Following a comprehensive assessment of new studies, the Australian Pesticides and Veterinary Medicines Authority (APVMA) has concluded that there is no evidence to indicate that insecticide, chlorpyrifos could cause potential neurodevelopment effects reported in some studies to occur at or below doses that inhibit AChE activity.
Further, animal studies consistently indicated that there is no age-related differential sensitivity to chlorpyrifos. On this basis, cholinesterase inhibition remains the most sensitive and relevant adverse effect caused by chlorpyrifos and is therefore the most appropriate endpoint for the establishment of health based guidance values used to protect the entire population including pregnant women, infants and children.
Chlorpyrifos is a broad spectrum, non-systemic organophosphorous insecticide with contact, stomach and respiratory action. It acts by inhibiting the enzyme, acetyl cholinesterase (AChE), which is important for the transmission of nerve signals. Chlorpyrifos was first introduced for use in Australia in the mid-1960s.
The Australian Pesticides and Veterinary Medicines Authority (APVMA) commenced a reconsideration of chlorpyrifos due to concerns about toxicology, occupational health and safety (OHS), residues, trade, environment, efficacy and crop safety. These issues were assessed and an interim review report released in 2000, along with the implementation of various regulatory measures.
The current acceptable daily intake (ADI) for chlorpyrifos is 0.003 mg/kg bw/d, based on the no observed adverse effect level (NOAEL) of 0.03 mg/kg bw/d for the inhibition of plasma cholinesterase activity in a 28 day study in humans, and applying a 10-fold safety factor to account for potential variability in sensitivity. The current acute reference dose (ARfD) for chlorpyrifos is 0.1 mg/kg bw, based on the NOAEL of 1 mg/kg bw for the inhibiton of erythrocyte AChE activity in a single dose human study, and applying a 10-fold safety factor to account for potential variability in sensitivity. Based on an assessment of the new published studies, the current ADI and ARfD for chlorpyrifos remain appropriate.
Chlorpyrifos is currently in Schedule 6 of the Standard for the Uniform Scheduling of Medicines and Poisons (SUSMP), except when included in Schedule 5 or in prepared potting or soil mixtures containing 100 g or less of chlorpyrifos per cubic metre. The Schedule 5 entry includes chlorpyrifos in aqueous preparations containing 20% or less of microencapsulated chlorpyrifos, when in controlled release granular preparations containing 10% or less of chlorpyrifos and when in other preparations containing 5% or less of chlorpyrifos except in prepared potting or soil mixtures containing 100 g or less of chlorpyrifos per cubic metre. Based on an assessment of the new published studies, the poison schedule remains appropriate.