J. A. Knuteson

Atmospheric volatilization of methyl bromide, 1,3-dichloropropene, and propargyl bromide through two plastic films: transfer coefficient and temperature effect

Atmospheric emission of methyl bromide (MeBr) and its potential alternative chemicals such as 1,3-dichloropropene (1,3-D) and propargyl bromide (PrBr) can contribute to air pollution and ozone depletion (for MeBr). One of the main sources of these chemicals is from agricultural soil fumigation. To understand the volatilization dynamics, emission of MeBr, 1,3-D, and PrBr through a polyethylene-based high-barrier film (HBF) and a virtually impermeable film (VIF) was measured using an air flow and sampling system that produced >90% mass balance. The experiment was conducted outdoors and was subjected to ambient daily temperature variations. The HBF film was found to be very permeable to 1,3-D and PrBr, but somewhat less permeable to MeBr. The VIF film was very impermeable to 1,3-D, PrBr, or MeBr. Measured volatilization flux, in general, exhibited strong diurnal variations which were controlled by film temperature. Unlike the HBF film, a time lag (∼12 h) was observed between high-temperatures and high-emission flux values for the VIF film. An impermeable film may be used as an effective means of controlling the atmospheric emission of MeBr and its alternative chemicals.

Surface application of ammonium thiosulfate fertilizer to reduce volatilization of 1,3-dichloropropene from soil

Atmospheric emission of the soil fumigant 1,3-dichloropropene (1,3-D) is of environmental concern because of its toxicity and carcinogenicity. Thiosulfate fertilizers have been found to rapidly transform 1,3-D in soil to non-volatile ions which are less toxic. We investigated the use of surface application of ammonium thiosulfate (ATS) for reducing 1,3-D volatilization. In packed soil columns, emission of 1,3-D applied by sub-surface injection decreased with increasing ATS application rate and the amount of water used for delivering ATS. When ATS was applied in 9 mm water at 64g m ˇ2 , total 1,3-D emission was reduced by 61%. The reduction was 89% when ATS was applied at 193 g m ˇ2 . Bioassays showed that ATS application did not affect the effectiveness of 1,3-D for controlling citrus nematodes. In field plots where a 1,3-D emulsified formulation was applied via sub-surface drip, surface spray of ATS reduced 1,3-D emissions by 50%, and by 71% when the surface was also covered with polyethylene film. ATS application had no effect on the efficacy of root-knot nematode control or tomato yields. These results suggest that surface application of thiosulfate fertilizers may be a feasible and effective strategy for minimizing 1,3-D emissions. # 2000 Society of Chemical Industry

Emissions of 1,3-Dichloropropene and Chloropicrin after Soil Fumigation under Field Conditions

Soil fumigation is an important agronomic practice in the production of many high-value vegetable and fruit crops, but the use of chemical fumigants can lead to excessive atmospheric emissions. A large-scale (2.9 ha) field experiment was conducted to obtain volatilization and cumulative emission rates for two commonly used soil fumigants under typical agronomic practices: 1,3-dichloropropene (1,3-D) and chloropicrin. The aerodynamic method and the indirect back-calculation method using ISCST3 and CALPUFF dispersion models were used to estimate flux loss from the treated field. Over the course of the experiment, the daily peak volatilization rates ranged from 12 to 30 μg m(-2) s(-1) for 1,3-D and from 0.7 to 2.6 μg m(-2) s(-1) for chloropicrin. Depending on the method used for quantification, total emissions of 1,3-D and chloropicrin, respectively, ranged from 16 to 35% and from 0.3 to 1.3% of the applied fumigant. A soil incubation study showed that the low volatilization rates measured for chloropicrin were due to particularly high soil degradation rates observed at this field site. Understanding and quantifying fumigant emissions from agricultural soil will help in developing best management practices to reduce emission losses, reducing adverse impacts to human and ecosystem health, and providing inputs for conducting risk assessments.

Effect of organic material on field-scale emissions of 1,3-dichloropropene

Soil fumigation is important for growing many fruits and vegetable crops, but fumigant emissions may contaminate the atmosphere. A large-scale field experiment was initiated to test the hypothesis that adding composted municipal green waste to the soil surface in an agricultural field would reduce atmospheric emissions of the 1,3-dichloropropene (1,3-D) after shank injection at a 133 kg ha(-1) application rate. Three micrometeorological methods were used to obtain fumigant flux density and cumulative emission values. The volatilization rate was measured continuously for 16 d, and the daily peak volatilization rates for the three methods ranged from 12 to 24 μg m(-2) s(-1). The total 1,3-D mass that volatilized to the atmosphere was approximately 14 to 68 kg, or 3 to 8% of the applied active ingredient. This represents an approximately 75 to 90% reduction in the total emissions compared with other recent field, field-plot, and laboratory studies. Significant reductions in the volatilization of 1,3-D may be possible when composted municipal green waste is applied to an agricultural field. This methodology also provides a beneficial use and disposal mechanism for composted vegetative material.