Water & Enviro Week 7

Pollution

Direct or indirect introduction (from humans) of substances or heat into water which may give rise to any harm

Point source

Well defined pollution source from a single point

Non point sources

Pollution enters from dispersed and uncontrolled source

Examples of point sources

1. Discharges from sewage treatment

2. Industrial wastewater

3. Piped discharges of farms

4. Leakage from small domestic sewage

Separate sewer systems

Sewer water does not combine pipes with stormwater en-route to being treated

Combined sewer system

Storm water discharge can be combined with sewage system during heavy rain

Control of point sources

Relatively easy - technology, regulation and discharge standards

Examples of non point sources of pollution

1. Runoff from agricultural land

2. Wash off of litter, dust and dry fallout

3. Landfill seepage

Conservative pollutants

Not affected by natural processes - concentration only reduced by dilation

Non conservative pollutants

Degrade via natural self purification processes

Toxic substances

Contaminants that directly kill organisms or inhibits their metabolic activity / reproductive behaviour

Lethal toxicity

Death by direct poisoning

Sub lethal toxicity

Toxicity below that level causes death - affects growth/reproduction/behaviour

Acute Exposure

Exposed to large doses over a short period of time

Chronic exposure

Exposed to a low dose of contaminant over a long period of time

Cumulative

Effect is increased by successive exposures/doses

Toxicity test end point

Concentration required to produce lethal effect on 50% of the population

Chronic toxicity tests

Examine effects on general wellbeing & survival of organisms

Additive effect

Overall toxicity is sum of toxic effects of each toxic substance

Synergistic effect

Overall toxicity > additive effect of all toxic substances present

Antagonistic effect

Overall toxicity < toxic substances were present alone

Bioaccumulation

Toxic pollutants build up in tissue within aquatic organisms faster than can be broken down & excreted

Biomagnefication

Increase in concentration of pollutant moving up the food chain