HL Deb 11 April 1994 vol 553 cc80-2WA
The Countess of Mar

asked Her Majesty's Government:

Why they maintain that there is no connection between nerve gas and organophosphorus compounds used commercially when the symptoms of, and the treatment for, acute exposure are the same.

Viscount Cranborne

Responsibility for the subject of this question has been delegated to the Chemical and Biological Defence Establishment under its Chief Executive, Doctor G. S. Pearson, CB. The agency is therefore responding to the question.

Letter to the Countess of Mar from the Director General of the Chemical and Biological Defence Establishment, Dr. Graham Pearson, dated 11 April 1994.

  1. 1. Your Parliamentary Question to Her Majesty's Government of 28 March 1994 asking why they maintain that there is no connection between nerve gas and organophosphorus compounds used commercially when the symptoms of, and the treatment for, acute exposure are the same has been passed to me to reply as Chief Executive of the Chemical and Biological Defence Establishment.
  2. 2. The structure of organophosphorus nerve agents is significantly different from that of the organophosphorus sheep dips and their purpose is different. For an organophosphorus nerve agent, the phosphorus atom in the structure has the following linkages:
    1. a. a double bond to an oxygen atom
    2. b. a direct link to a carbon atom, and usually,
    3. c. a direct link to a halogen or a sulphur atom attached to a carbon atom
    4. d. a direct link to an oxygen atom attached to a carbon atom
    Such nerve agents principally attack the body through the respiratory system although some nerve agents also WA 81 attack the body through the skin. For an effective nerve agent attack, the agent will need to vaporise over time and result in a downwind hazard area.
  3. 3. In contrast, the organophosphorus sheep dips have the following chemical linkages to the phosphorus atom in the structure:
    1. a. one or two direct links to an oxygen atom attached to a carbon atom
    2. b. no direct link to a carbon atom and, may have:
    3. c. a phosphorus double bond to a sulphur atom
    and consequently have a much reduced mammalian toxicity. For an effective sheep dip there is no requirement for the material to vaporise over time as the route of attack is through contact with the insects. Indeed, the organophosphrus sheep dip compounds have extremely low volatility and this renders any inhalation exposure insignificant.
    4. WA 82
  4. 4. The organophosphorus sheep dips are designed to have high insecticidal activity and low mammalian toxicity. The difference in the structure of nerve agents and sheep dips exploits differences in the metabolism of insects and mammals. For example, in insects the double bond between phosphorus and sulphur in some sheep dips is metabolised into the more toxic double bond between phosphorus and oxygen. Such metabolic changes occur more slowly in mammals such as sheep or man. In addition, mammals detoxify the sheep dip materials much more rapidly than do insects.
  5. 5. It should be recognised that in the case of nerve agent attacks, the material is used in essentially pure form. In so far as sheep dips are concerned, the organophosphorus component is only present as a small proportion of a mix containing several other materials. It is not easy therefore to extrapolate from organophosphorus nerve agents to sheep dip materials.