CHIRONOMID LARVAL DEFORMITY FREQUENCIES, MORTALITY, AND DIVERSITY IN HEAVY-METAL CONTAMINATED SEDIMENTS OF A CANADIAN RIVERINE WETLAND

Sediment sampling at point source locations in the Niagara River water shed revealed an area in a Class One Provincially Significant Riverine Wetland that was located near the discharge of a stainless steel comp any. The site had unusually high concentrations of heavy metals and oi ly wastes in its sediments, The impacts of these oil and heavy metal c ontaminated sediments on an invertebrate population of midge (chironom id) larvae was assessed using both lab and field techniques. The midge larvae were the dominant invertebrates in this section of the river. Twenty-six percent of the chironomids from sites located 10 to 800 m d ownstream of the stainless steel company's point source were deformed. A lab study was carried out to determine what percentage of the obser ved deformities could be attributed to the heavy metal content of the sediments and what percentage was due to the organic fraction. Sedimen ts collected near the point source were tested and found to be acutely toxic. Sediments collected 60 m downstream of the point source were t eratogenic. The frequency of mentum deformities for chironomids reared in clean sediments (control aquaria) was only 2.2%, A similar deformi ty frequency (2.2%) was observed at the clean sediment reference site in the Welland River watershed. Of the 97 chironomids removed from the de-oiled heavy metal contaminated sediments in the test aquarium, 10. 3% displayed deformities. This is believed to be one of the few times that chironomid deformities were induced in a controlled lab study in which heavy metal concentrations similar to those found in the field w ere used. Copyright (C) 1996 Elsevier Science Ltd