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Radioactivity concentrations in Soils in Beijing, China from 2019 to 2025

This study analyzed 137 soil samples from all 16 administrative districts of Beijing between 2019 and 2025, finding that natural radionuclide concentrations (²²⁶Ra, ²³²Th, ⁴⁰K) were generally consistent across years but higher in mountainous areas, while artificial ¹³⁷Cs levels remained low, indicating no significant industrial releases and overall values within global ranges.

Original authors: qinghua Meng, yuxia kong, bin bai, yongzhong ma, limeng cui

Published 2026-07-27

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CC BY 4.0

Original authors: qinghua Meng, yuxia kong, bin bai, yongzhong ma, limeng cui

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the ground beneath your feet as a giant, silent library. Most of the books on the shelves are just regular dirt and rocks, but hidden inside are tiny, invisible "ghosts" called radionuclides. Some of these ghosts have been hanging out since the Earth was formed, like ancient ancestors who never leave the house (these are natural radionuclides). Others are more recent visitors, like travelers who arrived after big global events in the mid-20th century (these are artificial radionuclides). While we can't see them, they are always there, gently whispering energy into the world. Scientists care about these whispers because if the volume suddenly gets too loud, it could mean someone is messing with the library—perhaps by dumping industrial waste or having a nuclear accident. So, checking the soil is like listening to the library's background noise to make sure everything is still quiet and safe.

This is exactly what a team of researchers from the Beijing Center for Disease Prevention and Control did in a new study. They decided to take a deep dive into the soil of Beijing, China, acting like radio-active detectives. Between 2019 and 2025, they didn't just look at one spot; they traveled to all 16 districts of the city, collecting 137 different soil samples. Think of it as taking a giant, multi-year "sniff test" of the city's dirt to see if the background noise of radiation had changed. They were specifically listening for four types of radioactive "ghosts": Radium-226, Thorium-232, Potassium-40, and Cesium-137. The first three are the natural, long-term residents, while Cesium-137 is the artificial one, usually left over from old nuclear tests or accidents.

The team used a super-sensitive machine, kind of like a high-tech Geiger counter on steroids, to count how much energy these ghosts were giving off. They found that the natural residents were behaving exactly as expected. The levels of Radium-226, Thorium-232, and Potassium-40 stayed pretty steady year after year, with average numbers hovering around 25.6, 31.4, and 585 Bq/kg respectively. The data showed no significant changes from 2019 to 2025, suggesting that no one was dumping extra radioactive trash into the soil during this time.

However, the geography of Beijing did play a role in the story. The city has mountains in the northwest and flat plains in the southeast. The researchers discovered that the soil in the mountains had slightly higher levels of Radium-226, Thorium-232, and Cesium-137 compared to the flat plains. It's as if the mountains are holding onto these radioactive particles a bit tighter than the flatlands, but this is a natural difference, not a sign of pollution.

When it came to the artificial ghost, Cesium-137, the news was very reassuring. The average level found was a tiny 0.86 Bq/kg. The researchers noted that this number is actually lower than what was found in Beijing decades ago, which makes sense because Cesium-137 slowly fades away over time (it has a half-life of about 30 years). Crucially, the study found no evidence of any new, detectable releases of this artificial radionuclide in the soil between 2019 and 2025.

In the end, the paper concludes that the soil in Beijing is safe and stable. The levels of natural radiation fall right within the normal range seen all over the world, and there are no signs of new industrial pollution or nuclear leaks. The researchers suggest that keeping an ear on this background noise is still important, just in case the story changes in the future, but for now, the library of Beijing's soil is quiet, safe, and behaving exactly as nature intended.

Technical Summary: Radioactivity Concentrations in Soils in Beijing, China (2019–2025)

Problem Statement
Soil serves as a fundamental component of terrestrial ecosystems and a primary medium for human radiation exposure. While natural radionuclides (such as $^{226}\text{Ra}$ , $^{232}\text{Th}$ , and $^{40}\text{K}$ ) and artificial radionuclides (specifically $^{137}\text{Cs}$ ) are ubiquitous in the environment, continuous and region-specific monitoring is essential to distinguish natural background variations from potential anthropogenic contamination. In Beijing, rapid urbanization and industrial adjustments, including changes in coal consumption, necessitate an updated assessment of soil radioactivity to establish a reliable baseline and detect any significant industrial releases or artificial radionuclide deposition.

Methodology
The study conducted a comprehensive investigation across all 16 administrative districts of Beijing over a seven-year period (2019–2025).

Sampling Strategy: A total of 137 soil samples were collected annually between March and April. Sites were selected in flat, open areas using a five-point sampling method to collect surface soil (0–5 cm depth). Visible impurities were removed, and subsamples were mixed to form homogeneous composites.
Sample Preparation: Samples were oven-dried at 105°C, sieved through a 50-mesh (300 µm) sieve, and sealed in polyethylene containers. They were stored for four weeks to allow daughter radionuclides to reach radioactive equilibrium with their parents.
Instrumentation: Measurements were performed using a GEM-MX7080P4 p-type high-purity germanium (HPGe) gamma-ray spectrometer equipped with a composite lead shield. The system was calibrated using standard reference materials traceable to the National Institute of Metrology, China.
Analysis: Specific gamma-ray peaks were analyzed to determine activity concentrations: $^{226}\text{Ra}$ (via $^{214}\text{Pb}$ and $^{214}\text{Bi}$ peaks), $^{232}\text{Th}$ (via $^{208}\text{Tl}$ and $^{228}\text{Ac}$ peaks), $^{40}\text{K}$ , and $^{137}\text{Cs}$ . Counting times ranged from 48 to 72 hours.
Statistical Approach: Data analysis utilized SPSS software. Pearson correlation was used for relationships between radionuclides, while the Kruskal-Wallis test and Mann-Whitney U test assessed differences across years and land types (plains vs. mountains), with Bonferroni correction applied for multiple comparisons.

Key Results

Temporal Stability: The annual mean activity concentrations for the study period were:
- $^{226}\text{Ra}$ : 23.2 – 27.6 Bq/kg (7-year mean: 25.6 Bq/kg)
- $^{232}\text{Th}$ : 29.2 – 32.4 Bq/kg (7-year mean: 31.4 Bq/kg)
- $^{40}\text{K}$ : 563 – 621 Bq/kg (7-year mean: 585 Bq/kg)
- $^{137}\text{Cs}$ : 0.72 – 1.06 Bq/kg (overall mean: 0.86 Bq/kg)
  No statistically significant differences were observed in the activity concentrations of any of these radionuclides across the years 2019 to 2025 ( $P > 0.05$ ).
Spatial Variations:
- Topography: Samples collected from mountainous areas showed significantly higher concentrations of $^{226}\text{Ra}$ , $^{232}\text{Th}$ , and $^{137}\text{Cs}$ compared to those from plains ( $P < 0.05$ ).
- Potassium: No significant difference in $^{40}\text{K}$ concentrations was found between mountain and plain soils ( $P > 0.05$ ).
Correlations: A strong positive correlation was identified between $^{226}\text{Ra}$ and $^{232}\text{Th}$ ( $r = 0.896, P < 0.001$ ), suggesting a shared geological origin.
Comparative Analysis: The $^{137}\text{Cs}$ levels in this study (mean 0.86 Bq/kg) were notably lower than values reported in Beijing during 1982–1987. The $^{226}\text{Ra}$ levels were higher than those reported in a 1988 Beijing study, which the authors speculate may be due to anthropogenic enrichment from coal use or phosphate fertilizers, though no significant industrial release was detected in the current period.

Significance and Claims
The authors conclude that the data support the finding that there were no significant industrial releases of naturally occurring radionuclides and no detectable releases of the artificial radionuclide $^{137}\text{Cs}$ in Beijing's soils between 2019 and 2025. The average activity concentrations of $^{226}\text{Ra}$ , $^{232}\text{Th}$ , and $^{40}\text{K}$ fall within the global range reported by UNSCEAR.

The study establishes these measurements as baseline reference values for environmental radioactivity in Beijing. The authors assert that maintaining regular and continuous monitoring is critical for understanding regional radioactive backgrounds, detecting potential contamination from anthropogenic nuclear activities, and enabling scientific responses to unexpected radioactive pollution incidents. The paper does not propose new applications or future experimental directions beyond the necessity of continued monitoring.

Technical Summary: Radioactivity Concentrations in Soils in Beijing, China (2019–2025)

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