J. Great Lakes Res. 25(1):171–178 Internat. Assoc. Great Lakes Res., 1999 Observations on the 10-Day Chironomus tentans Survival and Growth Bioassay in Evaluating Great Lakes Sediments Daniel J. Call * , Karsten Liber a , Frank W. Whiteman b , Timothy D. Dawson c , and Larry T. Brooke Lake Superior Research Institute University of Wisconsin-Superior Superior, Wisconsin 54880 ABSTRACT. A 10-day bioassay with larval chironomids (Chironomus tentans) was used to evaluate sediment samples from harbors at Michigan City, IN, St. Joseph, MI, Grand Haven, MI, and Toledo, OH for toxicity, based upon the endpoints of survival, dry weight, and growth. Larval responses in sediment samples from each harbor were compared to responses of larvae in reference sediments collected from or near each harbor. An inverse relationship between the number of survivors and mean organism dry weight or growth indicated that food was limiting in the bioassay for some samples. The confounding nature of this interaction was minimized by evaluating effects on the basis of total biomass per replicate. A site from Toledo Harbor was the most toxic. Reduced larval growth at this site indicated the likelihood for a negative populational impact. The importance of reference sediment selection was noted, as the assessment of sediment quality varied considerably for Toledo Harbor depending upon the particular ref- erence sediment that was used for statistical comparisons. INDEX WORDS: Chironomus tentans, harbor sediments, bioassay, toxicity. 171 INTRODUCTION Contaminated sediments are responsible in most cases for the classification of areas within the Great Lakes as Areas of Concern, or AOCs (Zarull and Mudroch 1993, U.S. EPA 1994a). AOCs are de- graded to the extent that beneficial uses of the water are impaired. Evaluations of sediment quality should include biological toxicity tests, chemical analyses, and benthic macroinvertebrate community structural analyses (Chapman 1986, 1989; Reynold- son and Zarull 1993). While methods for perform- ing chemical and community structural analyses have existed for decades, the development of stan- dardized biological testing methods for sediments is more recent. Chironomus tentans is one species for which methods have been developed, and this species has been used in evaluating sediment toxic- ity in recent years (e.g., Giesy and Hoke 1989; Giesy et al. 1990; DiToro et al. 1991; Ankley et al. 1993, 1994a; Ingersoll et al. 1995). The C. tentans toxicity bioassay was evaluated in this study with sediment collected from four Great Lakes harbors. These harbors are periodically dredged, and a knowledge of possible effects of the sediment upon benthic fauna may be used in deci- sions regarding the extent to which dredging may be allowed, as well as in determination of disposal sites for dredged materials. METHODS Sediment samples were collected from four Great Lakes harbors by the U.S. Army Corps of Engi- neers (ACOE) in March and April, 1993. Three samples were collected from Michigan City, Indi- ana, St. Joseph, Michigan, and Grand Haven, Michigan harbors. Eight samples were collected from the harbor at Toledo, Ohio. Each of the first three harbors also had a reference sediment col- lected from the same general area, while reference sediments were collected from both a shallow water and a deep water site near Toledo Harbor. Sampling locations were selected to provide sediments that ranged in contamination levels from low to high based on historical information (Bridges et al . * Corresponding author. E-mail: dcall@staff.uwsuper.edu a Present address: Toxicology Centre, University of Saskatchewan, 44 Campus Drive, Saskatoon, Saskatchewan, Canada S7N 5B3. b Present address: Mid-Continent Ecology Division, U.S. Environmental Protection Agency, 6201 Congdon Blvd., Duluth, MN 55804. c Present address: Integrated Laboratory Services, 6201 Congdon Blvd., Duluth, MN 55804.