Table 4 Heavy metal contents in mg kg^− 1

Pig manure

BDL

74 ± 2

84 ± 5

NA

400 ± 50

Catfish sediment

BDL

41

89 ± 6

NA

120 ± 10

Cattle manure

BDL

BDL

BDL

NA

100 ± 10

Sludge of DWWTP

BDL

119 ± 14

582 ± 265

NA

440 ± 30

Bio-sludge of RWWTP

BDL

BDL

14 ± 5

NA

130 ± 60

Che-sludge of RWWTP

1

34

167 ± 15

NA

143 ± 10

Sewage Sludge [28]

5 ± 1

133 ± 14

121 ± 16

Catfish sediment [24]

0.02 ± 0.003

0.03 ± 0.01

59 ± 18

2.54 ± 1

Cattle manure [29]

0.1

2

1.4

16.4

Pig manure [26]

0.3 ± 0.07

9 ± 2

22 ± 1

986 ± 69

Vietnam Technical Regulation on Fertilizer Quality [30]

< 5

< 200

< 2

Chinese Standard of Organic Fertilizer [31]

3

50

150

2

British Specification for Composted Materials [32]

1.5

200

100

1

200

Canadian Standard of Compost Quality- Category A [33]

3

150

210

0.8

400

Canadian Standard of Compost Quality- Category B [33]

20

500

1060

5

757

European regulation on fertilising products [34]

1.5

120

100

300