Geoscience Reference
In-Depth Information
Mercury
Mercury (particularly as methyl Hg) can both bioaccumulate and biomagnify in
the food chains and may undergo long-range transport when released to the
atmosphere. Contamination of fish by mercury has been observed in many
regions. Methylmercury is the most toxic form of mercury in the environment
and bioaccumulates in aquatic food chains. Many lakes have been found to have
levels of Hg in fish exceeding the dietary recommendations of the World Health
Organization of 0.5 m g g −1 wet weight (ww). The United States Environmental
Protection Agency is even more restrictive, and recommends 0.18
μ
g g −1 ww as a
Federal Advisory limit for consumption of mercury-contaminated fish (US-EPA
2003). Methylmercury is deleterious for the development of the central nervous
system of unborn children (Mergler et al . 2007). High body burdens of mercury
may also be a risk factor for acute coronary events (coronary heart disease and
infarction) in middle-aged men (Virtanen et al . 2005).
In Scandinavia, fish in thousands of lakes have mercury levels above the health
guideline, making them unsuitable for human consumption. However, ecosystem
characteristics are important (Munthe et al . 2007a). Hg is bioaccumulated in the
form of methylmercury. Thus, the specific ecosystem capacities for the production
and transport of methylmercury determine the final bioaccumulation rates
(Munthe et al . 2007b). Examples from Arctic and mountain regions include
observations of high Hg levels in the piscivorous Arctic charr population of
Arresjøen, Svalbard, where the highest concentration was 0.44
μ
g g −1 ww, despite
concentrations of this metal in the sediment and lake water being very low
(Rognerud et al . 2002). In 1993, five brown trout from Lochnagar were analysed
for Hg in muscle and the concentrations were found to range from 0.04 to
0.08
μ
g g −1 ww (Rosseland et al . 1997). In 2001, the Hg levels were higher still,
ranging from 0.035 to 0.23
μ
g g −1 ww.
The effects of temperature increases
Temperature influences the majority of physico-chemical properties and pro-
cesses that determine the environmental behaviour of chemical compounds,
affecting thermodynamic aspects (e.g. equilibrium constants, partition constants,
absorption isotherms, vapour pressure and solubility) as well as kinetic aspects
(e.g. transport, and reaction rates). Hence, variations in temperature can affect
the dynamics, transport and fate of contaminants in the environment, especially
in the aquatic environment.
Temperature also determines the relative proportion of water phases in each
ecosystem. Warmer climate leads to higher air humidity and less snow and ice in
cold areas. Longer ice-free periods can increase catchment soil erosion elevating
the release of previously deposited contaminants bound to soils, but modelling
and quantitative evaluation of these processes is difficult due to the complexity
of the interactions and to the uncertainties in many of the parameters implied.
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