Which pesticide is considered least toxic to humans?

The least toxic pesticide to humans among the options provided is ortho boric acid. This compound is often used as an insecticide and is known for its relatively low toxicity levels when handled properly. Boric acid works by disrupting the metabolism of pests, leading to dehydration and death, but it does not pose significant health risks to humans when used according to guidelines.

While methyl chlorid, multihion, and Premise 75 can be effective in controlling pests, they have higher toxicity levels associated with human exposure. Methyl chloride is a solvent that can be quite harmful if inhaled or absorbed through the skin. Multihion, a type of organophosphate pesticide, is also linked to neurotoxic effects and can be dangerous if proper safety precautions are not taken. Premise 75, containing the active ingredient imidacloprid, is a neonicotinoid, which has shown toxicity in humans and other non-target organisms.

In contrast, ortho boric acid's low toxicity profile makes it a more favorable choice, especially in residential settings where safety is a concern. When used as directed, it poses minimal risk to humans while still being effective against various pest species.