Transcript

Environmental Chemistry

IB Option EPart 4: Soil & Waste

Soil Degradation Soil quality has been altered in such a way that it

lowers crop production. Can be caused by changing weather patterns,

or by anthropogenic factors such as acidification contamination erosion salinization

from industrialization, irrigation, overgrazing, overharvesting of trees

Salinization from constant or excess irrigation.

Salts from irrigated water accumulate in soil long after the water evaporates.

Plants die from toxic levels of salt or inability to take up water from salty soil with their roots.

Nutrient depletion intensive farming –

no time for fields to be fallow; no organic fertilizers used

Soil pollution can be caused by

industrial discharge use of pesticides and fertilizers illegal dumping of spent engine oil, etc.

all lead to groundwater pollution.

Soil Organic Matter (SOM) organic constituents of the soil

Biological – humus provides source of energy and source of essential nutrient elements nitrogen, phosphorus and sulfur to sustain healthy growth.

Soil Organic Matter (SOM) organic constituents of the soil

Physical – humus helps soil retain moisture; dark color of humus absorbs heat.

Soil Organic Matter (SOM) organic constituents of the soil

Chemical – humus acts like clay with its cation exchange capacity. Contains active sites which enable it to bind to nutrient cations. Also acts as acid-base buffer.

Common organic soil pollutants Hydrocarbons and other VOCs Pesticides, herbicides & fungicides Polyaromatic hydrocarbons (PAHs) Polychlorinated biphenyls (PCBs)

Table 7: Methods of Waste DisposalMethod Advantages DisadvantagesLandfill Efficient method to deal with large

volumesFilled land can be used for building or other community purposes

Local residents may object to new sitesOnce filled, needs time to settle, and may require maintenance as methane released

Open Dumping

InexpensiveConvenient (for the dumper)

Causes air and ground water pollutionHealth hazard: encourages rodents and insects Unsightly

Ocean Dumping

Source of nutrientsConvenient and inexpensive

Danger to marine animalsPollutes the sea

Incineration Reduces volumeRequires minimal spaceProduces stable, odor-free residueCan be used as a source of energy

Expensive to build and operateCan cause pollutants, e.g. dioxins, if inefficiently burnedRequires energy

Recycling Provides a sustainable environment ExpensiveDifficulty in separating different materials; not possible in all cases

Table 8: RecyclingMaterial Description CommentsMetals Mainly aluminum and steel. The metal are

sorted, then melted and either reused directly or added to the purification stage of metals formed from their ores

Particularly important for metals such as aluminum, which require large amounts of energy to produce directly from ore

Paper Taken to the plant, sorted in grades. Washed to remove inks, etc., made into a slurry to form new types of paper, such as newspaper and toilet rolls.

Energy required to transport. Composting may be as efficient.

Glass Sorted by color, washed, crushed, then melted and molded into new products

Glass is not degraded during the recycling process, so can be recycled many times

Plastics Industrial plastic is already sorted, but household waste plastic must first be sorted. Degraded to monomers by pyrolysis, hydrogenation, gasification, and thermal cracking, then repolymerized

Fewer pollutants formed, and energy used to recycle rather than to make from crude oil. Better to reuse than to recycle.

Table 9: Plastics Recycling Codes (no need to memorize, just an “FYI” item)

Code Symbol

Abbrev. Name Typical Use

1 PET Polyethylene terephthalate Fizzy drink bottles and oven-ready meal trays2 HDPE High-density polyethylene Bottles for milk and washing-up liquids3 PVC Polyvinyl chloride Food trays, cling film, bottles for squash,

mineral water and shampoo

4 LDPE Low-density polyethylene Carrier bags and bin liners5 PP Polypropylene Margarine tubs, microwavable meal trays6 PS Polystyrene Yogurt pots, foam meat or fish trays,

hamburger boxes, vending cups, plastic cutlery, protective packaging for electronic goods and toys

7 OTHER Any other plastics that don’t fall into any of the above categories

E.g. melamine, which is often used in plastic plates and cups

Table 10: Nuclear WasteType Low Level Waste High Level Waste

Characteristics low activity; radioisotopes have relatively short half lives

high activity; radioisotopes have long half-lives

Examples items that have been used in areas where radioactive materials are handled (rubber gloves, paper towels, protective clothing, etc.)

spent fuel rods from nuclear power plants

Disposal Stored in steel containers in concrete-lined vaults OR stored in cooling ponds until it loses much of its activity and then; filtered through ion exchange to remove Sr and Cs and then dispersed

Fuel rods cased in ceramic or glass, packed in metal containers and buried deep in the earth in a location where geologists believe it won’t affect groundwater

Water and Soil Precipitation of heavy metal ions and

phosphates from water

When a salt is labeled “insoluble,” it really means that it has a very low/slight solubility in water.

MX(s) M+(aq) + X-(aq)

Water and Soil Precipitation of heavy metal ions and

phosphates from water

When a salt is labeled “insoluble,” it really means that it has a very low/slight solubility in water.

Solubility product, ksp=[M+][X-]

Water and Soil Many metal sulfides have very low

solubility products, but can still be precipitated out by bubbling other compounds through the water, making use of the common ion effect.


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