Final answer:
The complexity in defining a poison in toxicology is due to the wide variety of toxic substances and their context-dependent impacts on living systems. The science of toxicology covers adverse effects ranging from individual toxins to environmental hazards, and not all substances are toxic at all doses or in all contexts.
Step-by-step explanation:
The statement from a pharmacology textbook that toxicology is regarded as the science of poisons, but developing a strict definition for poison is problematic, essentially highlights the complexity of toxic substances and their effects on biological systems. This complexity arises due to the vast array of potential toxins and the fact that a substance's impact can vary widely depending on factors such as dosage, exposure route, and individual sensitivities. Moreover, the term poison can be applied to substances that range from naturally occurring toxins to synthetic chemicals, and from medicinal drugs used improperly to environmental hazards.
Point (c) The definition of poison varies and poses challenges is most accurate in explaining the statement. Toxicology encompasses more than just the types of substances; it examines the adverse effects on living organisms and ecosystems, accounts for both intentional and accidental poisoning, and considers a wide range of harmful exposures, including environmental toxins. Additionally, the definition of what constitutes a 'poison' can differ depending on the context—what is a poison in one setting may be a useful compound in another, as illustrated by the varying roles of substances in medicine, pest control, or manufacturing.