This paper describes the measurement of AChE enzyme activity on control (non-farming) participants and farming participants and the value of incorporation of these measurements into routine Point of Care (POC) health clinics. Organophosphates are still used widely in South West Victoria and globally and the actions and attitudes of farmers and workers using these pesticides are vital to farmer wellbeing and that of their families. When examining enzyme activity as an index of chemical exposure and potential effect, it is important to establish the criteria determining whether there has been an effect. In biological monitoring there are several ways to evaluate data;
Examination of grouped data from farmers, farming spray contractors, non-farming rural residents and non-farming town residents provides a blunt instrument for drawing associations between general farming practices and use of chemicals, broad environmental exposure and effect.
Comparison of individual data against standards or guidelines outlining acceptable levels of the measured index, suggest unacceptable (or clinically relevant) levels of exposure have taken place. It is generally accepted that depression of AChE by 70% or more may be associated with the appearance of acute symptoms. The question remains as to what value represents 100% activity. As was the case with this sample group, cholinesterase activities are normally distributed within populations, and those with normally lower cholinesterase activity may be misidentified as chemically-exposed, whereas those with higher cholinesterase activity may be identified as unexposed, even where there may be significant inhibition relative to an even higher ‘normal’ cholinesterase. A comparison of country specific data may be preferable since the general Australian population may differ significantly from the US data set used by EQM. A recent study undertaken by Suratman et al. reported mean erythrocyte AChE for 27 unexposed blood donors from South Australia was 3.24 U/mL (standard deviation ±0.40) and 29.6 u/g Hb (SD ±3.0) . This suggests that using Australia specific data with concomitantly lower population background values, fewer workers are now identified as possibly exposed or poisoned. This approach, however, is still flawed as it depends upon individual data comparisons with population distributions. Low AChE does not necessarily mean inhibited AChE.
Comparison of individual data with established individual baseline measures (ideally preceding exposure or employment) allows for individual trends in measurements to be related to recent occupational practices or regional factors affecting more widespread chemical exposure . There can also be difficulties, in establishing ‘true’ or stable baseline estimates for individuals, especially where farmers may handle anticholinesterase insecticides on an ongoing or year-round basis, and short breaks or vacations may not be sufficient to allow AChE to return to baseline levels. Similarly, while some farmers may suspend insecticide use, neighbours may continue using them. This increases the possibility of more persistent general community exposure to insecticides which may contribute to a low level depression of cholinesterase, upon which the effects of further occupational or environmental exposures may be superimposed. It is important that test results be interpreted in conjunction with reported use of personal protective equipment (PPE).
This research has revealed that a reasonably high number of farming participants (92.7%) reported use of ‘some form’ of PPE when mixing and applying chemicals, with gloves being the most widely adopted form of protection and face protection the least utilised (51% reported never using face protection). A report by Franklin et al. (2015), suggests that understanding how individuals perceive threats, make decisions and adopt new ideas, provides insight into the ways that barriers to PPE use can be identified, and intervention can be designed and evaluated. Work on occupational noise exposures by Williams reported that whilst conducting a test and providing participants with a result is helpful, it is not enough to incite practice change .
A later study undertaken by Brumby et al. on noise induced hearing loss on farms showed that provision of accurate individual hearing loss measurement in combination with noise levels on farm and education has proven an effective method for improving farm safety practices and reducing individual noise exposure . These contributions are important when considering farmers exposures to OP’s and possible future interventions to adopt new safety practices.
Point of Care (POC) testing is covered by ISO 22870 Point of care testing –requirements for quality and competence, but this refers mainly to distributed locations, such as GP clinics and pharmacies, rural health clinics, nursing homes, sports medicine clinics and extends to workplace drug screening . There is little guidance on the application of POC testing in the circumstances described here in relation to OP exposure. In particular, the timing of further tests should be based on the nature of the work and previous test results. According to Safework Australia 2013 guidelines a worker having greater than 20% inhibition from baseline values should be retested within 12 weeks .
Workers must be advised of their results (that is, percentage depression of cholinesterase in relation to chemical use and possible exposure) to permit them to understand the basis for any restrictions or changes to work practices. Participants in this study were provided with a summary of their health measurements and AChE results at the conclusion of the study along with education on reduction of exposures. This generated considerable interest amongst participants with many recognising fluctuations in AChE measures may reflect personal exposure. Whist this is positive whether participants have changed their behaviours and safety practices to reduce exposure is yet to be quantified. The retention rate of 93% of participants returning for 4 consecutive monitoring sessions indicated that farmers involved in this study remained engaged and were concerned about possible exposure to organophosphates. In spite of these individual fluctuations in AChE levels, the current data suggests there was no significant difference in observed average AChE activity between farming and non-farming participant groups, although the sample size was relatively small. This is consistent however, with a 2012 study by Pasiani et al. of Brazillian farmers which found significant differences between the mean AChE activities of the farmer group during both non-exposure and exposure periods .
This result reflects the responses provided by farming participants when the type of chemicals used in the weeks prior to and during the study. Whilst only 14.6% of participants (farming only) reported using organophosphate pesticides throughout the study, it was the equal top chemical group used along with the single herbicides; glyphosate and MCPA. This is reflective of the variety of agrichemical use within different farming enterprises (cropping (29.1%), sheep (40%) or cattle/dairy (1.8%)). Given the short timeframe in which the research was undertaken the chemicals reported may not have been a true representation of the variety of agrichemicals used by this group of farmers. Further work is required to better determine the true extent of anticholinesterase chemical use throughout western Victoria.
It is important that producers who are routinely using OPs establish their baseline AChE activity and have access to regular AChE activity checks for comparison with baseline. A 2001 study by Dyer et al. suggests that differences in patterns of availability and domestic use of anticholinesterase chemicals including chlorpyrifos and similar agents (that may be banned elsewhere), by nominally ‘control’ populations may affect peripheral cholinesterases and may influence our adoption of standard or guideline values. In addition, chlorpyrifos may affect plasma cholinesterase whereas other agrichemicals such as dimethoate and diazinon more potently effect erythrocyte cholinesterase .
Participants were provided with counselling regarding their health and behaviour measurements and AChE levels in accordance with Australian AgriSafe™ guidelines using US normal data. It would be preferable to provide country or region specific comparisons to allow workers a better understanding of their own chemical exposure.
Incorporation of POC testing into health clinics and emergency care is highly dependent on health professional’s attitude, skills and knowledge and availability of testing equipment. The competency of health professionals is crucial to the retention of farming participants who require follow up cholinesterase monitoring. Rajapakse et al. 2014 suggest that greater experience by health professionals in seeing AChE test results upon an acute poisoning presentation is associated with increased knowledge . The results of this study further prepare health providers for integration of appropriate cholinesterase measurement into POC health check procedure. The critical window for exposure to toxicants may occur years before the onset of neurological symptoms . This work further highlights pesticide exposure as a risk for farmers and their families, leading to work that will permit quantitation of environmental exposure and early detection in the workplace and homes of farming and non-farming individuals. These types of data may also be included in epidemiological studies of chronic diseases. Research has also shown links between cholinesterase activity and vascular complications in diabetic patients . As diabetes is a disease of increasing concern to the farming and rural population in Australia, continuing to develop a database of health and lifestyle data which includes chemical usage and cholinesterase activity would be valuable to further understanding and addressing complex Australian public health comorbidities . It is now known that consideration of both time and frequency of interventions is vital to ensure behaviour change is successful. Ongoing interaction in some form is required to further embed changes in attitudes, practices and behaviour .