Toxicologic Assessment of the Army's Zinc Cadmium Sulfide Dispersion Tests (1997) / Chapter Skim
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I: Cadmium Exposure Assessment, Transport, and Environment Fate
I: Cadmium Exposure Assessment, Transport, and Environment Fate
Pages 337-359
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From page 338... ...
CAD M ~ U M ~ N OUTDOOR A! R Cadmium metal and cadmium salts have low volatility and exist in air primarily as fine suspended particulate matter.
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From page 339... ...
In the United States, a person who breathes 20 m3 of air per day and spends ~ 0% of his or her time outdoors will have an estimated cadmium intake of 0.~-0.8 Friday in urban cities or less than 0.02 Friday in rural areas. CADMIUM IN WATER Cadmium enters drinking water directly from pollution-source releases to surface water and groundwater or from deposition from air to surface water, from soil runoff to surface water, or from leaching from rocks and soils into groundwater.
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From page 340... ...
data and data from other industrial nations from the northern hemisphere, the subcommittee believes that the daily cadmium intake from food ranges from 10 to 60 be CADMIUM IN SOIL (SOIL INGESTION AND DERMAL UPTAKE) Human intake of cadmium in soil occurs through soil ingestion that results from hand-to-mouth activities.
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From page 341... ...
In rural areas with cadmium concentrations in air of 0.005 ~g/m3, cadmium was contributed to the house-dust pool at around 600 m/d. That implies that the cadmium deposition rate on household surfaces is about 3 ~g/m2 per day in areas with an air concentration of 0.005 ~g/m3.
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From page 342... ...
Assuming that the indoor air of the house has a dust loading of 50 ~g/m3 and that that would be the same in household air would yield respective indoor air concentrations of 0.007 ,ug/m3 in rural areas, 0.02 ~g/m3 in urban areas, and 0.07 ~g/m3 in industrial areas. Given that these levels are comparable with those of outdoor air, resuspended dust inside homes is not likely .
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From page 343... ...
The relative contributions of the various pathways to total potential dose for a 70-kg adult are as follows: Inhalation of cadmium in air indoors and outdoors Water ingestion Food products Soil ingestion Dermal contact Contact with house dust Smoking Total daily intake 0.002-0.02 ~g/d 2-20 ~g/d 10-60 1lg/d 0.02-0.2 ~g/d ~0.2% 0.002-0.12 1lg/d ~0.002% 0.3-3 ~g/d (2-8 1lg/~) 12-84 1lg/d ~0.02% ~20% ~76% (for smokers)
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From page 344... ...
have reviewed and compared a number of sorption models for cadmium in soil-water and sediment-water systems. They report that in soils estimated Kin values range from ~ to 9,000 with a typical value (at low water concentrations)
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From page 345... ...
, where Cp is cadmium concentration in the plants in contact with contaminated air, mol/kg; Ca is the cadmium concentration in air above the plants, mol/m3; vat is the deposition velocity that represents the rate of cadmium transfer from air to plant surfaces, m/~; Mp is the mass of the plants per unit area of land, kg/m2; and Rp is the first-order rate constant that accounts for all cadmium removals from plants (wash-off, biodegradation, arid so on)
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From page 346... ...
Before the specific behavior of ZnO ~Cd0.2S in the environment can be fully characterized, there is a need to determine both the rates and end products of ZnO~Cd02S transformation reactions in air, surface soil, vegetation surfaces, surface water (rivers, lakes, and ponds) and snow.
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From page 347... ...
it should be noted that active pools such as the atmosphere, soils, lakes, rivers, and ocean pools are subject to large inputs of cadmium from human activities. The exchange of cadmium between compartments occurs along established pathways involving stream, ice, and groundwater flows; atmospheric transport and deposition; volcanism; uplift; weathering; sedimentation; and biologic mobilization.
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From page 348... ...
This contact is the basis for estimating potential doses used in health risk assessments. Potential dose, expressed as average daily dose, is the amount of material
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From page 349... ...
, which is the ratio of cumulative intake for an exposure event, in micrograms of cadmium, divided by the overall product of concentration and time the time integral of the exposure concentrations in air. DIRECT EXPOSURE: INHALATION OF CONTAMINATED AIR To determine the potential dose ratio, we first determine dose, which is the product of inhalation rate, JR, m3/h; the time-averaged cadmium air concentration during the exposure time, Cair, 1lg/m3; and the exposure time, ET, in h.
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From page 350... ...
TABLET-2 Summary of Potential Dose Ratios for Direct and Indirect Exposure Pathwaysa Exposure Pathway Direct or Indirect Contact with Air Potential Dose Ratio, fig ,ug-h/m3 of Cumulative Air Exposure Inhalation Inhalation of resuspended soil outdoors Dermal contact with and ingestion of Inciirect house dust Inhalation of resuspended house dust Indirect Deposition on vegetation in home Indirect gardens Deposition on surface drinking-water Indirect supplies Direct 1.0 Indirect 0.0005-0.002 ~ 0.12 2.2 0.24-0.8 Potential dose ratio is the ratio of total uptake or intake of cadmium in micrograms, divided by the integrated air exposure, in micrograms per cubic meter per hour.
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From page 351... ...
The concentration of cadmium added to soil as a result of deposition from air can be estimated as CS0i} = (cair X V6O X ET) /(MSoil~, where CSOi~ is the concentration of cadmium aclded to soil, Egg; V6O is the outdoor deposition velocity of FP, assumed to be 20 m/h; Cair is the cadmium concentration in air during an event, ~g/m3; ET is the exposure time, h; and MSoi, is the mass inventory of surface soil, which, on the basis of soil depth of l cm and a soil density of 1,600 kg/m3, is 16,000 g/m2.
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From page 352... ...
To estimate dermal and ingestion exposures to the cadmium transported to house dust, it is necessary to determine the cadmium concentration inside houses after dispersion and how much of this is deposited on household surfaces. To make this preliminary calcuration, we assume that air concentrations of cadmium in houses went up in proportion to outdoor concentrations Grin the esrno~,r~ timr' AT hilt ~ -- <~ - - - r ~ ~ ~ 1 ~ 1 ~ .
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From page 353... ...
However, there is much greater uncertainty associated with it than with the direct inhalation-dose estimate. INHALATION OF RESUSPENDED HOUSE DUST To make a preliminary estimate of the potential dose, we assume that air concentrations of cadmium in houses due to house dust are all attributable to resuspension of house dust and that the particle Toad indoors is around 50 ~g/m3 Cdustto indoor air ~ CdUS~ (pLg/g)
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From page 354... ...
/(Mveg) ' where Cveg is the concentration of cadmium added to vegetation during an exposure event, ~g/kg; Cair is the average cadmium concentration in air during an event, ~g/m3; Via is the deposition velocity of FP from air to vegetation, assumed to be ~ O m/h; ET is the exposure time, h; and MVeg is
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From page 355... ...
fig. Thus, the potential dose ratio for ingestion of homegrown vegetables is potential dose ratio (homegrown foods)
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From page 356... ...
' where Cwa~er is the concentration of cadmium added to surface water during an exposure event, 1lg/L; Cair is the average cadmium concentration in air during an event, ~g/m3; Vclo is the outdoor deposition velocity of FP, assumed to be 20 m/h; ET is the exposure time, h; and Vwa~er is the mass inventory of surface water, L/m2. On the basis of data in the Water Encyclopedia, we estimate the average depth of surface water as 5 m, which gives a typical value of Vwa~er of 5,000 L/m2.
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From page 357... ...
1985. Airborne trace elements in Great Smoky Mountains, Olympic, and Glacier National Parks.
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From page 358... ...
1995. Dietary intakes of pesticides, selected elements, and other chemicals: FDA total diet study, June 1984-Apri!
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