Exposure to mixtures of chemicals are greater than expected on the basis of effects of exposure to each chemical individually. This is known as synergism.

Synergism refers to the phenomenon where the combined effect of exposure to two or more chemicals is greater than the sum of their individual effects. In other words, the interaction between chemicals in a mixture can lead to a stronger or more potent effect than what would be predicted based on the effects of each chemical individually.

Factors contributing to synergistic effects:
Synergistic effects can occur due to various factors, including:

1. Mode of action: Different chemicals can target different biological pathways or mechanisms within an organism. When these chemicals act on the same biological pathway or mechanism, they can have a cumulative effect, amplifying their overall impact.

2. Enhanced absorption: Chemicals in a mixture can influence the absorption and distribution of other chemicals in the body. This can result in increased exposure to certain chemicals, leading to a stronger overall effect.

3. Potentiating effects: Some chemicals can enhance the toxic effects of others by increasing their toxicity or altering their metabolism within the body. This can result in a synergistic effect when combined with other chemicals.

4. Interactions at the cellular level: Chemicals can interact with cellular processes and pathways, leading to enhanced or altered effects when combined. These interactions can disrupt normal cellular functions and result in a synergistic effect.

Implications of synergistic effects:
Understanding synergistic effects is important in assessing the risks associated with exposure to chemical mixtures. The combined effect of chemicals can be significantly different from what would be predicted based on the effects of each chemical individually. This means that relying solely on the toxicity data of individual chemicals may underestimate the potential harm posed by a mixture.

Synergistic effects can have serious implications for human health and the environment. They can lead to increased toxicity, enhanced risks of adverse health effects, and even the development of new or unexpected effects that were not observed with individual chemicals. Therefore, it is crucial to consider the potential for synergistic effects when evaluating the safety of chemical mixtures and establishing regulatory guidelines.

In conclusion, synergism refers to the phenomenon where exposure to mixtures of chemicals results in a greater effect than what would be expected based on the effects of each chemical individually. This interaction between chemicals can have significant implications for human health and the environment, highlighting the need for comprehensive assessments of chemical mixtures to ensure the protection of public health.