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

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.

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.

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

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. .

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.

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).

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

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

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

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

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.

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.