Agrichemical spray drift and odour

Abstract

Many agrichemical sprays, in particular some herbicides and insecticides, result in a strong odour when applied by either ground or aerial spraying techniques. This odour may be evident downwind from the application site for several hundreds of metres or even kilometres. The detection of the odour alerts people to the presence of chemicals in the air, and in many cases those affected think that they are being exposed to harmful levels of the active ingredient of the spray. The purpose of this study was to investigate the levels of odour generated during the application of several common herbicides, the level of exposure of the general public when the odours are detected, and the potential risk of adverse health effects resulting from that exposure. In addition, the hypothesis that the majority of the odour associated with many agrichemicals is due to manufacturing impurities and/or additives in the commercial formulations was tested.

Commercial formulations of 2,4-dichlorophenoxyacetic (2,4-D) acid in the form of the butyl ester (2,4-D butyl ester), ethylhexyl ester (2,4-D ethylhexyl ester) and triethanolamine salt (2,4-D amine) were studied because of current concerns regarding their use. A common alternative, 4-methyl-2-chlorophenoxyacetic acid (MCPA) was also studied.

A commercial formulation of 2,4-D ethylhexyl ester was used to test the hypothesis that the majority of the odour associated with many agrichemicals is due to manufacturing impurities and/or additives. Using dynamic dilution olfactometry, pure 2,4-D ethylhexyl ester was determined to be odourless. 2,4-dichlorophenol, which has an intense odour, was identified as a manufacturing impurity in the formulation. An estimate of its odour threshold (1.95 ppb) was measured using the technique of dynamic dilution olfactometry. Other significant odorants in the formulation were iso-octanol and an aromatic solvent. The aromatic solvent is responsible for the majority of the odour associated with the 2,4-D ethylhexyl ester formulation, assuming no significant masking or synergistic effects between the odorants.

The odour concentrations generated from the spraying of the herbicides under simulated aerial application conditions were measured using dynamic dilution olfactometry. The mean odour concentrations for 2,4-D ethylhexyl ester (22,350 OUc/m³) and MCPA (23,400 OUc/m³) were about 2-fold higher than the values for 2,4-D butyl ester (12,070 OUc/m³) and 2,4-D amine (10,000 OUc/m³). Chemical analysis of the odours determined that the calculated level of airborne active ingredient when the odour of each herbicide was "just detectable" (the odour threshold) were all lower than 0.2 µg/m³.

The calculated odour safety factor between the concentration of active ingredient at the odour threshold for each herbicide and its Threshold Limit Value - Time Weighted Average were all high and of a similar magnitude, ranging from 58,100 for 2,4-D butyl ester to 80,600 for MCPA. It was concluded that detection of faint or even strong odours from the herbicides as a result of spray drift will not result in exposures of toxicological significance to members of the public. kilometres. The detection of the odour alerts people to the presence of chemicals in the air, and in many cases those affected think that they are being exposed to harmful levels of the active ingredient of the spray. The purpose of this study was to investigate the levels of odour generated during the application of several common herbicides, the level of exposure of the general public when the odours are detected, and the potential risk of adverse health effects resulting from that exposure. In addition, the hypothesis that the majority of the odour associated with many agrichemicals is due to manufacturing impurities and/or additives in the commercial formulations was tested.

Commercial formulations of 2,4-dichlorophenoxyacetic (2,4-D) acid in the form of the butyl ester (2,4-D butyl ester), ethylhexyl ester (2,4-D ethylhexyl ester) and triethanolamine salt (2,4-D amine) were studied because of current concerns regarding their use. A common alternative, 4-methyl-2-chlorophenoxyacetic acid (MCPA) was also studied.

A commercial formulation of 2,4-D ethylhexyl ester was used to test the hypothesis that the majority of the odour associated with many agrichemicals is due to manufacturing impurities and/or additives. Using dynamic dilution olfactometry, pure 2,4-D ethylhexyl ester was determined to be odourless. 2,4-dichlorophenol, which has an intense odour, was identified as a manufacturing impurity in the formulation. An estimate of its odour threshold (1.95 ppb) was measured using the technique of dynamic dilution olfactometry. Other significant odorants in the formulation were iso-octanol and an aromatic solvent. The aromatic solvent is responsible for the majority of the odour associated with the 2,4-D ethylhexyl ester formulation, assuming no significant masking or synergistic effects between the odorants.

The odour concentrations generated from the spraying of the herbicides under simulated aerial application conditions were measured using dynamic dilution olfactometry. The mean odour concentrations for 2,4-D ethylhexyl ester (22,350 OUc/m3) and MCPA (23,400 OUc/m3) were about 2-fold higher than the values for 2,4-D butyl ester (12,070 OUc/m3) and 2,4-D amine (10,000 OUc/m3). Chemical analysis of the odours determined that the calculated level of airborne active ingredient when the odour of each herbicide was "just detectable" (the odour threshold) were all lower than 0.2 µg/m3.

The calculated odour safety factor between the concentration of active ingredient at the odour threshold for each herbicide and its Threshold Limit Value - Time Weighted Average were all high and of a similar magnitude, ranging from 58,100 for 2,4-D butyl ester to 80,600 for MCPA. It was concluded that detection of faint or even strong odours from the herbicides as a result of spray drift will not result in exposures of toxicological significance to members of the public.