Future trends in soil cadmium concentration under
current cadmium fluxes to European agricultural soils
Erik Smolders and Laetitia Six
Katholieke Universiteit Leuven, Belgium
Mineral P fertilisers contain traces of Cd derived from rock P
with different Cd:P ratios
Nziguheba and Smolders, 2008
Where the story begins...
Nauru
Soil Cd increases with cumulative application of P-fertilisers in
experimental plots in Australia. The HCl soluble soil Cd increases from
0.03 to 0.06 mg kg-1 soil (Williams & David, 1974).
Archived soil samples illustrate rising soil Cd concentrations.
Sources: soil Cd in Broadbalk, Rothamsted (1846 -1980)
Jones et al., 1987
Natural stock of Cd in topsoil: 100-1000 g Cd/ha
Annual Cd mass balances in European agricultural topsoils
in g Cd/ha/year
Rothamsted
UK
Hutton and
Symon, 1986
1846-1980
Input
Moolenaar
and Lexmond,
1998
8
4
P-fertiliser
3
2
Atm. dep.
4
1
Other
1
Output
n.d.
2
Crop offtake
0.6
Leaching
1.6
Net balance
2-5
(measured)
<8
2
2003: proposal for a Cd limit in EU mineral fertilisers
based on mass balance calculations
Predicted change in soil Cd in European agricultural soil after 100 years application of
inorganic P fertilizers at different Cd levels. Means (● ) and 10th -90th percentile of
different simulations Calculations in the CSTEE report (2002) a, right side, updated 2013
Measured deposition: factor 4 decrease over about 20 years
Country
1985-2002
EU-15+1
1.4 (1.1)
2010
0.4
3
EU-27+1
0.35 (0.21)
0.2
Comments
Mean & standard deviation of measured deposition
in EU 1985-2002 (n= 44 ))
Deposition estimated from emissions (EU 2007)
3 is worst case scenario (CSTEE 2002),
Mean & standard deviation of measured deposition
in EU in 2010 (n= 44 ))
Deposition estimated from emissions
Wet-only deposition collector approved by EMEP
P-fertilizer consumption in EU: factor 1.4 decrease over last
15 years
9000
8000
6000
5000
3
10 tonnes P2O5
7000
4000
3000
2000
1000
1980
1985
1990
1995
year
2000
2005
2010
Soil acidity (pH) is main driver for the Cd leaching
OH
OCd+
OH
O
O Ca
OH
+ 4Cd2+
OCd+
O
O Cd
+ 3H+ +Ca2+
OCd+
More H+ (lower pH): reaction to the left=Cd more
soluble
Solid:liquid distribution of Cd in soil expressed in
KD=Cdsoil/Cd soil solution (concentration ratio)
Pore water KD values of Cd in 151 European soils
Degryse et al. 2009
Predicted change in soil Cd over 100 years in 540
potential European scenarios: soil pH is the main driver
Average scenario: 15% depletion
Six and Smolders, 2014
Key changes between the 2002 assessment and current
assessment
2002
2012
factor change
Input
Atmospheric deposition (g/ha/y)
Fertiliser use (kg P2O5/ha/y)
Lime/manure/sludge (g Cd/ha/y)
1.5 (0-3)
1.6
0
0.35
0.80
0.15
4-fold lower
2-fold lower
marginal increase
Output
Average soil pH
6.5
5.8
KD model
two models
Change in soil Cd in 100y
at average fertiliser Cd
slight accumulation
2.3-fold increase
Cd output
new model prediction of new
in between that
of two earlier
models
15%depletion
Trends of wheat grain Cd in Sweden: from accumulation to
depletion
Kirchmann et al. 2009
Conclusion
•
Cd input to European soils has decreased due to
lower emissions and lower mineral P use
• Cd output from soil may be higher than initially
estimated: average soil pH (CaCl2 0.01M) is 5.8 in
arable soils
• Burden of fertiliser on foodchain Cd has reduced but
political pressure on setting strict limits remains