Superfund Research Program
Fate and Transport of Metals in the Aberjona River Watershed
A suburb of Boston, Massachusetts, the city of Woburn was a center of leather production for over three centuries. From colonial times until the mid-1800s, Woburn's leather tanneries supported the local shoe and boot industry. By 1865, Woburn had risen to the top of the country's leather tanning industry, a trend that continued into the 1880s when the city had 26 large tanneries producing millions of dollars worth of leather. Woburn gradually lost its position as a leader in the leather industry; however, leather tanning continued there on a smaller scale into the 1980's.
While leather production supported Woburn's manufacturing base during most of the community's existence, the city's industrial activities began to diversify at the turn of the century. Throughout the early- to mid-twentieth century, numerous factories were built in Woburn to manufacture a variety of products including glue, sulfuric acid, and arsenic-based insecticides. Woburn's leather production and other diverse manufacturing activities made the city an established industrial leader in eastern Massachusetts for over 150 years.
Today, this city of 36,000 residents contains two Superfund sites on just under 13 square miles of land.
Of all the past industrial activities in Woburn, leather tanning and chemical manufacturing have contributed the most to the legacy of environmental contamination left behind in the city and its major waterway, the Aberjona River. Tanning wastes containing chromium, arsenic, and other hazardous chemicals have been found at several sites in the city. Sediment records show that the river has been contaminated by arsenic and chromium since the mid-1800s, which is about the time chrome tanning was developed. At the Industri-Plex Superfund site in North Woburn, tons of arsenic, chromium, and other wastes were released into the environment during the manufacture of leather, glue, and various industrial chemicals.
Because the Aberjona River watershed is highly populated and highly contaminated, it is important to identify the processes and pathways that may lead to human exposure to the watershed's contaminants.
Researchers at the Massachusetts Institute of Technology (MIT) are studying the fate and transport of arsenic and chromium throughout the Aberjona River watershed to determine how much health risk is associated with the area's metal contamination.
An important focus of this research is to understand the identity and quantity of metals delivered to wells G&H, two former municipal wells that delivered water to the Woburn community between 1964 and 1979. The contaminated wetlands surrounding these two wells have been designated as a Superfund site and linked to increased human health problems in Woburn.
An important discovery by this group of researchers is that much of the arsenic in the Aberjona watershed originates as arsenite, a reduced species that is both more toxic and mobile than arsenate, another form of arsenic commonly found in the environment. Arsenite is more mobile than arsenate in freshwater systems because it is more soluble in water and it does not bind to sediments as strongly as arsenate. The researchers also determined that much of the arsenite is discharged from a small man-made lake (the Hall's Brook Storage Area) that is adjacent to the Industri-Plex Superfund site.
One of the first steps in quantifying the amount of metals transported to wells G&H between 1964 and 1979 has been to determine the water flow paths between the river and the wells. To accomplish this, the MIT researchers developed a new piezocone technique, which they have used to map and model the subsurface stratigraphy that connects the contaminated river to the aquifer that supplied water to wells G&H. A piezocone is a device that allows scientists to develop a detailed picture of the variation of the subsurface, including variations in the permeability of different soil layers. Using the newly developed piezocone technique, the researchers identified strata of sand and peat in the wetland area between the river and the wells.
In complementary research, the MIT scientists have mapped the distribution of arsenic and chromium in the wetland and related this to the wetland's structure and hydrology. They recently discovered that the peatland separating the Aberjona River from the wells contains elevated concentrations of arsenic and chromium. The peat had apparently trapped arsenic and chromium as river water infiltrated it. This sorption of the metals to the peat may be a major sink for arsenic and chromium in the wetland between the river and the wells. However, the scientists are quick to point out that there is evidence for the existence of other flow paths (e.g., through the sand layers), which may or may not be sorptive for the metals.
The MIT scientists are also conducting studies in the Upper Mystic Lake, which is the terminus of the Aberjona River and a popular recreational spot for the Boston area. The researchers are investigating how arsenic moves between the lake's sediments and the surface water, where humans and wildlife could potentially be exposed to the metal. What they discovered is that arsenic is mobilized from the lake's sediments on a regular, seasonal basis.
Because lake chemistry affects the mobility of metals in freshwater systems, the scientists are also studying how iron, which plays a major role in the behavior of many environmental contaminants and is ubiquitous in the environment, affects the transport of arsenic in the Upper Mystic Lake. These studies clearly demonstrate that remobilized arsenic in the lake is associated with remobilized iron. Taking this research a step further, the scientists have preliminary evidence that nitrate, a strong oxidant, may be controlling the onset and magnitude of arsenic and iron remobilization from the sediments, as well as the speciation of the two metals in the water column. Considering that the majority of nitrate inputs into urban lakes results from human activities, these findings could have important implications for the management of lakes with arsenic contaminated sediments.
These studies are significant for characterizing the fate and movement of the arsenic and chromium in the Aberjona watershed, information that will allow for a better determination of human exposure processes. Because the 25-square mile watershed includes parts of seven local communities in the Boston area and is used recreationally for fishing, swimming, and boating, it is important to understand where the watershed's metal pollutants are now, how they are transformed, and where they will be transported in the future. This knowledge is necessary to prevent human exposures to these toxic compounds.
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To learn more about this research, please refer to the following sources:
- Zeeb PJ, Hemond HF, Germaine J. 1997. Design and performance of a portable piezocone driver for high resolution profiling of wetland sediments. Geotechnical Testing Journal 20(2):191-198.
- Spliethoff HM, Mason RP, Hemond HF. 1995. Interannual variability in the speciation and mobility of arsenic in a dimictic lake. Environ Sci Technol 29(8):2157-2161. doi:10.1021/es00008a041 PMID:22191370
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