Prepared by: Zachary du Preez, COH® MAIOH, Principal Advisor (Occupational Health and Hygiene), SHSS, May 2021
Organophosphate (OP) pesticides are a group of man-made hazardous chemicals that are used as pesticides in the agricultural industry in Australia. OP pesticides work by damaging an enzyme called acetylcholinesterase. This enzyme is critical for controlling nerve signals in the body. Damage to this enzyme kills pests but can also cause unwanted side effects in workers and others if exposed. Exposure to OP pesticides can occur via inhalation, skin contact or accidental ingestion.
Exposure to OP pesticides can cause both acute and chronic health effects. The symptoms of acute poisoning include headaches, nausea, respiratory problems, vomiting, bradycardia, miosis, dermatitis and burns. Chronic exposure effects include cognitive, motor and sensory deficiencies and neurological diseases.
Workers in the agricultural industry that are involved in preparing, decanting, mixing, loading and applying organophosphate pesticides are at the greatest risk of exposure. Other farm workers may also be at risk of exposure if they come in contact with or clean OP pesticide spray equipment, do not follow re-entry intervals or do not wear correct personal protective equipment when re-entering a sprayed area.
When health monitoring is required
Organophosphate pesticides are a hazardous chemical mentioned in schedule 14 of the Work Health and Safety Regulation 2011 and a business must provide health monitoring to a worker if:
- the worker uses, handles, generates, or stores organophosphate pesticides,
- the work is ongoing, and
- there is a significant risk to the worker’s health because of exposure to organophosphate pesticides.
Whether there is a significant risk to the worker’s health depends on the frequency, duration, and level of exposure. Carrying out a risk assessment is the best way to decide if there is a significant risk to health or not.
The following table outlines when health monitoring may be required:
Note: If the risks are significant but not adequately controlled or there is uncertainty about the degree of risk, health monitoring is required.
Type of health monitoring required
Health monitoring must be carried out by or under the supervision of a registered medical practitioner with experience in health monitoring. The type of health monitoring required is listed in schedule 14, table 14.1, column 3. Another type of health monitoring can be used if recommended by the doctor conducting or supervising the health monitoring provided it is an equal or better type than listed in the schedule.
The type of health monitoring for organophosphate pesticides listed in the schedule includes:
- Demographic, medical and occupational history including pattern of use
- Physical examination
- Biological monitoring (blood testing)
- Baseline estimation of red cell and plasma cholinesterase activity levels by the Ellman or equivalent method (blood test).
- Estimation of red cell and plasma cholinesterase activity towards the end of the working day on which organophosphate pesticides have been used (to compare with the baseline).
Blood testing is considered biological health effect monitoring and can be used to detect a reduction in red cell and plasma cholinesterase activity levels because of exposure to OP pesticides. However, blood testing may only monitor effects from moderate to high exposures and an individual baseline needs to be calculated prior to ongoing health monitoring. To obtain a baseline a worker must first be free from OP pesticide exposure for at least 30 days and then have a minimum of two blood tests between three and 14 days apart. If the tests differ by more than 20% a third sample should be taken. The workers’ baseline level is the average of the two or three blood tests.
The guidance value to compare ongoing blood tests results is 70% of the individual workers’ baseline, i.e. a 30% reduction in activity, as outlined in Safe Work Australia’s Health monitoring – guide for organophosphate pesticides.
Urine testing can be used as biological exposure monitoring and is used to detect six common OP dialkyl phosphate (DAP) metabolites in urine. Urine testing is a more accurate method to detect low or chronic exposure, however urine testing does not indicate whether exposure has caused a health effect. Urine testing is also unable to distinguish the particular OP pesticide that caused exposure so additional information or testing is required to pinpoint the potential source/s.
Safe Work Australia’s Health monitoring – guide for organophosphate pesticides provides guidance values when interpreting the results of urinary (DAP) metabolite levels:
- less than 100 μmol/mol creatinine — indicates low occupational exposure or high non-occupational exposure
- 100-1000 μmol/mol creatinine — indicates medium level occupational exposure
- greater than 1000 μmol/mol creatinine — may be associated with a drop in the blood cholinesterase level — indicates high occupational exposure
Urinary (DAP) levels greater than 100 μmol/mol creatinine indicate that work practices may need to be reviewed and health monitoring, including blood testing, may be required.
A worker in the agricultural industry requires health monitoring for OP pesticides if:
- the worker generates, handles or stores OP pesticides, AND
- the work is ongoing, AND
- there is a significant risk to the worker’s health because of exposure.
Where health monitoring is deemed necessary, a registered medical practitioner carrying out or supervising the health monitoring may conduct blood testing or recommend another type of monitoring, like urinary (DAP) testing. Urinary (DAP) testing can be used to estimate workers’ exposure, confirm if controls are effective and determine whether health monitoring, including blood testing, is required.
Safe Work Australia guidance:
Health monitoring when you work with hazardous chemicals guide
Health monitoring for persons conducting a business or undertaking guide
Health Monitoring for Exposure to Hazardous Chemicals Guide for Medical Practitioners
Organophosphate pesticides health monitoring