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Plastics are a type of synthetic polymer found in certain types of clothes, bottles, bags, food wrappings and containers

Most plastics are not biodegradable and persist in the environment for many centuries

Large visible plastic debris (> 1 mm) is defined as macroplastic, while smaller debris (< 1 mm) is defined as microplastic

Macroplastic debris can be degraded and broken down into microplastic debris by UV radiation and the action of waves

Ocean currents will concentrate plastic debris in large oceanic convergence zones called gyres

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Alien Species are predators, parasites, or pathogens used to reduce or eliminate a pest as a method of biological control.

Harmful Effect:
Cane toads were introduced in Australia to control beetles that had become pests of sugar canes. However, the toads were unable to climb up into the sugar cane to feed on the beetles, an instead, attacked native species of insect.

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The increase in the concentration of a substance at a particular trophic level is called biomagnification

biomagnification refers to the tendency of pollutants to concentrate as they move from one trophic level to the next

Because pollutants become concentrated by biomagnification, higher trophic levels are more susceptible to their toxic effects

The pesticide DDT caused egg-shell thinning and population declines in species of birds that fed on exposed insects

Heavy metals (like mercury) released into waterways via industrial processes may become concentrated in fish

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Bioaccumulation is the gradual build up over time of a chemical in a living organism.

This occurs either because the chemical is taken up faster than it can be used, or because the chemical cannot be broken down for use by the organism and cannot be metabolized.

An example of bioaccumulation is the use of DDT as an insecticide in the 1950s and 1960s. Birds of prey were badly affected because it made the shells of their eggs very thin, causing them to break easily when the birds tried to incubate them.

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Eutrophication is the enrichment of an ecosystem (typically aquatic) with chemical nutrients (nitrates, phosphates, etc.)

The nutrients can be introduced via leaching from soil by rainfall or released as part of sewage

Eutrophication is common around agricultural lands where the use of artificial fertilisers are prevalent

An increase in nutrient supply within waterways will result in several ecological consequences:

A rapid growth in algal populations will occur (algal blooms) as a result of the increased availability of nutrients

As the algae die, there will be a subsequent spike in the numbers of saprotrophic microbes (decomposers)

The saprotrophs will consume available quantities of dissolved oxygen, leading to deoxygenation of the water supply

Eutrophication will also increase the turbidity of the water, which will reduce oxygen production by photosynthetic seaweeds

This will stress the survival of marine organisms, potentially leading to a reduction in biodiversity within the ecosystem

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DDT is a synthetic pesticide sprayed on crops and can be used against malaria mosquitoes.

It's washes into waterways in low concentrations, where it is biomagnified up the food chain.

Consequences:
- Stored in fats and accumulates quickly
- Very high concentrations in large fish and seabirds.
- It is responsible for reduced reproductive function and shell thinning in birds, which has impacted populations of large birds of prey.