Final answer:
The least emphasized consideration in the setting of standards for toxic exposure historically has been long-term effects. Research predominantly focused on immediate, high-dose exposures, neglecting the complex chronic effects that arise from prolonged low-dose exposure to contaminants.
Step-by-step explanation:
Historically, in the setting of standards for toxic exposure, the consideration that has been emphasized the least is b) Long-term effects. Initially, toxicological research concentrated on acute, high-dose exposures and the immediate, serious health threats they posed. This focus overshadowed the subtler and potentially equally harmful chronic effects that emerge from low-dose exposures over an extended period. It is only more recently that the complexities of long-term health impacts, such as endocrine disruption and genetic expression alterations, have come to the forefront of toxicological studies. This shift in focus has expanded our understanding of how contaminants affect health in less obvious ways, such as through modulation of the hormonal system, which regulates numerous biological functions across a wide array of species.