Radiological impact of almost a century of phosphate industry in Flanders, Belgium

In Belgium, since about 1920, the phosphate industry has been an important industrial activity. It is principally situated in Flanders, the northern part of Belgium, and produces mainly phosphoric acid, fertilizers, and cattle food. At its height, between 1980 and 1990, it processed between 1.5 and 2.0 Mt of phosphate ore of varying origin per year. In total, more than 60 Mt of ore were handled, containing about 72 TBq of 226Ra and 3.5 TBq of 232Th. Three different processing techniques in six large production sites gave rise to 50 Mt of phosphogypsum and 2.7 Mt of calcium fluoride sludge, all mainly stored on large deposits. In addition, limited recycling of phosphogypsum as building material has occurred in the past. Also, 10 Mt of phosphogypsum was discharged into a large tidal river. One plant still produces 0.25 Mt of gypsum per year. Liquid effluents, containing 13 TBq of radium chloride, were discharged into two small rivers, thus contaminating over 200 ha of land. Approximately 8 TBq of 226Ra and 0.6 TBq thorium ended up in finished products such as fertilizers. Despite these large production figures, so far the radiological impact for the Flemish population has been limited, but this might worsen in the future. The major risk consists in establishing residential areas on land that is contaminated with 226Ra because of liquid effluents or on forgotten gypsum deposits. Doing so might lead to enhanced indoor radon concentrations. In three isolated cases, we found houses built on gypsum deposits where the increased indoor radon levels raised the annual radiation dose to the inhabitants by about 4 mSv.