The Department of Fisheries, Aquaculture and Environment released results Friday of pesticide analysis of samples collected from the Profit's Pond semi-natural salmon and trout rearing facility in West Prince.
Samples were collected as part of an investigation into fish mortalities that occurred earlier this month in two holding tanks which draw water from the pond.
Clair Murphy, Director of the Department's Water Resources Division, released the results of the pesticide analysis. He said a sample collected from the fish tank where approximately 1,500 four to six-inch brook trout died showed low levels of metribuzin, a pre and post-emergent herbicide used for weed control; and chlorothalonil, a commonly-used fungicide. A second sample collected from the centre of Profit's Pond, where some 39,000 salmon par are kept, showed a low concentration of metribuzin.
Murphy said the concentration of both chemicals was low compared to the acute toxicity levels for trout.
"The Canadian Water Quality Guidelines for the Protection of Freshwater Aquatic Life indicate that the acute toxicity level for metribuzin is 42,000 to 76,000 parts per billion (ppb). The highest concentration of this compound was found in the fish tank at 0.6 ppb. A concentration of 0.3 ppb was found in the pond."
With regard to chlorothalonil, Murphy said the acute toxicity threshold for trout is 250 parts per billion. The concentration found in the fish tank was 3.3 ppb, and there was no detection of the fungicide in the pond water.
"Based on the Aquatic Life Guidelines, the concentrations of pesticides found in the samples analyzed would not represent a health risk to fish," Murphy said.
Workers at Profit's Pond discovered the fish mortalities the morning of July 18. Somewhere in the range of 5,000 to 6,000 fish were lost. Murphy noted there was a heavy rain July 17 which resulted in the water having high suspended sediment content.
Results of autopsies conducted on the dead fish at the Atlantic Veterinary College earlier this month indicated that the primary cause of death was acute gill disease.
Where the functional capacity of gill tissue to transfer oxygen from the water into the blood stream is impaired by gill disease or some other factor, the fish eventually suffocate. Murphy explained any environmental factors such as high levels of suspended sediment or reduced dissolved oxygen levels in the water would further reduce the gill efficiency.
"Both fish tanks, as well as the pond water, showed high levels of suspended sediment during the event. There was also some evidence to suggest the dissolved oxygen levels may have been somewhat reduced," he said.
Murphy indicated the investigation of cropping activities in the Long Creek watershed upstream of Profit's Pond has not revealed clear evidence of serious runoff from any particular location.
"Investigators have talked with several farmers in the watershed and have received excellent cooperation," he added.
The investigation is continuing.