monitoring the pollution of one single metal over a period of time (Turekian and Wedepohl, 1961; Loska et al., 1997): low degree (CF < 1), moderate degree
(1 ≤ CF < 3), considerable degree (3 ≤ CF < 6), and very high degree (CF ≥ 6). Thus the CF values can monitor the enrichment of one given metal in sediments over a period of time.