Pesticides Exposure Assessment of Kettleman City Using the Industrial Source Complex Short-Term Model Version 3

Abstract

Kettleman City, California, reported a higher than expected number of birth defect cases between 2007 and 2010, raising the concern of community and government agencies. A pesticide exposure evaluation was conducted as part of a complete assessment of community chemical exposure. Nineteen pesticides that potentially cause birth defects were investigated. The Industrial Source Complex Short-Term Model Version 3 (ISCST3) was used to estimate off-site air concentrations associated with pesticide applications within 8 km of the community from late 2006 to 2009. The health screening levels were designed to indicate potential health effects and used for preliminary health evaluations of estimated air concentrations. A tiered approach was conducted. The first tier modeled simple, hypothetical worst-case situations for each of 19 pesticides. The second tier modeled specific applications of the pesticides with estimated concentrations exceeding health screening levels in the first tier. The pesticide use report database of the California Department of Pesticide Regulation provided application information. Weather input data were summarized from the measurements of a local weather station in the California Irrigation Management Information System. The ISCST3 modeling results showed that during the target period, only two application days of one pesticide (methyl isothiocyanate) produced air concentration estimates above the health screening level for developmental effects at the boundary of Kettleman City. These results suggest that the likelihood of birth defects caused by pesticide exposure was low.

A Procedure to Select Meteorological Data for Air Dispersion Modeling of Pesticide Applications in California

“…Structural fumigation of residential houses is used in the case study for 3 reasons: 1) This type of fumigation has only 1 application method, and its emission information is sufficient for a modeling test; 2) only 1 pesticide (sulfuryl fluoride) is registered for structural fumigation in California, and its high‐use area is where ASOS stations are mostly available; and 3) structural fumigation modeling involves 2 types of sources. Source 1 (ground‐level area source) is usually used to simulate air dispersion of numerous pesticides applied on agricultural fields (Ross et al ; Segawa et al ; Johnson et al ; Tao et al ). Pesticide emissions during agricultural uses depend heavily on various application methods.…”

“…Modeling was set up and operated using AERMOD View of Lakes Environmental with AERMOD version 16216. In Phase II, 3 types of hypothetical sources on flat terrain were configured to simulate 2 types of pesticide applications (Figure ), described below: Source 1: Ground‐level area source simulating pesticide applications on the ground such as agricultural fields (Tao et al ); it was a square area of 70 m × 70 m (1.2 acre) with a nominal emission rate of 10 ‐4 g/s·m 2 . Source 2: Two‐layer area source simulating a treatment period of a structural fumigation (Tao ); 1 layer was at ground level and 1 layer was at 1.5 m height. Both layers had a square area of 21.55 m × 21.55 m (5000 ft 2 ) and a nominal emission rate of 5 × 10 –5 g/s·m 2 . Source 3: Point source simulating an aeration period of a structural fumigation, a 3.05‐m (10 ft) high stack with a diameter of 0.457 m (1.5 ft) in the middle of 1 side of a structure.…”

“…Source 1: Ground‐level area source simulating pesticide applications on the ground such as agricultural fields (Tao et al ); it was a square area of 70 m × 70 m (1.2 acre) with a nominal emission rate of 10 ‐4 g/s·m 2 .…”

“…Compared to other parameters in the literatures, LWS conditions tend to have relatively stronger monotonic association with high concentration estimates. A previous modeling study estimating potential exposure of 19 pesticides around a California community also suggested that wind speed less than 2 m/s resulted in higher estimated concentrations (Tao et al ). If 1 variable could help screen out potential meteorological stations, the computational burden to identify the worst‐case scenario data could be significantly reduced.…”

“…• Source 1: Ground-level area source simulating pesticide applications on the ground such as agricultural fields (Tao et al 2013); it was a square area of 70 m × 70 m (1.2 acre) with a nominal emission rate of 10 -4 g/s·m 2 . • Source 2: Two-layer area source simulating a treatment period of a structural fumigation (Tao 2015); 1 layer was at ground level and 1 layer was at 1.5 m height.…”