The research, conducted by a team led by Jamaluddin Fitrah Alam of Hasanuddin University in Makassar together with collaborators from Indonesian and Malaysian institutions and published in Environmental Monitoring and Assessment, involved sampling surface seawater and surface sediment at twelve coastal stations: nine sites located within active seaweed farms and three control sites with no farming activity. Samples were collected during two field campaigns in January and March 2022, allowing the researchers to evaluate short-term temporal variability over a two-month window. This paired design, combining spatial contrast with temporal repetition, is methodologically significant because many earlier studies of aquaculture-associated microplastics relied on single campaigns or lacked proper non-farming reference sites, making it difficult to attribute contamination to the farms themselves.

In the laboratory, the team followed established protocols for extracting microplastics from both matrices. Water samples were processed to concentrate suspended particles, while sediment samples underwent density-based separation to float plastic particles away from mineral grains. Extraction was carried out under controlled conditions with contamination safeguards, and the recovered particles were visually identified and characterized by shape, color, and size under a stereomicroscope. Because visual identification alone can overestimate microplastic counts when natural fibers or pigmented non-plastic particles are mistaken for synthetic ones, the researchers subjected a representative subset of particles to Fourier Transform Infrared (FTIR) spectroscopy, an analytical technique that shines broadband infrared light through or onto a particle and records which wavelengths are absorbed. Each polymer type—polypropylene, polyethylene, polystyrene, and so on—has a distinctive absorption fingerprint, allowing chemical confirmation of the material rather than relying on appearance alone.

The quantitative results painted a picture of widespread but spatially heterogeneous contamination. In surface seawater, microplastic abundance at seaweed-farming sites ranged from 300 to 1,600 particles per cubic meter, while non-farming sites recorded between 500 and 800 particles per cubic meter. In surface sediments, the concentrations were 10 to 170 particles per kilogram of dry weight at farming sites and 30 to 110 particles per kilogram dry weight at non-farming sites. Perhaps counterintuitively, the ranges at non-farming sites fell comfortably within the ranges observed at farming sites, suggesting that the mere presence of seaweed cultivation did not produce a detectable elevation in particle counts. The overlap was not merely marginal: farming sites contained both the highest water-column value (1,600 particles per cubic meter) and, in sediments, values that spanned nearly the full range seen across the survey.

To test whether these descriptive patterns held up statistically, the team applied a mixed-effects analysis, a modeling framework that separates fixed effects of interest from random variability among individual stations. The model tested the effects of site category (farming versus non-farming), sampling campaign (January versus March), and their interaction on microplastic abundance in each matrix. The outcome was unambiguous: none of these factors had a statistically significant effect on particle abundance in either water or sediment. In other words, neither the type of site nor the passage of time between the two campaigns explained a meaningful share of the observed variation. This null result is scientifically valuable. It indicates that short-term monitoring windows in dynamic tropical coastal systems may miss hydrodynamically driven fluctuations, and it supports the interpretation that microplastics in Takalar Waters arrive from a broad, mixed contamination signal permeating the entire nearshore environment.

The physical and chemical characteristics of the recovered particles added further forensic texture to the story. Fibers and fragments together accounted for more than 60 percent of all identified microplastics, a composition typical of coastal waters affected by domestic wastewater, fishing gear degradation, and the weathering of larger plastic debris. Fibers in particular are associated with laundry effluent, rope, netting, and textile waste, while fragments arise from the mechanical and photochemical breakdown of rigid plastic items. Blue and black particles dominated the color spectrum—consistent with the coloration of fishing ropes, nets, and containers widely used in coastal communities—and the majority of particles were smaller than one millimeter, the size fraction most readily ingested by zooplankton, filter-feeding invertebrates, and larval fish. Particle size matters ecologically because ingestibility rises sharply as particle diameter falls into the range of planktonic food items, opening pathways for transfer up marine food webs.

FTIR analysis of the representative particle subset identified polypropylene as the dominant polymer, accounting for 57 percent of the spectroscopically confirmed particles. This finding is telling. Polypropylene is a lightweight, buoyant, chemically resistant thermoplastic used extensively in ropes, nets, ropes, buoys, food containers, and packaging—all items abundant in both artisanal fisheries and everyday coastal life. Its low density relative to seawater keeps it suspended near the surface, where the study’s water sampling occurred, and where seaweed farming infrastructure also operates. The prevalence of polypropylene is therefore compatible with multiple source scenarios: aquaculture gear, fishing activity, or household waste carried by currents and rivers. The study’s authors are careful to note that FTIR analysis of a subset rather than the full particle inventory means polymer-level conclusions carry sampling uncertainty, a limitation common to microplastic research given the labor-intensive nature of spectroscopic characterization.

The context of Takalar’s economy makes these findings particularly consequential. The regency is one of Indonesia’s premier seaweed production centers, cultivating carrageenan-bearing eucheumatoid species such as Kappaphycus alvarezii that support livelihoods across coastal villages and feed a global hydrocolloid industry. Seaweed aquaculture in Indonesia is widely promoted as a sustainable, low-input form of coastal development that improves community wellbeing while requiring no feed, freshwater, or fertilizer inputs. But the industry faces growing scrutiny over contamination: edible seaweeds can concentrate microplastic particles on their mucilaginous surfaces, and prior work has documented microplastics in commercial seaweed products in Indonesia, East Asia, and elsewhere, raising food safety questions for a commodity increasingly consumed directly or as an additive. Demonstrating that farms in Takalar are not distinguishable from surrounding waters is therefore good news for producers, but it is not a clean bill of health for the environment.

The researchers also frame their results against the broader literature on microplastic dynamics in tropical archipelagic seas. Previous Indonesian studies have documented high microplastic loads in the waters around Surabaya, Banten Bay, and the Flores Sea, and archipelago-wide surveys have confirmed the ubiquity of synthetic particles in sub-surface waters throughout the Indonesian throughflow region. Ocean sediments are increasingly recognized as the ultimate global sink for marine microplastics, with particles delivered there by biofouling-driven vertical transport, aggregation with organic matter, and the biodeposition activity of filter feeders. In a seaweed-farming context, the three-dimensional structure of the crops themselves and their associated epiphyte communities can alter local hydrodynamics and particle settling, which is precisely why the absence of a farming-site effect in Takalar is informative—it suggests that any such structural effects were small relative to the overwhelming background signal from the wider coastal system.

The study’s limitations are candidly acknowledged and point the way forward. Two sampling campaigns separated by eight weeks constitute only a short-term baseline; monsoonal shifts, seasonal river discharge, and tidal cycles operate over longer periods and can redistribute particles dramatically. The authors highlight the need for broader spatial coverage spanning more of the Takalar coastline and adjacent waters, direct hydrodynamic measurements—currents, tides, and wave climate—to mechanistically explain particle transport, and direct comparisons of environmental particles with candidate source materials such as farming ropes, fishing nets, and household plastics. Polymer fingerprinting matched against these source materials could move the field from documenting contamination to attributing it, enabling targeted mitigation rather than generalized concern.

For now, the Takalar study delivers a compact but important contribution: a short-term baseline for one of Indonesia’s most economically significant seaweed regions, evidence that seaweed farming within this system is embedded in, rather than driving, the local microplastic burden, and a set of particle characteristics—fiber-dominated, sub-millimeter, blue and black, polypropylene-rich—that will help future source-tracking efforts. As global demand for seaweed-derived carrageenan and other hydrocolloids continues to grow, and as microplastic contamination of seafood attracts increasing public health attention, studies of this kind provide the evidentiary foundation on which coastal managers, certification schemes, and farming communities can build practical responses. The microplastics are there, threaded through the water and sediment of Takalar Waters; what the new data show is that the seaweed farmers are fellow inhabitants of a contaminated coastal environment, not its architects.