What happens to the level of toxicity when two or more pesticides are combined?

When two or more pesticides are combined, the level of toxicity may indeed increase due to several factors, such as synergistic effects. Synergy refers to a scenario where the combined effect of two substances is greater than the sum of their individual effects. In other words, one pesticide may enhance the toxicity of another, leading to a more harmful overall effect on target organisms or the environment.

Additionally, different chemical mechanisms of action can interact in ways that may not be predictable based solely on their individual toxicity levels. This increase in toxicity can also extend to non-target organisms, highlighting the importance of considering the potential risks involved when using multiple pesticides in a single application or treatment strategy.

The notion of toxicity remaining the same or decreasing does not account for these complex interactions, which is why the possibility of increased toxicity is the most accurate answer. Unpredictability, while true in certain contexts, is generally less emphasized in terms of combined chemical effects compared to clear scenarios of increased toxicity.