How is soil pollution defined?

Soil pollution is defined as the contamination of soil with harmful substances, which can negatively affect the soil's health and the organisms that live within it. This contamination typically occurs through various means, such as the application of pesticides, industrial waste disposal, agricultural runoff, or the presence of heavy metals. The presence of these harmful substances can disrupt soil structure, alter its chemistry, and harm living organisms, including plants, animals, and microorganisms essential for maintaining ecological balance.

In contrast, other options represent different concepts related to soil but do not adequately capture the definition of soil pollution. For instance, natural formation of soil is a process that describes how soil forms over time through natural processes, while improvement of soil quality refers to practices that enhance the soil's ability to support plant life, leading to better agricultural productivity. Reduction of soil fertility pertains to the decline of soil's capacity to nourish plants, which may be a consequence of pollution but does not define soil pollution itself. Thus, the correct answer emphasizes the harmful nature of pollution and its impact on soil health.