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The chelating agent NTA (nitrilotriacetic acid) eliminated acute lethality of zinc and copper during 4 days of experimental dosing in a small creek. Caged salmon died in 4 h in the “polluted” zone, where added metals were 4 to 7 times the lethal threshold, and dead wild eels were also found. Downstream, with equi-molar NTA added, caged fish survived without marked signs of stress, and normal behavior of a wild eel was noted.
Benthic invertebrates were much more tolerant of metals than anticipated, and subtle changes in the community could not be documented by the deliberately minimal design of the experiment (pairs of Surber samples before and after treatment). The only demonstrated change in numbers was the virtual disappearance of blackfly larvae in the polluted zone, with no change in the control and anti-polluted zones. Cluster analysis of benthic samples also suggested effectiveness of NTA; the two polluted samples were distinct from a grouping which contained all other samples (“clean,” “before,” and “anti-polluted”). No effects were demonstrated for diversity index, genera, or total numbers.
As a side-issue, the experiment demonstrated that immature stoneflies and caddisflies, but not blackflies, can survive for 4 days in concentrations of zinc and copper that are at least 4 times the lethal level for salmonid fish. The relative tolerances of other taxa were uncertain because of small sample size, high variance, and few replicates.
zinc, copper, NTA, toxicity, detoxification, chelation, fish, invertebrates
Professor, University of Guelph, Guelph, Ontario