Salty Dust: - PowerPoint Presentation

Slide1

Salty Dust:

Increasing the accessibility and mobility of toxic metals

Dr.

James KingSlide2

AcknowledgementsRichard Reynolds, Harland Goldstein, Jim Yount, George

Breit, Suzette MormanGeorge Nikolich, Jack Gillies, Vic EtyemezianSlide3

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) LakeSlide4

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 surfaceSlide5

Dust Emission MechanicsDirect entrainment

Highly dependent on surface conditionsGenerates relatively smaller amounts of dustSensitive to wind regime

F

=

Au

*

3 5

Saltation Bombardment

Dependent on sand supply conditions

Fetch effects are important

q = Bu*3Surface Roughness

Vegetation, rocks, and crusts can modify the efficiency of dust emission mechanicsSlide6

Playa Surface Characteristics

Relatively stable with time

Typically

very hard

Variable &

Dynamic

Soft – in areas of fluffy & puffy sediment

Hard – in areas of crust

Wet playa

Dry playa

Hard, compact surfacesSlide7

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 Playa

Typically

compact clastic sediment (commonly

mud cracked)

Evaporite minerals deposited originally in lake bedsSlide8

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

playaSlide9

Field study & Monitoring siteFranklin Lake Playa, USA

Mojave Desert

Franklin Lake

Amargosa River

Carson Slough

Ash MeadowsSlide10

Quickbird

satellite images

0.6-m resolution

April 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:

a

60,000 m

3

day

-1

Evaporation:

b

22,800 m

3

day

-1Precipitation: 100mm yr -1 Pan Evap. 2500 mm yr -1aDudley & Larson, 1976; bCzarnecki & Stannard, 1997) Slide11

Groundwater Ion Content Trends

Franklin Playa

Carson Slough

Ash MeadowsSlide12

Groundwater Metal Trends

85

180

190

83

93

As (ppm)

As (ppm) predicted in anhydrous salts (Cl) by mass balance from evaporationSlide13

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 metalsSlide15

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 fluxSlide16

Salt Crust Arsenic Spatial Trends

As

SO

4

:

Cl

Ratio in ground waterSlide17

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

groundwaterSlide18

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 IncubatorPhysiologically 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

biofluidsSlide20

Extractions from dust in simulated

biofluids

Intestinal

Gastric

Lung

85

180

190

83

93

As (ppm)

As (ppm) predicted from ClSlide21

Summary on accessibility of toxic metalsExtractions from dust in simulated biofluids demonstrate that for both

Ar and U, the potential for concentrations exceeding current ingestion limits could be reachedFor 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 dustDifferences in the accessibility of Ar

and U exists between the three tested

biofluids

, with the intestinal

biofluid having the lowest ability to access the metalsSlide22

Summary of mobilitySulfate salts are the most mobile; easily precipitating from the groundwater and concentrating further when erodedToxic 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 accessibilityFurther work is currently under way to model wind erosion emissions based on local climate and surface conditionsSlide23
Slide24

PI-SWERL

Portable In-Situ Wind ERosion Laboratory