A Review of the Chemistry, Pesticide Use, and Environmental Fate of Sulfur Dioxide, as Used in California

Abstract

Sulfur dioxide (SO₂) is an atmospheric pollutant that is moderately persistent in the atmosphere and highly water soluble. When applied as a pesticide, SO₂ may be transported, deposited, or transformed in various chemical reactions. SO₂ participates in the sulfur biogeochemical cycle, which involves complex reactions of sulfur-containing compounds between abiotic and biotic components of ecosystems. The main degradation route of SO₂ is atmospheric oxidation, and sulfur oxides may undergo long-distance transport prior to removal from the atmosphere by wet or dry deposition. According to the Pesticide Use Reporting (PUR) database maintained by the California Department of Pesticide Regulation (DPR), SO₂ use in California from 2010 to 2015 was primarily for fumigations (96%), including treatments of postharvest grape products and winery equipment sterilizations. Other site uses contributed less than 5% of reported statewide SO₂ use from 2010 to 2015. A slight increasing trend in use of SO₂ as a pesticide was observed from 2010 to 2015, with the highest reported uses of SO₂ within California counties during the months of July–November. Although the primary sources of SO₂ in the environment are anthropogenic emissions from the combustion of fossil fuels, emissions of SO₂ from pesticide uses have the potential to contribute to the environmental and public welfare impacts of SO₂ pollution. Oxidation of atmospheric SO₂ may contribute to the negative environmental and public welfare impacts of acid rain, which include toxicity to aquatic organisms, fish, and terrestrial vegetation, and corrosion of man-made materials.

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Appendix

Table 6 Sulfur dioxide product formulations and uses

Table 7 Sulfur dioxide product application rates and requirements for grape fumigation

Table 8 Total cumulative pesticide use of sulfur dioxide (pounds of active ingredient^a) reported in California from 2010 to 2015, summarized by county

Table 9 Total cumulative pesticide use of sulfur dioxide (pounds of active ingredient^a) reported in California from 2010 to 2015, summarized by crop or site

Table 10 Sulfur dioxide 1-h federal design values (continued on next page)^{a, b}