PFAS, Mass Death of Oysters, Design Flaws in Erosion Control—When ‘Water’ Breaks Down, Where Does Life in Setouchi Begin to Crumble?

Groundwater becomes undrinkable. Oysters growing in the sea die. Erosion control dams, meant to protect rivers, are dismantled due to design flaws.

In the regions surrounding the Seto Inland Sea, three layers of anomalies related to ‘water’ are simultaneously unfolding: groundwater, seawater, and river water. Each incident occurs in a different location and for different reasons, but they converge on a single question: When trust in water is shaken, where does life begin to crumble?

It is important to note that these issues are not the kind of stories reported as ‘major disasters.’ They quietly infiltrate daily life—turning on the tap, shucking oysters, walking along river paths—making them difficult to see. While they remain obscured, only the costs and anxieties for residents continue to accumulate.

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Groundwater—The Reality of ‘Unserved Water’ Exposed by PFAS Contamination

In the Kamiyasu area of Asaminami Ward, Hiroshima City, PFAS (per- and polyfluoroalkyl substances) have been detected in groundwater at concentrations exceeding the national provisional guideline value (50 nanograms per liter for the sum of PFOS and PFOA). Hiroshima City’s investigation has confirmed contamination at 13 sites, marking it as one of the largest PFAS contamination incidents in the city.

A structural problem emerges here. There are areas in Kamiyasu where there is no access to public water supply. For residents who have relied on groundwater, the fact that ‘this water is undrinkable’ means the very foundation of their lives, which exists beyond the tap, is disappearing.

Are there alternatives? Extending the water supply main is said to cost tens of millions of yen, and discussions about who will bear this burden have only just begun. If the residents are to shoulder the costs, the amount per household will not be insignificant. While installing water purifiers is an option, maintaining activated carbon filters capable of removing PFAS also incurs ongoing costs.

Additionally, there are health risk concerns. PFAS are known to accumulate in the body, and long-term exposure has been internationally linked to cancer risks and impacts on immune function. However, as of now, no specific health damages have been reported among residents in Kamiyasu. It is essential to distinguish between fact and speculation. Yet, it cannot be said that ‘it is safe because no harm has occurred’—residents are left in a state of uncertainty.

The essence of this issue is not just the contamination itself. When groundwater is contaminated in areas without access to public water supply, is there even a system in place to protect the residents? In urban areas, switching water pipes can address the issue. However, in regions that have depended on groundwater without public water supply, the moment contamination is discovered, there are no ‘alternatives.’ The gaps in infrastructure are made visible by environmental risks.

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Seawater—The Ongoing Anxiety of Unexplained Mass Death of Oysters

Hiroshima Prefecture is a major production area for oysters, accounting for about 60% of the national output. In this Hiroshima, reports have emerged of mass deaths among farmed oysters.

The prefecture’s investigation has not identified any clear causes directly linked to the mass deaths—such as specific pathogens or sudden changes in water quality. The investigation results stating that ‘no signs were observed’ imply that the reason for the deaths remains unknown.

Oysters are known to be extremely sensitive to changes in water quality. They are said to filter about 200 liters of seawater per day, absorbing the state of the sea directly into their bodies. While it is undeniable that a combination of factors—rising water temperatures, changes in salinity, nutrient imbalances, and trace chemicals—could be at play, it cannot be definitively stated.

Here, it is essential to clarify the boundary between fact and speculation. There is currently no scientific evidence linking PFAS contamination directly to the mass deaths of oysters. While it is theoretically possible that PFAS contamination in groundwater could affect coastal areas via rivers, there is no data to support this yet. It is crucial to avoid drawing causal relationships too easily.

However, the anxiety felt by aquaculture operators exists on a different level, independent of causation. One operator stated, ‘The scariest thing is not knowing the cause. There’s nothing we can do to address it.’ The fear of facing the next season without knowing the cause—this reflects a shaking of trust in the ‘system’ of the sea.

Oyster farming in Hiroshima is an industry with an annual production value of about 20 billion yen, and its ripple effects extend to processing, distribution, and dining. If mass deaths become normalized, it will not only affect the management of individual aquaculture operators but also the very structure of the regional economy.

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River Water—What the Design Flaw in Erosion Control Dams Reveals

The third ‘water’ is the river.

A design flaw has been discovered in the erosion control dam construction on the Jinan River in Sanyoshi City, commissioned by Hiroshima Prefecture. It has been revealed that the structure does not meet the prefectural standards, and the decision has been made to dismantle and reconstruct the completed structure.

Erosion control dams are infrastructure designed to protect downstream communities from debris flows and landslides. Hiroshima Prefecture experienced significant landslides during the 2018 Western Japan Heavy Rain, and erosion control projects are positioned as public works directly linked to the lives of residents. The fact that there was a flaw in the design raises questions not only about technical issues but also about the quality control systems of public works themselves.

The costs associated with dismantling and reconstruction will, of course, be covered by public funds—meaning taxpayer money. While specific amounts have not been disclosed, the construction costs for erosion control dams generally range from tens of millions to hundreds of millions of yen, and including dismantling costs will inevitably exceed the initial budget significantly.

What should be questioned here is not just ‘who made the mistake’ in terms of accountability. At which point in the processes of design, construction, and inspection did the checks fail to function? This needs to be viewed as a systemic issue. Was it merely a superficial inspection that led to the claim of ‘confirmation’? Was there a system in place involving multiple eyes? If preventive measures are not implemented as part of the system, the same mistakes will be repeated.

For residents, the fact remains that ‘the place that was supposed to be protected was actually not protected.’ This reality resurfaces as anxiety with every heavy rain.

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The Common Structure Reflected in the Three ‘Waters’

PFAS contamination of groundwater, mass deaths of oysters in seawater, and design flaws in erosion control for rivers. These three incidents occur in different water systems and for different reasons. However, there are commonalities in their structures.

First, the quiet erosion of everyday trust. Tap water, oysters on the table, safety along the river—because none of these are consciously recognized as ‘given,’ when they are shaken, residents are left unsure of what to rely on.

Second, the ambiguity of who bears the costs. The costs of extending the water supply, compensation for aquaculture losses, and the costs of reconstructing erosion control dams—all of these lack clear answers to the question of ‘who will pay?’ As a result, either residents, taxpayers, or both will end up bearing the burden.

Third, the absence or dysfunction of systems is being exposed. The response to contamination in areas without public water supply, the investigation system for unexplained mass deaths, and the quality control of public works—all of these reveal that the ‘system was absent’ only after problems arise.

These are not flashy disasters. That is why they are less likely to make national news. However, for the people living in the region, it is the very sensation that the foundations supporting their daily water, food, and safety are gradually tilting.

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Whose Comfort Is This Question For?

When discussing environmental issues, the question often arises: ‘What should we do?’ However, the first question should be, ‘Who is struggling at this very moment?’

Residents in Kamiyasu, where groundwater has become undrinkable. Aquaculture operators facing the next season without knowing the cause. Residents of Sanyoshi City who learned that the erosion control dam did not meet standards.

There is still no system in place to ease their burdens. Or perhaps, the systems that should have existed were not functioning.

Water does not make a sound when it breaks. The color of the water coming from the tap does not change, and the sea shines the same blue as yesterday. That is why it is necessary to pursue numerical data, listen to voices from the field, and continuously document the gaps in the system.

The water of Setouchi is quietly beginning to change. We must not overlook who stands at the forefront of that change.