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Table 5 Enrichment factor (EF) of heavy metals in sediments of lakes along a rural to urban gradient in central China and grade standards for EF (Birth 2003)

From: Heavy metal gradients from rural to urban lakes in central China

Group EF           Grade standards for EF
Mn Cu Zn As Ni Cd Pb Co Cr Fe Value Enrichment status
A 3.7 ± 0.8 6.9 ± 3.5 4.0 ± 0.6 1.7 ± 0.9 2.9 ± 1.0 7.9 ± 2.5 3.1 ± 0.9 3.9 ± 0.7 4.9 ± 2.9 3.0 ± 0.7 < 1 No enrichment
B 1.3 ± 0.1 4.5 ± 3.2 3.3 ± 0.2 1.2 ± 0.1 1.8 ± 0.2 4.7 ± 0.9 2.8 ± 1.0 1.4 ± 0.1 2.0 ± 0.6 1.5 ± 0.1 1–3 Minor enrichment
C 2.0 ± 0.7 3.4 ± 1.2 3.4 ± 1.0 1.9 ± 1.1 3.2 ± 1.4 8.4 ± 4.8 2.5 ± 1.0 2.6 ± 1.2 2.7 ± 1.2 2.5 ± 1.0 3–5 moderate enrichment
D 2.4 ± 0.7 4.8 ± 2.7 4.3 ± 1.8 2.1 ± 1.2 3.4 ± 1.7 5.5 ± 1.8 2.8 ± 1.2 2.8 ± 1.4 2.9 ± 1.3 2.6 ± 1.2 5–10 Moderately severe enrichment
E 2.1 ± 1.3 4.2 ± 2.1 4.3 ± 2.0 2.5 ± 1.2 4.4 ± 1.8 5.9 ± 3.3 3.0 ± 1.2 3.7 ± 1.6 3.8 ± 1.5 3.4 ± 1.2 10–25 Severe enrichment