Which of the following is a common indicator of organic pollution in water?

Biochemical Oxygen Demand (BOD) is a crucial measure used in water quality testing to indicate the level of organic pollution. BOD assesses the amount of oxygen that microorganisms will consume while decomposing organic matter in water. A high BOD value suggests a significant presence of organic material, which can lead to low levels of dissolved oxygen, adversely affecting aquatic life.

Water bodies with elevated BOD levels typically indicate contamination from organic sources, such as sewage or agricultural runoff. For wastewater treatment facilities, monitoring BOD is essential to determine the effectiveness of the treatment process and the potential environmental impact of the effluent discharged into natural waters.

In contrast, while chlorine residual, phosphate levels, and pesticide residues each play roles in assessing water quality, they do not directly measure the organic pollution in the same way that BOD does. Chlorine residual indicates the level of chlorine used for disinfection, phosphate levels are connected to nutrient pollution leading to algal blooms, and pesticide residues pertain to chemical contaminants. None of these are as directly indicative of organic matter presence as BOD.