Fate of PCB congeners in an industrial harbor of Lake Michigan

Abstract

We have quantified the release of polychlorinated biphenyls (PCBs) from Indiana Harbor and Ship Canal (IHSC) to Lake Michigan and the atmosphere. Navigational dredging is planned for this system, and there is concern that dredging will result in releases of PCBs. We have analyzed greater than 158 PCBs in surficial sediment, water, suspended particles, and air. We predicted the release of PCBs from sediments to water and from water to air. To quantify the level of confidence in our calculations, we used a Monte Carlo simulation for each congener flux. We determined that 4 +/- 0.05 kg of summation operatorPCBs were released from the sediment to the water and 7 +/- 0.1 kg of summation operatorPCBs were volatilized from the water to the air annually. We measured input from the upstream regions of the canal system of 45.0 kg yr(-1) and export to Lake Michigan of 43.9 kg yr(-1). The summation operatorPCBs mass balance accounts for nearly all the PCB inputs and losses to the navigational regions. The congener profiles in sediment, water, and air support our determination that the contaminated sediment is a major source of PCBs into the water and air above it. We have shown that the system is currently a significant source of PCBs to the air and to Lake Michigan, even under quiescent conditions.

Figure 1

Indiana Harbor and Ship Canal, East Chicago, Indiana. The blue circles (○) and red diamonds (◇) represent the sites where sediment and water samples, respectively, were collected.

Figure 2

Seasonal variation of meteorological and hydraulic conditions, and transfer coefficients for PCB52. Top plot depicts air-water coefficients and bottom one, sediment-water coefficients. Note the difference in scale on the right for each parameter. The green lines on the top plot describe the air and water temperatures (dash line), respectively. Transfer coefficients are strongly dependent on the congener. See text for abbreviations.

Figure 3

The top plot is the net air/water flux and the bottom plot is the net sediment/water flux for PCB congeners in IHSC. The bars represent the arithmetic average and the error bars represent the 97.5^th percentile. Note the different scales for the vertical axes.

Figure 4

Histograms of simulated PCB fluxes during the sampling period for three congeners. Top left plot depicts PCB52 and top right depicts PCBs147/149 (coeluting congeners) for the air/water interface. Bottom left plot depicts PCB52 and bottom right depicts PCB205 for the sediment/water (bottom plots) interface.

Figure 5

The steady state mass budget for total PCBs in IHSC for 2006 in kg per year. The ranges shown for sediment, water and air fluxes are the 2.5^th and 97.5^th percentiles. Asterisk (*) means negative values.