Volatile pollutants from former industrial sites can degrade the buildings' indoor air quality that were built after the industrial activities. Since 2010, environmental assessments have been conducted in French establishments hosting sensitive populations identified as being on or near potentially contaminated former industrial sites. These projects are based on historical studies traditionally carried out as part of managing contaminated sites, to determine which substances should be analyzed. They pinpoint former activities likely to have stored or used pollutants. We show that the historical information collected is not effective in targeting sites with increased probability of mercury being present in soil gases. Environmental history has demonstrated the existence of large-scale artisanal contamination, both prior to and concomitant with the industrial era. Classic historical studies would not take into account artisanal activities, which are less documented than industrial activities. We carried out additional research for three schools located in three different Parisian districts. Although information on activities which could have emitted mercury was relatively imprecise (in terms of location, type and duration of activities) and uncertainties exist about the completeness of the archival documents available, our investigations identified several mercury-using activities that had not been identified during the classic historical study. However, we have shown that the number of activities identified does not provide information on how mercury has affected soil gas. Consequently, although a more extensive historical research improves knowledge about the presence of potential mercury-using activities, our study shows that a systematic analysis of mercury as part of the assessment of establishments hosting sensitive populations remains relevant. This approach should be applied to other cities around the world.