The sky is falling III: The effect of deposition from static solid rocket motor tests on juvenile crops

- Static rocket motor tests deposit entrained soil and combustion products on crops.
- Typical deposition events showed little impact on crops, unlike previously evaluated worst-case scenario.
- TFS chloride concentrations, 1000 times greater than area soils and 100 times greater than other anions, suggest it's the main cause of the impacts.
- Crops grown outdoors may be less susceptible to deposition impacts than crops grown in greenhouse.

A mixture of combustion products (mainly hydrogen chloride, aluminum oxide, and water) and entrained soil, referred to as Test Fire Soil (TFS), can be deposited on crops during static solid rocket motor tests. The impact of a reported worst-case event was previously evaluated by exposing corn and alfalfa to 3200-g TFS/m2 at 54 days after emergence. Exposures via soil and leaves were evaluated separately. Reduced growth (soil exposure) and leaf “scorch” (leaf exposure) were attributed mainly to the high chloride concentrations in the TFS (56,000 mg/kg).A follow-up study was conducted to evaluate the effect of a typical deposition event (70-g TFS/m2, estimated by radar during several tests) and exposure (soil and leaves simultaneously) on juvenile corn, alfalfa, and winter wheat. Younger crops were used to examine potential age sensitivity differences. Impact was evaluated by comparing the growth, elemental composition, and leaf chlorophyll content of treated and untreated plants. The relationship between deposition exposure and response was also addressed.Growth of corn, alfalfa, and winter wheat exposed to a typical TFS loading was not impacted, although slightly elevated concentrations of aluminum and iron were found in the leaves. At the highest loadings used for the exposure-response experiment, concentrations of chloride and calcium were higher in TFS-exposed corn leaves than in the untreated leaves. Overall results indicate that exposure to a typical deposition event does not adversely impact juvenile crops and that younger plants may be less vulnerable to TFS. However, higher TFS loadings can cause leaf scorch and increase the leaf concentrations of some elements.

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