Salty Dust:

Salty Dust: Salty Dust: - Start

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Increasing . the accessibility and mobility of toxic . metals. Dr.. James King. Acknowledgements. Richard Reynolds, Harland Goldstein, . Jim . Yount. , George . Breit. , Suzette . Morman. George Nikolich, Jack Gillies, Vic Etyemezian. ID: 309894 Download Presentation

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Salty Dust:




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Presentations text content in Salty Dust:

Slide1

Salty Dust:

Increasing the accessibility and mobility of toxic metals

Dr.

James King

Slide2

Acknowledgements

Richard Reynolds, Harland Goldstein, Jim Yount, George Breit, Suzette MormanGeorge Nikolich, Jack Gillies, Vic Etyemezian

Slide3

Why salty dust?

Aral Sea dust storm

April 18 2003

NASA MODIS

Photo by W. Cox, GBUAPCD

Evaporite-mineral dust contain

elevated As, Cr, Cu, Ni, Pb, Th, U, SeNo current limits on inhalation of toxinsBioaccessibility of toxic metalsSpatial variability of metal content in dust vs. groundwater chemistryInfluences from climatic variability

Dust from Owens (dry) Lake

Slide4

Types of Playas

WET

DRY

(Stone,

1956; Neal, 1965; Rosen, 1994)

Ground water is at or near the surface (< 4 m)

Ground water is far below the surface (> 4 m) or cannot interact with surface

Slide5

Dust Emission Mechanics

Direct entrainmentHighly dependent on surface conditionsGenerates relatively smaller amounts of dustSensitive to wind regimeF = Au*3 5Saltation BombardmentDependent on sand supply conditionsFetch effects are importantq = Bu*3Surface RoughnessVegetation, rocks, and crusts can modify the efficiency of dust emission mechanics

Slide6

Playa Surface Characteristics

Relatively stable with timeTypically very hard

Variable & DynamicSoft – in areas of fluffy & puffy sedimentHard – in areas of crust

Wet playa

Dry playa

Hard, compact surfaces

Slide7

Playa Sediment Types

Wet Playa

Fluffy

sediment – very soft; abundant evaporite minerals produced continuously; high volume of pore space

Puffy sediment – soft, hummocky surface; fewer evaporite minerals.Crusts – salts and carbonate

Dry PlayaTypically compact clastic sediment (commonly mud cracked)Evaporite minerals deposited originally in lake beds

Slide8

Dust Emission from

Playas

Wet playa

Dry playa

Conditions may promote dust

emission. Efflorescent salts in near-surface sediments produce mineral fluff & soft surfaces

Low levels of dust emission when sediment supply is limited and surface is undisturbed

Hard, compact surfaces

Franklin Playa

April 2005

Wet playa

Dry

playa

Slide9

Field study & Monitoring siteFranklin Lake Playa, USA

Mojave Desert

Franklin Lake

Amargosa River

Carson Slough

Ash Meadows

Slide10

Quickbird

satellite images

0.6-m resolutionApril 2006

Czarnecki, J.B., 1997. USGS Water Supply Paper, 2377.

Ash Meadows

Carson Slough

Ash

Meadows:

0.7

1.5

16

90

Specific Conductivity (mS cm

-1)

Spring Discharge:

a60,000 m3 day-1

Evaporation:b22,800 m3 day-1

Precipitation: 100mm yr -1 Pan Evap. 2500 mm yr -1

a

Dudley & Larson

, 1976;

b

Czarnecki &

Stannard

, 1997)

Slide11

Groundwater Ion Content Trends

Franklin Playa

Carson Slough

Ash Meadows

Slide12

Groundwater Metal Trends

85

180

190

83

93

As (ppm)

As (ppm) predicted in anhydrous salts (Cl) by mass balance from evaporation

Slide13

Trace Metal and Ion Content with Depth

As

U

Cl

SO

4

Franklin Playa Auger

Sediments

Evaporation Front:

Slide14

Surface

Evaporation front

Water table

Groundwater

vapor generated

Evaporation

Metals move with water

Water vapor rises with few metals

Metals accumulate in residual water

Chloride concentrated

Sulfates precipitated, few metals

Thick evaporation zone

evaporation zone

Thin

evaporation zone

Evap.

front

Water table

Groundwater

Evaporation

Metals move with water

Sulfates, chlorides precipitated with metals

Slide15

Surface and Dust sediment collection

Bulk dust collection

Dust

Wind-tunnel

Tests

Assess the potential vulnerability

of surfaces to wind erosion

Simulated winds to ~ 20 m/s to measure PM

10

dust flux

Slide16

Salt Crust Arsenic Spatial Trends

As

SO

4

:

Cl

Ratio in ground water

Slide17

Mobility of

Sulfates

ground water

crust

dust

ground water

dust

dust

dust

ground water

ground water

crust

crust

crust

Fractionation increases sulfate in crust and dust

Sulfates are mobile

SO

4

& Cl increase in

groundwater

Slide18

Bioaccessibility of Toxic Metals

Extraction pH

Temp (C)

Time Mixing control method

Gastric 1.5 37 I hr Shaker in Enviro Chamber

Intestinal 5.5 37 I hr Shaker inEnviro Chamber

Lung 7.4 37 24 hr Incubator

Physiologically based extractions in simulated

biofluids

to assess

bioaccessibility

of

As, Cd, Cr,

Pb

, Mo,

Sb

, W Se, U, etc.

Slide19

Uranium

Arsenic

Intestinal

Gastric

Lung

North

South

Extractions from dust in simulated

biofluids

Slide20

Extractions from dust in simulated

biofluids

Intestinal

Gastric

Lung

85

180

190

83

93

As (ppm)

As (ppm) predicted from Cl

Slide21

Summary on accessibility of toxic metals

Extractions from dust in simulated

biofluids

demonstrate that for both

Ar

and U, the potential for concentrations exceeding current ingestion limits could be reached

For these results there is no bias of the accessibility of

Ar

or U based on dust chemistry – this simplifies any prediction of other potential sources of toxic dust

Differences in the accessibility of

Ar

and U exists between the three tested

biofluids

, with the intestinal

biofluid

having the lowest ability to access the metals

Slide22

Summary of mobility

Sulfate

salts are the most mobile; easily precipitating from the groundwater and concentrating further when eroded

Toxic metals, in this case mainly As and U, are precipitated with the salts but mainly rely on the movement of chlorides to accumulate at the surface

The conceptual model proves that any history of a thin evaporation zone could lead to concentration of toxic metals near the surface if present in the groundwater and therefore groundwater chemistry alone is not a good predictor of the potential mobility and accessibility

Further work is currently under way to model wind erosion emissions based on local climate and surface conditions

Slide23

Slide24

PI-SWERL

Portable In-Situ Wind

ERosion Laboratory

Slide25

Slide26

Slide27

Slide28

Slide29


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