Dimethylarsinic acid, also known as cacodylic acid, is an organoarsenic compound formerly used as an arsenical herbicide and now measured as one of the organic arsenic species determined as contaminants in foods, particularly seafoods. Unlike inorganic arsenic, its toxicity is lower, but speciation analysis distinguishes it from more hazardous forms when assessing dietary exposure. Regulatory monitoring of total and inorganic arsenic in rice and seafood relies on methods that separate the species accurately. Dietary exposure assessments weigh the lower toxicity of organic species against the higher hazard of inorganic arsenic.