Environ. Sci. Technol. 2008, 42, 5435–5440
Iodine-131: A Potential Short-Lived, Wastewater-Specific Particle Tracer in an Urbanized Estuarine System J O S E P H P . S M I T H , * ,†,§ S A R A H D . O K T A Y , † JOHN KADA,‡ AND CURTIS R. OLSEN† Environmental, Earth, and Ocean Sciences (EEOS) Department, University of Massachusetts, Boston, 100 Morrissey Boulevard, Boston, Massachusetts 02125-3393 USA and U.S. Department of Energy, Environmental Measurements Laboratory (EML), 201 Varick Street, New York, New York 10014-7447
Received June 25, 2007. Revised manuscript received May 5, 2008. Accepted May 15, 2008.
The short-lived, fission-produced radioisotope, 131I (t1/2 ) 8.04 days), was detected in wastewater, surficial sediment, and suspended particulate matter (SPM) samples collected from New York Harbor (NYH) between 2001 and 2002. Iodine-131 is used as a radiopharmaceutical for medical imaging, diagnostics, and treatments for conditions of the thyroid. It is introduced into the municipal waste stream by medical facilities and patients and is subsequently released into the estuary via wastewater effluent. Measured 131I activities in surface sediments were correlated with those of 7Be (t1/2 ) 53.2 days), a naturally occurring radioisotope that is widely used to quantify particle dynamics, sediment focusing, and short-term sediment deposition and accumulation in aquatic systems. Surficial sediment 131I activities were also compared with measured trace metal (Cu, Pb) and organic carbon (OCsed) concentrations which can be linked to wastewater inputs. These preliminary results from NYH introduce 131I as a potentially valuable source-specific, shortlived biogeochemical tracer (timescales 500 MW), colloids, and particles (17–21, 30, 31, 24, 34–37). Microbial activity involving extracellular enzymes is thought to enhance the incorporation of iodine into organic species (34, 35, 38). Uptake by freshwater and marine algae, particle surface interactions, colloidal flocculation, and coprecipitation can “trap” a fraction of dissolved radioiodine in the particulate phase (17–19, 31, 34–36, 38, 39). Once associated with the particulate phases it can be deposited in the sediments (17–20, 31, 34, 35, 38). Long-lived 129I has been shown to serve as an excellent radiotracer in aquatic systems (17–21), and there is some precedence for using short-lived 131I as a biogeochemical tracer as well. Ravera and Giannoni (39) tracked temporal variations in Chernobyl fallout through VOL. 42, NO. 15, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 1. Map of the New York/New Jersey Harbor Estuary with detail showing 2001 and 2002 surficial sediment sampling locations in inner NYH. The dashed line represents the June 2004 transect for a large-volume SPM sample. The Mohawk River is north of study area and not shown. planktonic uptake of 131I in two lakes in Northern Italy. Iodine131 was shown to behave conservatively when injected as a tracer to evaluate the fate of wastewater-borne nutrients in the hypoxic to anoxic shallow subsurface of the Florida Keys (40). In the past, a variety of wastewater-borne tracers such as Ag, caffeine, and indicator organisms such as fecal coliform bacteria and Clostridium perfringens have been used to examine the input of contaminants to estuaries through urban wastewater and CSOs (7, 8, 41, 42). Coupling 131I with these and other wastewater specific tracers may prove to be a powerful approach in defining the impact of wastewaterborne contaminants in dynamic urbanized aquatic systems. The short half-life of 131I would make it especially useful as a tracer on timescales of weeks to months. This study focuses on 131I as a short-term particle tracer, but since the bulk of iodine in the surface waters of aquatic systems exists in the dissolved phase (33), it also has potential as a water mass tracer and tracer for wastewater-sourced soluble materials. Preliminary data on 131I activity in wastewater, surficial sediment, and suspended particulate matter (SPM) samples collected from New York Harbor (NYH) between 2001 and 2002 are presented to introduce 131I as a potential, sourcespecific (wastewater), short-lived biogeochemical tracer in urbanized aquatic systems.
Study Area and Methods Study Area. The highly urbanized lower Hudson River is a turbid, partially mixed estuary located on the northeastern coast of the United States. Freshwater flow varies between 150 - 1500 m3/sec and is dominated by the Hudson and Mohawk Rivers. Tidal flow ranges between 3000 and 10 000 m3/sec (12). Tidal variations on ebb-flood and spring-neap tidal scales, changes in river flow, and geomorphology all have a large influence on circulation patterns in the lower estuary (43, 44). The lower Hudson River Estuary (LHRE) receives ∼70-100 m3/sec of wastewater from over 30 sewage treatment facilities serving over 10 million people in the NY/ 5436
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NJ area, as well as discharges from ∼400 industrial sources and over 700 CSOs. Wastewater can account for as much as 40% of the freshwater budget during low-flow conditions, and ∼90% of the wastewater discharge occurs in the lower 30 km of the estuary and inner New York Harbor (NYH) (41, 45). The North River Water Pollution Control Plant (NRWPCP) is located on the upper west side of Manhattan Island and discharges into the Hudson River (Figure 1). It is a secondary treatment (activated sludge) facility and is one of the largest of the 14 wastewater treatment plants servicing New York City. It handles the waste from nearly 600 000 residents living on the mid to upper west side of Manhattan and has a nominal capacity of about 7.5 m3/s (645 million liters per day (LPD)) and a peak capacity of 14.9 m3/s (1285 million LPD) (46). The NRWPC service area includes many major medical treatment, research, and training facilities that regularly conduct imaging, diagnostics, and treatments using radiopharmaceuticals including procedures involving 131I. Even at maximum treatment doses for 131I, most patients require less than a day of hospitalization or are given the radioisotope as outpatient treatment (22). For Na131I treatments, Fenner and Martin (29) found that 90% of the administered dose was excreted by the patient within 75 h. Both hospital sewer lines and residential sewer lines potentially contribute medical isotope activity into the local sewer system (22, 25–29, 47). Methods. Samples were collected using a 3 inch diameter, hand-deployed, messenger-activated gravity core from select sites in NYH on October, 2001 and July, 2002 (Figure 1). Sediment cores were sectioned at 1 cm intervals with care taken to preserve and sample the 0-1 cm surface layer. The term “surficial sediment” is used to refer the sediment core sections representing ∼0-1 cm below the sediment/water interface. Surficial sediment sections were sealed in plastic lined Al cans for analysis. In August 2004, approximately 4 L of wastewater was collected from the NRWPCP effluent stream. One bulk (unfiltered) 250 mL subsample was collected and sealed in
TABLE 1. Surficial Sediment 131I (AI-131) and 7Be (ABe-7) Activities and Surficial Sediment Organic Carbon (OCsed), Cu, and Pb Concentrations Collected from Sites in NYH in 2001 and 2002. #
station
depth cm
date
1 2 3 4 5 6
Pier 32 Pier 40 Pier 32 Holland Tunnel Duct Ellis Island South Cove
0-1 0-1 0-1 0-1 0-1 0-1
10/12/01 10/12/01 7/23/02 7/24/02 7/24/02 7/24/02
AI-131 mBq/g 6.0 ( 1.1 5.7 ( 1.2 3.3 ( 0.8 4.4 ( 1.6
