The following statements about "chemistry and health" are incorrect: () A. Iodine supplementation must be beneficial to human health B. "Hemodialysis" uses colloid.

A. Scientific iodine supplementation is beneficial to health, and excessive use of iodine products is extremely harmful. High iodine is as harmful to the body as low iodine, which will cause iodine goiter and even iodine-induced hyperthyroidism, so A is wrong;

B. Blood is a colloidal dispersion system, which can't penetrate the semi-permeable membrane, so "hemodialysis" uses the properties of colloid, so B is correct;

C. Chromium is a heavy metal and toxic. Taking "poison capsules" with excessive chromium content will cause harm to human body, so C is correct;

D. oil is a solvent for fat-soluble vitamins. When fat-soluble vitamins A, D, E and K are ingested together with oil, oil can promote the absorption of these vitamins, so D is correct;

So choose a.