Rainwater in Jakarta Carries Plastic Additives, Study Finds

Rain falling on one of the world’s most densely populated coastal megacities is not as clean as it looks. A new study from researchers at Universitas Indonesia and Cheng Shiu University in Taiwan has found evidence of plastic contamination in both rainwater and water stored in rainwater harvesting systems in the Greater Jakarta coastal region of Indonesia, raising fresh questions about how urban plastic pollution travels through the atmosphere and into the water supplies that households increasingly depend on.

The research, published in the journal Microplastics and Nanoplastics, focused on two coastal sampling sites in Greater Jakarta, a metropolitan area of more than thirty million people where land subsidence, saltwater intrusion and failing piped infrastructure have pushed many communities toward alternative water sources. Rainwater harvesting systems, which collect and store rooftop runoff for domestic use, have become an attractive coping strategy in this setting. But until now, little was known about whether the water these systems capture carries microscopic plastic particles and the chemical additives that leach from plastic products.

The team, led by Annisa Fitri Mustafa of the School of Environmental Sciences at Universitas Indonesia, together with colleagues including corresponding author Hayati Sari Hasibuan, set out to establish a baseline. Rather than counting plastic particles visually, as many earlier studies have done, they employed two of the most sensitive analytical techniques available for environmental contamination. Microplastic polymers were identified using pyrolysis gas chromatography-tandem mass spectrometry, known as Py-GC/MS/MS, a method that thermally breaks plastic molecules into characteristic fragments that can be identified with high confidence. Plastic additives were measured with ultra-high performance liquid chromatography-tandem mass spectrometry, or UHPLC-MS/MS, which can detect trace organic chemicals at extremely low concentrations.

The results paint a nuanced picture. In samples drawn from the rainwater harvesting systems, the researchers detected three common plastic polymers: polyvinyl chloride, or PVC, polyethylene terephthalate, or PET, and polymethyl methacrylate, or PMMA. PVC is ubiquitous in pipes, gutters and building materials, while PET is the polymer of beverage bottles, and PMMA, better known as acrylic, appears in construction and consumer products. Critically, the polymer composition and concentrations differed between the two sampling locations, suggesting that contamination is not uniform but shaped by local conditions.

That site-specific variation matters, the authors argue, because it hints at multiple contamination pathways. Rainwater passing over roofs, gutters and storage tanks can pick up fragments shed by the harvesting infrastructure itself, particularly where PVC piping and plastic tanks are involved. At the same time, atmospheric deposition may deliver plastic particles and dissolved additives directly into open storage. Jakarta’s intense urban activity, from traffic and waste burning to construction, generates a constant load of airborne particles, and plastic debris is increasingly recognized as a component of that urban aerosol. The study suggests that the observed contamination may reflect interactions among local environmental conditions, atmospheric deposition and the materials of the harvesting systems themselves.

The chemical side of the analysis proved equally revealing. After careful blank correction, the researchers detected plastic additives in both rainwater and rainwater harvesting system samples. These additives, which include compounds such as bisphenol A and phthalate plasticizers like DEHP, DBP and DEP, are incorporated into plastics to improve flexibility, durability or heat resistance. They are not chemically bound to the polymer matrix, meaning they can migrate out of plastic products and into surrounding water over time. Several of these compounds are recognized endocrine disruptors, capable of interfering with hormone systems even at low doses, which is why their presence in harvested drinking water sources warrants attention.

Intriguingly, no target microplastic polymers were detected above the method detection or quantification limits in the analyzed rainwater sample, even though additives were found in it. The authors are careful about how this discrepancy is interpreted. One possibility is that dissolved or particulate chemical additives travel through the atmosphere differently from intact polymer particles, or that the limited sampling did not capture polymer-contaminated rainfall events. The study was explicitly designed as a preliminary baseline investigation with a limited sampling design, and the researchers acknowledge potential blank-related uncertainty for some additives and the absence of direct source attribution. They stress that the findings should be read as preliminary baseline evidence rather than definitive measurements of exposure.

That cautious framing is a hallmark of the study’s quality assurance approach. The analytical work relied on method detection limits, quantitative detection limits, initial and continuing calibration verification, and multiple reaction monitoring in the tandem mass spectrometers, all standard tools of good laboratory practice. Pyrolysis-gas chromatography with tandem mass spectrometry is increasingly favored in microplastics research because it avoids some of the visual misidentification problems that plague microscopy-based counts, and pairing it with liquid chromatography-tandem mass spectrometry allows both the particles and their chemistry to be assessed in parallel.

For Jakarta, the findings arrive at a politically and environmentally sensitive moment. Large parts of the Greater Jakarta coastal plain are sinking by several centimeters each year, and Indonesia is proceeding with plans to relocate its capital while investing heavily in water infrastructure. In neighborhoods where piped water is unreliable or saline, rooftop harvesting is often promoted as a resilient, decentralized solution. The new results do not argue against rainwater harvesting, but they do suggest that system design, materials selection and maintenance could influence the quality of stored water. First-flush diversion, filtration, and the use of less additive-rich storage materials are among the practical questions that follow from this work.

The authors call for future studies with expanded sampling, improved quality control and direct characterization of rainwater harvesting system materials, which would allow contamination to be traced to specific components of the collection infrastructure. They also point toward the need to understand how atmospheric deposition varies across the urban landscape, and whether seasonal monsoon dynamics in the Indonesian archipelago modulate the delivery of plastic particles and additives to rooftop catchments. As microplastics research matures worldwide, studies like this one underscore that the plastic pollution problem is not confined to rivers and oceans. It now extends into the sky above cities and into the rain that falls from it, quietly entering the alternative water systems on which millions of coastal residents may depend.

Subject of Research: Microplastic polymers and plastic additives in rainwater and rainwater harvesting systems in coastal Jakarta, Indonesia

Article Title: Microplastics and plastic additives in rainwater and rainwater harvesting systems in the Greater Jakarta Coastal Region, Indonesia

Article References: Mustafa, A. F., Ika, A. R., Chen, J.-W., Hartono, D. M., Hasibuan, H. S., & Chang-Chien, G.-P. (2026). Microplastics and plastic additives in rainwater and rainwater harvesting systems in the Greater Jakarta Coastal Region, Indonesia. Microplastics and Nanoplastics. https://doi.org/10.1186/s43591-026-00228-y

Image Credits: AI Generated

DOI: 10.1186/s43591-026-00228-y

Keywords: microplastics, plastic additives, rainwater harvesting, Jakarta, Indonesia, PVC, PET, PMMA, phthalates, bisphenol A, coastal water quality, Py-GC/MS/MS