Suggest reasons for the following: 1. A water sample collected from the surface

Question

Suggest reasons for the following:

1. A water sample collected from the surface of a lake at dawn had a much lower dissolved oxygen content than a similar sample collected at dusk

2. Ultra trace amounts of several pesticides were found on home grown tomatoes that do not use pesticides

3. The polyaromatic hydrocarbons could not be extracted from the surface of sediment samples using microwave assisted extractions with hexane

4. Extraction of a water sample known to contain aromatic amines was not successful, no amines were extracted

Explanation / Answer

1.) Dissolved Oxygen content Decreases with increase in temperature.

3.) because PAHs which consist of fused benzene rings are hydrophobic in nature with very low water solubility and high octanol-water partition coefficient. Hence, they tend to adsorb tightly to organic matter in soil rendering them less susceptible to biological and chemical degradation. Prolonged aging time in contaminated soil promotes the sequestration of PAH molecules into micropores and increases the recalcitrance of PAHs towards treatment.

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