Laboratory studies and data from field populations show that while zebra mussels do bioaccumulate contaminants, tissue levels from field populations are only somewhat elevated in relation to background concentrations. Testing of the zebra mussel using the Toxicity Characteristic Leaching Procedure (TCLP) and the Leachate Toxicity Test (LTT) has indicated that zebra mussel waste should not be considered hazardous based on U.S. and Canadian regulations. Currently, large volumes of zebra mussels are being disposed of at approved landfills, generally without chemical analyses.
De Kock and Bowmer (1993) studied cadmium (Cd) as an example contaminant and indicated the time for D. polymorpha to reach a steady state when exposed to Cd (40 to 60 days) in the field. The harmful effects of Cd on zebra mussels are discussed, and experiments are described where Cd has been transferred from contaminated zebra mussels to ducks. Organochlorine contaminants are also discussed in relation to the bioaccumulation capabilities of these organisms. The most important points are that zebra mussels are accepted as being good bioaccumulators of aquatic contaminants and are important food chain organisms. Stab et al. (1996) discussed the determination of organotin compounds in the food web of a shallow freshwater lake in The Netherlands. Van Hoof et al. (1997) studied the effects of biomagnification of PCB congeners within the food web of Saginaw Bay, Lake Huron.
Doherty et al. (1993) present data from leachate tests of zebra mussels and compare results with disposal criteria concentrations for the United States and Canada. For a summary of these data, see Table 4., “Toxicity Testing by United States (TCLP) and Canadian (LTT) Standards.” Doherty et al. (1993) tested zebra mussels from two power plants on Lake Erie for contaminants and for leachable contaminants using the TCLP for the United States and LTT for Canada. The zebra mussels from either of these two facilities would not be classified as hazardous waste according to United States (USEPA 1990) and Canadian criteria (Ontario Regulation 309).
The bioaccumulation potential of the zebra mussel and its distribution as a function of a PCB gradient is addressed by Pilote et al. (1995) and the bioaccumulation of contaminants is covered in USACE Technical Note ZMR-1-16 (Tatem 1994). This topic is also addressed in a Buffalo, New York study by Roper et al. (1996). Please see Technical Note ZMR-1-27 for more information.
Other field studies indicate that the zebra mussel is able to create dense populations where contaminants are available and filter the water to accumulate and retain contaminants, especially hydrophobic or lipophilic compounds. The following five tables present some of the contaminants identified in zebra mussel populations and the concentrations that were observed.
Table 1. Inorganic and organic contaminants in suspended sediment and zebra mussel pseudofeces from the Netherlands. Background tissue concentrations are compared to zebra mussels exposed for 271 days at a contaminated location.
Table 2. Organic and metal contaminants in zebra mussel tissues from western Lake Erie (N=4).
Table 3. Concentrations of elements, DDE, and PCBs in zebra mussel tissues and shells from New York state waters.
Table 4. Regulatory action levels for leachable contaminants in the United States (USEPA 1990) and Canada (Ontario Regulation 309, Schedule 4)
Table 5. Summary of organic and metal contaminant concentrations and percent lipids for shell, tissue, and whole zebra mussel, size class 16-19 mm, from western Lake Erie.