Q12 — DMSO₄ Poisoning Case Study

Theoretical A Real exam question — full text reproduced under IBO's CC BY-NC-SA 4.0 license

A terminal cervical cancer patient arrived at the emergency room and received intravenous therapy and oxygen, but her condition did not improve. Medical personnel noticed a garlic-like odor, typically caused by sulfur-containing substances, emanating from her mouth, and white crystals formed in a blood sample taken from her. Subsequently, the medical staff began losing consciousness and having convulsions.

This 1994 incident at Riverside General Hospital was initially thought to be mass hysteria, later suspicion fell on DMSO₄: prior to admission, the patient had applied excessive amounts of DMSO-based ointments for analgesic purposes. While DMSO itself is non-toxic to humans, DMSO₄ is classified as a warfare agent. It rapidly undergoes the following reaction:

$$DMSO_4 + 2H_2O \rightarrow 2CH_3OH + H_2SO_4 \quad (1)$$

Skeletal structures of DMSO, DMSO2, and DMSO4, each showing two methyl groups attached to a central sulfur with increasing numbers of double-bonded oxygens (one for DMSO, two for DMSO2, and two double-bonded plus two ester-linked oxygens bridging back to the methyl groups for DMSO4). Figure 1. DMSO, DMSO₂, and DMSO₄ structures. DMSO₄ can be produced by successive oxidation reactions of DMSO and DMSO₂.

Compound	DMSO	DMSO₂	DMSO₄
Enthalpy of formation (kJ/mol)	-150	-373	-687
Solubility in water (g/L)	≥150	150	28

On your answer sheet, indicate “T” for true statements and “F” for false ones.

A. Out of the three involved substances, DMSO₂ most probably accounts for crystals in the collected blood.

B. DMSO can increase the rate of absorption of compounds through biological membranes.

C. The enthalpies of formation indicate that DMSO can rapidly change into DMSO₂ and then into DMSO₄ by being exposed to oxygen at room temperature.

D. Cervical cancer metastases in the ureters have likely restricted the only pathway of eliminating DMSO and its derivatives.

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Question reproduced from IBO 2024, Theoretical Exam Part A, licensed under CC BY-NC-SA 4.0 — attributed to the International Biology Olympiad. Open the full exam PDF · Community solutions (unofficial)