HL Deb 27 November 1995 vol 567 cc25-8WA
The Countess of Mar

asked Her Majesty's Government:

Why the figure for the fall in blood Anticholinesterase (AChE) activities when the classic condition of organophosphate poisoning may occur was revised from 50 per cent. in the December 1980 version of Guidance Notes MS 17 from the Health and Safety Executive to 30 per cent. in the revised version of October 1987.

Why Section 19 of the December 1980 version of Guidance Note MS 17 from the Health and Safety Executive which detailed five "accurate and sensitive" methods for measuring cholinesterase activity in body fluids was omitted from the October 1987 version.

Why, when Sections 18 and 25(a) of the December 1980 version of Guidance Note MS 17 from the Health and Safety Executive made the point that the only efficient method of assessing cholinesterase activity in individuals must involve comparative measurements "over a period of time" and that this could occur only when "a single laboratory is involved" (Section 18) and "for comparability of serial results one laboratory should be used for all tests" (Section 25(a)), this recommendation was dropped from the October 1987 version.

Why Section 20 of the December 1980 version of Guidance Note MS 17 from the Health and Safety Executive, which read, "cholinesterase activity in normal whole blood and plasma varies between individuals. In order to interpret the significance of a measurement on a sample taken during or after exposure of a worker it is essential to be able to relate this to control measurements made in that individual during a time when he was not exposed to organophosphates. In the absence of such a baseline measurement a minor, but genuine, degree of cholinesterase inhibition due to exposure may be missed", was reduced to, "Interpretation of measurements in exposed subjects is greatly assisted if pre-exposure levels are available", in the October 1987 version.

Why Section 23 of Guidance Note MS 17 from the Health and Safety Executive (December 1980), which reads, "The success of any system of surveillance designed to detect or avoid toxic effects depends upon the following:

  1. (a) the availability of pre-exposure information;
  2. (b) carrying out the procedure on a regular basis using the appropriate technology, suitably trained staff and with the full co-operation of employees and management",
was revised to merely a procedure which "should be considered" in the October 1987 version.

Why Section 24, under "Health Surveillance", of Guidance Note MS 17 from the Health and Safety Executive which states that a scheme for monitoring workers would include, "(a) pre-exposure medical assessment to confirm fitness for such work and detect individuals with increased risks, e.g. those with liver disease or nervous disorders", was omitted from the October 1987 version.

Who were the authors of the original Guidance Note MS 17 from the Health and Safety Executive of December 1980 and of the revised version of October 1987.

Why section 27 of the 1980 edition of Guidance Note MS 17 from the Health and Safety Executive headed "Electrophysiological Monitoring" was replaced by the statement "Doubts have been expressed as to the value of EMG measurements as part of routine monitoring", and upon what evidence was this decision made.

Lord Lucas:

HSE Guidance Note MS 17, "Biological monitoring of workers exposed to organo-phosporous (OP) pesticides", gives practical advice for the monitoring of workers who regularly work with OPs. It was first published in 1981 and revised most recently in 1987. A 1985 conference on cholinesterases organised by the Association of Clinical Biochemists prompted the revision of the guidance. Developments in medical and scientific understanding made it possible to remove some of the discursive scientific reasoning and replace it with more precise statements. A search of HSE's file records and databases has revealed no sign of the papers associated with the original draft of MS 17, and we conclude that they were probably destroyed at the nine-year review. Papers associated with the 1987 revision are extant, but do not always show the reasoning behind a particular alteration, only that it was made and agreed.

On the specific points raised in the Questions:

(1) The figure for the fall in blood cholinesterase activity associated with the clinical symptoms of OP poisoning was revised from "about 50%" in 1980 to 70% in 1987 ("a fall to 30% of normal pre-exposure values"). This reflected the latest scientific findings on the toxicology of OPs. In practical terms a more important value is the reduction in cholinesterase activity that should prompt medical intervention. This should be well before any clinical effects would be apparent. The 1987 version (Section 26) recommends a medical examination if blood cholinesterase activity falls "by more than 30%" which is stricter than the value of 50% or more in the 1980 version and provides a margin of safety between the intervention point and the appearance of symptoms.

(2) The 1980 version of MS 17 listed five methods which had been applied to the measurement of cholinesterase and implied that one of them was not accurate or sensitive. The Ellman spectrophotometric method was considered to be the most appropriate and convenient. By 1987 standards the titrametric, manometric and electrometric methods would not be considered to have the necessary precision; accuracy and convenience of producing a rapid answer. The 1987 version refers to the electrometric and spectrophotometric methods and gives a specific reference for an automated version of the Ellman spectrophotometric method developed in HSE's Occupational Medicine and Hygiene Laboratory. The records do not show why the radiometric method is not mentioned, but it may have been judged less satisfactory because it involves the use of hazardous radio-isotopes.

(3) Any interpretation of cholinesterase activity measurements must consider the method used because of the different physical effects that are measured and the different units of activity that the result is expressed in. To reduce any variations due to the methodology, the 1980 version advises that results can be compared over time only when using a single laboratory. The records do not show the reasoning that led to this being removed in the 1987 version, but instrumentation improvements have meant that the precision obtainable is considerably better than in 1980. This together with the emphasis on a single spectrophotometric method would remove some of the variability between laboratories. Even greater precision would be obtained if one laboratory were to be used.

(4) There are differences in emphasis in Section 20 of the 1980 and 1987 versions, but the overall message is the same. Both versions acknowledge the natural variation of cholinesterase activity in individuals. Both recommend the measurements of cholinesterase activity before exposure and at periodic intervals during exposure (Section 25). The difference is that in the 1980 version such pre-exposure values are considered "essential" to interpret post-exposure measurements, while the 1987 version states that the interpretation of measurements in exposed workers is "greatly assisted" if pre-exposure values are available. The records do not show the reasoning that led to this change, but the current version sensibly recognises that in the absence of pre-exposure measurements useful results can still be obtained, although small changes may be overlooked.

(5) Section 23 of the 1980 version and Section 24 of the 1987 version both indicate what a successful programme of monitoring is dependent on. The phrase "should be considered" in Section 25 of the 1987 version refers to when monitoring is required. The equivalent in Section 24 of the 1980 version advised that regular health surveillance was "not required for occasional users of OPs", but that it was "desirable for those regularly exposed to large quantities of OPs [e.g. aerial crop-spraying pilots or ground contractors]". The 1987 version contains the stricter recommendation that regular monitoring "should be considered for anything more than occasional exposure to OP compounds, e.g. garden use". This represents a considerable increase in the number of people likely to be subject to regular monitoring for the effects of OP exposures.

(6) The guidance on the need for a pre-exposure medical assessment was removed because of the difficulty of reliably detecting individuals with liver disease or nervous system disorders. It also reflected a change of emphasis in MS 17—from guidance on health surveillance (in 1980) to guidance on biological monitoring (in 1987). Guidance on health surveillance and pre-employment medical assessments is now given in other guidance and in the approved code of practice under the Control of Substances Hazardous to Health Regulations.

(7) The 1980 and 1987 versions of MS 17 were prepared by HSE medical and scientific specialists following wide consultation, including advice from a committee with representatives from MAFF, Civil Aviation Authority, Chemical Defence Establishment and the University of Liverpool.

(8) Electromyograph (EMG) measurements were recognised to be of uncertain value in the 1980 version of MS 17 which stated that "the EMG method remains a research method requiring further evaluation". The records do not show the reasoning that led to this change, but EMG measurements are designed to detect subtle changes to neuromuscular function using highly specialised techniques to eliminate possible sources of error and are therefore not a suitable routine measure of exposure to OPs. In addition, a 1986 WHO report (Environmental Health Criteria (EHC) 63, Organophosphorous Insecticides: A General Introduction, a full copy of which will be placed in the Library) concluded that, "EMG does not appear to give a highly sensitive measure of exposure to an ingested organophosphorous compound". This makes the technique unsuitable for routine biological monitoring purposes. The 1987 version therefore correctly noted that EMG is most likely to be used in the investigation of cases of suspected OP poisoning. It will, for example, be used in this way in the recently announced epidemiological study funded by HSE, MAFF and DH.