Changes in Mercury Levels in Great Lakes Fish Between 1970s and 2007

Abstract

A number of initiatives have curtailed anthropogenic mercury emissions in North America over the last two decades; however, various factors, including long-range transport of global emissions, may complicate the response of fish mercury levels to remedial actions. Since the Great Lakes of North America are together the largest surface freshwater body in the world and are under the influence of many complicating factors, trends of mercury in fish from the Great Lakes can reflect the overall impact of mercury management actions at local, regional, and perhaps global scales. Here we present a comprehensive view of mercury trends in Canadian Great Lakes fish using two large (total 5807 samples), different (fillet and whole fish), and long-term (1970s-2007) monitoring data sets. The spatial differences in lake trout and walleye mercury levels during this period have generally been within a factor of 2-3 with Lakes Erie and Superior having the lowest and highest concentrations, respectively. These spatial differences have diminished in the recent years (2000-2007). The concentrations have generally declined over the three decades (mid-1970s to 2007); however, in recent years, the concentration trends are flat in Lake Ontario walleye and appear to be increasing in Lake Erie walleye. There was a mismatch in the Lake Ontario lake trout and walleye temporal trends, which shows the importance of considering more than one fish species for proper spatial/temporal trend assessments.

The presence of EU priority substances mercury, hexachlorobenzene, hexachlorobutadiene and PBDEs in wild fish from four English rivers

“…Ideally, a range of species from different trophic levels and/or a range of other samples such as water and sediment would be monitored to allow for temporal and spatial trends to be observed even when they differ between species (Bhavsar et al, 2010) or media and to test for the impact of factors such as sex differences, age, home range etc., but this has to be balanced with the expense of time and money involved and the need to limit the impact on the studied ecosystems from removing too many individuals. We have chosen roach as a relatively common species where sufficient numbers are present at most sites to allow for removal of usually 10 individuals without negative impact on the populations.…”

Development of a risk assessment tool for mercury in fish.

“…Hg is third (after arsenic and lead) on the 2011 Agency for Toxic Substances and Disease Registry (ATSDR) priority list of 275 hazardous substances, which includes substances that present the most significant potential threats to human health in the United States 1 (ATSDR, 2011). It is released into the environment through both natural and anthropogenic sources and can exist in three forms: elemental, inorganic, and organic (Bhavsar, 2010;Mousavi et al, 2011). In freshwater ecosystems, the organic form (e.g.…”

“…All humans are exposed to some level o f Hg, and fish is the primary source o f Hg exposure among the general population (Bhavsar et al, 2010). ).…”

“…However, it is noted by Bhavsar (2010) that Hg concentrations in fish typically increase with age, and that fish size is obtained as a surrogate measure for the duration o f contaminant exposure because it is easy and inexpensive to acquire (Bhavsar, 2010).…”

“…Studies also show differences in Hg concentrations in pelagic and benthic species; animals living in close association with sediments (in which they bury and from where they feed) are eventually more exposed to sediment-associated contamination than other fish (Storelli et al, 2007). Almost all o f the Hg found in biological systems has been absorbed in the form of MeHg and all freshwater fish in North America, and perhaps in the world, have at least trace levels of Hg in their tissues (Bhavsar, 2010). MeHg can bioaccumulate and biomagnify within aquatic food webs and is highly absorbable to both fish and human consumers via ingestion (95 to 100%) compared to inorganic Hg (5 to 10%) (Storelli et al, 2007;Chan et al, 2003).…”