Water Pollution W1

Definitions, sources + transport of pollutants

Ecologists’ view

Intro of foreign materials into env should be kept at a level which no detectable biological change results

Economists’ view

Discharge/other action which occasions economic damage to man

USA Env protection agency definition

“Any substances in water, soil, or air that degrade the natural quality of the environment, offend the senses of sight, taste, or smell, or cause a health hazard. The usefulness of the natural resource is usually impaired by the presence of pollutants and contaminants”

Characteristics of pollution events

The pollutant

The source of the pollutant

The transport medium (air, water, soil)

The target (organism, ecosystem)

Holdgate’s pollution model (1979)

Notes:

No reason why pollutant can’t travel through air/water/soil at some point.

Chemical transformations may amplify/reduce impact.

Not all pollutants reaches target (deposition).

Discrete point source

e.g., sewage leak

Easier to identify + control

Diffuse source

e.g., acid rain, fertilisers

Harder to track causes + more likely to be affected by physical/biological factors that make it harder to deal with.

Example sources of pollution

Agricultural, e.g., fertilisers

electricity generation e.g., water vapour greenhouse gases

Derelict gas works

Metal Mining e.g., relicts on landscape, uses a lot of water + draining releases lots of metals.

Metal industries e.g., atm pollutants

Urban + industrial sources e.g., litter, car tyres, vehicle exhausts

Waste disposal + transport e.g., spillages

Effect generating properties

Toxicity e.g., consumption affects organisms

corrosion of metals e.g., impact on building from acid rain

Pathway determining properties

Affects distance + rate of dispersion in env.

e.g., organic material dissolved in water is controlled by its solubility

Primary pollutants

exert harmful effects in form in which they enter the environment

e.g., nitrates from fertilisers

secondary pollutant

pollutants are synthesised as a result of chemical processes in the env, often from less harmful precursors

e.g., ozone , which is formed when hydrocarbons and NOx combine in sunlight

Advection

(gravity) - movement with water mass

Diffusion

(turbulence + particle motion) - spreading out of material in water mass

Dispersion key factors

vertical movement restricted by:

• depth

• stratification

inputs without loss lead to accumulation of pollutants in:

• lakes + seas

• Lakes + sea sediments

Stratification

density of water depends on temperature

—> affects where pollutants sit in water

During stratification there is a limited exchange of water between strata.

Seasonal stratification

Winter

• less dense cold water over warmer, more dense water

Spring

• wind mixing plus low solar heating means less stratification

Summer

• solar warming makes surface water less dense than deeper, colder water

Autumn

• wind mixing plus low density difference, low solar heating

Epilimnion

Upper strata

Hypolimnion

Lower strata

(have less access to oxygen)

Air pollution

Move air movement at higher boundaries - so pollutants higher up will experience diffusion + advection faster.

There is some exchange between troposphere + stratosphere at equator.

Gases in stratosphere don’t wash out unless degraded by strong radiation above ozone.

Dispersion in horizontal plane

Generally less restricted dispersion.

Transport tends to be with wind in turbulent boundary layer.

Turbulence + thus dispersion is controlled by solar radiation, wind speed, cloud cover + topography (roughness of landform).

Important factors in soil pollution

soil composition + structure (wet, dry, anaerobic, aerobic, acid etc.)

pollutant properties (polar, non-polar, hydrophobic, hydrophilic, liquid, gas)

Soil properties of reactions

Soil at surface is more organic, so has more reactions.

Bottom soil more mineral.

Dry fields with cracks - rain flows through gaps + doesn’t come into contact with soil. If fields ploughed rain will percolate.

Exposure pathways of pollutants for humans

Air - inhalation

water - consumption of water or ingestion of aquatic organisms

Soil - plants being ingested

Indoor pollution

fabric of building e.g., asbestos

importing substances e.g., lead workers (but windows in these factories means pollutants can be diluted)