The Department of Fisheries, Aquaculture and Environment has received results of pesticide analysis of samples collected during the investigations into three incidents of fish mortalities earlier this month. The department received reports of dead fish in Indian River, French River and Mount Herbert August 9.
In Indian River, approximately 2,500 trout were collected over a two-kilometre stretch of stream. There was a heavy rainfall in the area the day before the fish were discovered, with the weather station in Kensington reporting 16.2 mm of rain.
As part of the investigation into the fish mortalities, water, sediment and fish samples were collected and taken to the Atlantic Veterinary College (AVC) for analysis.
Clair Murphy, director of the department's Water Resources Division, said results from the AVC toxicology lab indicate pesticides were detected in water samples taken from two locations in Indian River.
At the uppermost sampling location, Murphy said a number of pesticides were detected in a sample taken from a pool of standing water adjacent to the stream. However, the concentrations were all well below levels which would be toxic to fish.
The second samples were taken from a pool of standing water at the base of a large drainage area approximately 350 metres above the main stream. Murphy said a number of products were detected with two insecticides, azinphos-methyl and endosulfan, being present at high concentrations.
Murphy said the concentration of azinphos-methyl was measured at 73.2 parts per billion (ppb), which is several times greater than reported toxicity values. The concentration of endosulfan at 8.2 ppb was also several times higher than reported toxicity levels.
"Given the concentrations of these insecticides in the pool of standing water, it is quite probable surface water runoff containing pesticides reached the main stream," Murphy said.
Samples collected from the stream itself did not show any significant levels of pesticides, but Murphy said that is to be expected.
"The dead fish were discovered approximately 24 hours after the heavy rainfall so anything that was present in the stream water would have been flushed through the system by the time the investigation could be initiated," he explained.
Murphy said the autopsies of the fish specimens did not provide conclusive information as to the precise cause of death. Although the fish had begun to decay prior to their collection, autopsy observations were consistent with death by anoxia or a toxic event, he said.
"The examination of the stomach contents did suggest that the fish were eating normally prior to death," Murphy noted. "In addition, the lab report indicates that there was no evidence of infectious disease in the fish."
In Mount Herbert, the report of dead fish came to the toll-free Environmental Emergency Response number late in the evening of August 9. A total of 58 fish were collected: 42 trout, from four to 23 cm in length, and 16 sticklebacks.
Murphy said the investigation focused on a carrot field on Fullerton's Creek which showed evidence of runoff and erosion. There was no standing water from which to take samples during the initial investigation. However, investigators took sediment samples from the field, the buffer zone between the field and the stream, and the stream itself.
As well, Murphy said a thunder storm moved through the area when investigators were on site and they were able to collect samples of runoff water.
Murphy said the report from the AVC toxicology lab indicates that three compounds, one fungicide and two herbicides, were detected in both the sediment samples and runoff water samples.
"The fungicide, chlorothalonil, was found at moderate to high concentrations in relation to its toxicity levels, while the herbicides, linuron and prometryn, were detected at low concentrations relative to their toxicities to fish," he added.
No pesticides were detected in the water samples taken from the stream.
Murphy said autopsies of the fish specimens from Fullerton's Creek indicate that the deaths were sudden, most likely the result of anoxia or the introduction of a toxic substance. There was no sign of infectious disease, he said.
In the case of the fish mortalities in French River, a total of 50 trout, from five to 40 cm in length, were collected August 9. Two kilometres east of where the dead fish were discovered, more than 50 mm of rainfall was recorded over a period of approximately 35 minutes the previous evening.
Murphy said the lab reports on French River indicate trace amounts of pesticides were detected in sediment samples and samples of foliage taken from a suspect field. No pesticides were detected in the water samples or sediment samples taken from the stream.
Murphy said autopsies of the fish specimens from French River again indicate the deaths were sudden, most likely the result of anoxia or the introduction of a toxic substance.
The Department of Fisheries, Aquaculture and Environment is continuing the investigation into all three incidents of fish mortalities.