What environmental factor can lead to accelerated breakdown of pesticides in a lawn?

The correct choice highlights the role of high pH as a significant environmental factor that can accelerate the breakdown of pesticides in a lawn. Pesticides often undergo chemical reactions influenced by the pH of the environment they are in; a higher pH typically results in increased degradation rates of certain pesticides. Many herbicides and insecticides are designed to be stable under neutral conditions, but when exposed to higher pH levels, chemical hydrolysis or other degradation processes can occur more rapidly, thus diminishing the effectiveness of the pesticide.

In contrast, other factors such as low humidity, excessive rainfall, and low temperature generally do not facilitate the breakdown of pesticides in the same manner. Low humidity might slow down degradation due to reduced moisture necessary for hydrolysis, while excessive rainfall can lead to runoff and wash away pesticides before they break down. Low temperatures often slow down chemical reactions and biological processes that could otherwise lead to degradation, thus enhancing the persistence of the pesticide in the environment.