Conventional agricultural practices rely heavily on the use of chemicals to achieve high animal and crop productivities. For cattle, this includes a large variety of organic compounds such as veterinary pharmaceuticals, pesticides, and disinfectants, many of which find their way into manure. Manure is often applied on cropland for fertilization, providing opportunities for environmental contamination of these agricultural chemicals. To assess the presence of chemicals in manure, manure samples from seven farms in PA, MD, and VA were collected and analyzed using liquid chromatography – high-resolution mass spectrometry (LC-HRMS). This was accompanied by an extensive survey of chemicals used on each of the farms to create a chemical list for suspect screening analysis. Manure samples were processed using both QuEChERS and aqueous extractions. For LC-HRMS analysis, both electrospray ionization (ESI) and atmosphere pressure chemical ionization (APCI) were used in positive and negative modes. Two acquisition methods were tested including data-independent and data-dependent MS2. Non-targeted analysis was carried out using Compound Discoverer to identify and annotate the detected chemicals. Furthermore, a pesticide standard mix containing more than 1,000 compounds was used in combination with a random forest regression to provide semi-quantification of the identified compounds. These results will highlight the potential and extent for agricultural chemicals to contaminate manure as affected by the various manure management strategies and chemicals used on the sampled farms.

Anthropogenic chemicals in cattle manure: Combining high-resolution mass spectrometry and machine learning to identify unknown chemicals and predict their concentrations

ACS Spring 2022

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