The invention discloses the use of a treatment composition for preventing, or reducing, the production of contaminants selected from microorganisms and microorganism-produced toxins by contacting the substrate with the composition. The composition comprises a water glycerol mixture and calcium hydroxide in which the percentage by mass of glycerol in the water glycerol mixture is between 5% and 95%, at least some of the calcium hydroxide is dissolved in the water glycerol mixture and the concentration of the dissolved calcium hydroxide in the water glycerol mixture is at least 1.5 times higher than the maximum concentration of dissolved calcium hydroxide which can be obtained in water alone, thereby preventing or reducing the production of the contaminants. The extent of the prevention or reduction is at least 1.5 times more than the corresponding prevention or reduction produced by a treatment composition comprising water and calcium hydroxide only.
