Pest Management Regulatory Agency
8 November 2012
ISSN: 1925-1025 (PDF version)
Catalogue number: H113-28/2012-10E-PDF (PDF version)
This page is a summary of the Re-evaluation Decision. If you would like more detail, please request the full Re-evaluation Decision.
To obtain an electronic copy of the document, Re-evaluation Decision RVD2012-10, Malathion, please contact our publications office.
Should you require further information please contact the Pest Management Information Service.
After a thorough re-evaluation of the insecticide malathion, Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the Pest Control Products Act, is granting continued registration of products containing malathion for sale and use in Canada.
An evaluation of available scientific information found that, under the revised conditions of use:
The PMRA's pesticide re-evaluation program considers potential risks as well as the value of pesticide products to ensure they meet modern standards established to protect human health and the environment. In 1999, Health Canada announced in Re-evaluation Note REV99-01, Re‑evaluation of Organophosphate Pesticides, that 27 organophosphate active ingredients, including malathion, would be re-evaluated in Canada. The re-evaluation of malathion draws on data from registrants, published scientific reports, information from other regulatory agencies and any other relevant information available.
In 2003, the PMRA published a proposed re-evaluation consultation document (PACR2003-10, Re-evaluation of Malathion) for malathion use as an adulticide in mosquito abatement programs, and followed with a document (REV2003-03, Re-evaluation of Malathion: Assessment of Use in Mosquito Abatement Programs) which described the mitigation measures to be implemented for malathion use as an adulticide. The required label changes for related end-use products, as described in REV2003-03, have been implemented.
In addition, the technical registrant of malathion in Canada, Cheminova Canada Inc., voluntarily discontinued a number of residential uses including structural (pet quarters, indoor uses); companion animals (pet treatment); turf (broadcast turf/lawn treatment); and residential outdoors (broadcast/turf lawn treatment). The changes to the related product labels have been completed.
The regulatory approach regarding the overall re-evaluation of malathion was presented in the consultation document Proposed Re-evaluation Decision PRVD2010-18, Malathion. This Re‑evaluation Decision describes this stage of the PMRA's regulatory process concerning the re‑evaluation of malathion and summarizes the Agency's decision and the reasons for it.
Comments received during the consultation process were taken into consideration. These comments, however, did not result in substantial changes to the proposed regulatory decision as described in PRVD2010-18. Appendix I of Re-evaluation Decision RVD2012-10, Malathion summarizes comments received and provides the PMRA's response.
This decision is consistent with the proposed re-evaluation decision stated in PRVD2010-18. To comply with this decision, registrants of products containing malathion will be informed of the specific requirements affecting their product registrations.
The key objective of the Pest Control Products Act is to prevent unacceptable risks to people and the environment from the use of pest control products. Health or environmental risk is considered acceptable if there is reasonable certainty that no harm to human health, future generations or the environment will result from use or exposure to the product under its conditions or proposed conditions of registration. The Act also requires that products have value when used according to the label directions. Conditions of registration may include special precautionary measures on the product label to further reduce risk.
To reach its decisions, the PMRA applies hazard and risk assessment methods as well as policies that are rigorous and modern. These methods consider the unique characteristics of sensitive subpopulations in both humans (for example, children) and organisms in the environment (for example, those most sensitive to environmental contaminants). These methods and policies also consider the nature of the effects observed and the uncertainties present when predicting the impact of pesticides. For more information, please refer to the following:
Based on the available information, malathion is authorised for use in the European Union.
In the United States, malathion is registered for use in agriculture for various uses including food and feed crops, homeowner outdoor uses, ornamental nursery stock, building perimeters, pasture and rangeland, as well as regional pest eradication programs. In 2006, the United States Environmental Protection Agency (USEPA) reviewed the safety and benefits of all uses of malathion and concluded that ecological and human health risks were not of concern. Under their registration review program, the USEPA published a workplan to update the risk assessments for malathion. A final registration review decision is expected in 2015.
Malathion is a group 1B Resistance Management Mode of Action (MoA) non-systemic, broad spectrum organophosphate insecticide and acaricide. It disrupts nervous system function by inhibiting the acetylcholinesterase enzyme. It is currently used to control a broad range of insect pests on a wide variety of sites including: aquatic non-food sites; empty food storage areas; greenhouse (food and non-food crops); human habitat and recreational areas; industrial oilseed and fibre crops; livestock for food; seed treatment; stored food and feed; structural sites; terrestrial feed and food crops; outdoor ornamentals; and residential outdoor sites.
It is applied using conventional ground and aerial application equipment by farmers, farm workers, professional applicators and the general public.
Additional risk-reduction measures are required on malathion labels. Malathion is unlikely to affect your health when used according to the revised label directions.
Potential exposure to malathion may occur through the diet (food and water) or when handling and applying the product. When assessing health risks, two key factors are considered: the levels where no health effects occur in animal testing and the levels to which people may be exposed. The dose levels used to assess risks are established to protect the most sensitive human population (for example, children and nursing mothers). Only uses for which the exposure is well below levels that cause no effects in animal testing are considered acceptable for registration.
Toxicology studies in laboratory animals describe potential health effects from varying levels of exposure to a chemical and identify the dose where no effects are observed. The health effects noted in animals occur at doses more than 100-times higher (and often much higher) than levels to which humans are normally exposed when malathion products are used according to label directions.
The target for malathion is the nervous system including effects on neurobehavioural parameters and acetylcholinesterase, an enzyme necessary for normal functioning of the nervous system. Overexposure may produce a variety of symptoms in animals and humans including nausea, dizziness, sweating, salivation, runny nose and watery eyes. This may progress to muscle twitching, weakness, tremor, incoordination, vomiting, abdominal cramps and diarrhea in more serious poisonings. Cholinesterase inhibition has been observed with oral, dermal and inhalation exposure. Young animals have been shown to be more sensitive to this effect of malathion.
Malathion was not found to be genotoxic or teratogenic. Based on the scientific evidence, malathion is unlikely to pose a carcinogenic risk for humans. Following administration to pregnant rabbits, an increase in resorptions (embryo-fetal loss) has been observed in the presence of maternal toxicity. Due to the nature of this endpoint and its potential implications on the health of the unborn child, extra protective measures were applied during the risk assessment to further reduce the allowable level of human exposure to malathion. The risk assessment protects against these effects by ensuring that the level of human exposure is well below the lowest dose at which these effects occurred in animal tests.
Dietary risks from food and water are not of concern.
In its evaluation of risk from the exposure of malathion and its metabolite malaoxon, the PMRA has adopted protective and conservative estimates of residues to compensate for the high potency factor of malaoxon in food and water, and for data gaps. In particular, the PMRA has compensated for malaoxon residues that were, for the most part, below analytical detection.
The PMRA has also considered exposure arising from on-site consumption of treated produce at Pick-Your-Own operation.
Reference doses define levels to which an individual can be exposed over a single day (acute) or lifetime (chronic) and expect no adverse health effects. Generally, dietary exposure from food and water is acceptable if it is less than 100% of the acute reference dose or chronic reference dose (acceptable daily intake). An acceptable daily intake is an estimate of the level of daily exposure to a pesticide residue that, over a lifetime, is believed to have no significant harmful effects.
For malathion, acute dietary risk for children and infants was the highest and reached 101% of reference dose, but is considered below the level of concern due to the conservative assumptions. Chronic risk for children reached 66% of reference dose and is not of concern.
Dietary exposure from Pick-Your-Own operations was estimated by adding the acute exposure from all forms of fresh fruit, in this case apple and strawberry, to the chronic exposure. Calculated MOEs exceed the target MOE for all sub-populations, and are not of concern.
Overall, the PMRA has concluded that risk to health from dietary exposure is not of concern.
Residential risks from the use of malathion on vegetable gardens, ornamentals, and in mosquito abatement programs are not of concern.
Malathion is registered for use on residential ornamental and vegetable gardens, on exterior wall surfaces, around foundations, under fences and shrubs, and around buildings. Malathion is also registered for use in mosquito abatement programs, where bystanders could potentially be exposed by the inhalation route or by being exposed to malathion residues on turf. Estimates of exposure reach the target Margin of Exposure (MOE) for adults and children for all application and most post-application exposure scenarios, and are therefore not of concern.
Residential risks from potential exposure to malaoxon on decks and playstructures are not of concern.
Malaoxon is a degradation product of malathion which forms on hard surfaces such as decks and playstructures. Estimates of exposure for children, adolescents, and adults using default assumptions and chemical-specific monitoring data reach the target MOE, and are therefore not of concern.
Aggregate risk from exposure incurred at "Pick-Your-Own" orchard or berry facilities is not of concern.
"Pick-Your-Own (PYO)" facilities are considered commercial farming operations that allow public access for harvesting in large-scale fields or orchards treated with commercially labelled malathion products. Exposure estimates that aggregate the dermal exposure incurred during harvest and the dietary exposure from consuming fresh fruit, reached the target MOE for orchard and berry crops, and are therefore not of concern.
Occupational (mixer/loader/applicator) risks are not of concern when products are used according to revised label directions.
Most occupational risks due to malathion are not of concern for agricultural scenarios. Based on the precautions and directions for use on current labels, risk estimates associated with certain mixing, loading and applying activities reach target MOEs, and are not of concern. For those uses that do not reach the targeted MOEs, mitigation measures such as additional personal protective equipment, engineering controls, or restrictions on amount handled per day are required to reduce potential exposure and protect worker's health.
Occupational postapplication risks are not of concern.
Postapplication occupational risk assessments consider exposures of workers entering treated sites in agriculture. Most occupational postapplication risks are not of concern if proposed protective measures are followed. When the proposed mitigation measures such as lengthened restricted-entry intervals (REIs) are considered, the risk estimates for postapplication workers meet the target MOE, and are not of concern.
Malathion poses a potential risk to terrestrial and aquatic organisms, therefore additional risk reduction measures need to be observed.
When malathion is released into the environment some of it can be found in soil and surface water. Malathion is very soluble in water and does not adsorb strongly to soils and therefore may leach into groundwater and enter surface water in runoff. Water monitoring has revealed malathion residues in groundwater as well as surface water, albeit infrequently and at low concentrations.
Malathion breaks down into several transformation products through hydrolysis and biotransformation at rates that depend on environmental conditions. The major transformation products, identified in biotransformation studies (mono- and dicarboxylic acid of malathion, demethyl mono and di-carboxylic acid of malathion), are expected to be non-persistent in the environment. Malaoxon, the oxidation transformation product that is primarily responsible for the toxicity of malathion, is also expected to be non-persistent. Both malathion and malaoxon readily hydrolyse under alkaline and neutral conditions, and become increasingly stable under acidic conditions. In soil, malathion is not expected to phototransform but may photolyze in natural waters containing photosensitizing agents. Malathion is not expected to volatilize significantly and is demonstrated to have low potential for bioaccumulation in fish.
Malathion poses a risk to both terrestrial and aquatic organisms. Birds are at risk in and around the site of application due to the consumption of contaminated food items, and the risk cannot be mitigated. In order to minimize the potential exposure to aquatic organisms, strips of land between the agricultural field and the aquatic areas (buffer zones) will be left unsprayed. The width of these buffer zones will be specified on the product label.
Malathion is registered for use on a broad spectrum of sites for the control of a wide variety of pests.
In Canada, malathion is registered to control a wide range of pests including beetles, bugs, crickets, earwigs, flies, grasshoppers, lice, mites, moths, spiders, thrips and ticks on a broad spectrum of sites.
Malathion for the control of a wide variety of chewing pests.
Malathion is a non-systemic insecticide and acaricide with contact, stomach, and respiratory action. Malathion is suited for control of a wide variety of chewing insects. Chewing insects, in general, are non-selective in their feeding behaviours as they typically ingest macerated whole‑leaf tissue. Insecticides with stomach-poison activity are more effective in controlling insects with chewing mouthparts such as beetles, grasshoppers and moth larvae.
Malathion contributes to insecticide resistance management.
Malathion, being a MoA group 1B insecticide, plays an important role in delaying resistance when used in rotation with insecticidal active ingredients from different MoA groups. In recent years, the registrations of several carbamate and organophosphate insecticides (MoA groups 1A and 1B, respectively), have been discontinued (for example, trichlorfon, phosalone, carbofuran, etc.) or their use patterns have been amended, limiting their use to specific sites or to specific application methods (for example, diazinon). This limits the availability of other active ingredients from MoA groups 1A and 1B to rotate with insecticides with differing modes of action.
Registered pesticide product labels include specific instructions for use. Directions include risk‑reduction measures to protect human and environmental health. These directions must be followed by law.
Risk-reduction measures are required to address potential risks identified in this assessment (Appendix II of Re-evaluation Decision RVD2012-10, Malathion). These measures, in addition to those already identified on existing malathion product labels, are designed to further protect human health and the environment. The following key risk-reduction measures are required.
To protect mixer/loader/applicators using commercial products:
To protect workers entering treated sites, restricted-entry intervals are to be implemented.
To protect homeowners using domestic products, specification that the higher application rate of 30 g a.i./L is to be used only for dwelling foundation applications.
Data are required as a condition of continued registration under section 12 of the Pest Control Products Act. The registrants of this active ingredient must provide these data (See Appendix III of Re-evaluation Decision RVD2012-10, Malathion) or an acceptable scientific rationale to the PMRA within the timeline specified in the decision letter.
The relevant test data on which the decision is based are available for public inspection, upon application, in the PMRA's Reading Room (located in Ottawa). For more information, please contact the PMRA's Pest Management Information Service.
Any person may file a notice of objection regarding this decision on malathion within 60 days of the date of publication of this Re-evaluation Decision. For more information regarding the basis for objection (which must be based on scientific grounds), please refer to the Pesticides and Pest Management portion of Health Canada's website (Request a Reconsideration of Decision) or contact the PMRA's Pest Management Information Service.