Pollutants and Trophic Levels
In ecosystems, pollutants — especially non-degradable ones — move through the various trophic levels via food chains and food webs.
- Non-degradable pollutants are those materials that cannot be broken down or metabolized by living organisms.
- Example: Chlorinated hydrocarbons such as DDT.
- Even small amounts of such chemicals in the environment can accumulate and reach high enough levels within organisms to cause serious harm. This movement and buildup involve two key processes:
- Bioaccumulation
- Biomagnification
1. Bioaccumulation
Bioaccumulation refers to the entry and buildup of pollutants in an organism directly from the environment. |
- There is an increase in the concentration of a pollutant from the surrounding environment to the first organism in a food chain.
2. Biomagnification
Biomagnification is the process by which pollutants become progressively concentrated at each successive trophic level in a food chain |
- In other words, the concentration of the pollutant increases from one link in the food chain to the next.
For biomagnification to occur, a pollutant must: · Be long-lived (not easily broken down) · Be mobile (able to move and enter organisms) · Be soluble in fats (lipophilic, so it is retained in fatty tissues) · Be biologically active (causing harmful effects) |
- If a pollutant is short-lived, immobile, water-soluble (excreted easily), or biologically inactive, it is less likely to biomagnify or cause damage.
Impacts and Examples
- Pollutants tend to accumulate in fatty tissues of organisms.
- In mammals, pollutants can be detected in milk, which is rich in fat — making young animals particularly vulnerable.
- Example: DDT (a pesticide) is a classic example of a pollutant that bioaccumulates and biomagnifies through ecosystems.
Thus, biomagnification explains why top-level carnivores and humans are most affected by environmental toxins despite their low environmental concentration.
