Estuary of River Anjarakkandy; representational image
Shagil Kannur, Wikimedia Commons
Radiation is usually associated with nuclear plants, medical equipment or industrial accidents. But radiation is also part of the natural world. It exists in rocks, soil, sediments and even in our bodies. In most places, the levels are low enough not to cause concern. The situation is different in areas where radioactive minerals occur naturally in higher concentrations. Here, understanding where natural background radiation ends and environmental risk begins becomes much more important.
A recent study of Kerala’s Kayamkulam Estuary brings this issue into sharp focus. Published in Environmental Pollution and Management, the paper “Spatial distribution and radiological risk assessment of natural radionuclides in sediments from Kayamkulam Estuary, Kerala” examines uranium-238 (²³⁸U), thorium-232 (²³²Th) and potassium-40 (⁴⁰K) in sediments from ten locations. The study is particularly relevant because Kayamkulam lies close to Chavara, a recognised natural high background radiation area.
The numbers immediately stand out. Average concentrations were 343.8 Bq/kg for uranium-238, 583.9 Bq/kg for thorium-232 and 910.2 Bq/kg for potassium-40, all substantially above global averages. More striking, however, was the variation between locations. At the southern end of the estuary, near Chavara, uranium reached 1,834 Bq/kg and thorium 3,511 Bq/kg.
That does not mean people living around Kayamkulam are facing an immediate radiation emergency. The study does not establish that, and sediment measurements alone cannot answer the question of human exposure. What the findings do show is that some parts of the estuary deserve much closer attention, particularly because sediments are constantly being moved, deposited and disturbed.
Kayamkulam Estuary stretches for around 24 kilometres between Sankaramangalam and Karthikapalli, across parts of Kollam and Alappuzha districts. Its proximity to Chavara makes it an important setting for understanding how naturally occurring radioactive materials behave in a coastal environment. Researchers collected sediment samples from ten sites, taking triplicate samples at each location and analysing them using gamma-ray spectrometry.
An estuary is a constantly moving system. Rivers bring material from the land, tides move water back and forth, waves redistribute sediments, and floods and storms can shift material that has accumulated over years. Even the type of sediment matters. Fine-grained sediments can retain uranium and thorium more effectively because they have a greater surface area, while potassium-40 is often associated with minerals such as feldspar and mica.
This helps explain the sharp differences across Kayamkulam. The northern stations generally recorded lower concentrations, while S9 and S10, near Chavara, recorded the highest levels of all three radionuclides. The researchers associate this pattern mainly with geological conditions, sediment characteristics and the area's proximity to the Chavara high-background radiation zone. They also acknowledge that human activities may influence how these elements are distributed.
That qualification is important. The study does not conclude that industrial activity is responsible for the elevated radiation levels. Instead, it points towards a more complicated interaction between natural geology, sediment movement and possible human influences. Future research will need to separate these factors more clearly.
The sediments themselves are central to the story. Radionuclides can remain attached to sediment particles for long periods, but they can also be moved when those sediments are disturbed. Floods, storms, dredging and construction can all change where sediment settles. The radiation map of the estuary today, therefore, may not look the same after a major disturbance.
The researchers did more than measure radionuclide concentrations. They also calculated indicators such as radium equivalent activity, absorbed dose rate, annual effective dose, excess lifetime cancer risk and internal and external hazard indices.
Some results are particularly striking. Mean radium equivalent activity was 1,248.9 Bq/kg, compared with the cited global benchmark of 370 Bq/kg. The average absorbed dose rate was 549.7 nGy/h, against a world average of 59 nGy/h. Estimated annual outdoor effective dose averaged 0.67 mSv/year, although individual locations ranged from 0.19 to 3.77 mSv/year.
The strongest results came from S10. Radium equivalent activity reached about 7,055 Bq/kg, while the absorbed dose rate exceeded 3,077 nGy/h. The estimated annual effective dose was 3.77 mSv/year. The gamma representative level index reached 24.53, while the external and internal hazard indices were 19.05 and 24.01 respectively.
These figures deserve attention, but they need to be read carefully. High concentrations of radionuclides in sediment do not automatically mean that people living nearby are receiving the same radiation dose. Actual exposure depends on how people use and interact with their surroundings. Someone who regularly handles exposed sediment, works in dredging or spends long periods in a hotspot could have a very different exposure pathway from someone with little contact with the sediment. Consumption of contaminated aquatic organisms, if such contamination is established, could represent another pathway.
This is why the next stage of research must go beyond sediment measurements. The study calls for epidemiological investigations and wider monitoring of soil and water, particularly around identified hotspots.
The distinction between hazard and risk is particularly important here. The study identifies elevated environmental radiological hazards in parts of the estuary. It does not, by itself, establish that Kayamkulam residents are experiencing specific health effects. That requires exposure assessment and, where appropriate, epidemiological research.
The right response, therefore, is neither to dismiss the findings because the radiation is naturally occurring nor to present them as proof of an immediate public-health crisis. The study provides a warning signal. The next task is to understand what that signal means for the people, ecosystems and livelihoods connected to the estuary.
The immediate priority should be to move beyond a one-time study and build a long-term monitoring system for Kayamkulam, Chavara and surrounding coastal areas. Ten sampling locations provide a useful baseline, but they cannot capture all the changes taking place in an estuary. Sampling should be repeated across seasons and after floods, cyclones and other events that can disturb and move sediments. Sediment cores could also show how radionuclide levels have changed over time, helping distinguish long-standing geological patterns from newer changes.
Radiation monitoring should become part of coastal and sediment management. Authorities need to look at radiation levels alongside sediment type, erosion, deposition, tidal movement, dredging and industrial activity. Dredging deserves particular attention because disturbing large quantities of sediment could redistribute naturally enriched radioactive material. Sediment from high-background areas should therefore be tested before it is dredged, transported or reused.
The investigation should also move into the food chain. Researchers point to the possibility of radionuclides entering and accumulating in aquatic organisms. Fish, shellfish and other benthic organisms from high-concentration areas should be tested alongside water and sediment. This would help establish whether elevated sediment concentrations are actually reaching the food chain.
There is also a strong case for making the findings easier for local communities to understand. People living around the estuary should be able to access monitoring results, sampling locations and straightforward explanations of what the numbers mean. Good communication is essential: communities need neither false reassurance nor unnecessary alarm.
Most importantly, Kerala needs to establish where the radionuclides are coming from. The study points to natural geology, mineral composition and sediment movement, while also raising the possibility of phosphate-related inputs. Uranium concentrations reached 148.5 ppm and thorium 864.78 ppm. More detailed mineralogical and isotopic studies could help separate natural enrichment from human influences. That distinction matters because natural radiation cannot simply be removed, but human activities that increase exposure or redistribute radioactive material can be managed.
The Kayamkulam study is ultimately about more than radiation. It exposes a larger challenge in the way coastal risks are managed. Estuaries are divided among departments dealing with fisheries, pollution, water quality, coastal regulation, industry and disaster management. But the environment does not follow administrative boundaries. What happens to sediment or water in one part of an estuary can affect another.
The uneven radiation pattern makes a blanket assessment particularly inadequate. Some locations recorded lower concentrations, while others, especially S10, emerged as clear hotspots. The study found that every sampling site crossed at least one recommended limit for one or more of the radiological indicators assessed. That makes it important to understand where the hotspots are, how stable they are and whether the radioactive material is moving.
The answer should not be fear, but neither should it be complacency. Kerala needs better science, regular monitoring and clearer planning.
An integrated Kayamkulam–Chavara radiological monitoring programme would be a sensible starting point. Radiation measurements should be combined with sediment studies, aquatic ecology, water-quality monitoring and exposure assessment. Hotspots should be mapped and followed over several years rather than assessed only once. The findings should feed directly into decisions on dredging, coastal construction, sediment disposal and environmental clearances.
Climate change makes this even more important. Stronger floods, intense rainfall and coastal storms can move and resuspend sediments that have remained undisturbed for years. Climate change does not create these naturally occurring radionuclides, but it can change the conditions under which they are transported and redistributed.
The lesson from Kayamkulam is straightforward: natural does not automatically mean harmless, just as elevated readings do not automatically mean a public-health crisis. What matters is understanding how exposure can occur and acting on the evidence.
The study has given Kerala an important baseline. The next step is to turn that evidence into sustained monitoring, honest communication with local communities and better coastal planning. The aim should be simple: understand the warning now, while there is still time to manage the risks it may reveal.