Biogeochemistry of Trace elements
Chapter 4. 微量元素由土壤作物到人體食物鏈之傳輸轉變及模式建立
台大農化系
陳尊賢
soilchen@ccms.ntu.edu.tw, tel: 2369-8349
Printed on Oct. 29, 2004
Cd concentration and its pool in the environment
 Cd concentration and pool in the atmosphere, hydrosphere, biosphere, and lithosphere
(book, p111, Table 1)
 Cd in the soil (typical conc. 0.1-1 mg/kg in uncontaminated soils (book, p112, Table 2)
 Cd in the sewage sludge amended-soil in UK (typical conc. 0.1-26 mg/kg in
uncontaminated soils

Behavior of Cd in the Environment
 US Cd environment flow chart system (Yost, 1984) (book, p113, Fig 1)
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Cd dynamics in agricultural systems
 The level of Cd are increased by 1-3 μg/kg/annual in Danish soils, by 27-55% in the
soil burdens of Rothamsted Experimental Station in the UK
 Mass balance or soil budget approach have been proposed in UK, Germany, and
Denmark (book, p114-115, Table 3 and Fig 115)
 The rate of change of Cd is ΔCd = (A+B+C+D+G)-(H+F)

Cd inputs
 Input from atmosphere deposit, phosphate fertilizers, and sewage sludge
 Global estimations of Cd inputs to the soils (book, p116, Table 4)
 Cd input in atmosphere deposit in European community is 0.6-25 g/ha/annual, in New
York city is 44.4g/ha/annual.
 Mean value is about 20 g/ha/annual between 1966-1980, higher than a nationwide mean
of 3 g/ha/annual in UK.
 6.5-71 mg/kg in the P fertilizer in US, Senegal, Morocco, and Tunisia.
 Soil amendments, especially in phosphate rock, such as 3.5g/ha/annual is reported in
Germany, 4.3 g/ha/annual in UK, and 5g/ha/annual in Rothamsted Station.

Cd outputs
 Estimates of annual loss by leaching and associated processes is 5g/ha/annual, and 1.5
g/ha/annual.
 0.3 g/ha/annual in agricultural land in Denmark, 7 g/ha/annual in forest in Tennessee
 Plant accumulation: Cd offtakes in wheat grain varying from 0.09-0.43 g/ha/annual.
(book, p119, Fig 4)
 Cd offtakes in lettuce varying from 0.25-21 g/ha/annual.
 Cd offtakes in cabbage varying from 0.09-43 g/ha/annual.
 In general, Cd offtakes in the crops varying from 1.0-2.5 g/ha/annual.

Cd in food crops grown in sewage sludge-treated soils
 Concentration factors –value (CF-value) or accumulation ratio (AR)=(Cd in the
plant/Cd in the soils)
 (CFA-value) =(Cd in the atmosphere/Cd in the plant) (20-50%) (book, p121, Table 6)
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Cd conc. in different plants grown under same soil condition, ranging from 0.05-0.5 mg
Cd/kg DW (book, p121, Fig 5)
 Mean Cd conc. in potato tubers (0.06-0.12 mg Cd/kg DWT) (book, p122, Table 7)
 Mean Cd conc. in cereal grains (0.004-0.75 mg Cd/kg DWT) (book, p123, Table 8)
 Mean Cd conc. in edible comp of food crop (book, p124, Table 9)
 Roots > stem and leaves > tubers or grains (book, p125, Fig 6).


Soil factors affecting Cd bioavailability
 Monovariate: Log plant Cd = a + b log Soil Cd (book, p125)
 Liming affecting on the reduce the bioavailability: 43% for cabbage, 41% for lettuce.
 Multivariate equations: (book, p127)

Temporal changes in crop Cd concentrations
 Cd conc. changes in 6 years tests of application 10 and 100 tons/ha/annual of swage
sludge (book, p129, Fig 7)

Prediction concentration of Cd in crop
 Log P = a + b log Cd DTPA
 Soil extractants: DTPA, EDTA, 0.1M sodium nitrate, 0.05M calcium chloride.

Dietary exposure to Cd from food crops
 Kidney is the main target organ for Cd residue time for >30 yrs.
 Provisional tolerable weekly intake (PTWI) of 400-500 μg/ from diets per person is
acceptable.
 Acceptable daily intake (ADI) for Cd in Japan is 325 μg/person/day, is 1μg/kg body/per
day.

Cd conc. in foods and total diet studies
 National means of Cd dietary exposure (0.1-0.4 mf Cd/week/p) (book, p135, Table 11).
 Cd exposure profile in different countries (15-50 μg/ day/person) (book, p136, Table
12).
 30-40% of the total dietary exposure of Cd is from cereal consumption in European
community.

Assessment Models of Cd exposure
 Four methods of exposure assessment: standard or total diet study, duplicate meal, fecal
analysis, and diary studies.
 Case study in UK (book, p139, Table 13)
 Maximum permissible conc. (mg/kg DWT) in food (Book, p140, Table 14).
 Cd transfers in agroecosystem (book, p141, Fig. 9)
 USEPA
 WHO suggested 525μg of PTWI for dietary exposure, or 70μg/day.
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
Speciation of Cd in foods
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