Trend Analysis Reveals a Recent Reduction in Mirex Concentrations in Coho (Oncorhynchus kisutch) and Chinook (O. tshawytscha) Salmon from Lake Ontario

Abstract

Lake Ontario, bordering both Canada and the United States, is the only Great Lake with persistent, significant levels of mirex in its biota. Some models suggested that it would take hundreds of years before mirex disappeared from the ecosystem. From 1977 to 1996 the mirex concentrations in coho and chinook salmon greater than 2 kg in weight exceeded the 0.1 mg/kg Food and Drug Administration (FDA) action level for mirex. To determine temporal trends in salmonine mirex levels, slopes and elevations of the regression lines of mirex concentration versus fish weight were compared for each of the six sampling years (1977, 1982, 1986, 1992, 1996, and 1999) by ANCOVA with weight as a covariate. Within 24 years of mirex being banned, mirex least-squares mean concentrations in salmon fillets had decreased significantly. ANCOVA revealed that the slope of the 1999 regression line was significantly flatter (P < or = 0.014) than the slopes of all other regression lines except 1996 (P = 0.966). A Tukey test revealed that the elevation of the 1999 regression line was also significantly lower than all other years (P < 0.001). Based on our results, mirex concentrations in the fillets of most salmon under the size of 12 kg are now below the 0.1 mg/kg United States FDA action level for human consumption. Models suggest that mirex reductions in biota are most likely due to the settling of mirex-contaminated organisms to the sediments and the loss of mirex from the lake through the St Lawrence River. A third mechanism is suggested as the cause of the higher rate of reduction observed in the mid to late 1990s--the control and removal of contaminated groundwater at the former Hooker Chemical site on the Niagara River, the major source of mirex in the watershed of Lake Ontario.

An Assessment of Mirex Concentrations along the Southern Shorelines of the Great Lakes, USA

“…6). The rapid decline in mirex concentration reported here is in agreement with published results by Makarewicz et al [25] who has reported decrease of more showing assessment of temporal trends at the four sampling sites in Lake Ontario than 50% in salmon (Onchorhynchus kisutch and O. tshawytscha) from Lake Ontario. Additionally, the Herring Gull Monitoring Program reported a significant decline of mirex in herring gull eggs [26] .…”

“…Mirex which has a Henry's Law Constant of 5.41 x 10 -2 (m 3 atm mol -1 ), can undergo volatilization, transferring a fraction of the compound into the atmosphere under ambient conditions [5] . Because mirex has a low Henry's Law Constant, Makarewicz et al [25] determined losses due to volatilization to be relatively small and comparable to those from the photolysis. The rates of mirex photolysis and volatilization may be minimal; however, the cumulative losses from these chemical processes coupled with the large surface area (244,000 km 2 ) of the Great Lakes may contribute to a significant amount of mirex being removed.…”

Long‐term changes in legacy trace organic contaminants and mercury in Lake Ontario salmon in relation to source controls, trophodynamics, and climatic variability

“…Because contaminant concentrations in alewife are lowest in the smallest individuals (e.g., Madenjian et al 1995) stocking would be expected to reduce the rate at which contaminants are transferred from alewife to their predators. Supporting this idea, surveys by Rand et al (1994) found that the average size of Lake Ontario alewife decreased steadily from 1974 to 1990, with direct observations and modeling simulations showing that [mirex] and [PCB] in alewife have decreased substantially over the past 20+ yr (Madenjian et al 1995;Makarewicz et al 2003). Growth-related contaminant dilution in alewife would have contributed to the reduction of contaminants in Lake Ontario coho and chinook salmon for a period immediately following the 1976-1977 winterkill, with the relative influence of enhanced salmonine stocking increasing after the recovery of the alewife population in the early 1980s.…”

“…Dodecachloropentacyclodecane (mirex) was first produced in 1959, with maximum use occurring in the mid-1960s (Oliver et al 1989;Wong et al 1995). It was used in the United States as a pesticide and fire retardant and for the production of some plastics and entered Lake Ontario via the Niagara and Oswego rivers (Makarewicz et al 2003). The use of PCBs and DDT was banned in Canada and the United States in the early 1970s, with mirex use being banned since [1977][1978].…”

Assessing historical versus contemporary mercury and lead contamination in Lake Huron sediments

“…Toxic pollutants and their distribution in the environment are increasingly under scrutiny (Bosworth and Thibodeaux, 2006;Gewurtz et al, 2007;Gewurtz et al, 2008;Hillery et al, 1998;Kolak et al, 1998;Makarewicz et al, 2003;Marvin et al, 2004a;Marvin et al, 2004b;Song et al, 2005a;Sun et al, 2006). There seems to be much debate as to whether enough is being done by various levels of government to help regulate outflows into Great Lakes waters.…”