Pirimicarb
(endorsed 2011)
Guideline
Based on human health concerns, pirimicarb in drinking water should not exceed 0.007 mg/L.
Related chemicals
Pirimicarb 9 CAS 23103-98-2) belongs to the carbamate class of chemicals. There are many pesticides in this class, including aldicarb, bendiocarb, carbaryl, carbofuran, methiocarb, methomyl and oxamyl (Tomlin 2006).
Human risk statement
With good water quality management practices, the exposure of the general population is expected to be well below levels that may cause health concerns.
If present in drinking water as a result of a spillage or through misuse, pirimicarb would not be a health concern unless the concentration exceeded 0.007 mg/L. Excursions above this level even for a relatively short period are of concern, as the health-based guideline is based on short- to medium-term effects.
With good water quality management practices, pesticides should not be detected in source waters used for drinking water supplies. Persistent detection of pesticides may indicate inappropriate use or accidental spillage, and investigation is required in line with established procedures in the risk management plan for the particular water source.
General description
Uses: Pirimicarb is a post-emergent insecticide for the control of aphids in pastures and a variety of agricultural crops and ornamentals.
There are registered products that contain pirimicarb in Australia. The products are intended for professional use and are available as concentrated solutions, powders and granular formulations. Products are intended for application as a concentrated or dilute spray using high volume application spray equipment such as aircraft or ground boom. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to pirimicarb and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of pirimicarb may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Typical values in Australian drinking water
Pirimicarb has been routinely monitored by water utilities in Australia. No detections above analytical limits of detection have been reported in the reviewed reports.
Treatment of drinking water
Pirimicarb undergoes photochemical and metabolic degradation. Greater than 99.5% removal of pesticides has been reported with the ozonation, biological activated carbon filtration and reverse osmosis treatment (Bonne et al. 2000). Reverse osmosis alone was able to remove 99% of the influent concentration of pirimicarb in a challenger test conducted using two different type of membranes (Bonne et al. 2000).
Measurement
Pirimicarb can be analysed by on-line solid phase extraction followed by high-performance liquid chromatography-tandem mass spectrometry. The method can achieve a limit of quantitation (LOQ) of 0.4 µg/L. Solid-phase microextraction followed by gas chromatography–mass spectrometry can achieve a LOQ of 0.1 µg/L (Carabias-Martinez et al. 2005). Solid-phase extraction followed by high-performance liquid chromatography coupled to atmospheric pressure electrospray ionisation mass spectrometry can also achieve a LOQ of 0.1 µg/L (Nogueira et al. 2003). Solid-phase extraction followed by liquid chromatography with diode array detection can achieve a LOQ of 0.02 µg/L (Van Hoof et al. 2002). Single-drop microextraction followed by gas chromatography–mass spectrometry can achieve a LOQ of 50 ng/L (Saraji and Esteki 2008). Dispersive liquid–liquid microextraction coupled with high-performance liquid chromatography–diode array detection can achieve a LOQ of 0.6 ng/mL.
History of the health values
The current acceptable daily intake (ADI) for pirimicarb is 0.002 mg per kg of bodyweight (mg/kg bw), based on a lowest-observed-effect level (LOEL) of 0.4 mg/kg bw/day from a short-term (90-day dietary) study in dogs. The LOEL is based on haemotoxicity. The ADI incorporates a safety factor of 200, and was established in 1987.
The previous health value was 0.005 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Pirimicarb is readily absorbed via the gastrointestinal tract of mammals. It is readily metabolised and rapidly excreted, mostly in expired air, with the remainder excreted in urine and faeces. It has a low potential for bioaccumulation.
Acute effects: Pirimicarb has moderate acute oral toxicity and moderate acute dermal toxicity. It is not a skin sensitiser.
Short-term effects: Short-term dietary studies conducted in mice, rats, dogs and monkeys reported haematological effects in dogs as the most sensitive toxicological endpoint. A study in rats reported decreased bodyweight gain and food consumption at the highest dose of 75 mg/kg bw/day. A study in dogs reported increased incidence of megaloblasts in bone marrow at 0.4 mg/kg bw/day. This LOEL is the basis for the current ADI. Effects in dogs at higher doses included plasma cholinesterase inhibition, decreased bodyweight gain and effects indicative of bone marrow dysfunction. A study in monkeys reported plasma cholinesterase inhibition at doses of 7 mg/kg bw/day and above.
Long-term effects: Long-term dietary studies have been conducted in mice, rats and dogs. In mice, no effects were reported up to doses of 60 mg/kg bw/day. A two-year study in rats reported decreased bodyweight gain at 25 mg/kg bw/day and above. Plasma cholinesterase was inhibited at the highest dose of 75 mg/kg bw/day. A study in dogs reported increased erythroid/myeloid ratio in females at the highest dose tested of 4 mg/kg bw/day.
Carcinogenicity: There was some evidence of an increased incidence of lung tumours in mice but only at very high dose levels, well in excess of the likely level of human exposure.
Genotoxicity: Pirimicarb is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: One and three-generation reproductive studies in rats did not produce any evidence of reproductive effects. Developmental studies in mice, rats and rabbits reported foetotoxicity and maternotoxicity at high dose levels that are well in excess of the likely level of human exposure.
Neurotoxicity: Special neurotoxicity studies in rats by short-term oral administration found no evidence of delayed neurotoxicity at doses up to 25 mg/kg bw/day.
Poisons Schedule: Pirimicarb is included in Schedule 5 and 6 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on its concentration and use. Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline of 0.007 mg/L for pirimicarb was determined as follows:
where:
0.4 mg/kg bw/day is the LOEL based on a short-term (90-day) dietary study in dogs.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the assumption that 10% of the ADI will arise from the consumption of drinking water.
2 L/day is the estimated maximum amount of water consumed by an adult.
200 is the safety factor applied to the LOEL derived from animal studies. This safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation, with an additional safety factor of 2 for the use of a LOEL instead of a no-observed-effect level.
References
NOTE: The toxicological information used in developing this fact sheet is from reports and data held by the Department of Health, Office of Chemical Safety.
Bonne PAC, Beerendonk EF, van der Hoek JP, Hofman JAMH (2000). Retention of herbicides and pesticides in relation to aging of RO membranes. Desalination, 132(1-3):189-193.
Carabias-Martinez R, Garcia-Hermida C, Rodriguez-Gonzalo E, Ruao-Miguel L (2005). Behaviour of carbamate pesticides in gas chromatography and their determination with solid-phase extraction and solid-phase microextraction as preconcentration steps. Journal of Separation Science, 28(16):2130-8.
DoHA (2010) The Poisons Standard; Schedule 1-Standard for the Uniform Scheduling of Medicines and Poisons, Department of Health and Ageing, Commonwealth of Australia, Canberra.
NHMRC (National Health and Medical Research Council), NRMMC (Natural Resources Management Ministerial Council) (2004). Australian Drinking Water Guidelines. National Water Quality Management Strategy, Paper 6. NHMRC and NRMMC.
Nogueira JM, Sandra T, Sandra P (2003). Considerations on ultra trace analysis of carbamates in water samples. Journal of Chromatography A, 996(1-2):133-40.
Saraji M, Esteki N (2008). Analysis of carbamate pesticides in water samples using single-drop microextraction and gas chromatography-mass spectrometry. Analytical and Bioanalytical Chemistry, 391(3):1091-100.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
Van Hoof F, Van Wiele P, Acobas F, Guinamant J-L, Bruchet A, Schmitz I, Bobeldijk I, Sacher F, Ventura F, Boleda R (2002). Multiresidue determination of pesticides in drinking and related waters by solid-phase extraction and liquid chromatography with ultraviolet detection: interlaboratory study. Journal of AOAC International, 85(2):375-83.
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