The Department of Fisheries, Aquaculture and Environment has received the last of the laboratory analysis from nine incidents of fish mortalities this summer.
Minister of Environment Chester Gillan said results of fish tissue analyses have been received from the Environment Canada laboratory in Moncton. Minister Gillan said the lab report indicates the insecticide azinphos-methyl was detected in fish collected during the initial investigation into the incident in the Wilmot River July 10. That event saw 4,500 fish collected over a five-kilometre stretch in the upper end of the Wilmot River, from Norboro to the area of Miller's Pond in Kelvin Grove. Results of water sample analyses reported in August also indicated that azinphos-methyl was detected in high concentrations in water samples taken from pools of standing water at the edge of fields adjacent to the stream.
Minister Gillan said there were no pesticides detected in the fish tissue from the other incidents of fish mortalities; however, he cautions that result is not unexpected.
"Pesticide products continue to degrade in fish tissue even after the fish has died, so from the time an incident occurs until investigators collect the samples and the laboratory is able to properly preserve them, any products that may have been in the fish tissue continue to break down," said Minister Gillan. "Beyond that, the analysis itself is difficult. There are so many organic compounds in a fish tissue sample as compared to a water sample, that it is much more difficult for laboratory technicians to extract any one particular product."
Looking at the results of the laboratory analysis of water and sediment samples, as well as the circumstances surrounding the incidents, Minister Gillan said experts in the Department of Fisheries, Aquaculture and Environment have concluded that pesticides were the likely cause of at least seven of the nine incidents of fish mortalities this summer.
"If we look at the circumstances of these incidents, they followed periods of heavy rainfall where there was evidence of runoff," he said. "As well, the water temperature and dissolved oxygen readings were normal in all cases, and there were no signs of infectious disease. And finally, pesticides were detected in water samples taken during the investigations."
Because the number of fish collected was relatively small and limited to a short length of stream, Minister Gillan said there is some question about the cause of the fish mortalities which occurred in the Tryon River and the east branch of the Westmoreland River on August 20.
"While pesticides may have been the cause of the fish mortalities, investigators have not been able to determine that conclusively in these two incidents," the minister added.
Minister Gillan said Environment Canada is continuing to consider charges in four of the incidents of fish mortalities: the incidents reported July 10 and July 19 in the Wilmot River, and the incidents reported July 19 in the Clyde and North Rivers. He said the investigation has been closed on the other cases, either because the cause of the fish mortalities is not clear or there is insufficient evidence to proceed.