December 5, 2000

Use/Usage:

Over 13 million lbs of diazinon are applied annually. Use is on a variety of agricultural corps and livestock (about 20% of usage), on turf and for residential control of various insects indoors and outdoors (about 80% of usage). For non-ag use, the largest share is in homeowner outdoor insect control for turf and gardens (39%). Other large usage is in lawn care operators (19%) and pest control operators (11%). Indoor homeowner use is also registered. California, Texas and Florida are states with the most significant usage. Diazinon is about 1% of the Pest Control Operator (PCO) market for indoor insecticides.

Formulations:

Diazinon is registered as dust, granules, wettable powders, seed dressings, emulsifiable solutions, impregnated materials, encapsulated materials, concentrates and ready-to- use solutions.

Toxicity:

Diazinon endpoints are based on plasma, red blood cell and/or brain cholinesterase inhibition for all exposure routes and durations. Because route specific toxicity studies are available, dermal and inhalation absorption factors are not necessary. For inhalation, the standard uncertainty factor of 100 was applied with an extra 3X uncertainty factor due to the lack of a NOAEL in a rat 21-day inhalation study. Therefore, for inhalation exposures of all durations, an MOE of 300 is acceptable. For dermal short-term exposure, the target MOE of 100 is acceptable. For intermediate- and long-term dermal exposure, a 3X safety factor was added to account for the extrapolation from a 21-day dermal exposure to a longer term exposure. For intermediate- and long-term dermal exposure, a target MOE of 300 is acceptable.

Food Risks:

Acute and chronic dietary risk from food are acceptable (highest sub-population is 63% for acute and 22% for chronic (children 1-6 years old).

Water Risks:

Diazinon parent is moderately mobile and persistent. Based on monitoring data, there is no risk concern for either groundwater or surface derived drinking water exposure for chronic or acute. Modeling data indicate a possible concern for infants and children age 1-6 (acute), and children 1-6 and females age 13+ (chronic) from surface derived drinking water only. Water estimates do not include metabolites, since toxicity and monitoring data for these are lacking.

Residential Risks:

The Agency has concerns for potential children's exposures in the home. Potential routes of exposure for children may include inhalation of vapors and airborne particles and dermal contact.

Occupational Risks:

Occupational "handler" exposure to diazinon can occur during mixing, loading and application activities. Post application exposure may occur during scouting, irrigation, cultivation, harvesting and handling seeds. The majority of occupational risk estimates for handlers exposed to diazinon exceed the Agency's level of concern, even with personal protective equipment (PPE) and/or engineering controls. The majority of post application exposures exceed EPA's level of concern at the currently established restricted entry interval (REI) of 24 hours.

Ecological Risks:

Diazinon is highly toxic to birds, mammals, honey bees and other beneficial insects. It is also very highly toxic to freshwater fish and invertebrates following acute exposure. The endangered species levels of concern are exceeded for terrestrial wildlife, aquatic life and terrestrial plants.

Incidents:

Diazinon is one of the leading causes of acute insecticide poisoning for humans and wildlife. For humans, the rate of incidents is not high relative to its large volume of usage. The majority of incidents occur in the home. It also is one of the top causes of bird kill incidents.