Atmospheric deposition flux estimates for chlorpyrifos and trifluralin in the chukchi sea

Authors: McConnell, Laura; Rice, Clifford; CHERNYAK, SERGEI - University Of Michigan

Submitted to: Book Chapter
Publication Type: Book / Chapter
Publication Acceptance Date: 9/30/2009
Publication Date: 10/23/2009
Citation: Mcconnell, L.L., Rice, C., Chernyak, S.M. 2009. Atmospheric deposition flux estimates for chlorpyrifos and trifluralin in the Chukchi Sea. Book Chapter. p. 215-219.

Interpretive Summary: During the 1993 U.S.-Russian BERPAC expedition, residues of agricultural pesticides, trifluralin and chlorpyrifos were detected in seawater, ice, surface microlayer, fog, and air of the Bering and Chukchi Seas. Aside from the possible local uses of chlorpyrifos for household pest control on board ships or perhaps at a few land-based military installations, there are few non-atmospheric sources for these pesticides. Thus, gas exchange, wet deposition, and dry particle deposition fluxes of trifluralin and chlorpyrifos were estimated in order to determine loadings for these pesticides into this remote sea. Measured concentration values and physical properties of the chemicals were used to derive these estimates. Gaseous air/water exchange can be modeled using an air/water exchange coefficient (Henry’s law constant) that was adjusted for temperature and salinity parameters in this region. Gas exchange and gas stripping by rain (especially for chlorpyrifos) accounted for most of the air-water transfer, while little deposition occurred through particle-associated deposition. For chlorpyrifos, there was a net gas exchange flux out of the water and to the air (-1.8 to -2.8 g/h); however, for trifluralin, there was a net deposition of this pesticide into the water, i.e., 4.6 to 5.0 g/h. Using these values, it was determined that over the duration of the sampling period there was a net influx of 117g of trifluralin each day and a loss of 57g of chlorpyrifos for the Chukchi Sea.

Technical Abstract: During the 1993 U.S.-Russian BERPAC expedition, residues of agricultural pesticides were detected in seawater, ice, surface microlayer, fog, and air of the Bering and Chukchi Seas. Gas exchange, wet deposition, and dry particle deposition fluxes of trifluralin and chlorpyrifos were estimated using measured concentration values and physical properties of the chemicals adjusted for environmental conditions. Henry’s law constant (HLC) values, adjusted according to temperature and salinity, were used in a fugacity-based model to describe the flux into the Chukchi Sea, which is the northernmost of these two seas. HLC values measured in distilled water, saline water, and Chukchi Sea water and surface microlayer samples were used to generate flux values. Gas exchange and gas scavenging by rain (especially for chlorpyrifos) accounted for most of the air-water exchange with very little predicted from particle-associated deposition. Over the surface area of the Chukchi Sea, volatile fluxes of chlorpyrifos were larger than adsorption, so the net gas exchange flux is from water to air (-1.8 to -2.8 g/h). For trifluralin, adsorption is greater than volatilization, resulting in a net flux into surface waters ranging from (4.6 to 5.0 g/h). Gas exchange results using temperature-adjusted HLC values in saline water (33‰) compared most favorably to results from the natural water HLC’s. Using the air/water constants most typical to prevalent field conditions for this area (e.g., values determined with actual subsurface samples and values adjusted to prevailing temperatures), the resulting input is 117g of trifluralin each day and a loss of 57g of chlorpyrifos. More air and water concentration values and water and air quality parameters are needed from various arctic waters and during different seasons to establish more accurate estimates of pesticide fluxes in this important region.