future trends in soil cadmium concentration under current cadmium fluxes to european agricultural...
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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
NauruWhere the story begins...
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
Annual Cd mass balances in European agricultural topsoilsin g Cd/ha/year
Rothamsted UK
1846-1980
Hutton and Symon, 1986
Moolenaar and Lexmond,
1998
Input
P-fertiliser
Atm. dep.
Other
8
3
4
1
4
2
1
Output
Crop offtake
Leaching
n.d. 2
0.6
1.6
Net balance 2-5
(measured)
<8 2
Natural stock of Cd in topsoil: 100-1000 g Cd/ha
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
Country 1985-2002 2010 Comments EU-15+1 1.4 (1.1) Mean & standard deviation of measured deposition
in EU 1985-2002 (n= 44 )) 0.4 Deposition estimated from emissions (EU 2007) 3 3 is worst case scenario (CSTEE 2002), EU-27+1 0.35 (0.21) Mean & standard deviation of measured deposition
in EU in 2010 (n= 44 )) 0.2 Deposition estimated from emissions
Measured deposition: factor 4 decrease over about 20 years
Wet-only deposition collector approved by EMEP
year
1980 1985 1990 1995 2000 2005 2010
103 tonnes P
2O5
1000
2000
3000
4000
5000
6000
7000
8000
9000
P-fertilizer consumption in EU: factor 1.4 decrease over last 15 years
Soil acidity (pH) is main driver for the Cd leaching
OHOH
OH
OO Ca
OCd+
OCd+
OCd+
OO Cd+ 4Cd2+ + 3H+ +Ca2+
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 soilsDegryse et al. 2009
Predicted change in soil Cd over 100 years in 540 potential European scenarios: soil pH is the main driverAverage scenario: 15% depletion
Six and Smolders, 2014
Key changes between the 2002 assessment and current assessment
2002 2012 factor changeInputAtmospheric deposition (g/ha/y) 1.5 (0-3) 0.35 4-fold lowerFertiliser use (kg P2O5/ha/y) 1.6 0.80 2-fold lowerLime/manure/sludge (g Cd/ha/y) 0 0.15marginal increase
OutputAverage soil pH 6.5 5.8 2.3-fold increase
Cd outputKD model two models new model
prediction of new in between that
of two earliermodels
Change in soil Cd in 100yat average fertiliser Cd slight accumulation 15%depletion
Kirchmann et al. 2009
Trends of wheat grain Cd in Sweden: from accumulation to depletion
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