Observations on the 10-day Chironomus tentans survival and growth bioassayin evaluating Great Lakes sediments

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 fro m each harbor were compared to responses of larvae in reference sediments c ollected from or near each harbor. An inverse relationship between the numb er of survivors and mean organism dry weight or growth indicated that food was limiting in the bioassay for some samples. The confounding nature of th is interaction was minimized by evaluating effects on the basis of total bi omass per replicate. A site from Toledo Harbor was the most toxic. Reduced larval growth at this site indicated the likelihood for a negative populati onal impact. The importance of reference sediment selection was noted, as t he assessment of sediment quality varied considerably for Toledo Harbor dep ending upon the particular reference sediment that was used for statistical comparisons.