By: John P. Buchweitz, PhD, DABT, Nutrition and Toxicology Section Chief; Andreas F. Lehner, PhD, Analytical Chemist; Justin Zyskowski, Nutrition and Toxicology Research Assistant; Mick Fulton, DVM, PhD, DACVP, Avian Pathologist

Poultry Farm 31 M Sprague Lr
Photo credit: Michigan Department of Agriculture and Rural Development

In early February 2020, a Midwest egg producer contacted the Michigan State University Veterinary Diagnostic Laboratory’s (MSU VDL) avian pathologist, Dr. Mick Fulton, regarding concerns for the potential introduction of an herbicide contaminant into the food/feed system. More specifically, the producer had been alerted that a flaxseed feed ingredient was determined to be adulterated with the herbicide Haloxyfop. Accordingly, both the producer and pathologist had concern for the potential that layers may excrete the herbicide via eggs and hence a question of food safety emerged. Haloxyfop is a pre- and postemergence herbicide produced in the form haloxyfop-methyl and haloxyfop-ethoxyethyl.

These chemicals are used primarily to control annual and perennial grasses in sugar beet, oilseed, potatoes, leafy vegetables, onions, sunflowers, strawberries and other crops (1); however, there are no current registrations for products containing haloxyfop by the United States Environmental Protection Agency (EPA) according to the National Pesticide Information Retrieval System (2). Therefore, the flaxseed feed ingredient which contained haloxyfop residues was most likely of foreign origin.

Because haloxyfop is not a registered herbicide in the United States, there are also no established residue tolerances for this compound, or its esters, associated with any agricultural commodity produced in the U.S. Therefore, the lack of a specified residue tolerance for haloxyfop within the code of federal regulations (40 CFR Part 180 Subpart C) (3) renders contaminated products to be “adulterated.” For the current case, this means that there is “zero tolerance” for any quantifiable concentration of haloxyfop in eggs produced at the facility in question.

For comparison, the European Union (E.U.) Commission on Food Safety has an established maximum residue limit (MRL) for haloxyfop in all agricultural products, including eggs, of 0.01 mg/kg (10 μg/kg) (4) which is equivalent to the lower limit of analytical determination. This is the legally defined default value for analytical tests conducted for herbicide/ pesticide residues in the E.U. and essentially equates to a numerically established “zero” tolerance. This clearly defined value by the E.U. becomes a proverbial “line-in-the-sand” for exports to the E.U. In a similar manner, the U.S. Food and Drug Administration (FDA) also implements a level of quantitation that must be attainable across analytical laboratories performing routine regulatory analyses. (5)

For the given case, the MSU VDL staff worked diligently to develop and validate a method specific to the extraction, detection, and quantitation of haloxyfop in eggs as low as 1 μg/kg within 10 days of receiving samples. To be consistent with FDA (and the E.U.), results at or below 0.01 mg/kg (10 ug/kg) were deemed “trace”. Unfortunately for the producer, quantifiable residues above the limits of quantitation defined by these regulatory authorities were determined to be present in the products.

This case serves as another example of the importance of the MSU Veterinary Diagnostic Laboratory working across disciplines in a timely manner to ensure the safety of our food supply both here in Michigan and beyond.


(1) Extension Toxicology Network Pesticide Information Profiles: Haloxyfop. Revised 9/95. Accessed: March 20, 2020.

(2) National Pesticide Information Retrieval System. Accessed: March 20, 2020.

(3) U.S. Code of Federal Regulations March 20, 2020. Accessed: March 20, 2020.

(4) European Commission Pesticide Database: Current MRL values. Revised July 4, 2016. Accessed: March 20, 2020.

(5) U.S. Food and Drug Administration. Pesticide Analytical Manual Volume I. 3rd Edition. 1999. Accessed: March 25, 2020.