The correct answer is C. Potassium dichromate.

The questions describes a case of allergic contact dermatitis due to occupational exposure to potassium dichromate, also known as chromium, in wet cement. This allergen is present in wet cement as well as leather, such as leather gloves.

Carba mix is a rubber accelerator that can cause dermatitis to gloves and the “bleached rubber syndrome” in which elastic socks and waistbands cause ACD due to release of carba mix after being washed in bleach.

Formaldehyde is a preservative found in many industrial and household products and is frequently positive in hand eczema but is not specific to construction or concrete.

Nickel sulfate is an inexpensive metal used in jewelry and clothing and the most common positive on patch testing in North America.

Thimerosal is a mercury-containing preservative that frequently causes positive patch test reactions but is very rarely relevant. It is still contained in some vaccines, which are safe and should be recommended even for thimerosal allergic patients.

References: Mowitz M, Zimerson E, Hauksson I, Pontén A. Chromate and amine contact allergies in workers manufacturing precast concrete elements. Contact dermatitis. 2016 Dec;75(6):363-9.

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