What is the first product of organic matter decomposition that indicates "fresh pollution"?

The first product of organic matter decomposition that indicates "fresh pollution" is ammonia. During the initial stages of decomposition, microorganisms break down proteins and amino acids found in organic matter, resulting in the release of ammonia as they metabolize nitrogen-containing compounds. This process typically occurs in environments where there is an influx of organic waste or material, such as in sewage or heavily polluted water bodies.

Ammonia serves as a significant indicator of recent or fresh organic pollution because its presence signals that there has been a relatively recent introduction of organic material into the environment that is currently undergoing bacterial decomposition. This is particularly relevant in environmental monitoring and assessing water quality, where high levels of ammonia can indicate adverse conditions for aquatic life due to its toxicity.

In contrast, while sugars, carbon dioxide, and hydrogen sulfide are also products of decomposition, they are not as immediate or definitive indicators of fresh pollution. Sugars may be present in the environment but do not specifically point to organic pollution levels, carbon dioxide is a byproduct of respiration and decomposition that occurs later in the process, and hydrogen sulfide is associated with deeper stages of anaerobic degradation rather than the early phases of fresh pollution. Thus, ammonia is the most appropriate indicator of "fresh pollution."