kukier chaney-2005-effect of biosolids on phytoavailability of cd
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Effect of Biosolids on Phytoavailability of Cd in Long-term Amended Soil.
U. Kukier1, R.L. Chaney2, J.A. Ryan3,
W.L. Daniels1, R.H. Dowdy4, and T. Granato5
Virginia Tech, Blacksburg, VA; USDA-ARS Beltsville, MD; US EPA Cincinnati, OH
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Experimental DesignSoil were collected from paired
long-term biosolids-amended and unamended soils
from controlled field tests in Maryland, Minnesota and Illinois.
Soil pH was adjusted to 6.5±0.2 in 0.01 M Ca(NO3)2.
Cd-salt added at rates 0, 2.5, 5.0, 7.5, 10 mg Cd kg-1 soil.
Cd-nitrate was enriched in 111Cd.
Romaine lettuce was grown in the greenhouse for 35 days after transplanting.
Four replications in randomized complete blocks.
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New Test of Biosolids Cd Adsorption vs. Uptake (Kukier, Chaney, Ryan et al.)
• Long-term Biosolids Amended Field Plots:–Add long ago (1978-1978)
–Different sources of biosolids applied once.
– Incorporated and then cropped regularly.
–Each control and biosolids-amended soils amended with 111Cd(NO3)2 at 0, 2.5, 5.0, 7.5 and 10.0 mg Cd/kg
• Soils collected from plow layer in 2001:–Processed as moist soils to maintain soil biology.
–Soil pH adjusted to 6.5 in 0.01 M Sr(NO3)2
–Fertilizers added for normal growth of Romaine lettuce.
–Lettuce and soil analyzed for Cd and 111Cd, and other elements to evaluate long-term effects of biosolids.
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Biosolids Application Sites, Rates, and Time Since Application
Sampling Biosolids Cumulative Years Total Treatment Application since last Soil Cd Rate application
Mg ha-1 mg kg-1
Hayden Farm Control 0 - 0.20Maryland Heat Treated 224 24 1.16
Composted 672 24 1.51Nu-Earth 50 22 1.76Nu-Earth 100 22 3.44
Minnesota Control 0 - 0.33Low Rate 60 20 2.75Medium Rate 120 20 5.30High Rate 180 20 8.50
Fulton Co. Control 0 - 0.23Chicago Biosolids 643 16 32.1
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Composition of Biosolids In the Different Field Plots
Biosolids Cd Zn Fe
mg/kg mg/kg %
Heat-Treated 13.4 1329. 8.3
Composted 7.2 731. 4.1
Nu-Earth 212. 4140. 2.5
Twin Cities 140. 1890. 0.9
Chicago 263. 3660. 4.6
EPA-APL (mg/kg) 39. 2800. .
EPA-CPLR (kg/ha) 39. 2800. .
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0 2 4 6 8 10 12 140
10
20
30
40
50
60
70
80Hayden Farm PlotsBiosolidsExperiment
100 t/haNu Earth
50 t/ha Nu-Earth
672 t/ha Compost
224 t/ha Heat-Treated
Control
Ro
main
e L
ett
uce C
d, m
g/k
g D
W
Soil Total Cd, mg/kg DW
Phytoavailability of Cd added to Long-Term Biosolids-Amended Soils.
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Romaine Lettuce grown on Hayden Farm Control and Long-Term Biosolids Compost-amended (672 t/ha) soils with 0-10 mg Cd/kg, at pH 6.5 in Ca(NO3)2. Reduced uptake/toxicity of Cd to lettuce (control vs. biosolids-amended).
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Phytoavailability of Cd added to Long-Term Biosolids-Amended Soils
0 2 4 6 8 10 12 140
10
20
30
40
50
60
70
80
13.4 ppm Cd
Hayden Farm PlotsBiosolidsExperimentBeltsville, MD
672 t/ha Compost7.2 ppm Cd
224 t/ha Heat-Treated
Control
R
om
ain
e L
ett
uce C
d, m
g/k
g D
W
Soil Total Cd, mg/kg DW
pH=6.5
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Phytoavailability of Cd added to Long-Term Biosolids-Amended Soils.
0 2 4 6 8 10 12 14 16 18 200
10
20
30
40
50
60
70
80Dowdy's Field PlotsMinneapolis, MNBiosolids with105-186 mg Cd/kg
180 t/ha
120 t/ha
60 t/ha
Control
R
om
ain
e L
ett
uce C
d, m
g/k
g D
W
Soil Total Cd, mg/kg DW
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Phytoavailability of Cd added to Long-Term Biosolids-Amended Soils.
0 5 10 15 20 25 30 35 40 45
0
10
20
30
40
50
60
70
80
Chicago-Fulton Co. Long-TermBiosolids Amended
Chicago-Fulton Co. Control Soil
Ro
main
e L
ett
uce C
d, m
g k
g-1 D
W
Soil Total Cd, mg kg-1
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Phytoavailability of Biosolids Cd:• Biosolids Cd remains in labile pool for indefinite
period, as does most soil Cd.
• Persistent biosolids effect reduces uptake of Cd compared to untreated soils.
• Phytotoxicity of added Zn is very effective limit to excessive bioavailable Cd in crops.
• With high quality biosolids, bioavailable crop Cd is not increased even when Cd is increased.
• High Cd:Zn ratio in biosolids promotes crop Cd uptake and bioavailability of crop Cd.
• Subsistence rice diets had high influence on absorption of Cd by affected humans.–Polished rice is deficient in Fe, Zn and Ca for
humans
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Does increased consumption of fruits and vegetables increase risk from biosolids Cd?
• Some claim that the EPA 503 Rule is not protective because it ignores higher Cd intake by highly exposed gardeners if they ate the current US Dept. Agr. recommended diet.
• The USDA “Diet Pyramid” recommends eating more leafy and root vegetables, fruits and whole grains, some with high Cd uptake slopes, than earlier USDA/FDA/EPA model diets used in risk assessment.
• These claims ignore the presence of Zn in biosolids which serves as a limit on maximum crop Cd due to Zn phytotoxicity, inhibits Cd uptake by crops, and inhibits Cd bioavailability to animals.
• Because food Cd with 1:100 Cd:Zn ratio has essentially zero Cd bioavailability as found experimentally for lettuce and Swiss chard, increased garden foods consumption cannot comprise dietary Cd risk from gardens.
• Cannot extrapolate from rice-Cd risks to other crops (e.g., wheat, lettuce) without data to show these foods can cause human risk when grown on soil with low Cd:Zn.
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CONCLUSIONS Biosolids provide long term protection Cd is in labile form Modern high quality biosolids contain low Cd
levels and low Cd:Zn ratios and cannot cause high accumulation of Cd in crops.
Risk from Cd in crops depends on bioavailability of that Cd, and crop Zn inhibits Cd risk. Usual Cd:Zn ratio of <1:100 prevents undue Cd absorption in consumers.