Enviro Chem Exam 2- Toxic Chemicals and Heavy Metals, Waste

Oxidation states of Hg?

• Harmful: methyl mercury (organic mercury)

• Common: elemental/metallic Hg

Oxidation states of Cr?

• Harmful: Cr(VI)

• Common: Cr(III)

Oxidation states of Pb?

• Harmful: Pb²⁺

• Common: Pb⁰_, Pb(IV)

Oxidation states of As?

• Harmful: Arsine = AsH₃

• Common inorganic/organic

Toxic effects of Hg?

Neurotoxicity, birth defects, respiratory damage

Toxic effects of Cr?

Carcinogenic, kidney failure, ulcers (stomach, skin, nose lining)

Toxic effects of Pb?

Organ toxicity, central nervous system, liver damage

Toxic effects of As?

Cardiovascular disease, cancer, skin disorders

Infamous environmental contamination of Hg?

Minamata disaster – Japan 1956 mercury contaminated water dumped into Minamata bay (locals poisoned by consuming fish)

Infamous environmental contamination of Cr?

Hinkley Groundwater Contamination – 1952-1956 gas company dumped Cr contaminated water around Mt. Hinkley – levels rose to be toxic (highly contaminated) – people affected, lung cancer

Infamous environmental contamination of Pb?

Kabwe Lead Poisoning – Lead/Zn mine in Africa (owned by colonial companies) – toxic waste never cleaned up, eventually got into water, air contamination, health impacts in children and miners

Infamous environmental contamination of As?

Bangladesh Arsenic Poisoning – Early 1990s/200s Arsenic contamination through wells, tapped into contaminated groundwater aquifers (As contaminated)

Remediation efforts/chemistry of Hg?

Bioremediation using plants + microorganisms to modify Hg compounds into less harmful states; chelating agents (EDTA) to complex Hg ions

Remediation efforts/chemistry of Cr?

Precipitate Cr out using iron salts + hydroxide; planting crops to absorb Cr (alfalfa)

Remediation efforts/chemistry of Pb?

Pb + Fe₂(SO₄)₃ à PbFe₃ (plumbojarosite) – reduces bioavailability

Remediation efforts/chemistry of As?

Physical methods – combining contaminated soil w/uncontaminated and doing acid washes; microorganisms to degrade As (convert into different forms or absorb); adsorption w/activated alumina or iron oxides

What are the different types of garbage waste?

• Industrial waste: demolition debris, refinery sludge, construction materials

• Municipal solid waste: food wastes, disposable goods, used electronics

How is garbage typically disposed of?

Landfills and incineration

What is the first stage of garbage decomposition?

• Aerobic bacteria converts nitrogens to nitrates (which has harmful effects)

• Longest stage; can continue for years

What is the second stage of garbage decomposition?

• Anaerobic bacteria converts organics into carboxylic acids, carbonic species, and H2

• Nitrogens are converted into ammonia

• pH drops to 4-5 as metals are solubilized into leachate

What is the third stage of garbage decomposition?

• Different anaerobic bacteria convert organics into CO2 and CH4

What is leachate?

Water has filtered through solid materials and dissolved some of the components/chemicals (like VOCs, bacteria, heavy metals, salts)

Types of recycling?

• Pre-consumer recycling: using waste generated during manufacturing process

• Post-consumer recycling: reuse materials recovered from domestic and commercial consumers (ex. aluminum, paper, plastic, glass)

Why is aluminum recycling the most efficient?

• Can be recycled indefinitely without loss of quality

• Saves 95% of energy needed to produce new Al

Why is paper recycling the not as efficient?

• Saves 25% of energy needed to produce new paper

• Quality loss over time

What is plastic made up of and why are they so commonly used/produced?

Polymeric organic molecules such as polyethylene and polystyrene (aka. styrofoam); cheap to produce but expensive to recycle and are resistant to degradation

What are the 4 primary techniques of reusing plastics?

• Reprocess

• Depolymerize

• Transform

• Burn

Reprocessing of plastics?

Most common; re-melt or reshape into a new product (physical) (ex. bottles turned into carpet/clothing fiber)

Depolymerization of plastics?

Breakdown to molecular constituents (chemical); difficult to reuse

Transform of plastics?

Turned into a lower quality substance to make other materials (chemical) (ex. plastic turned into liquid lubricant)

Burning of plastics?

Produces energy