Pesticide Profile - Diazinon

Quick Facts:

• Chemical name: O,O-diethyl 0-2-isopropyl-6-methyl(pyrimidine-4-yl) phosphorothioate

• Trade names: Basudin, Dazzel, Gardentox, Kayazol, Knox Out, Nucidol, Spectracide

• Pesticide type: insecticide, acaricide

• Class: organophosphate

• Mechanism of action: cholinesterase inhibitor

• Major routes of exposure: inhalation, contact, ingestion

• U.S. regulatory status: approved for use in many home and garden products, some formulations are restricted use - applied only by licensed professionals. In 1988, the use of diazinon on turf farms and golf courses was cancelled.

• Current use: approximately 6 million pounds are used in the U.S. annually; 70% of this use is by homeowners and professional applicators for structural and lawn pest control around residences and public buildings. The remaining 30% is  agricultural and veterinary use.

• Diazinon is one of the most common pesticides used on lawns.

• Diazinon is 100 times more acutely toxic to birds than to mammals and has been responsible for many avian mortality incidents in the U.S.

• Diazinon volatilizes from plant surfaces and is found in air, rain, and fog samples throughout the U.S. It is estimated that 9% of diazinon applied to orchards volatilizes to the atmosphere and can be transported away from application sites.

Background

Diazinon was first described in 1953. Since then, it has become one of the most commonly used pesticides in the U.S. Diazinon has been linked to serious human health effects and is the sixth most common pesticide involved in accidental deaths. Diazinon is highly toxic to birds. U.S. EPA tests show that birds grazing on treated lawns for 15-80 minutes can receive a lethal dose. More than 200 acute avian mortality incidents are recorded in EPA databases, some of them involving hundreds of birds. Another major route of exposure is the ingestion of insects and other invertebrates that contain diazinon residues. Birds of the family Icteridae, blackbirds, grackles, orioles, and meadowlarks, and Turdidae, robins and bluebirds, commonly feed on or near suburban parks and lawns. These birds are susceptible to secondary exposure and possible poisoning by diazinon and may also expose their young to diazinon when they bring contaminated insects back to the nest. Reproduction studies have shown that diazinon reduces both the clutch-size and number of surviving hatchlings when it is fed to birds at sub-acute doses. The potential for negative reproductive effects in the environment is substantial, given current usage rates, especially among urban and suburban bird populations. 

Household use of diazinon is perhaps the most environmentally harmful, as millions of pounds of the insecticide applied to lawns and gardens are washed into urban and suburban waterways. The EPA has determined that diazinon is mobile in the environment and may be persistent enough to significantly impact water resources. One study in King County, Washington in 1998 found diazinon levels that exceeded standards for long-term exposure in nine of ten urban streams. The United States Geological Survey National Stream Water Quality Network found diazinon in all major U.S. river systems sampled, including the Rio Grande, Mississippi, Columbia, and Colorado. Because of the high volume of water flowing in these rivers, the pesticide concentrations reported indicate a high total mass of transported diazinon. In many cases, the concentration of diazinon in waterways exceeds levels deemed unsafe to aquatic organisms by the EPA. Apart from acute poisonings of birds by diazinon, the damage that this compound has on aquatic life forms affects birds indirectly by reducing diversity and numbers of prey items, and by exposing many birds to diazinon through secondary routes. Ducks, kingfishers, herons, grebes, eagles, ospreys and shorebirds are susceptible to the effects of diazinon through the ingestion contaminated prey.

While agricultural use comprises only 30% of the total pounds of diazinon applied, the percent of all acreage planted that is treated with daizinon is quite high for certain crops; brussell sprouts, cranberries, head lettuce, apricots, and nectarines included.

Environmental Effects

Fate

• Persistence: Diazinon is moderately persistent in soils and in water. In the environment, diazinon appears to degrade by hydrolysis in water and by photolysis and microbial metabolism in soil. It dissipates from impervious surfaces by volatilization. The estimated half-life of diazinon in soils is from 17 to 39 days, depending on conditions. The range of degradation in water is estimated through laboratory studies and varies with pH. The half-life at pH 5 is 12 days, at pH 7 the half-life is 138 days.

• Bioaccumulation: Diazinon residues accumulated in bluegill sunfish in laboratory studies with maximum mean bioconcentration factors of approximately 500x in all tissues sampled. Most of the accumulated residues were eliminated from fish tissues in seven days.

Ecotoxicity 

• Diazinon is classified as moderately to practically nontoxic to small mammals on an acute oral basis. However, it is very highly toxic when fumes are inhaled at 3.5 milligrams per cubic meter directly after application.

• Diazinon is highly toxic to honey bees and other non-target, beneficial insects.

• Diazinon is highly toxic to fish.

• Diazinon is very highly toxic to freshwater and marine invertebrates.

• Diazinon is very highly toxic to birds. Representative LD50's:

LD50 Canada goose                        6.16 mg/kg
LD50 mallard                                  1.44 mg/kg
LD50 house sparrow                          7.5 mg/kg

Incidents

Based on information available in the US EPA Ecological Incident Information System (EIIS), diazinon has caused the second largest number of total known incidents of bird mortality of any pesticide, exceeded only by carbofuran. The national trend is that diazinon incidents have been increasing, with the highest numbers of incidents reported in the past seven years. As with all pesticide mortality incidents, the number of reported kills represents only a small fraction of the total.

• Long Island, New York, 1985. Approximately 700 brant were found dead on a golf course soon after diazinon had been applied.

• In a study which looked at wildlife mortality related to diazinon use, Stone and Gradoni (1985) reported that 23 species of birds had been documented in 54 separate incidents in the U.S. before 1985 including great blue heron, snow goose, Ross' goose, brant, Canada goose, wood duck, American black duck, mallard, gadwall, American wigeon, ring-necked pheasant, American coot, killdeer, mourning dove, downy woodpecker, bluejay, green jay, American robin, common grackle, and house sparrow.

• Oak Park, Illinois, 1991. The routine application of diazinon to the lawn of a condominium complex resulted in the death of 47 mallards.

• Anchorage, Alaska, 1999. Five common ravens were found in a suburban area of Anchorage. The birds were found unable to fly and salivating excessively. A laboratory analysis revealed that the birds had died from consuming insect larva poisoned with diazinon. No evidence of inappropriate pesticide use was discovered after an investigation. The birds were most likely exposed to diazinon through normal application during landscaping

Plan of Action

Like chlorpyrifos, another commonly used organophosphate, consumer use in the yard and in the home accounts for the largest percentage of total pounds of diazinon applied in the United States. ABC is seeking cancellation of all diazinon uses on lawns and green spaces. ABC is also urging the EPA to severely restrict diazinon use in orchards. Currently, there is no regulation of most diazinon uses by homeowners, besides label recommendations. Given that most of the household pesticide products containing chlorpyrifos were canceled in June 2000, it is realistic to expect increased regulation of diazinon through the reregistration process set in motion at the EPA by the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Food Quality Protection Act (FQPA). The American Bird Conservancy is continuing to work with the several U.S. governmental agencies involved to ensure that the effects of pesticides on birds and other wildlife are not overlooked.