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