Dissertation: Respiratory health effects of livestock farm emissions in neighbouring residents

Recent studies have highlighted the large contribution of agriculture to fine particulate matter (PM) air pollution, and the public health impact that may result from agricultural emissions.The aim of this thesis was to explore associations between air pollution from livestock farms and respiratory health of non-farming residents living in close proximity to farms in a rural area in the Netherlands.

A questionnaire survey was conducted among 12,117 adult patients from 21 general practitioner practices in a rural area with the highest farm density of the Netherlands. In total, 2,494 questionnaire participants participated to a health examination which consisted amongst others of a lung function measurement and collection of serum. Exposure to livestock farms was computed for each subject based on their home address and the location of farms in their vicinity.

Living in close proximity to livestock farms was associated with both positive and negative effects on respiratory health. Subjects living with more than 15 farms within 1 ,000 m had a reduced lung function. This reduction in lung function is possibly caused by pollutants from livestock production. Also, lung function was lower when measured after weeks with higher ammonia levels (the main source is livestock production). Our results indicate that the association with the number of livestock farms was especially apparent in patients with COPD, while the association with ammonia was observed in the whole population.

This study also found positive health effects. Prevalence of self-reported asthma, COPD, and nasal allergies was lower among residents living at short distances from a farm compared to residents living further away. In addition, living at short distances from livestock farms seems to protect against atopy (based on levels of IgE antibodies in serum). The negative associations between atopy and livestock farm exposure were somewhat stronger in subjects who grew up on a farm.  Nonetheless, COPD patients living in close proximity to farms reported more respiratory symptoms and medication usage.

Respondents' attitude towards farming may be a source of bias in our study since concerns about environmental hazards may influence self-reported outcomes. A score was developed to measure the attitude towards farming. In general, the study population had a positive attitude towards farming, in particular if participants were more familiar with farming. Both self-reported symptoms and exposure to livestock farms were associated with a more negative attitude, which is a concern for our epidemiological study. Awareness bias might have played a role here. However, no indication was found that the associations between proximity to farms and respiratory health were confounded or modified by attitude.

To protect neighbouring residents from potentially harmful farm emissions, the expansion of new livestock farms should be prevented, especially in areas with a high number of farms. Furthermore, it is important that livestock farms lower their emissions. Ammonia contributes to atmospheric secondary PM_2.5, and has been identified as a major contributor to PM_2.5 in urban areas as well. Therefore, reducing livestock farm emissions will positively contribute to respiratory health of both neighbouring residents and people living outside rural areas.