Heavy Metal Inorganic Contaminants

Naturally-Occurring Elements with High Atomic Weight

Exposure and Water Quality

Availability – the contaminant is in a form that has the potential to impact water quality, organism health, ecological health.

Mobility – the contaminant is in a form that allows it to disseminate in the environment.

Toxicity – the contaminant is in a form that is biologically harmful to organisms.

Availability/Mobility Depends Partly on Compound Solubility

HgNO3 SolubleHgCO3 Poorly soluble

PbNO3 solublePb(OH)2 poorly soluble

H3AsO4 SolubleAlAsO4 Poorly Soluble

CdCl2 solubleCdCO3 poorly soluble

Poor water solubility often limits a contaminant’simpact on aquatic systems and organisms.

Pb2+

Hg2+

AsO4-

Cd2+

IonsCompounds

Toxicity Depends Partly on the Form of the Metal

AsO3-3

AsO4-3

Both are toxic, but AsO3-3 is

Between 2x and 10x more toxic

Cr3+

Cr207-

Cr3+ is an essential micronutrientCr207

-2 is highly toxic

Hg2+

CH3Hg+

Both are toxic, but Hg2+ is rapidly excretedCH3Hg+ is slowly excreted and accumulates

(organic ion)

(Oxidation States)

Forms of Inorganic Metal Contaminants

1. As the dissolved ion (e.g. Hg2+)

2. As insoluble ionic compounds (e.g. Cd2+ + CO32- = CdCO3)

3. As organic compounds (e.g. CH3Hg+)

4. Bound to dissolved and particulate organics

5. Bound to solid mineral particulates (soils, dust)

All Affect Availability, Mobility, and Toxicity

Solid

Arsenic (As)

AsO3-3

AsO4

-3

Dominant Forms of Arsenic in the Environment

Arsenite Greater Toxicity and Mobility

Arsenate Less Toxic, Binds with Soil and Sediment Particles(aluminum and iron)

Limits Mobility

Arsenic is Naturally Occurring

Mobilization of arsenic in the environment arises from anthropogenic activities related to mining and ore processing,

metallurgy, agriculture, industry.

Natural waters, in general, contain low levels of total arsenic

Several arsenic-containing compounds are produced industrially

InsecticidesHerbicidesFungicidesDyesAnimal DipsWood Preservatives

Approximately 3400 cattle-dipping vats were constructedthroughout Florida from 1906 through 1962

Cattle Dipping VatsThe vats were generally filled with an Arsenic solution that killed ticks

In terrestrial, aerobic environments, arsenic tends to associate with aluminum and iron naturally found in soils, limiting mobility

AsO4-3

Southern Cattle Fever

Wood Preservation

Chromated Copper Arsenate

CCA

Water-soluble pesticide used to treat exterior grade lumber

47.5% CrO3, 34% As2O5, 18.5% CuOExtends wood usable lifetime 20-40 yearsUsed until 2004Ubiquitous in built environmentEnvironmental health risks identified over a decade ago

What is CCA Wood?

Courtesy of Julia Gress

AsO4-3

Children’s exposure to As from CCA wood staircases results in increased risk of potential health effects

Exposure and potential health risks are from ingestion of dis-lodgeable As and As-contaminated soil.

Gress, Julia, J. T. Lessl, X. Dong and L. Q. Ma. 2014. Assessment of children’s exposure to arsenic from CCA-wood staircases at apartment complexes in Florida. Sci. Total Environ. 476–477: 440–446

19 ppm As

Study: Assessment of Children’s exposure to As from CCA-wood Staircases

Assessment Measures

Soil As concentrations (Binding to Soil Particulates)

Dislodgeable As (DA) quantities on railings and steps

Dislodgeable As (DA) on objects stored under staircases

Estimates of Average Daily Dose (ADD), Lifetime Average Daily Dose (LADD), cancer risk

Courtesy of Julia Gress

Soils (ingestion) Dislogeable from Railings Dislogeable from Objects

Apt. A

Apartment complexes

A B C D0

5

10

15

20

25

Bioaccessible

As

(mg/

kg)

Soil Cleanup Target Level

Total

SOIL As Concentrations Around Staircases

Courtesy of Julia Gress

Amounts of Dislodgeable As on railings (µg/100 cm²)

Railing A-2

Railing D-4

16

Stairs at A serve 2 apartments, stairs at D serve 4 apartments with more residents/apt than A

A-1 A-2 A-3 D-3 D-40

1

2

3

4

5First pair of shoes

Second pair of shoes

DA

(µg/

100

cm2)

Courtesy of Julia Gress

DA on soles of shoes

Stairs at A serve 2 apartments

Stairs at D serve 4 apartmentsand more total residents

17

Apt. Complex

LADD (mg/kg/day)

Soil ingestion

LADD (mg/kg/day)

DA ingestion

Combined LADD

Lifetime Avg. Daily Dose

Cancer risk

A 1.0 x 10-5 4.0 x 10-

7

1.0 x 10-

5

1.6 x 10-5

B 8.1 x 10-6 0 8.1 x 10-

6

1.2 x 10-5

C 2.1 x 10-6 4.0 x 10-

6

6.1 x 10-

6

9.2 x 10-6

D 5.2 x 10-6 2.0 x 10-

5

2.6 x 10-

5

3.9 x 10-5

Risk above 1.0 x 10-6 considered significant. (USEPA)First field study to validate USEPA’s CCA-wood exposure model.

16X

12X

9.2X

39X

Estimated Exposure Doses and Cancer Risk

18

Apt. Complex

LADD (mg/kg/day)

Soil ingestion

LADD (mg/kg/day)

DA ingestion

Combined LADD

Lifetime Avg. Daily Dose

Cancer RiskAbove EPAStandard

A 1.0 x 10-5 4.0 x 10-

7

1.0 x 10-

5 10x

B 8.1 x 10-6 0 8.1 x 10-

6 8x

C 2.1 x 10-6 4.0 x 10-

6

6.1 x 10-

6 6x

D 5.2 x 10-6 2.0 x 10-

5

2.6 x 10-

5 26xRisk above 1.0 x 10-6 considered significant. (USEPA)

Estimated Exposure Doses and Cancer Risk

19

• Total soil As: 1.7 – 66.6 mg/kg

• Bioaccessible As: 1.4 - 25.2 mg/kg (18-

86% of total)

• DA on railings much higher when cracked and weathered

• Significant DA found on objects stored under steps

• Cancer risk higher than acceptable at all complexes

Conclusions

Naturally-Occurring Groundwater Arsenic Generally is a Broader Issue than Anthropogenic Sources

Bonus

1. The form in which an inorganic contaminant exists can determine toxicity. T/F2. Arsenic is a naturally-occurring element. T/F3. Painting CCA wood increases the amount of dislogeable arsenic. T/F4. Arsenate is highly mobile in the environment. T/F5. CCA stands for chromated copper arsenate. T/F

Naturally-Occurring Groundwater Arsenic Generally is a Broader Issue than Anthropogenic Sources

AsO3-3

AsO4-3

Both are toxic, but AsO3-3 is

Between 2x and 10x more toxic

AsO3-3 Is the form of arsenic in groundwater

Naturally-Occurring Groundwater Arsenic

Arsenic in Bangladesh

Ranked among the world's 10 poorest countries

http://www.youtube.com/watch?v=S62n06GqZI0

Bangladesh Prior to 1970s

One of the highest infant mortality rates in the worldPrincipally due to waterborne disease.

Ineffective water and sewage systemsPeriodic monsoons and floods

cholera, dysentery

water-borne pathogens

Deaths Due to Surface water contamination: 250,000/yr

The Solution: Tap groundwater resources

• easy• inexpensive• available

First 1 million tube wells replaced dug wells with aid from

World GovernmentsUNICEF

World Bank

12 million hand-operated tube wellsdeliver water to over 80% of the

rural village population

Infant mortality and diarrheal illness reduced by 50%

Wells in Floodplain and Delta Sediments

Arsenic containing Water Bearing Unit

Natural erosion ofarsenic-bearing rocksto water-bearing units.

Tube Well depths between 20m and 100 m

Himalayas

Majority of wells > 50 ppb arsenic Some wells contain 500 - 1000 ppb

WHO/U.S limit: 10 ppbBangladesh limit: 50 ppb

Delta and Floodplain Regions

Exposure Estimates

Above 10 ppb: 57 million peopleAbove 50 ppb: 35 million people

Early Symptoms:

Skin lesions and thickeningStrong skin pigmentation

Accumulative Toxin

Long-term Exposure

breathing problemsperipheral nervous system

lung and skin cancerdeath if exposed to high levels

2005 Studies

Tube wells replaced many dug wells about 30 years ago.

56.8% exceeded arsenic concentrations of 50 ppb, with 19.9% > 300 ppb

Next: Mercury