CICEET Progress Report for the period 9/01/01 through 3/01/02

Project Title: Atmospheric Deposition of Currently Used Pesticides to the St. Jones River Reserve and Upper Delmarva Peninsula
Principal Investigator(s): Alba Torrents and Laura McConnell

Accomplishments
Scheduled Tasks:
For the reporting period, we had proposed two main tasks:

1. Laboratory development and validation of automated rain sample collection method for currently used pesticides.
2. Collection of weekly air samples and daily precipitation samples from the three collection sites. January and February months of 2002 were omitted due to equipment limitations in cold weather.

Progress on Tasks
Task 1 has been completed and we currently have a validated automatic rain sample protocol. Technical support staff at two of the sites has been trained and staff at the third site will be trained late march (see preliminary results).

Samples have been collected at two sites as scheduled, Choptank, MD and Lewes, DE. Sample collection at, St. Jones River Reserve, DE will be initiated in March. Collected samples are currently being extracted and analyzed.

Also, to achieve our main goal of being able to determine deposition loads, a good understanding or air-water-particle partitioning is needed. In this, we have initiated experiments to determine Henry constants of targeted pesticides as a function of temperature and other water parameters of interest.

Also, the student that will perform her PhD research as part of this project has been trained and is currently extracting and analyzing samples from last season.

Difficulties Encountered
Initiation of sample Collection at the St. Jones River Reserve, DE had to be postponed due to the lack of electricity at the site. Work is underway and the equipment has been ordered to initiate sampling in March.

Anticipated Success in Meeting Project Objectives in Scheduled Project Period
Work is being conducted as planed. We are a little behind on the St. Jones samples.

Preliminary Results
Methodology
Figure 1 illustrates the deployment of the rain and air samplers in the field. The automatic sample collection method has been validated in the laboratory before deployment. Experiments were conducted using pesticide spiked distilled water passed through the funnel and sampling train. The extraction method efficiency is speed dependency, with the best speed ranging from 30-50 mL/min. (see Figure 2). Sample volume did not have a significant effect on overall recoveries (see Figure 3). Spike recovery experiments for selected pesticides resulted in average recoveries of 68- 104 % with a standard deviation 3-21.5 % up to a sample volume of 10 L or the equivalent of 5 cm of precipitation. Minimum detection limits range from 0.22 ng/L for β-endosulfan to 2.7 ng/L for diazinon.

Sampling and data Analysis
In the samples collected during 1999-200 and currently being analyzed, preliminary wet fluxes have been determined, and so far they indicate that can not be directly correlated with usage in the watershed (see Figure 4). More data is needed to asses the reasons for the observed deviations.

As part of the goal to increase our understanding on air-water-particle partitioning, we have started to assess the validity of current partition models. In air filters, atrazine and metolachlor are being observed continuously. The highest particle-phase concentrations of atrazine and metolachlor were observed in May with the maximum values of 820 and 1070 pg/m³, respectively. Vapor-particle partitioning can be estimated from models based on physicochemical properties. The most widely used model is the adsorption model developed by Junge (Junge, 1977) and Pankow (Pankow, 1987) and is shown in Eq.(1).

Φ=cΘ/(P_L+cΘ) (1)

Where f is the fraction of airborne chemical associated with atmospheric particles. P_L is the saturation liquid-phase vapor pressure of the adsorbed chemical. The parameter c is related to the heat of desorption from the particle surface, the heat of vaporization of the liquid-phase sorbate and adsorption sites on the particle surface. The value of c is usually taken as 17.2 Pa.cm (Pankow, 1987). Θ is the particle surface area concentration and a value of 3.5 x 10^-6 cm²/cm³ is used for sites characteristic of background air with some local source influence (Bidleman, 1988). Using published physical chemical properties under measured temperature conditions, we can compare calculated Φ values (Φ_pred) with measured Φ values (Φ_obs). Paired air and particle phase concentrations of atrazine and metolachlor above quantification limits were used to calculate observed particle-phase fractions (Φ_obs). Particle-phase concentrations may be somewhat inflated since only one filter was used (Bidleman, 1988). There was no second filter to correct for adsorption of gaseous organic compounds to the filter itself. A comparison of Φ_pred and Φ_obs over time is graphically illustrated in Figure 5. Φ_obs values were about 1.4-15 and 0.67-53 times as high as Φ_pred values for atrazine and metolachlor, respectively, indicating that the model underestimates the sorption of these polar chemicals to aerosols. Alternatively, this may indicate that atrazine and metolachlor are not at equilibrium in the atmosphere. While these observations are based on limited data, this is a question that needs further study.

Tasks and activities for next reporting period

Tasks for the next reporting period
During the next six months most of our work will be on the continuing collection of samples at Lewis and initiating sample collection at St. Jones. We will continue to extract and analyze samples. Effort will continue in the lab to determine pertinent partition coefficients as time allows it.

Also, as part of a WRRC sponsored project, we had 18 months of similar data set that will be analyzed and will help in prioritize our effort on the determinations of site specific partition coefficients.

Work plan to accomplish tasks
One PhD student is about to finish her course requirements and starting on May will be working full time on this project (currently she spends two days a week in this project).

Late March, the sampling equipment will be set at St. Jones and one of their staff will be trained to start sampling at that site.

Sampling will be conducted as scheduled (air) and as weather dictates (rain). Sample extraction, analysis and data analysis will be conducted as scheduled.

Concerns or difficulties
At this point, we have no concerns or difficulties.

Expenditures
Up to date, only funds transferred to collaborators and equipment purchase had been used. Student working on this project has been supported by a fellowship that ends in May. She will be supported from this grant after May. Expenditures are accordingly low but will soon catch up to the scheduled plan.

Funds allocated to be transferred to St. Jones to help on the technical support will be re-routed to help them in the purchase of a piece of equipment, to facilitate transfer and reduce administration costs.

References:
Bidleman, T.F.1988. Atmospheric processes. Environ. Sci. Technol., 22(4): 361-367.

Junge, C.E., 1977. Basic considerations about trace constituents in the atmosphere as related to the fate of global pollutants. Fate of Pollutants in the Air and Water Environment. I.H. Siuffet (ed). Part I. Advances in Environmental Science and Technology. J. Wiley, New York: 7-25.

Pankow, J.F. 1987. Review and comparative analysis of the theories on partitioning between the gas and aerosol particulate phases in the atmosphere. Atmos. Environ. 21: 2275-2283.