Summertime transport of current‐use pesticides from California's Central Valley to the Sierra Nevada Mountain Range, USA

Abstract

Aricultural activity in California's Central Valley may be an important source of pesticides that are transported in the air to the Sierra Nevada Mountain Range, USA. Pesticides applied to this intensive crop production area may volatilize under warm temperatures typical of the valley and be transported through the atmosphere to be deposited in the cooler, higher elevation regions of the Sierra Nevada Mountains. To determine the extent of summertime atmospheric transport of pesticides to this region, high‐volume air, dry deposition, and surface water samples were collected in the Central Valley and at different elevations in California's Sequoia National Park. Results revealed that the highest residue concentrations were those of compounds with heavy summertime agricultural use. A significant drop in pesticide concentrations in both air and water samples was observed within a few 100‐m elevation from the valley; however, levels remained relatively constant between ∼500 and 2,000 m. Water concentrations from two areas above 3,000 m contained levels less than a tenth as high as those at lower elevations. Possible effects of the pesticides were estimated using measured water concentrations to calculate total exposure of three aquatic species to organophosphate insecticides. Aggregate exposure calculations showed concentrations were well below 96‐h LC50 values for rainbow trout and stonefly but concentrations may be harmful to amphipods.

Gas-phase pesticide measurement using iodide ionization time-of-flight mass spectrometry

“…The resulting atmospheric concentrations vary, and these currentuse pesticides have been detected hundreds of meters to kilometers away from application sites in both gas and particle phases (Coscollà et al, 2010(Coscollà et al, , 2008LeNoir et al, 1999). Atrazine, trifluralin, and metolachlor have been observed near application areas in concentrations ranging from < 1 ng m −3 to as high as 61 µg m −3 , and in urban and remote locations that are far from sources with concentrations < 2 ng m −3 (Foreman et al, 2000;Majewski et al, 2014;Peck A.M, 2005;Bedos et al, 2006;Coscollà et al, 2010).…”

“…For detection of pesticides in the atmosphere, air samples are typically collected on solid-phase micro-extraction (SPME) fibers or other adsorbent materials with sampling times of 2 h-1 week (Bedos et al, 2006;Glotfelty et al, 1989;LeNoir et al, 1999;Majewski et al, 2014;Peck A.M, 2005). These solid adsorbents are analyzed by offline techniques, typically gas chromatography coupled to mass spectrometry (GC-MS) or electron capture detection (GC-ECD) (Bedos et al, 2006;Coscollà et al, 2010;Foreman et al, 2000;Glotfelty et al, 1989;LeNoir et al, 1999;Majewski et al, 2014;Peck A.M, 2005;Rice et al, 2002).…”

“…These solid adsorbents are analyzed by offline techniques, typically gas chromatography coupled to mass spectrometry (GC-MS) or electron capture detection (GC-ECD) (Bedos et al, 2006;Coscollà et al, 2010;Foreman et al, 2000;Glotfelty et al, 1989;LeNoir et al, 1999;Majewski et al, 2014;Peck A.M, 2005;Rice et al, 2002). These measurement approaches are adequate for offline quantitation of airborne pesticides, with detection limits for trifluralin ranging from 1.3 pg m −3 (GC-MS) to 0.4 µg m −3 (GC-ECD) with sample collection times of 24 and 2 h, respectively (Peck A.M, 2005;Bedos et al, 2006).…”

“…These measurement approaches are adequate for offline quantitation of airborne pesticides, with detection limits for trifluralin ranging from 1.3 pg m −3 (GC-MS) to 0.4 µg m −3 (GC-ECD) with sample collection times of 24 and 2 h, respectively (Peck A.M, 2005;Bedos et al, 2006). These techniques have proven successful in quantifying atmospheric pesticide concentrations, although offline analysis introduces steps that can alter a compound's structure and reduce sampling efficiency (Coscollà et al, 2010;LeNoir et al, 1999;Peck A.M, 2005;Rice et al, 2002), and it is inadequate for rapid ambient measurement. Rapid measurements are necessary for (i) observing pesticide drift in real time to understand meteorological effects; (ii) directly measuring volatilization and surfaceatmosphere fluxes by eddy covariance or other micrometeorological approaches; (iii) determining whether agricultural workers are exposed to low concentrations over a long period of time or high concentrations over a short period of time, and thus for identifying activities that can be targeted to reduce exposure; and (iv) laboratory smog chamber or flow reactor measurements in which oxidation chemistry is typically observed on timescales of minutes.…”

“…While the ecological implications of these observations have been the focus of much research, little work has focused on their atmospheric chemistry, despite the fact that many of these pesticides are transported through the atmosphere (Bedos et al, 2006;Coscollà et al, 2008;LeNoir et al, 1999;Majewski et al, 2014;Peck A.M, 2005;Rice et al, 2002;Sauret et al, 2000;Tabor, 1965;White et al, 2006). The chemical fate of compounds in the atmosphere -including oxidation, gas-particle partitioning, and surface deposition -ultimately controls their chemical identities and concentrations, and thus their impact on ecosystems and human health.…”