Trace elements database: An inexpensive tool for monitoring soils and defining reference values

About 250,000 soil-tests are performed in France each year at the request of farmers. Tens of thousands of these analyses are carried out as part of sewage treatment plant sludge management (in accordance with the 8 January 1998 decree) and therefore relate to soil trace elements content. The number and diversity of origin of the samples make these soil-test results an interesting and original source of information regarding the variability of cultivated topsoil.

Since 1998, the national BDETM programme (database on trace metal elements) has been compiling the results concerning the trace metal element content (Cd, Cr, Cu, Hg, Ni, Pb, Zn and Se) of these analyses. Agro-pedological data determined on the same samples are sometimes included. Important additional information on the sampling sites (town, geographical coordinates, etc.) and the analyses themselves (laboratory, method used, etc.) is also centralised in the database. These results were collected from various data providers: research laboratories, environment consulting companies, chambers of agriculture, departmental directorates for territories, laboratories and the Ministry for Ecological Transition and Territorial Cohesion. This programme was carried out during three data collection campaigns, initiated by ADEME and conducted by INRAE, in 1998, 2010 and 2025.

Currently, the BDETM contains the results of analyses of nearly 150,000 samples collected over 30 years. Using appropriate statistical procedures, we demonstrate that this type of approach provides an often-underutilised operational tool for obtaining valuable information on the spatial distribution of trace elements levels and their evolution over time.