Factors affecting the rate of pollutant degradation

Factors affecting the rate of pollutant degradation

1. pH

   • At a low pH, toxic metal ions become more mobile, inhibiting enzyme action in detritivores and decomposers, thus reducing their ability to break down pollutants.
     • Metal + acid -> salt + hydrogen
   • Moving too far from the optimum pH reduces the rate of metabolic activity in microbes and thus reduces the rate at which they degrade pollutants (eg. crude oil).
   • In water with a very high pH (above 8-9), pesticides typically break down more rapidly via alkaline hydrolysis.

2. Temperature

   • High air temperatures allows for increased rate of chemical reactions on the material surface of a pollutant.
     • High temperature allows for a rapid rate of reaction (in most cases) by provding more energy for reactions to take place.
   • Low atmospheric temperature above Antarctica allow for the degradation of ozone molecules by chlorine free radicals into diatomic oxygen and chlorine monoxide. Chlorine only become chemically active under such low temperatures.
   • Low temperatures allow the formation of stratospheric clouds that provide a surface for chemical reactions to take place, increasing the rate of ozone degradation.

3. Light intensity

   • High light intensity can cause the photochemical degradation of pollutants (eg plastics). This occurs when plastic absorbs UV rays, breaking bonds within the polymer and leading to photo-oxidation.
   • High light intensity allows for algae and cyanobacteria to degrade pollutants (eg. pesticides, herbicides and dyes) more rapidly through the excretion of specific enzymes. High light intensity allows these organisms to generate more energy via photosynthesis.
   • High light intensity allows for rapid phytodegradation of organic pollutants (eg. pesticides) by plants. This process involves the metabolising and destroying of contaminants within plant tissues. High light intensity provides more energy for photosynthesis to take place.

4. Oxygen concentration

   • High concentration of oxygen allows for rapid aerobic bacterial or fungal digestion of organic and inorganic pollutants (eg. sewage) into inorganic nutrients.
   • High concentration of oxygen allows for the oxidation of sulfide ores, resulting in sulfur dioxide.
     • This process increases the solubility of many metals (including heavy metals, making them more harmful to the environment).
   • In an environment with a low oxygen concentration, microorganisms anaerobically digest organic pollutants (eg. sewage or food waste) into simpler matter at a slower rate than aerobic digestion.

5. Degradation is the process by which substances are broken down. It can involve both biotic and abiotic processes.