The Igeo consists of seven grades,

The Igeo consists of seven grades, whereby the
highest grade (6) reflects 100-fold enrichment
above background values. Förstner et al. (1993)
listed geoaccumulation classes and the corresponding
pollution intensity for different indices as presented
in Table 5. The index has been applied by
many researchers (e.g., Singh and Hasnain, 1999;
Bakan and Balkas, 1999; Zhang et al., 2007) to distinguish
heavy metal levels in anthropogenically enriched
sediments from preindustrial or natural background
levels in equivalent sediments.