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Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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OCR for page 1
1
INTRODUCTION
The passage of metals* through the atmosphere is integral to their
biogeochemical cycling. Because of the dynamic nature of the atmos-
phere, metals can be deposited in areas remote from their initial
sources. With the exception of mercury, the natural rates of atmos-
pheric emissions of metals are limited by their characteristically low
volatilities. Since the advent of industrialization, high-temperature
processes (e.g., smelting and fossil fuel combustion) have caused the
rates of emission of some metals to increase substantially. With
· . .
Increased emissions have come increased metal concentrations in the
atmosphere and in atmospheric deposition.
Worldwide, the known natural sources of metals in the atmosphere
are soil, seawater, and volcanic dusts and Gases. The anthropogenic
emissions are from industrial gases and particles, fossil fuel
combustion, and tillage. Recent reviews have shown that in eastern
North America and northern Europe, the rates of atmospheric deposition
of silver, arsenic, cadmium, copper, mercury, manganese, nickel, lead,
selenium, vanadium, and zinc are controlled by anthropogenic activities
(Galloway et al., 1982; Jeffries and Snyder, 1981~. There are many
other metals (beryllium, cobalt, molybdenum, tin, tellurium, and
thallium) whose rates of deposition have probably increased, but data
are lacking to prove it.
The shift from natural control to anthropogenic control of
atmospheric metal deposition represents a significant perturbation of
biogeochemical cycles of these potentially toxic substances. Given
this, the next obvious questions to ask are as follows:
.
Do these elevated rates of atmospheric metal deposition cause
changes in terrestrial and aquatic ecosystems?
*Of the 18 elements that are the focus of this report, 15 are true
metals. Selenium, arsenic, and tellurium are not strictly classified
as metals, although they exhibit some metallic properties. For the
sake of simplicity in this report, the generic term "metals. is used to
describe the entire set of 18, without reference to the 3 exceptions.
1
OCR for page 2
2
· What is the interaction between increased metal deposition
into terrestrial and aquatic ecosystems and their concurrent
acidification by acid deposition?
Indeed, there has been considerable speculation on these points, and it
has been suggested that perhaps some of the biological effects of acid
deposition, both in the aquatic and In the terrestrial environments,
may be due not only to the increase in hydrogen ion concentration per
se, but also to changes in the total concentration or speciation* of
certain metals (Baker and Schofield, 1980; Eriksson et al., 1980;
Scheider et al., 1979; Schofield, 1980; Suns et al., 1980~. In the
present study we examine these questions and attempt to identify those
metals that merit further attention in this regard.
We chose to focus our attention on those metals that have been
classified as every toxic and relatively accessible in an environmental
context (Wood, 1974~. A number of metals were deleted from this com-
pilation, because very few or no environmental data were available
(gold, bismuth, palladium, platinum, and antimony) , and aluminum was
added because of its known implication in the response of watersheds to
acid deposition. Chromium was omitted because it is considered to be
normally reduced to Cr(III) in the environment. In this form chromium
is less toxic than in other valence states, but more importantly, it in
relatively immobile (NRCC, 1976; Sheppard et al., 19847. The final
list of 18 metals considered in this report includes the following
elements: silver {Ag), aluminum (Al), arsenic (As), beryllium (Be),
cadmium (Cd), cobalt (Co), copper (Cu), mercury (Eg), manganese (Mn),
molybdenum (Mo), nickel (Ni), lead (Pb), selenium {Se), tin (Sn),
tellurium (Te), thallium (T1), vanadium (V), and zinc (fin). Since this
review focuses on the interaction between increased metal deposition
and freshwater acidification on a regional basis, we exclude the local
impact of point sources (e.g., smelters). The environmental behavior
of each of these metals has been analyzed according to a framework of
17 questions, designed to generate definitive statements about effects
and/or specific recommendations for research in areas where our
ignorance is profound. The questions are indicated in Figure 1.1.
In Chapter 2 these questions have been grouped together and
addressed in general terms. At the end of the chapter the data are
summarized in condensed tabular presentations, to describe the state of
knowledge for each metal. Detailed tabular summaries containing
references, and indicating whether the answers to the questions are
known, partially known, or unknown, can be found in the Appendix. The
conclusions and recommendations are presented in Chapter 3.
*The term ~speciation. is defined in this report as the partitioning
among the possible physical-chemical forms of a particular trace metal
that together make up its total concentration.
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3
ATMOSPHERE
1. Is deposition controlled by human processes?
2. Do we know the speciation of the metals in
atmospheric deposition? (a) physical?
(b) chemical?
(c) dry vs. wet?
TERRESTRIAL ECOSYSTEMS
3. Does the metal accumulate
in the system?
4. Does the metal move in
solution to the lake?
5. Is there an interaction
of the metal with
acidification over the
pH range 7-4?
6. (a) Is the metal
bioavailable?
(b) Does the metal
bioaccumulate?
7. Does the metal have
biological effects on
the terrestrial system?
AQUATIC ECOSYSTEMS
8. Do we know the speciati on of the
metal in solution?
9. Does the metal increase in
concentration in the aquatic system?
10. Is there an interaction of the
metal with acidification of the
water col urn over the pH range
7-4?
(a)
Is the metal bioavailable in
the aquatic system?
(b) Does the metal bioaccumulate?-
(c) I.s the metal biomagnified?
(d) What is the inherent toxicity
of the metal?
12. Does the metal have biological
effects in the aquatic system?-
SEDIMENTS
, ,
15.
17.
13. Do we know the partitioning
of the metal in sediments?
14. Is the accumulated metal
readily recycled between the
sediments and the lake?
Is there an interaction of
the metal with acidification
over the pH range 7-4?
16. (a) Is the metal bioavailable?
(b) Does the metal bioaccumulate?-
Does the metal have biological
effects on the benthic system?-
FIGURE 1.1 Framework of relevant questions pertaining to trace metals .
Representative terms from entire chapter:
biological effects
