Quantification of odors and odorants from swine operations in North Carolina

A total of 331 different VOCs and fixed gases from swine facilities in North Carolina were identified by gas chromatography and mass spectrometry (GC/MS). Of these, 203 were found in air samples adsorbed onto Tenax ®, 112 were found in air samples adsorbed onto cotton material, and 167 different compounds were identified in the lagoon samples. The compounds identified were diverse, and included many acids, alcohols, aldehydes, amides, amines, aromatics, esters, ethers, fixed gases, halogenated hydrocarbons, hydrocarbons, ketones, nitriles, other nitrogen-containing compounds, phenols, sulfur-containing compounds, steroids, and other compounds. The vast majority of these compounds were present at concentrations below published odor and irritation thresholds. Yet human assessments indicated that odors (and irritant sensations) in the immediate vicinity of the swine houses (and even at distances beyond 1000 ft) were strong. Comparison of the findings from chemical and human assessments points to the importance of the cumulative effects of hundreds of compounds in producing odor and irritation downwind of swine operations. Many GC peaks from the samples were too small to allow identification of the compounds, but their presence may also contribute significantly to the odor and irritation. Several methodological difficulties were associated with the human odor assessments. Odorous air evaluated in the field was simultaneously collected in Tedlar ® bags for evaluation in the laboratory; however, intensity ratings in the field were higher than those in the laboratory. This is due to the fact that organic dust (dried fecal material and feed) adheres to Tedlar ® bags and the tubing of collection/delivery systems; therefore, only VOCs from the vapor phase (but not the dust) reach the nose of the panelists in sniffing air samples obtained in Tedlar ® bags. Future collection and measurement techniques need to be developed that can evaluate odors from dust and vapor phases simultaneously in the laboratory. Dispersion models also need to be developed that account accurately for odor intensities downwind of animal operations. Finally, safety standards for odor exposures need to be determined that consider the risk of simultaneous exposure to hundreds of low level compounds.