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EPA Researchers Evaluate Procedures to More Effectively Manage Clean-up Following Pesticide Misuse Incidents

Published October 22, 2019

Pesticides include any product intended to prevent, destroy, repel, or mitigate a pest. They might be used indoors or outside against weeds, insects, rodents, mold, microorganisms, or other unwanted organisms. Whether using a man-made or a biologically-based pesticide, it is very important to follow the label directions. In fact, pesticide labels are considered legal documents and provide directions for how and where the product should be applied. Applying any pesticide in a way that contradicts the label instructions is illegal and considered a misapplication.

When pesticide use or misuse results in indoor contamination, it is important to evaluate the extent of contamination and potential exposure risk, as well as the success of remediation efforts, if needed. In homes, buildings, or schools, people want to have confidence that the contamination has been cleaned up. Data obtained during the clean-up process helps decision makers determine whether allowing people to return into the previously contaminated space is safe and will not cause adverse health effects.

Contaminated surface areas (e.g., tables, countertops, floors) are of great concern because these surfaces serve as a potential route for re-exposure if the contamination is not properly removed.  Surface wiping is a sampling technique that is used to collect contamination from that surface, then the wipe is analyzed to determine if a hazard remains or if it has been properly removed.  Surface wipe sampling and analysis procedures are commonly used to collect data for this type of evaluation. However, sampling procedures vary widely, and their performance has not been well tested on porous surfaces or for high surface concentrations that may occur in misuse incidents.  Examples of varied sampling parameters include the size and type of wipe material, wipe solvent selection and volume, sampled surface area, and wiping technique. It is difficult to compare and interpret results if consistent and reproducible procedures are not used. For these reasons, EPA researchers evaluated clean-up options that can help determine what type of indoor contamination and remediation efforts should be used following pesticide misuse.

In a recent study, published in Science of the Total Environment, EPA researchers studied wipe sampling parameters specifically for the commonly used insecticides malathion and carbaryl. This study sought to understand how surface sampling variables affect the reliability, precision, and accuracy of sample results. The parameters evaluated included wipe material type, the solvent used to wet the wipe material, surface materials with varied composition and porosity, concentration effects, the number of sampling wipes needed to remove residues most efficiently from each surface, and the influence of different commercially available product formulations.

The researchers tested porous and non-porous surfaces usually found in the home, such as vinyl tile, plywood, painted drywall, stainless steel, and glass. The specific wipe materials tested, which are widely available and frequently used for clean-up, include pre-packaged sterile gauze, pre-cleaned cotton twill, cotton balls, filter paper, and a pre-packaged, pre-wetted isopropanol wipe.

The researchers developed a wipe sampling procedure for a one foot-squared area to allow for consistency and reproducibility during sampling. Researchers noted that wipe selection and solvent selection affect recovery results, so it is important to select proper wipes and solvents for clean-up success and reducing variability. The results suggest that multiple wipes improve the recovery of surface contaminants when a less compatible wetting solvent is used with the target chemical or a wipe that is not efficient at extracting the chemical from the surface due to size or composition. The data suggest that most of the targeted pesticides can be recovered from the surface with two consecutive wipes on the same area. Using more than two wipes did not significantly improve recovery results when used to wipe the same surface area.

Using pre-packaged wipes, like the isopropanol wipe material, reduces the number of variables associated with sampling. Surface materials that allow the chemical, or wiping solvent, to soak into the surface (e.g., painted drywall, vinyl tile) result in low recovery results because surface wipe sampling primarily collects contaminants that remain on the surface.  Surface materials that did not allow the chemical or solvent to soak into the surface (e.g., metal, laminate) resulted in higher recoveries. The research also noted that concentration (highly contaminated areas versus low contamination areas) did not adversely affect surface wipe recovery results.

State and local responders can use the data from this investigation to develop their own sampling procedures and improve their recovery results. For example, this information is being used by States to assist with developing their wipe sampling procedures to ensure that appropriate wipe materials and wipe wetting solvents are used for surface wiping during pesticide misuse incidents.