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United States Department of Agriculture

Agricultural Research Service

Research Project: Alternatives to methyl bromide soil fumigation for vegetable and floriculture production Title: MONITORING 1,3-DICHLOROPROPENE AND CHLOROPICRIN EMISSIONS FROM SOLID-TARP SHANK INJECTIONS AT TWO SITES NEAR FORT PIERCE, FLORIDA

item Chellemi, Daniel
item Ajwa, Husein -
item Sullivan, David -

Submitted to: Environmental Protection Agency Special Publication
Publication Type: Other
Publication Acceptance Date: May 10, 2010
Publication Date: May 10, 2010

Interpretive Summary: 1,3-dichloropropene (1,3-D) and chloropicrin are preplant soil fumigants registered for use in the United States for the control of soilborne pests in agricultural fields. Typically, they are applied to the soil two weeks or more before planting a wide variety of crops including tomato, pepper, strawberry, eggplant, various cucurbits, ornamentals, turf, and nursery seedlings. They also can be applied following harvest to end the crop production cycle and reduce soil populations of over-seasoning pests. Traditionally, these fumigants are injected into the soil using tractor-mounted injection shanks. Both of the mentioned soil fumigants are United States Environmental Protection Agency (USEPA) labeled Restricted Use Pesticides due to their high acute toxicity. On July 16, 2008 the USEPA proposed substantial label changes for chloropicrin and 1,3-dichloropropene (Federal Registrar, Volume 73, No. 137, Wednesday, July 16, 2008). As written, the exposure mitigation requirement will make it extremely difficult, if not impossible in some cases, for many growers to apply soil fumigants. Although fumigant emissions can be reduced significantly through the use of improved application methods/ technology and by taking advantage of specific soil edaphic and environmental conditions, the USEPA does not have sufficient data demonstrating flux rates for the reduced emissions scenarios. The goals of this fumigant flux study is to generate data demonstrating reductions in fumigant emissions using improved application methods and equipment, and to generate data suitable for determining whether or not emission models can be used to reliably extrapolate the results beyond the specific soil type and soil conditions that were directly evaluated in the specific treatment plots involved in this field study.

Technical Abstract: The methodology used in this field study was found to adequately characterize the emission rates for 1,3-dichloropropene and chloropicrin. The largest peak in atmospheric emission of 1,3-dichloropropene and chloropicrin occurred on November 18, approximately 24 hours after application (Fig. 25). The flux rate of chloropicrin during the peak emissions period was 49.83 and 46.49 µg m-2 sec-1, for Sites 1 and 2, respectively (Tables 9 and 10). The flux rate of 1,3-dichloropropene during the peak emissions period was 46.83 and 49.17 µg m-2 sec-1, for Sites 1 and 2, respectively (Tables 11 and 12). For chloropicrin, another large emissions peak occurred on November 19, approximately 48 hours after application. The flux rate during the 48 hr emissions peak was 25.67 and 39.03 µg m-2 sec-1, for Sites 1 and 2, respectively (Tables 9 and 10. The low disturbance application method used in Site 1 reduced the total atmospheric emissions 1,3-dichloropropene by 13.15% when compared to the conventional application in Site 2 (Fig. 26, Tables 11 and 12). The low disturbance application method reduced the total cumulative emissions of chloropicrin by 9.41% when compared to the conventional application in Site 2 (Fig. 26, Tables 9 and 10). The largest emission reduction by the low disturbance application occurred within the first 24 hrs after application (Fig. 27). Higher soil vapor concentrations of 1,3-D and chloropicrin were observed in Site1 (Fig. 29). This was especially notable for chloropicrin, where higher soil vapor concentrations continued up to 10 days after application. The increased organic carbon in Site 1 did not affect soil degradation of 1,3-D and chloropicrin (Fig. 30 and 31). Non-vapor soil concentrations of 1,3-D and chloropicrin in Site 1 were substantially greater Site 2 up to 10 days post-application. Chloropicrin degradation in soil is independent of changes in soil moisture (Gan et al., 2000). Higher nonvapor chloropicrin concentrations were detected in Site 1 despite higher water content at the sample depth (Fig 14h) supporting the conclusion by Gan et al. (2000). Elevated water content will impact volatilization and emission of 1,3-D and chloropicrin (Thomas et al., 2003; Thomas et al., 2004; Yates et al., 2002). Water contents above field capacity in the lower soil profile coupled with an 8 in fumigant application depth may have contributed to reduced atmospheric emissions of both fumigants in both sites. Reductions in soil porosity and the continuity of the pore spaces are critical factors affecting the movement of fumigants in soil (Goring, 1962; Jury et al. 1983; Kolbezen et al., 1974). This is especially true for the vapor phase, which diffuses at rates 10 to 100 times greater than the nonvapor phase (Lembright, 1990). The absence of pathways for the fumigant to escape via traces from the application shanks or fractured soil from pre-cultivation activities resulted in high vapor and nonvapor fumigant concentrations in Site 1 (low disturbance application method).

Last Modified: 8/25/2016
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