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2001 Progress Report: Characterization of the Chemical Lability and Bioavailable Fraction of Heavy Metals in Natural Waters Using In-Situ Diffusion Gradient in Thin-Film (DGT) Probes.

EPA Grant Number: R828162
Title: Characterization of the Chemical Lability and Bioavailable Fraction of Heavy Metals in Natural Waters Using In-Situ Diffusion Gradient in Thin-Film (DGT) Probes.
Investigators: Moffett, James W.
Institution: Woods Hole Oceanographic Institution
EPA Project Officer: Krishnan, Bala S.
Project Period: June 1, 2000 through May 31, 2002
Project Period Covered by this Report: June 1, 2000 through May 31, 2001
Project Amount: $224,949
RFA: Exploratory Research - Environmental Chemistry (1999)
Research Category: Engineering and Environmental Chemistry

Description:

Objective:

The overall objective of this project is to evaluate a new methodology for the determination of chemically reactive (bioavailable) concentrations of heavy metals in aquatic environments utilizing an in situ semipermeable membrane device. We propose that DGT probes may fill the void that currently exists in measurement capabilities by enabling inexpensive, rapid measurements of trace metals to be made that will vastly expand the existing database for metal bioavailability, particularly during nonsteady state (episodic) events such as floods and dredging. The objectives of the project are to:

• Evaluate whether DGT probes can provide a direct measurement of the biologically available fraction of trace metals in aqueous environments.

• Investigate the use of probes to provide information about sources, sinks, and transport of heavy metals in complex systems (e.g., Boston Harbor) by making time integrated measurements.

• Produce a comprehensive data set of trace metal speciation measurements in a variety of marine and fresh waters.

Progress Summary:

1. Preliminary Gel Deployments. Initial deployments of DGT devices with two different pore sizes of diffusion gel (>20 nm and <1 nm) were undertaken in the local waters of Eel Pond (Woods Hole) and Vineyard Sound. Deployments were made in both mesocosms and in situ. Comparisons of DGT calculated values with values determined by ICP-MS (inductively coupled plasma mass spectrometry) and by a widely used technique CLE-ACSV (competitive ligand exchange adsorptive cathodic stripping voltammetry) were made to determine that the gels were responding to theory. Initial results show that the method of DGT is working according to the theory.

2. Diffusion Coefficients. To determine the diffusion coefficients, a diffusion cell was manufactured to enable the diffusion coefficients of the different gels and molecular weight cutoff (MWCO) membranes to be measured. The diffusion cell was manufactured at our laboratory. This enabled the diffusion coefficients for the agarose (AGE), restricted gel (RGL), and University of Lancaster (APA) gels to be determined for Cu and Cd, with subsequent coefficients then calculated for Mn, Co, and Zn. Also, initial diffusion coefficients of the MWCO membranes were estimated.

3. Boston Harbor Sampling. Four fieldwork sampling trips to Boston Harbor were undertaken during 2001. Around 10 different sites within the inner harbor have been sampled. The sampling sites were chosen due to their different environmental conditions such as salinity and proximity to pollutant input sites. Two sites within the Charles and Mystic rivers also were sampled. The sampling was undertaken during March, May, July, and October.

DGT probes with AGE gel diffusion layers (pore size > 20 nm) and probes with the RGL diffusion layers (pore size < 1 nm) were deployed. These were held within a plexiglass holder made in our workshop. Three probes of each type were placed in the holders. The holder is attached to a polypropylene line with tie-wraps and suspended 1 m below the surface. A small float was used for buoyancy and plastic-coated lead diving weights were used to anchor the mooring. The DGT probes were deployed for a period of up to 24 hours. After retrieval, the probes are dismantled in the clean laboratory, and the resin gel is eluted with 1 M nitric acid. The acid eluent is then analyzed (after dilution) using our ICP-MS.

Data from a deployment in July showed a decrease in Cu concentration from Constitution Marina, which is near the Charles River Dam, out into the harbor. Pier 4 is only half a mile away from the Marina with the Coastguard Pier situated between the two. The data show that downstream from the Marina there is a decrease in Cu concentration; however, the ratio between the AGE and RGL reaches nearly 100 percent. This could be due to a large input of organic ligands, such as humic acids, from the freshwaters of the Charles River. However, data from the seaward end of Boston Harbor (Logan Airport and Calf Island) show lower values for Cu and also the largest difference between AGE and RGL values, indicating a large presence of natural ligands.

Future Activities:

1. Further deployments of moored probes with the Massachusetts Water Resource Authority (MWRA) are planned within Boston Harbor and the Mystic and Charles Rivers. Deployments also are planned to coincide with storm events and combined sewage overflow (CSO) activations.

2. Further development work will be undertaken with the DGT probes using the restricted gels and dialysis membranes. Initial problems using the dialysis membranes seemed to stem from the possibility that the pre-bought plastic probes were leaking. A comparison of these probes with some in-house manufactured probes should solve this problem.

3. Deployments within high traffic areas of Boston Harbor also are planned in conjunction with the Coastguard.

4. A proposal was recently funded within our institution by the Green Technology Awards to build a more sophisticated carousel system with an array of DGT probes that can be sequentially exposed to the water. Although independent of the EPA project, we plan to collect time-series data in Boston Harbor over a month-long period with integrated data points of up to 24 hours. This data could be of great value to our EPA project.

5. Trace metal data will be combined with data supplied by the MWRA such as information on nutrients, chlorophyll, Enterococcus (bacteria), and water clarity. This will produce a data set to enable the prediction of trace metal toxicity occurring in Boston Harbor.

Journal Articles:

No journal articles submitted with this report: View all 2 publications for this project

Supplemental Keywords:

Boston Harbor, trace metal speciation, DGT. , Ecosystem Protection/Environmental Exposure & Risk, Toxics, Sustainable Industry/Business, Scientific Discipline, Waste, RFA, Technology for Sustainable Environment, Sustainable Environment, Analytical Chemistry, Bioavailability, Chemistry, cleaner production/pollution prevention, Environmental Chemistry, New/Innovative technologies, National Recommended Water Quality, Monitoring/Modeling, Environmental Monitoring, copper, heavy metals, water quality, membrane technology, lead, cadmium, measurement, metals, sampling, Zinc, field monitoring

Progress and Final Reports:
Original Abstract
Final Report

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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