Field sampling methodology implemented within Project 21ROMD

Within each 2500 km² grid cell, two distinct types of soil samples were collected according to the standardized sampling methodology adopted in Project 21ROMD.

• Topsoil from agricultural land, Ap horizon, corresponding to a "surface soil" sample (TOP) collected from a depth of 0 ~ 20 cm, consistent with the most commonly used ploughing depth (20~25 cm) across much of Europe;
• Surface soil from permanent grasslands, consisting of the upper 10 cm (TOP 10 cm) of soil.
• It should be noted that, for grassland sampling, the sample was collected directly from the upper mineral soil layer and not from the pedological "0 horizon", with the organic layer removed prior to sampling.

These two soil types represent the primary substrate supporting the majority of agricultural production in both Romania and the Republic of Moldova, including cereal crops and other agricultural land uses.

The sampling coverage achieved within this project included 95 sampling points in the Moldova region of Romania and 32 sampling points in the Republic of Moldova, ensuring representation of the different soil types across both study areas.

For quality control purposes, a field duplicate sample was collected at every 20th sampling point, and analytical duplicates were subsequently prepared from these duplicate samples to verify measurement precision and reproducibility.

The sampling points were distributed as uniformly as possible across both countries to ensure representative spatial coverage. Although the sampling density was relatively low, this strategy enabled homogeneous coverage even in areas with limited agricultural activity, since suitable sampling locations could still be identified within each 2500 km2 grid cell. At this sampling density, the major geochemical patterns and regional differences in soil radioactivity can be reliably identified.

For indoor radon measurements, approximately 350 measurement points were established, including about 60 points in the Moldova region of Romania and 290 points in the Republic of Moldova.

Development of georeferenced maps and digital platform integration

An important outcome of the project was the development of georeferenced maps for the eastern region of Romania and the Republic of Moldova, which were subsequently integrated into the digital platform.

The georeferencing process involved assigning real-world geographic coordinates to field-collected data using QGIS, an open-source Geographic Information System software platform.

• Preparation of datasets containing geographic coordinates;
• Data import into the GIS environment;
• Definition of the Coordinate Reference System;
• Application of appropriate transformation methods;
• Validation of the final outputs;
• Generation of final cartographic products for analysis, visualization, and dissemination.

Indoor radon measurements and radiological protection assessment

Based on the data obtained from indoor radon measurements performed in public institutions and residential buildings, the distributions of indoor radon concentrations are presented in the Results section.

The analysis shows that, in several cases, the measured values exceed the internationally recommended reference level, highlighting areas where mitigation actions may be required.

The achievement of Objectives O3 and O4 was made possible through the coordinated contribution of all project partners. The team from the Republic of Moldova was responsible for the deployment of passive CR-39 detectors in educational institutions and for their retrieval after an exposure period of approximately three months.

Subsequently, the Romanian team contributed to the laboratory processing of the detectors, which included chemical etching and detector reading at IFIN-HH, for the determination of indoor radon concentrations.

Digital data flow, QGIS integration, and project platform

As a final project validation step, datasets related to indoor radon, soil radium, uranium, potassium, thorium, total specific activity, and ambient gamma dose rate from both the Republic of Moldova and the eastern region of Romania were integrated into QGIS as sample datasets.

These datasets were subsequently processed to generate dedicated thematic maps. The QGIS framework allows straightforward integration of future datasets, including additional measurements of naturally occurring radionuclides from the ²³⁸U and ²³²Th decay series, ⁴⁰K expressed in Bq/kg, as well as in situ measurements of U ppm, Th ppm, K %, and indoor or soil radon at national scale.

Furthermore, to increase the digital data flow capacity between Romania and the Republic of Moldova for monitoring soil radioactivity and radon, the project website DIGNORM 21ROMD was developed, where all generated maps and project outputs are publicly accessible.

For data security and integrity reasons, the full QGIS platform remains accessible only through authorized login and password credentials. Long-term maintenance and consistent integration of new datasets are recommended to be performed by the same trained IT operator to ensure data standardization and interoperability.