The word "more nontoxic", implies a comparative degree of a substance's safety for human use. In contrast to this, the antonyms of "more nontoxic" would be terms expressing a greater degree of toxicity or danger. Some examples of these antonyms include poisonous, hazardous, lethal, toxic, harmful, deadly or fatal. These words indicate that exposure to a particular substance or product can cause severe harm or even death. It is essential to be aware of antonyms like these when choosing cleaning products, chemicals, or other potentially harmful substances, as they can have a significant impact on one's health and well-being.