Why does potassium nitrite carry acute toxicity risk while having no cumulative effect in the body?

Why does potassium nitrite carry acute toxicity risk while having no cumulative effect in the body?
Potassium nitrite is grouped with sodium and calcium nitrite as a white to pale yellow, odorless powder that looks and tastes much like table salt and dissolves easily in water, making accidental ingestion a real hazard. Toxicity is acute rather than cumulative: nitrite is largely cleared within hours, but a single excessive dose oxidizes hemoglobin's ferrous iron to ferric iron, forming methemoglobin that cannot carry oxygen. Reported thresholds put poisoning at roughly 0.3-0.5 g and fatality at 1-3 g, with symptoms appearing within 10 minutes to 3 hours. Children and the elderly, with weaker metabolism, face higher risk at the same intake. This profile shapes handling, labeling and purity requirements across food, industrial and medical grades.