Bystander Exposures - Ultra Low Volume Adulticides
As part of EPA’s pesticide registration or registration review process, pesticides proposed or registered for use to control adult-stage flying insects (adulticides) are evaluated for safety to bystanders (people near where pesticides are being applied) who may be exposed to pesticides following applications using Ultra Low Volume (ULV) equipment. ULV Public Health Adulticides: Standard Operating Procedures (pdf) provides guidance to the public for assessing bystander exposures to pesticide drift from ground and aerial ULV adulticide applications. The SOP includes new ULV ground-based residue deposition data (data on the amounts of pesticide residues that reach the ground following an application) and re-evaluation of the existing dataset, as well as ULV aircraft input updates for use with drift modelling software that more accurately reflect present-day practice. A separate guidance and policy documents covers procedural guidance to assess occupational exposures for those who mix, load, and apply the adulticides. This new publicly available SOP will help protect public health and safety by updating assessment methods to reflect the most current exposure data and present-day application technologies.
Basics of ULV Adulticide Bystander Exposure Assessment
Adulticides are pesticides that target adult-stage flying insects (e.g., black flies, flying midges, and mosquitoes) to control mosquito populations. Professionals in public health agencies and private pesticide applicators apply adulticides over land using aircraft or truck-mounted sprayers. Adulticides are typically applied as ULV sprays (i.e., small quantities of a pesticidal active ingredient in relation to the size of the area treated) with smaller droplet sizes, higher release heights, and larger treatment areas that are different from conventional pesticidal applications. These ULV applications allow the pesticide to stay in the air, which increases efficacy by maximizing the potential for contact with flying insects.
Ground-Based ULV Bystander Exposure Assessment
Exposures to bystanders are expected from spray drift following ULV adulticide applications with ground-based truck-mounted sprayers. The Agency assumes that adulticides may drift and settle onto residential areas to include nearby lawns, patios, decks, driveways, and other outdoor spaces that adults and children can contact. Bystander exposures on lawns can occur from contact with the skin and from children contacting turf and then putting their hands in their mouths (hand-to-mouth) contact. The amount that settles or deposits onto outdoor residential spaces is determined as a fraction of what is applied and is based on data that measured the amount of adulticide that deposited on the ground following ground-based ULV adulticide applications compared to the total amount of adulticide applied. The standard methods used for estimating exposures from contact with these deposited lawn residues are described in the 2012 SOP for Residential Pesticide Exposure Assessment: Treated Lawns/ Turf (2012 Residential SOP: Treated Lawns/ Turf).
Bystander inhalation exposures are also expected from ground-based ULV adulticide applications. These exposures are estimated by calculating air concentrations in the breathing zone of potential bystanders using the standard well-mixed box (WMB) model described in the 2012 SOP for Residential Pesticide Exposure Assessment: Outdoor Fogging/Misting Systems (2012 Residential SOP: Outdoor Fogging/Misting Systems).
Aerial ULV Bystander Exposure Assessment
Bystander dermal and inhalation (adults and children) and child hand-to-mouth exposures are expected following aerial ULV adulticide applications. These exposures are estimated using the 2012 Residential SOPs: Treated Lawns/Turf SOP in conjunction with the AGDISPTM model. AGDISPTM was developed by the U.S. Department of Agriculture’s (USDA) Forest Service and was created under a Cooperative Research and Development Agreement between EPA, the U.S. Forest Service, and the Spray Drift Task Force (a consortium of approximately 40 pesticide registrants). AGDISPTM was designed to optimize agricultural spraying operations and has detailed algorithms for characterizing the release, dispersion, and deposition over and downwind of the application area. This model was originally created to be used in estimating downwind deposition of spray drift from aerial and ground boom applications. AGDISPTM is used to estimate deposition from aerial ULV adulticide applications by selecting parameters in the system intended to simulate modern day practices. The inputs used in AGDISPTM are based on pesticide product labels, information derived in consultation with professionals in the pesticide industry, as well as EPA assumptions to ensure health protective risk assessments. AGDISPTM inputs include the product application rate, aircraft type, minimum height of release, minimum wind speed, and droplet sizes needed for efficacy. The critical outputs from the AGDISPTM model for use in the exposure assessment of aerial ULV adulticide pesticide application include:
- The deposition fraction, or the fraction of the application rate applied expected to deposit on the ground downwind.
- The highest average air concentration of the active ingredient at the breathing zone for adults and children.
The AGDISPTM model also provides an estimation for off-target deposition and air concentrations that can be expected following an application which is the basis for estimating exposures following aerial ULV adulticide applications.
ULV Adulticide Bystander Exposure Calculator
While the ULV Adulticide SOP serves as the underlying documentation and rationale for EPA’s ULV adulticide bystander exposure assessment approach, the Agency has incorporated the standard assumptions and algorithms in an easy-to-use Microsoft Excel-based calculator tool. By standardizing the calculations, this ensures that each proposed ground-based and aerial adulticide risk assessment is handled similarly. Additionally, by making it publicly available at the link below, all stakeholders can transparently see how ULV adulticide bystander exposure assessments are conducted.