Environmental Engineering Reference
In-Depth Information
CHAPTER 1
Sources and Transport
A Global Issue
PHIL SWARTZENDRUBER and DANIEL JAFFE
CHEMICAL FORMS OF MERCURY IN WATER AND AIR
ANTHROPOGENIC SOURCES OF MERCURY IN THE AIR
Chemical Speciation
THE CHANGING GLOBAL CYCLE OF MERCURY
Sediments and Ice Cores as Archives of Geochemical Cycles
The Preindustrial Cycle
Evidence of Recent Changes in Deposition of Mercury
The Modern Mercury Cycle
REEMISSION OF PREVIOUSLY DEPOSITED MERCURY
MERCURY EMISSIONS: SUMMARY, UNCERTAINTY, AND VALIDATION
FROM RELEASE TO GLOBAL TRANSPORT
Aqueous Transport
Ocean Settling and Transport
Atmospheric Transport
Continental Export and Long-Range Transport
Global Transport
SOURCES OF MERCURY IN WATER
Atmospheric Wet and Dry Deposition
Industrial Point Sources
Mining Runoff
Methylated Species
NATURAL PROCESSES THAT EMIT MERCURY INTO THE AIR
SUMMARY
Chemical Forms of Mercury in Water and Air
The Roman deity, Mercury, was the god of trade, commerce,
thievery, and messengers. His reputation as a cunning and
swift messenger led to the modern adjective,
mercurial
,
meaning labile, volatile, and erratic. Many contemporary
scientists who study mercury would emphatically agree
that its behavior in the environment and in the labora-
tory often seems erratic and mysterious. Indeed, it was
only relatively recently that we became aware of the global
nature of mercury contamination, partly because of the
diffi culty in detecting it at the extremely low concentra-
tions that are typical in air and water. Thus, we encounter
an apparent paradox fi tting of Mercury's reputation; why
are there toxic levels of mercury in fi sh in remote regions
throughout the globe despite water and air concentrations
that are very low? The answer is a complex process of emis-
sion, transport, deposition, and accumulation up through
the food chain. All of the major steps in this process have
been clearly identifi ed, although a number of the specifi c
mechanisms remain poorly understood. In this chapter we
will give an overview of the chemical forms present in the
air and water, their sources, and how they are transported.
The chemical symbol for mercury, Hg, is derived from
the Latin name,
hydragyrum
, which means silver water.
Elemental mercury is found in the Earth's crust in only a
limited number of regions in the world. Mercury is more
abundant in mineral form, with cinnabar (HgS) being
the most prevalent. Several of the less abundant minerals
include calomel, Livingstonite, and Tiemannite. Mercury is
predominantly found in deposits formed by hydrothermal
systems, which are most common at convergent tectonic
margins. It also tends to be enriched in some base-metal ores
and present with other chalcophilic (having a sulfur affi nity)
elements (Kesler, 1994). The elemental form of mercury
(Hg
0
) has had a great number of uses historically, including
barometers, thermometers, electrical switches, fl uorescent
light bulbs, and ballast for submarines. Elemental mercury
has a unique combination of properties that seem to make
it ideal for these applications. Hg
0
is the only abundant
metal that is liquid at room temperature. It has a melting
