The Effects of Pollution (DP IB Biology)

Biomagnification of Pollutants

• Biomagnification is the increase in concentration of persistent or non-biodegradable pollutants with ascending trophic level through a food chain

  • Not to be confused with bioaccumulation, which is the build-up of pollutants within an organism, or within a single trophic level

• As pollutants are passed up the food chain from one trophic level to the next, they can become more concentrated due to the decrease in total biomass of organisms at higher trophic levels

  • I.e. the smaller organisms at the bottom of the food chain will each consume a small volume of pollutant, and then the organisms at the top of the food chain will consume many smaller organisms and receive a much larger dose of pollutant

Biomagnification of DDT

• Toxins such as DDT (dichlorodiphenyltrichloroethane) are persistent pollutants that can enter food chains

• DDT was a widely used insecticide in the mid-20th century that was found to have harmful effects on top predators such as birds of prey

  • When DDT was sprayed on crops, it would leach into waterways and eventually enter freshwater and marine ecosystems

  • DDT would then enter food chains via plankton and accumulate in the bodies of fish 

  • These fish would then be eaten by birds, which would accumulate higher concentrations of DDT

• Because DDT is persistent and does not break down easily, it can continue to accumulate in the bodies of animals at higher trophic levels, leading to harmful effects such as thinning of eggshells and reduced reproductive success

  • The thin eggshells could not withstand the weight of the parent bird during incubation, so the eggs would break and fewer young birds would hatch

  • Over time this resulted in reduced bird populations

• DDT has now been banned worldwide, with the exception of its use in areas where it is essential in dealing with mosquitos that transmit malaria

Biomagnification of DDT diagram

Through the process of biomagnification, the concentration of DDT in the tissues of organisms increases at successively higher trophic levels in a food chain

Biomagnification of mercury

• Mercury is another example of a pollutant that can accumulate through food chains

• Mercury is released into the environment through activities such as coal-fired power plants and gold mining

• Once in the environment, mercury can be converted by microorganisms into a highly toxic form called methyl mercury, which can accumulate in the bodies of fish

• As larger fish eat smaller fish, the concentration of methyl mercury within the tissues of these fish increases, leading to potential harm for humans who eat large predatory fish such as tuna or swordfish

Effects of Plastic Pollution

• Plastics have a large negative impact on both land and water habitats due to their non-biodegradable nature

• Plastics that can cause pollution problems include

  • Macroplastics; these are plastic items that are more than 5 mm in length, and include plastic bags, bottles, food packaging, and fishing nets

  • Microplastics; pieces of plastic that are less than 5 mm in length

    • Microplastics come from macroplastics that have been broken into smaller pieces by, e.g. wave action or UV rays

• In marine habitats:

  • Animals often try to eat plastic, e.g.

    • Turtles may attempt to eat a plastic bag that resembles a jellyfish

    • Albatrosses may accidentally consume plastic when they fish, giving it to their chicks when they regurgitate food; the chicks may later starve due to their stomachs being full of plastic

  • Animals become caught in plastic, such as fishing lines, leading to injuries and death

  • As the plastic breaks down it can release toxins that can lead to biomagnification in the food chain

  • Once it has broken down into very small particles, it is commonly ingested by animals and enters the food chain

NOS: Scientists can influence the actions of citizens if they provide clear information about their research findings

• The impacts of plastic pollution have become very well understood by the public in recent years due to effective communication of the findings of scientists

  • E.g. Popular wildlife documentaries have shown footage of sea birds feeding plastic to their chicks

• This type of clear science communication can change public behaviour

  • People have petitioned food companies and supermarkets to reduce their plastic packaging

  • People may shop at stores that use less plastic

  • People may get better at household recycling and taking their rubbish home

  • People may opt for non-plastic items in their home, such as bamboo toothbrushes or paper straws for drinking