What might happen if a pesticide has a long residual effect?

The correct answer is that a pesticide with a long residual effect might contaminate the food supply. Pesticides are intended to eliminate or control pests, but if they remain active in the environment for an extended period, they can inadvertently affect non-target organisms, including crops. This can lead to pesticide residues remaining on or in food products, which raises concerns for consumers, regulatory agencies, and food safety systems.

Long residual effects can mean that the pesticide continues to exert its effects long after application, increasing the likelihood that it will be present in the environment, including in soil and water supplies. When food is cultivated or prepared, these residues could potentially enter the food chain, posing health risks to humans and animals.

In contrast, while other potential outcomes exist, such as pest resistance and cost implications, these are not directly related to the immediate concern surrounding the contamination of food. Therefore, the long-term presence of pesticides in the environment is significant primarily for the risk of food contamination, making this the most relevant aspect of a pesticide's long residual effect.