130. A bioremediation mesocosm experiment has been carried out on a plot with 250 ppm aromatic molecules as
contaminants. After 15 days the level of aromatic molecules came down to 100 ppm at a temperature of 48
± 2°C. The electrical conductance of this site has increased over time because of the
1. Accumulation of NaCl
2. Evaporation of aromatics
3. Increase in organic acids
4. Production of CO2 

Question

A bioremediation mesocosm experiment has been carried out on a plot with 250 ppm aromatic molecules as contaminants. After 15 days the level of aromatic molecules came down to 100 ppm at a temperature of 48 ± 2°C. The electrical conductance of this site has increased over time because of the:

1. Accumulation of NaCl

2. Evaporation of aromatics

3. Increase in organic acids

4. Production of CO₂

Detailed Explanation

Bioremediation is the use of microorganisms to degrade and detoxify environmental contaminants like aromatic compounds (e.g., benzene, toluene, xylene).

In a mesocosm (a controlled outdoor experimental system), the microbial community metabolizes these pollutants under elevated temperature conditions, such as the 48 ± 2°C mentioned here.

Understanding Electrical Conductance

Electrical conductance of a solution (or soil slurry) is a measure of its ionic content. The more charged particles (ions) present, the higher the conductance.

What Happens During Aromatic Compound Breakdown?

1. Microbial degradation of aromatic hydrocarbons leads to:

   • Formation of intermediate metabolites, including organic acids such as acetic acid, lactic acid, and succinic acid.

   • These dissociate in solution, releasing H⁺ and other ions, thereby increasing the ionic concentration.

2. This results in a significant increase in electrical conductance of the surrounding environment.

3. Other options are less likely:

   • NaCl accumulation: Not typically a byproduct unless externally introduced.

   • Evaporation of aromatics: Would reduce contaminants but not increase conductance.

   • CO₂ production: Is a gas, and while it’s a valid metabolic product, it doesn’t contribute to ionic concentration directly.

✅ Correct Answer: 3. Increase in organic acids

Organic acids ionize, increasing the ionic strength and electrical conductance of the system over time.