Environmental Chem Exam 4

Methods for treating contaminated ground water

1. Bio-remediation

2. Pump and Treat

3. In Situ Remediation

Bio-remediation (Ground Water)

• Microbial processes are used to oxidize/reduce contaminants

• Limited applicability (good for chlorinated solvents)

Pump and Treat

• Typically occurs once the source of contamination has been removed

• Contaminated ground water is pumped out of the ground, treated, and then returned

• Due to re-contamination up return, this process must often be run continuously

Reducing Wall

• wall is constructed through which contaminated water posses

• metal iron fillings are embedded in the wall which acts as the reductant

Which form (valence) of arsenic is most toxic?

• As(111)

How is arsenic typically introduced to groundwater?

Anthropogenic Sources:

• Pesticides/herbicides

• Abandoned mine drainage

• Coal Combustion

Naturally contaminated underground water brought to ground water wells (greatest cause of contamination)

How is Arsenic removed from groundwater?

• Aeration

• Precipitation

How do the solubilities of lead carbonate, lead hydroxide and lead phosphate compare?

Lead carbonate- Low (sparingly soluble)

Lead Hydroxide- Lower than carbonate

Lead Phosphate- Extremely Insoluble

This makes phosphate the most effective anion for immobilizing lead in soils and groundwater.

Can you describe the factors that lead to a drinking water crisis in Flint, MI? What was the main contaminant, and what were some of the additional contaminants/problems?

• Detroit’s water system added phosphates, which helped form a protective passivation layer inside pipes.

• Flint did not add phosphates, so this protective layer broke down.

• As a result, lead and iron pipes oxidized, releasing Pb²⁺ (lead ions) and Fe²⁺ (iron ions) into the drinking water.

• High chloride levels in the water further accelerated pipe corrosion, worsening contamination.

Acute Toxicity

Rapid onset symptoms following single exposure

Chronic Toxicity

Slowly developed (ex years) but long lasting symptoms as a result of continuous exposures

Carcinogen

Substances that cause cance

Teratogen

substances that cause birth defects

LD50

The dose that proves lethal to 50% of the test animals

NOAEL

The-No-Observable-Adverse-Effects-Level

Threshold Level

the highest dose which is not lethal to any test animlas

POP- Persistent Organic Pollutant

• Can be much higher in an animal than its surrounding environment

DDT

Is a synthetic chemical pesticide classified as an organochlorine insecticide. It was one of the first modern synthetic insecticides, widely used in the mid-20th century to control mosquitoes and agricultural pests.

PCB

Polychlorinated Biphenyls

• PCBs are sometimes mistakenly thought of as pesticides because they belong to the same broad family of chlorinated organic compounds as DDT and other organochlorine insecticides.

• However, unlike DDT, PCBs are not insecticides. They are industrial pollutants that became notorious for their persistence and toxicity in the environment.

A compound with a low LD50 value would be more or less toxic than a compound with a high LD50 level

More

Are inorganic or organic pesticides more toxic?

Inorganic pesticides are generally considered more acutely toxic than most organic (carbon-based) pesticides because they are elemental or mineral compounds that do not break down easily, can accumulate in soils, and often interfere directly with biological systems. Organic pesticides, while not harmless, tend to degrade faster in the environment and are often less persistent.

Bioaccumulation

The gradual build up of harmful substances such as pesticides, heavy metals, or other pollutants, in living animals over time

Biomagnification

The process by which toxic materials become increasingly concentrated in organisms as they move up the food chain

Substances with a Kow value of approximately ____ to ____ are considered persistent organic
pollutants

4 to 7

Most human consumption of POPs comes from food or from drinking water?

Food

DDT is an example of which general type of pesticide?

Organochlorines

What is a PCB?

• Colorless or yellow solids/liquid

• Very low water solubility

  • Log Kow values generally in 4.5-7.5 range

  • Very persistent and strongly bioaccumulate

• Biomagnification is a real problem

What is a dioxin?

• Any phenol having a chlorine or bromine adjacent to the OH can be a source of a dioxin

• Incinerators are now the major source of anthropogenic dioxin environment input

Why are dioxins and PCBs important pollutants?

• they dont break down easily

• bioaccumulation and biomagnification

• health impacts

  • neurological defects

  • cancer

  • chloracne

PFAS

What are they?

• Large group of synthetic chemicals with strong carbon-fluorine bonds that make them extremely durable

Why they’re used?

• They resist heat, water, oil, and stains so they’re used in products like nonstick cookware, waterproof clothing, food packaging, carpets, and firefighting foam

Why they’re a concern:

• Because they dont breakdown, PFAS accumulate in the environment and in living organisms. Exposure has been linked to health risks such as immune system effects, liver damage, certain cancers, and developmental issues

Sand

Course: 2000 um - 200 um

Fine: 200 um - 20 um

Silt

20 um - 2 um

Clay

2 um >

Which type of particle (sand, silt, clay) is generally most responsible for soil fertility? Which
holds water the best?

Clay for both

Cation Exchange Capacity

the measure of how many positively charged ions a soil can hold and exchange

Sand- Low CEC

Clay - Med CEC

Organic Material - High CEC

How are heavy metals retained in the soil?

Adsorption onto cation exchange sites of clay particles

What anion can be used to insolubilize heavy metals

AVS- Acid Volatile Sulfides

Heavy metals can react with sulfide ions. This reaction form insoluble metal sulfides which are very stable and poorly soluble in water. Because these sulfides are insoluble, the metals become immobilized in the soil reducing their bioavailability and toxicity

Stabilization/Solidification

Effective for:

• Metals

• Nonvolatile organics

Not useful for

• PCBs

• Volatile organic compounds

Additional Considerations

• Broad application, variety of soils, fast, low cost

• Contaminant is not removed, delay tactic

Soil Vapor Extraction

Effective for

• VOCs (Boiling Point below 150 degrees)

Not Useful for

• PCBs

• Metals

Additional Considerations

• Soil- unsaturated, doesn’t work in clay or silt

• Water table has to be at least 10 ft deep

• usually used for gas spills

Thermal Desorption

Effective for

• VOCs

• SVOCs

• PCBs

Additional Considerations

• Soil- Sand/gravel, 10-20% moisture content

• Ex Situ

Soil Washing

Effective for

• PCBs

• Organochlorines

• Pesticides

Not useful for

• VOCs

Electrokenetic Remediation

Effective for

• Full charge metals

• Organic compound with significant dipole (TCE)

Additional Considerations

• Soil- high water content, low permeability (clay)

• Slow

Incineration

Effective for

• Chlorinate hydrocarbons

• PCBs

• Dioxins

• Ok for VOCs

Not Useful for

• Heavy metals

Bioremediation

Effective for

• Organics

Not useful for

• Metals

Phytoextraction

• Metals

• Shallow source of contamination

Phytodegradation

Organics