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EPA Contract No. GL985600-01

November, 2000

Prepared by:
Joseph V. DePinto
Jagjit Kaur

Great Lakes Program Department of Civil,
Structural, and Environmental Engineering
University at Buffalo  

Joseph V. DePinto
Victor J. Bierman, Jr.
Timothy J. Feist
Limno-Tech, Inc.
Ann Arbor, MI

Prepared for:
Unites States Environmental Protection Agency Great Lakes National Program Office
77 W. Jackson Blvd.
Chicago, IL 60604


(About PDF Files)


The information in this document has been funded by the U.S. Environmental Protection Agency’s (EPA) Great Lakes National Program Office. It has been subject to the Agency’s peer and administrative review, and it has been approved for publication as an EPA document. Mention of trade names or commercial products does not constitute endorsement or recommendation for use by the U.S. Environmental Protection Agency. 


Invasive Species

Photo of several zebra mussels clumped togetherThe Effect of Zebra Mussels on Cycling and Potential Bioavailability of PCBs:  Case Study of Saginaw Bay



Table of Contents 


Section 1


Section 2

2.1.1 Conceptual Approach for Multi-stressor Aquatic Ecosystem Model (SAGZM/PCB)
2.1.2 Saginaw Bay Multi-Class Phytoplankton Model
2.1.3 Zebra Mussel Bioenergetics Model
2.1.4 Coupled Phytoplankton Zebra Mussel Model (SAGZM)
2.1.5  Coupled Phytoplankton Zebra Mussel PCB Mass Balance Model 
          (Multi-Stressor Aquatic Ecosystem Model) - SAGZM/PCB
2.2 Partitioning
2.3 Bioaccumulation Model

Section 3

3.1.1 System Specific Data
3.1.2 Forcing Function, Loadings, Boundary, and Initial Conditions
3.1.3 Process Related Parameters
3.1.4 Chemical Specific Parameters
3.2 Temporal and Spatial Scales

Section 4

4.1 Screening Level Calibration
4.1.1 PCB Concentration in Sediments
4.1.2 PCB Concentration in Water Column
4.1.3 PCB Concentration in Zebra Mussels
4.1.4 Zebra Mussels as Biomonitors
4.2 Sensitivity Analysis
4.2.1 Organic Carbon Normalized Octanol Partition Coefficient Effect of  Log Kow on Water Column PCB Concentration Effect of Log Kow on SPCB Body Burden of Mussels Effect of Log Kow on Surficial Sediment PCB Concentration
4.2.2 Effect of Phosphorus and PCB Loads and Zebra Mussel Densities
4.2.3 Zebra Mussel Filtration on Different Types of Particles
4.2.4 Lipid Content of Zebra Mussels

Section 5

5.1 SAGZM/PCB Application
5.1.1 System Diagnosis and Interpretation
5.1.2 PCB Mass Stored in Zebra Mussels
5.1.3 Zebra Mussel Impact on Bioaccumulation in the Pelagic Lower Food Chain Effect of Mass Specific Concentration in Various Species Summary of Bioaccumulation Results

Section 6   

6.1 Conclusions and Recommendations
6.1.1  Conclusions
6.1.2  Recommendations
6.1.3  Model Limitations

Section 7  

7.1 References

Appendix (PDF 69Kb, 26 pages)

List of Figures (PDF 131Kb, 30 pages)

List of Tables


With the introduction of zebra mussels (Dreissena polymorpha), the Great Lakes have experienced many ecological changes. The aim of this work was to understand and quantify the effects of zebra mussels on cycling and bioaccumulation of polychlorinated biphenyls (PCBs) in Saginaw Bay, Lake Huron. The Bay has extensive areas of hard bottom, along with ideal temperature and food regimes suitable for zebra mussel colonization making it as an ideal study area. To accomplish the goal, a screening level multi-stressor aquatic ecosystem model was developed by integrating various processes involving nutrient-phytoplankton-zebra mussels-PCB dynamics.  

The developed integrated modeling framework of nutrients and fate and transport of PCBs is unique in determining the effect of Dreissena stressor in an aquatic system. The work has demonstrated that the invasion of mussels has led to a re-direction of the energy and nutrients from the pelagic food chain to the benthic food chain through enhanced removal of particles from the water column to the surface sediments. This additional particle flux is leading also to an increased flux of PCBs to the sediments. Assuming a constant load of PCBs to the system, PCB concentration in the sediments was higher than those in the absence of zebra mussels. This suggests that the introduction of mussels has transferred a portion of the contaminant inventory to the sediments.

The influence of mussels’ filtering activities on PCB concentration in lower pelagic food web was examined with bioaccumulation model. The model forecasts a shift in the pattern of bioaccumulation. The exact shift depends on the dominance of various ecosystem interactions and feedbacks in the system, especially the impacts of whether or not zebra mussels filter herbivorous zooplankton and blue-green algae.  

To further study the bioaccumulation of PCBs by zebra mussels, PCB body burden of mussels was calculated. The proximity of mussels to contaminant sources is a significant factor affecting the PCB levels in mussels. The high PCB level in zebra mussels in areas where PCB concentrations were high showed that zebra mussels closely track the environmental conditions. This highlights the use of mussels as biomonitors of contaminants. Also a sensitivity analysis of the selected model parameters indicated that PCB concentration in Dreissena was quite sensitive to Log Kow and lipid content.  

The presence of mussels has not only impacted the particle dynamics but also nutrient cycling in the system. So this integrated framework was applied to investigate the effect of trophic status of the system, which was simulated by using different external phosphorus loadings to the system. In modeled scenarios, enhanced production of algae with higher nutrient loads not only decreased the bioaccumulation of PCBs in the base of the food chain but also increased PCB concentration in the sediments that will eventually affect the bioaccumulation in the benthic food chain. It was found that in response to external phosphorus loadings, the water and sediment PCB concentration were directly proportional, whereas dissolved water and PCB concentration in phyptoplankton were inversely proportional. The developed modeling framework can serve as a foundation for evaluating the contaminant transport by mussels and to help direct further research to answer management questions.  


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