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Table 2 Pseudo-total concentrations of Cd, Cu, Pb, and Zn found in a variety of soils (if not specified) and other media (e.g., sediment, ash) in Singapore

From: Low presence of potentially toxic elements in Singapore urban garden soils

Ref.

Site

Cd

Cu

Pb

Zn

d

Forest; Nee Soon, upper Catchment [medians]

bdl

5 ± 5

13 ± 6

23 ± 6

d

Forest; Nee Soon, lower Catchment [medians]

bdl

12 ± 4

18 ± 7

33 ± 11

b

Golf course (3 locations)

NA

12–14

20–47

52–73

d

Disturbed lands, Nee Soon Catchment [medians]

bdl

16 ± 6

24 ± 9

43 ± 15

e

Forest soils (variable geology)

bdl–0.03

7–20

9–17

13–61

f

Park soils (4 locations)a

0.05–0.08

5–11

14–21

11–24

p

Park soils (3 locations)a

0.46–1.66

6–14

14–37

45–71

f

Airport/industrial area soils (2 locations)a

0.06–0.08

7–16

20–26

13–31

i

Reservoir susp. sediment (Kranji & MacRitchie)

NA

15–16

20–43

49–73

g

Residential soils (7 sites island-wide)

0.45–1.68

3–90

6–70

9–93

g

Reservoir sediments (3 sites)

0.79–1.73

8–61

15–65

1–68

d

Military lands, Nee Soon Catchment [medians]

bdl

44 ± 34

56 ± 37

77 ± 49

b

Forest; Nature Reserve (MacRitchie)

NA

6–19

9–38

29–123

b

Residential area (7 sites in Bishan)

NA

13–57

16–46

70–151

i

Reservoir sediments (MacRitchie)

NA

13–21

19–64

75–133

q

Mangrove sediment (S. Buloh & S. Khatib Bonsu)

0.18–0.27

7–32

12–32

51–120

g

Field soils (7 sites island-wide)

0.45–1.42

1–105

5–89

1–150

a

Parks (Island wide; 10 locations)

bdl

9–70

bdl–61

33–190

h

MacRitchie Reservoir sediments (9-m core)

~ bdl–0.40

~ 1–370

~ 1–55

~ 1–135

a

Gardens (10 locations island-wide)

bdl–3.2

10–76

bdl–37

71–164

a

Woodlands (10 locations island-wide)

bdl–6.4

11–50

bdl–33

19–146

c

Forest; Bukit Gombak [medians]

5.76 ± 5.16

36 ± 24

14 ± 6

100 ± 27

o

Johore Strait marine sediments

0.11–0.36

11–93

27–70

69–231

i

Reservoir sediment (Kranji)

NA

21–29

35–82

128–367

r

Estuary sediment (Punggol)

bdl–1.37

4–439

1–157

NA

s

Coastal sediments (island wide)

bdl–1.6

1–1781

1–82

95–281

t

River sediment (Singapore river)

~ 0.1–1.0

~ 15–95

~ 40–240

~ 100–600

b

Industrial (Jurong West; 7 sites)

NA

12–194

29–167

111–837

b

Road side soils (heavy traffic area)

NA

30–68

27–1981

124–938

k

Road sediment; residential [means]

0.71 ± 0.30

247 ± 54

69 ± 26

275 ± 55

k

Road sediment; commercial [means]

0.30 ± 0.10

98 ± 76

111 ± 15

620 ± 186

p

Industrial zone soils (8 locations)a

0.66–1.63

16–258

10–242

40–708

l

Suspended sediment; residential road runoff

0.89–3.03

11–74

5–206

16–941

l

Suspended sediment; industrial road runoff

2.13–8.59

30–671

25–182

112–2006

g

Industrial soils (3 sites)

1.11–3.21

1–485

51–235

15–3594

j

Residential road sediment

NA

203–1294

135–395

704–2105

k

Road sediment; industrial [means]

2.41 ± 1.0

9069 ± 3742

338 ± 56

1696 ± 446

j

Road sediment (industrial areas)

NA

251–4271

144–744

836–11,960

n

Fly ash from municipal incinerator

95

570

2000

6288

m

Fly ash, Tuas solid waste incinerator [means]

130

987

2120

8072

  1. Listed informally in order of increasing level of enrichment
  2. Most values are ranges, means ± standard deviation, or medians ± MAD; aindicates a range of means/medians; ~ signifies the values were estimated from a graph. ND is not determined; bdl is below detection limit
  3. References:
  4. (a) This study; see “Methods and materials” section for details on the analysis methods
  5. (b) Zhou et al. (1997); HCL–HNO3–HF digestion and a flame atomic absorption spectrophotometer for high concentrations and a graphite furnace atomic absorption spectrophotometer for low concentrations
  6. (c) Nguyen et al. (2020); microwave-assisted digestion methods EPA 3051a (USEPA 2017) followed by ICP-OES (Perkin Elmer 8300)
  7. (d) Nguyen et al. (2018); four-acid digestion protocol (MA300 method by Bureau Veritas Labs (Vancouver, Canada) and ICP-MS (Perkin Elmer ELAN 9000)
  8. (e) Leitgeb et al. (2019); pseudo-total element concentrations were determined by digesting soil samples with aqua regia using a microwave oven (MARS 6, CEM, Kamp-Lintfort, Germany) and by analysing the solution using ICP-OES (Optima 8300, Perkin Elmer, Waltham, MA)
  9. (f) Ng et al. (2006), samples digested using microwave oven (Milestone, Ethos D, Monroe, C.T., USA) with a mixture of 9 ml HNO3 and 3 ml of HF in a closed vent medium pressure vessel with a ramp to 180 °C at 600 W for 10 min and held at 180 °C, 600 W for 10 min
  10. (g) Chen (1999), mixed acid method (1 ml HF (49%) added to 14 ml 3:1 HCL (36%): HNO3 (68%) added by 20-min microwave digestion; analysis on ICP-AES
  11. (h) Chen et al. (2016); leached with ultrapure grade 1.75 mol/l HNO3–3 mol/L HCl in an ultrasonic bath, followed by analysis using a quadrupole inductively-coupled plasma mass spectrometry (Q-ICP-MS, VG PlasmaQuad 2+)
  12. (i) Chen et al. (1970); HNO3 digestion in a microwave followed by analysis with ICP Perkin-Elmer Plasma 400 Emission Spectrometer
  13. (j) Yuen et al. (2012); digestion with strong acids HNO3–H2O2–HF; analysis on a Thermo Scientific X Series2 Quadrupole ICP-MS
  14. (k)Joshi et al. (2009); digestion with a combination of strong acids (HNO3–H2O2–HF) in a microwave digester, and analyzed using inductively coupled plasma–mass spectrometry (ICP-MS, Perkin Elmer Elan 6100)
  15. (l) Joshi and Balasubramanian (2010); digestion of the filter paper containing suspended solids in a microwave digester with a combination of strong acids HNO3–H2O2–HF, followed by analysis on ICP-MS
  16. (m) Tan et al. (1997); sequential extraction; analysis on a Perkin-Elmer ICP Plasma Emission Spectrophotometer
  17. (n) Wu and Ting (2006); total digestion according to US EPA SW 846 Method 3050B using ICP-OES (Perkin-Elmer Optima 3000V)
  18. (o) Wood et al. (1997); digestion with a mixture of HNO3, HClO4, and HF; analysis by atomic absorption spectrometry (AAS)
  19. (p) Wang et al. (2022); means (3 reps) for three parks and eight industrial areas. ICP-OES; microwave-assisted digestion (details uncertain)
  20. (q) Cuong et al. (2005); micro-wave assisted HNO3-HF digestion; Perkin-Elmer AAnalyst 600 GFAAS
  21. (r) Nayar et al. (2004); digestion with suprapure HNO3; Perkin-Elmer AAnalyst 600 GFAAS
  22. (s) Goh and Chou (1997); digestion with suprapure HNO3; analysis on Hitachi Polarised AAS
  23. (t) Sin et al. (1991); digestion not specified; AAS/FASS
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CABI Agriculture and Bioscience

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