RR540 The HSE Grain Dust Study

1 Health and Safety Executive The HSE Grain dust Study workers' exposure to Grain dust contaminants, immunological and clinical response Prepared by the Health and Safety Laboratory for the Health and Safety Executive 2007 RR540 Research Report Health and Safety Executive The HSE Grain dust Study workers' exposure to Grain dust contaminants, immunological and clinical response J R M Swan, D Blainey & B Crook Health and Safety Laboratory Harpur Hill Buxton Derbyshire SK17 9JN Inhalation of airborne micro organisms and their associated contaminants in the workplace can cause a range of immunological and respiratory symptoms. The mechanisms through which these respiratory effects are caused are not all fully understood. The evaluation of worker exposure is essential for establishing causal relationships between occupational disease and one or several specific micro organisms or their associated contaminants.

2 This Study investigated the role of micro organisms and their associated contaminants in the development of immunological and clinical response in workers exposed to Grain dust . The objectives were: To assess the exposure of Grain workers in the UK to inhalable Grain dust , the microbial contaminants in Grain dust , including identification of the predominant micro organisms involved, and to endotoxin (bacterial cell wall toxins). To measure the prevalence of immunological response to Grain dust associated allergens in UK Grain workers. To examine the long term clinical and immunological effects of workplace exposure to Grain dust and its contaminants in terms of its effect on respiratory health. This was done by establishing a cohort of 321 workers exposed to Grain dust (farmers at 27 farms and dock workers at 2 docks in South East England) and maintaining as many as possible in the cohort for repeated immunoassay and clinical assessment over two Study phases, Phase 1 from 1990 to 1993 and Phase 2 from 1997 to 2003.

3 This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy. HSE Books Crown copyright 2007 First published 2007 All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means (electronic, mechanical, photocopying, recording or otherwise) without the prior written permission of the copyright owner. Applications for reproduction should be made in writing to: Licensing Division, Her Majesty s Stationery Office, St Clements House, 2 16 Colegate, Norwich NR3 1BQ or by e mail to hmsolicensing@cabinet ii CONTENTS 1 1 Organic dust , Grain dust and respiratory disease .. 1 Grain dust .. 1 The role of atopy in occupational allergy .. 2 Prevalence of allergic respiratory symptoms in UK workers.

4 2 The role of endotoxin in respiratory disease .. 3 The UK maximum exposure limit (MEL) for Grain dust .. 5 The Health and Safety Executive Grain dust survey: 5 2 MICROBIOLOGICAL EXPOSURE 7 Background .. 7 Study sites, Materials and Methods .. 7 Results summary and 11 Summary of microbiological exposure Study .. 23 Conclusions .. 30 3 IMMUNOLOGY Study .. 31 Aim .. 31 Study Population .. 31 Immunoglobulin G immunoassay .. 32 Immunoglobulin E immunoassay .. 33 37 Discussion; immunology results .. 45 4 CLINICAL Study .. 51 Introduction and Summary of Phase 51 53 55 Summary of findings Clinical Study .. 70 5 GENERAL DISCUSSION .. 72 6 QUESTIONS ADDRESSED BY THE Study .. 74 Has the MEL reduced sensitisation? .. 74 Did anyone develop new IgG or IgE during the Study ?.. 74 Should the MEL be reduced to reduce sensitisation?.. 74 Does new sensitisation result in new symptoms?

5 75 7 OVERALL 76 8 MAIN 78 9 ANNEX 80 10 REFERENCES .. 90 iii iv EXECUTIVE SUMMARY Objectives Inhalation of airborne micro-organisms and their associated contaminants in the workplace can cause a range of immunological and respiratory symptoms. The mechanisms through which these respiratory effects are caused are not all fully understood. The evaluation of worker exposure is essential for establishing causal relationships between occupational disease and one or several specific micro-organisms or their associated contaminants. This Study investigated the role of micro-organisms and their associated contaminants in the development of immunological and clinical response in workers exposed to Grain dust . The objectives were: 1. To assess the exposure of Grain workers in the UK to inhalable Grain dust , the microbial contaminants in Grain dust , including identification of the predominant micro-organisms involved, and to endotoxin (bacterial cell wall toxins).

6 2. To measure the prevalence of immunological response to Grain dust associated allergens in UK Grain workers. 3. To examine the long term clinical and immunological effects of workplace exposure to Grain dust and its contaminants in terms of its effect on respiratory health. This was done by establishing a cohort of 321 workers exposed to Grain dust (farmers at 27 farms and dock workers at 2 docks in South East England) and maintaining as many as possible in the cohort for repeated immunoassay and clinical assessment over two Study phases, Phase 1 from 1990 to 1993 and Phase 2 from 1997 to 2003. Main Findings UK Grain workers were frequently found to be exposed to more than 1 million bacteria and fungi per m3 air. Airborne bacteria exceeded 106 per m3 air and fungi exceeded 105 per m3 air at all the work places sampled. Levels of airborne endotoxin of over 10,000 EU/m3 were recorded at all but one workplace visited and personal exposures reached over 600 EU/m3 at every workplace.

7 The Maximum Exposure Limit (MEL) for Grain dust is an average of 10 mg/m3 of The Maximum Exposure Limit (MEL) for Grain dust is an average of 10 mg/m3 of total respirable dust in the air over an 8 hour period, and the maximum dust level should never exceed 30 mg/m3 measured over a 10 minute period. The MEL was introduced between Phases 1 and 2 of the Study . Throughout both phases of the Study , very high levels of dust were recorded with levels equal to, or greater than, 30 mg/m3 recorded in all work situations at 17 of the 19 workplaces visited. The predominant micro-organisms present differed between freshly harvested Grain and stored Grain and Grain for human and animal consumption, but not between different types of Grain . The microbial species identified were used to select relevant isolates for use in immunoassays.

8 In the immunoassays, large numbers of sera were expected to show positive immunoglobulin G (IgG) response as the prevalent micro-organisms are also common environmental allergens to v which everyone is exposed to some extent. Between 13 and 39% of dockers, 25 to 41% of farmers and 24 to 35 % of the controls tested positive to one or more of the work-related allergens throughout the Study . IgE sensitisation to work related allergens among the Grain worker cohort showed evidence of a decrease since the introduction of the Grain dust MEL, , there was an overall trend towards a decrease in IgE positive responses across the Study from Phase 1 to Phase 2. However, the long term trend towards improvement may not be shown clearly in this Study as the majority of the participants were occupationally exposed to Grain dust for many years before the MEL was introduced.

9 Although some workers who remained in the Study throughout developed new IgG response or positive IgE response during the Study , more workers lost their positive status than gained it. No dockworkers developed a sustained new positive status. There was a decrease in the number of non atopic workers who tested IgE positive to the work-related allergens, and none of the non-atopic dockworkers were IgE positive in Phase 2 of Study . However, 11% of non atopic However, 11% of non atopic farmers were still testing positive to one or more of the work related allergens at the end of the Study . This suggests that it is possible to reduce exposure levels to below those required to trigger an IgE response in non-atopic workers, but that farm workers continue to be exposed to levels of Grain dust and its contaminants that could trigger or maintain sensitisation.

10 In the two phases of the clinical Study , Grain workers were found to have a high prevalence of respiratory symptoms and sensitisation to environmental allergens including microorganisms, the Grain itself and storage mites. There was a close relationship between some respiratory symptoms (especially wheeze in a dusty place ) and the presence of specific IgE to environmental allergens. There was no association between specific IgG and symptoms or lung function. Not all respiratory symptoms could be explained by IgE mediated immunological sensitisation. The longitudinal exposure of Grain workers to high doses of endotoxin may be contributing to the development of work related ill health. Lung function was found to be inversely related to the duration of exposure to Grain dust in the first phase of the Study , but the cause(s) of impaired lung function could not be identified from this phase.