IB Environmental systems and societies 2.2H Pollutants and Human Activities Notes

Persistent Pollutants: some toxins never break down, so they build up in bodies and climb food chains

1. Non-biodegradable pollutants cannot be broken down by natural biological processes, so they stay in the environment for decades.
2. Common examples are PCBs, DDT, mercury, and microplastics.
3. Because they persist, these substances build up inside organisms through bioaccumulation and rise up food chains through biomagnification.

Bioaccumulation: a single organism collects toxin over its own lifetime

1. Bioaccumulation is the build-up of a persistent substance within one organism over its lifetime.
2. It happens when the organism absorbs a pollutant faster than it can excrete it.
3. Pollutants enter an organism in three main ways:
   1. direct absorption from water or soil,
   2. ingestion of contaminated food or prey,
   3. respiration of volatile pollutants.
4. Concentration therefore rises over time, especially in long-lived organisms.

Biomagnification: concentration climbs at each step up the food chain

1. Biomagnification is the increase in concentration of a persistent substance along successive trophic levels.
2. Each consumer eats many contaminated prey, so it takes in all the pollutant those prey had stored.
3. The toxin is not excreted, so it concentrates further at every level.
4. Top predators therefore carry the highest concentrations of all.

Bioaccumulation versus Biomagnification: the distinction examiners test most

Bioaccumulation acts within one organism; biomagnification acts between trophic levels.

Named Case Studies: Minamata and DDT show biomagnification harming people and wildlife

DDT and eggshell thinning in top predators