What is the excess amount of oil necessary to cause a sheen in water?

The correct answer indicates that an excess amount of oil between 15 to 20 parts per million (ppm) is necessary to cause a sheen in water. This range reflects the minimum concentration at which the oil can form a visible film on the water surface.

Sheens are typically the first visual indicator of oil contamination in aquatic environments. At concentrations lower than this range, oil may still be present but not in sufficient quantity to create noticeable surface effects. When oil concentrations exceed this threshold, they can disrupt the environmental balance, affecting marine life and water quality. Understanding these thresholds is crucial for compliance with environmental regulations and for effective pollution response strategies.