|Ashworth, Daniel - University Of California|
|Stanghellini, Mike - Trical Inc|
|Vanwesenbeeck, Ian - Dow Agrosciences|
Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2017
Publication Date: 12/13/2017
Citation: Ashworth, D., Yates, S.R., Stanghellini, M., Van Wesenbeeck, I.J. 2017. Application rate affects the degradation rate and hence emissions of chloropicrin in soil. Science of the Total Environment. 622:764-769. https://doi.org/10.1016/j.scitotenv.2017.12.060.
DOI: https://doi.org/10.1016/j.scitotenv.2017.12.060 Interpretive Summary: Chloropicrin (CP) is an important soil fumigant and its use is increasing in areas such as California. As a gas, CP moves through soil pores, killing plant pests; however, its volatile nature also leads to significant losses from soil to the atmosphere where it adversely affects air quality. In this work, we studied how the amount of CP added to the soil (application rate) affected the extent of its emissions. Unexpectedly, the percentage emission loss was strongly and positively related to application rate, ranging from 4 to 34% across the application rate range. This behavior differs from that of other soil fumigants, for which the percentage emissions remains relatively constant with increasing application rate. Based on degradation studies, we consider that a shorter half-life (faster degradation) at lower application rates limited the amount of CP available for emission. This work has significance to the risk assessment of CP use. For example, it suggests that low application rates likely lead to disproportionally low emission losses compared with higher application rates; such a relationship could be taken into account when assessing/mitigating risk, e.g., in the setting of buffer zone distances around fumigated fields.
Technical Abstract: Increasingly stringent regulations to control soil-air emissions of soil fumigants has led to much research effort aimed at reducing emission potential. Using laboratory soil columns, we aimed to investigate the relationship between chloropicrin (CP) application rate and its emissions from soil across a wide range of CP applications (equivalent to 56–392 kg ha- 1). In contrast to the known behavior of other fumigants, total emission percentages were strongly and positively related to application rate (i.e., initial mass), ranging from 4 to 34% across the application rate range. When combined, data from a previous study and the present study showed good overall comparability in terms of CP application rate vs. emission percentage, yielding a second-order polynomial relationship with an R2 value of 0.93 (n = 12). The study revealed that mass losses of CP were strongly disproportional to application rate, also showing a polynomial relationship. Based on degradation studies, we consider that a shorter half-life (faster degradation) at lower application rates limited the amount of CP available for emission. The non-linear relationship between CP application rate and CP emissions (both as % of that applied and as total mass) suggests that low application rates likely lead to disproportionally low emission losses compared with higher application rates; such a relationship could be taken into account when assessing/mitigating risk, e.g., in the setting of buffer zone distances.