What does the warning signal word indicate about a substance?

The warning signal word is essential in indicating the level of hazard associated with a substance. In this case, a signal word that suggests it is "moderately toxic" indicates that exposure to the substance can cause harm but does not present an immediate or critical risk to life or health under typical conditions of use.

Moderate toxicity means that caution is required when handling the substance, as it can lead to adverse effects, but the effects are generally less severe than those of highly toxic substances. Therefore, users should be aware that while they must take care, the threat level is not as alarming as terms indicating high toxicity.

The other options, referring to highly toxic, slightly toxic, or non-toxic substances, would denote different levels of risk. Highly toxic implies a more severe impact on health, slightly toxic suggests low-level hazards, and non-toxic indicates no significant risk. In contrast, the indication of moderate toxicity serves as a balanced warning, ensuring individuals are informed about the potential danger while also recognizing that it can be managed with appropriate precautions.