Otolithes ruber (54) and the lowest in Rastrelliger kanagurta (19.42). Microfibers were the most abundant shape with the highest numbers (35.52%) as compared to the rest of the MPs identified. Transparent microfibers were recorded as the highest in numbers followed by red, black, blue, and green. In this study, KOH with different concentrations and exposure times along with oxidizing agent hydrogen peroxide was tested (Protocols 3 and 4). Results showed these bases were highly efficient in obtaining optimal digestion of the samples. FTIR analysis confirmed that the majority of the polymers found in the fish guts were polyethylene and polypropylene. This study validated for the first time the presence of these polymers of plastic in marine fish from Pakistan.

Keywords: FTIR analysis; polyethylene; Karachi coast; polypropylene; Acanthopagrus arabicus

Protocols	Digestion Solutions	Concentration	Temperature °C	Exposure time	Equipment used
1	KOH	10%	60	5 days	Oven
1	NaOH	1M	60	5 days	Oven
2	H₂O₂	30%	60	2 days	Oven
2	NaCl	Saturated	60	2 days	Centrifuge
3	KOH	4M	Room temperature	3 – 4 Hours	Orbital shaker
3	H₂O₂	35%	Room temperature	3 – 4 Hours	Orbital shaker
4	KOH	4M	Room temperature	3 – 4 hours	Orbital shaker
	H₂O₂	35%
	FeSO₄	35%

Fish	Average TL (cm)	Average B.Wt (g)	Average MP/fish	Average MP/g
Lethrinus nebulosus	26.96	318	29.5	0.09
Rastrelliger kanagurta	22.24	148.28	19.42	0.13
Acanthopagrus arabicus	30.37	575.11	37.33	0.07
Otolithes ruber	47.1	1240	54	0.04
Euryglossa orientalis	24.58	186.66	39.16	0.22

Fish	Microfiber	Film	Foam	Fragment	Bead
Lethrinus nebulosus	92	31	3	13	38
Rastrelliger kanagurta	26	26	3	22	59
Acanthopagrus arabicus	93	96	16	71	60
Otolithes ruber	99	78	1	23	69
Euryglossa orientalis	100	50	2	24	59

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Instituto Internacional de Ecologia R. Bento Carlos, 750, 13560-660 São Carlos SP - Brasil, Tel. e Fax: (55 16) 3362-5400 - São Carlos - SP - Brazil
E-mail: bjb@bjb.com.br

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[1] Protocol 1: 10% KOH three times the volume of the sample was added to the beaker and kept at 60 °C in an oven for 5 days. Afterward, the sample was treated with 15 ml of NaOH and filtered. Protocol 2: 10 ml of 30% H₂O₂ was added to the beaker and kept at 60 °C in an oven for 2 days, centrifuged at 3000 rpm for 10 minutes, and filtered. 20 ml of saturated NaCl and centrifuged at 2000 rpm for another 10 minutes and filtered. Protocol 3: 30 ml of 4M KOH was added to the beaker and kept on the orbital shaker (KJ-201 BD) at 210 r/min for 1 hour. After keeping the sample at rest for 30 minutes, 5 ml of 35% H₂O₂ was added to the sample and kept on the shaker for another 30 minutes. After removal from the shaker, the sample was left for 2 hours and then filtered. Protocol 4: This protocol followed all the steps used in protocol 3 with an addition of FeSO₄ before filtration. It was used according to the gut content and feeding habits of the fish for complete digestion of hard shells and bones if any.