Pesticides and cognition: once bitten?

A recent interesting tweet from Prof. Keith Laws led me into this post. He posted a link to this study by Gunnell and colleagues* which conservatively suggested that approximately a third of suicides world-wide in 2002 were via pesticide ingestion. That's just over a quarter of million deaths in 1 year from pesticide self-poisoning. A very sobering statistic indeed.

An article by Starks and colleagues** looking at pesticide exposure and cognition has similarly caught my eye. I did make an initial attempt to talk about pesticides in relation to autism a while back on this blog and had promised to do some follow-up posts as a result. The post of rural vs. urban settings in relation with autism was a sort of reintroduction of the topic. This post is slightly different in that autism is not really part of the current study but rather looking at the effects of one or more high pesticide exposure events (HPEE) on cognitive abilities amongst pesticide applicators.

The basics:

• Neurobehavioural testing was carried out on 693 private pesticide applicators (all male) not previously reporting a physician-diagnosed pesticide poisoning event.
• Study recruits were assessed via various measures using NES3 to ascertain various CNS functions. This included tests such as: the Digit-Symbol test for visual scanning and information-processing ability, Sequences A, a test of motor speed and tracking and seven other tests.
• Participants were also asked about whether they had ever been involved in a HPEE via a questionnaire (prior to their enrollment in the study as part of the AHS). 
• The results indicated that about a quarter of participants reported at least one HPEE which included exposure to various -cides (herbicides, insecticides, fungicides, etc). Bearing in mind that participant numbers whilst in the 100s were not particularly large, a HPEE seemed to adversely affect scores on the Digit-Symbol and Sequence A tests. The authors were keen to point out that the overlap in what these tests looked at might suggest that these results were not just a chance finding.

Several things from this study stuck out for me. Aside from pesticide applicator perhaps being one of the less desirable jobs that I personally would like to do, the results suggested that even after one HPEE not counting as an acute poisoning event, there may very well be some lasting CNS effects. I know that this might seem unsurprising given what pesticides do and their various ways/routes of performing their job, but in a world of fallibility I wonder if this paper would make it to a potential applicators 'welcome to the job pack'?

* Gunnell D. et al. The global distribution of fatal pesticide self-poisoning: Systematic review. BMC Public Health. 2007; 7: 357.

** Starks SE. et al. High pesticide exposure events and central nervous system function among pesticide applicators in the Agricultural Health Study. International Archives of Occupational and Environmental Health. September 2011.