Sources of Radioactive Pollution: Natural and Human-Made Emissions

Radiation is everywhere. It seeps from the ground, rains down from outer space, and even exists inside our own bodies. Every person on Earth receives a dose of radiation every single day – most of it from completely natural sources. But human activities, from nuclear power generation to medical imaging, have added new layers of radioactive pollution to this natural background. Understanding where these emissions come from is the first step toward managing their risks effectively.

What is radioactive pollution? 🔗

Radioactive pollution refers to the presence of radioactive substances in the environment where they are undesirable or at concentrations that could pose risks to living organisms. Ionizing radiation is energy released by atoms in the form of electromagnetic waves (gamma or X-rays) or particles (neutrons, beta, or alpha). When unstable atoms undergo radioactive decay, they release this energy – and the sources of that energy can be broadly divided into natural and human-made categories.

On average, radiation exposure from all natural sources amounts to about 3 millisieverts (mSv) per year, though this figure can vary by several hundred percent depending on geographic location. The remainder comes from artificial sources, primarily medical procedures. Let’s break down both categories in detail.

Natural sources of radioactivity 🔗

Natural radioactivity has been present since the formation of the Earth. Natural radionuclides include primordial radioactive elements in the Earth’s crust, their decay products, and radionuclides produced by cosmic-radiation interactions. These sources are responsible for the majority of our annual radiation exposure.

Cosmic radiation 🔗

Our solar system’s sun and other stars in the galaxy emit a constant stream of cosmic radiation that regularly hits the Earth. This radiation primarily consists of high-energy charged particles from deep space. When these particles collide with molecules in the atmosphere, they produce secondary radiation – including muons, neutrons, and X-rays – that reaches the Earth’s surface.

The dose a person receives from cosmic rays depends heavily on altitude and, to a lesser extent, latitude. The average annual dose from cosmic radiation in the United States is about 0.29 mSv, and this value approximately doubles for every 1,828-metre increase in altitude. That means residents of high-elevation cities like Denver, Colorado, receive noticeably more cosmic radiation than those living at sea level. Air travel further increases exposure, adding an average dose of about 0.01 mSv per person per year in Canada.

When cosmic rays collide with atoms in the atmosphere, they can produce radioactive atoms known as cosmogenic radionuclides. Carbon-14 and tritium are well-known examples of cosmogenic radionuclides that are continuously created by this process. While they are rare, some reach the Earth’s surface and mix into soil and water systems.

Terrestrial radiation 🔗

Elements within the Earth’s crust are a major source of natural radiation, with the main contributors being natural deposits of uranium, potassium, and thorium. These radioactive elements are present in virtually all rocks, soils, and minerals across the planet. Their natural decay releases small but measurable amounts of ionizing radiation.

Traces of these minerals are also found in building materials, meaning that exposure to terrestrial radiation occurs both indoors and outdoors. The dose from terrestrial sources varies significantly by location – areas with higher concentrations of uranium and thorium in surface soils produce higher radiation levels. Certain regions experience exceptionally high terrestrial radiation, with annual doses reaching as high as 260 mSv in Northern Iran and 90 mSv in Nigeria.

Radon gas: the largest natural contributor 🔗

Radon is the largest source of natural radiation exposure on average. It is a colourless, odourless radioactive gas produced primarily by the decay of uranium-238 in soil and bedrock. Being an inert gas, radon moves readily through the ground and into the atmosphere.

Outdoors, radon typically dilutes to harmless concentrations. The problem arises when it seeps into enclosed spaces like homes and buildings, where it can accumulate to dangerously high levels. In the United States, the average effective whole-body dose from radon is approximately 200 mrem (2 mSv) per year. Since radon accounts for the single largest portion of natural radiation exposure, the U.S. EPA recommends testing homes for radon levels regularly.

Internal radiation from the body 🔗

Radioactivity isn’t only around us – it’s inside us. Our bodies contain naturally occurring radioactive elements, including potassium-40, carbon-14, and radium-226, present in blood and bones. Potassium-40 is the most significant internal source. A 70-kilogram person carries about 4,400 becquerels of potassium-40 activity. These internal radionuclides enter the body through food and drinking water – bananas, red meat, potatoes, and Brazil nuts all contain measurable amounts of radioactive potassium.

Human-made sources of radiation 🔗

While natural radiation dominates our total exposure, human activities have introduced entirely new sources of radioactive pollution since the discovery of nuclear fission. Roughly 18% of the average American’s annual radiation dose comes from anthropogenic sources, including medical X-rays (11%), nuclear medicine procedures (4%), consumer products (3%), and other sources (less than 1%).

Medical radiation 🔗

Medical sources are by far the most significant human-made source of radiation exposure. Modern healthcare relies extensively on radiation for both diagnosis and treatment. X-ray machines, CT scanners, fluoroscopy equipment, and radiation therapy devices all contribute to patient and occupational doses.

Globally, more than 4.2 billion diagnostic radiology examinations are performed annually, along with 40 million nuclear medicine procedures and 8.5 million radiotherapy treatments. The dose from individual procedures varies enormously – a simple chest X-ray delivers about 0.2 mSv, while an abdominal CT scan can deliver a dose equivalent to hundreds of chest X-rays.

Nuclear medicine uses radioactive pharmaceuticals (radiopharmaceuticals) to diagnose and treat diseases. Patients receiving these treatments temporarily become sources of radiation themselves, requiring precautions to protect those around them.

Nuclear power and the fuel cycle 🔗

Nuclear power plants generate electricity by using fission reactions in uranium to produce steam that drives turbine generators. While these facilities are designed with multiple safety layers, they do release trace amounts of radioactive material during normal operation. However, these releases are strictly regulated and kept well below harmful thresholds.

The public also receives some exposure from the broader nuclear fuel cycle – from uranium mining and milling to the disposal of spent fuel. Each stage of this cycle presents unique radiation control challenges. The U.S. Nuclear Regulatory Commission limits maximum annual radiation exposure to individual members of the public from nuclear operations to 1 mSv.

An interesting fact: coal-burning power plants typically release more radiation into the environment than nuclear power plants, due to uranium and thorium present in coal fly ash.

Nuclear weapons testing and accidents 🔗

Atmospheric nuclear weapons testing conducted between the 1940s and 1960s spread radioactive fallout across the globe. The Limited Test Ban Treaty of 1963 largely ended atmospheric testing, though France and China continued testing until 1974 and 1980, respectively. Long-lived isotopes like caesium-137 and strontium-90 from those tests remain detectable in the environment today.

Nuclear accidents, though rare, can cause severe localised contamination. The Chernobyl disaster (1986) and the Fukushima accident (2011) both released significant quantities of radioactive material, contaminating large areas and forcing mass evacuations.

Orphan sources: an overlooked danger 🔗

An orphan source is a self-contained radioactive source that is no longer under regulatory control – one that has been abandoned, lost, or misplaced. These sources originally served legitimate purposes in medicine, industry, and research, but fell outside oversight systems.

The danger of orphan sources is that unsuspecting people may come into contact with them. Orphan sources frequently end up mixed with scrap metal, and when melted during recycling, they contaminate the recycled products and create hazardous waste requiring expensive cleanup. The Nuclear Threat Initiative has documented numerous incidents worldwide where orphan sources caused serious radiation injuries and even fatalities. The Goiânia incident in Brazil (1987), where a stolen caesium-137 source from a medical device caused four deaths and widespread contamination, remains one of the most notorious examples.

Common consumer products also contribute small amounts of radiation exposure, including certain smoke detectors, luminous watches, and older television sets.

Technologically Enhanced NORM (TENORM) 🔗

Between purely natural and clearly artificial radiation sources lies a third, often overlooked category. Technologically Enhanced Naturally Occurring Radioactive Material (TENORM) is defined by the U.S. EPA as naturally occurring radioactive materials that have been concentrated or exposed to the accessible environment as a result of human activities such as manufacturing, mineral extraction, or water processing.

The key distinction is this: TENORM doesn’t involve creating new radioactive material. Instead, human industrial activities take naturally existing radioactive elements – uranium, thorium, radium, radon – and concentrate them or bring them to the surface where people can be exposed. While individual exposure to NORM is generally not considered a special safety concern, certain work activities can give rise to significantly enhanced exposures that may need regulatory control.

Oil and gas production 🔗

The petroleum industry is one of the largest generators of TENORM waste. During drilling, a mixture of oil, gas, and formation water is pumped to the surface, and because the extraction process concentrates naturally occurring radionuclides and exposes them to human contact, these wastes are classified as TENORM.

Radioactive material accumulates as mineral scale inside pipes, as sludge in storage tanks, and in produced water separated from petroleum. Concentrations can be as high as tens of thousands of picocuries per gram in wellhead piping scale. As oil fields age and produce more water relative to oil, TENORM contamination tends to increase.

Mining and mineral processing 🔗

Mining operations – whether for uranium, rare earths, phosphate, or metals – disturb geological formations that contain natural radioactivity. The major industrial sectors generating TENORM through mining include hard rock metal mining, rare earths mining, uranium mining, copper mining, and bauxite and alumina production.

Phosphate rock mining is particularly notable. Phosphate deposits contain elevated levels of uranium and its decay products. When phosphate rock is processed into fertiliser, radioactive by-products – especially phosphogypsum – are generated in enormous volumes. This material contains radium-226 and is typically stored in large stacks near processing facilities.

Coal combustion 🔗

Burning coal releases the naturally occurring uranium, thorium, and their decay products that were locked within the coal deposits. A 1978 Oak Ridge National Laboratory paper estimated that coal-fired power plants might contribute a whole-body dose of about 19 microsieverts per year to nearby residents within a 500-metre radius. The radioactive material can be released as fly ash, and when fly ash is used in concrete manufacturing, the radioactivity becomes incorporated into building materials.

Water treatment and other sources 🔗

Even drinking water treatment generates TENORM. When water treatment facilities filter out naturally occurring radionuclides from source water, the removed material concentrates in treatment residuals and sludge. Other TENORM sources include wastewater treatment residuals, fertiliser production wastes, and even certain consumer products like granite countertops and building materials.

The EPA continues to investigate the full scope of TENORM hazards because many of these materials have only trace radioactivity, while others carry significantly higher concentrations that could elevate exposure risks.

Why does understanding these sources matter? 🔗

Managing radioactive pollution effectively requires knowing exactly where radiation comes from and in what quantities. Natural background radiation is largely unavoidable and generally poses minimal health risks at typical levels. Human-made sources, particularly medical radiation, are more controllable and subject to strict regulation. TENORM occupies a regulatory grey area – it involves naturally occurring materials, yet human activities are responsible for increasing exposure levels.

The WHO notes that acute health effects like skin burns or radiation syndrome occur only at very high doses, while lower doses may increase long-term cancer risk. The distinction between natural and artificial sources doesn’t change radiation’s biological effects – a millisievert from radon is biologically equivalent to a millisievert from an X-ray. What matters is the total dose received and the ability to control it.

Regulatory frameworks around the world, from the U.S. NRC to the WHO, work to ensure that controllable sources are kept within safe limits. For natural sources like radon, mitigation measures – such as proper home ventilation – can significantly reduce exposure.

What do you think? Given that natural sources account for the majority of our radiation exposure, should public health campaigns focus more on radon awareness and home testing rather than primarily on industrial or nuclear sources? And as industries like oil and gas production continue to generate TENORM waste, how should regulatory bodies balance economic activity with radiation protection for workers and nearby communities?

References

1. https://www.epa.gov/radon
2. https://www.epa.gov/radtown/background-radiation
3. https://www.nrc.gov/about-nrc/radiation/around-us/sources/man-made-sources
4. https://www.who.int/news-room/fact-sheets/detail/ionizing-radiation-and-health-effects
5. https://www.nti.org/risky-business/addressing-radiological-risks-posed-orphan-sources/
6. https://www.epa.gov/radiation/tenorm-oil-and-gas-production-wastes
7. https://www.epa.gov/radiation/technologically-enhanced-naturally-occurring-radioactive-materials-tenorm