Fate of Summertime Airborne Organophosphate Pesticide Residues in the Sierra Nevada Mountains

Abstract

This study examines the processes of dilution, degradation, and sorption to plant foliage of organophosphate (OP) pesticides during the summertime in an air corridor originating in the southern Central Valley of California and moving into the nearby Sierra Nevada mountains. Residues of chlorpyrifos, methidathion, and their oxons were examined in air and pine needles at three sites in the southern Sierra to delineate the role these processes play in the atmospheric fate of these residues. At the site closest to the Central Valley, we found relatively high levels of parent OPs and oxons in needle and air samples. At higher elevations needles contained lesser amounts of OP residues and at lower frequency, while air primarily contained the oxon form. With increasing elevation the ratio of thion to oxon form of chlorpyrifos in air decreased from 1.85 to 0.46 indicating that atmospheric oxidation was occuring. Based on the amounts of foliar deposition found, we estimate that during summer months nearly 16 kg of chlorpyrifos and its oxon may enter Sequoia National Park plant foliage. We deduce that for airborne OP insecticides, foliar deposition is a significant summertime fate process, along with atmospheric degradation and dilution.

Fate in the Environment and Long-Range Atmospheric Transport of the Organophosphorus Insecticide, Chlorpyrifos and Its Oxon

“…Over a 4-d sampling period, concentrations were 1-100 ng CPY m −3 with some values as high as 250 ng CPY m −3 . These are similar to measured concentrations in the range 4-180 ng CPY m −3 adjacent to a citrus orchard at the Lindcove Field Station in California (Aston and Seiber 1997). Concentrations of a variety of pesticides, including CPY, have been measured at locations across Canada (Yao et al 2008).…”

“…The data in (Tables 1, 2, 3 and 4) confirm that measurable concentrations of CPY are found in air and other media remote from sources with a significant Mast et al (2012) Pine needles in Sequoia NP, 1994 10-125 ng g −1 dwt Aston and Seiber (1997) Sequoia NP, 1996 Dry deposition: 0.2-24 ng m −2 d −1 Surface water: 0.2-122 ng L −1 LeNoir et al (1999) Fate in the Environment and Long-Range Atmospheric Transport… frequency of detection. The key issue in this context is not one of presence/absence, because CPY and CPYO can be monitored in air at concentrations as little as 0.001 ng m −3 , which are much less than thresholds for adverse effects.…”

“…This behavior results in the possibility that the CPYO/CPY ratio can provide insights into the approximate "age" of the air parcel, although this ratio may be influenced by conversion during sampling and prior to analysis. This ratio was observed to be approximately 1.0 in the summer of 1994 at Lindcove near Fresno CA, which suggests a transit time of ~5 h (Aston and Seiber 1997). A test using SF 6 as a tracer gave comparable transit times.…”

“…Central Valley (CA) and Sierra Nevada CPY up to 180 and CPYO up to 54, lesser concentrations in Sequoia NP Aston and Seiber (1997) CPY and CPYO in air in Sequoia NP 0.16-17.5 LeNoir et al A comprehensive ecotoxicological risk assessment of CYP was developed for birds and mammals (Solomon et al 2001) and aquatic environments (Giesy et al 1999) that were near areas of application. The analysis of LRT of CPY and CPYO presented here extends those assessments to regions downwind of points of application.…”

“…There is also loss of mass of CPY by transport from air to the ground, specifically due to deposition in rain or snow, sorption to aerosol particles that subsequently are deposited by wet and dry deposition, and direct sorption to terrestrial and aquatic surfaces as shown by Aston and Seiber (1997), LeNoir et al (1999) and Bradford et al (2013). Estimates of these process rates can be made and the overall results can be compared to measured concentrations of CPY.…”