Biological and Environmental Effects of Arsenic

283 Pages·1983·3.76 MB·English

by  B.A. Fowler (Eds.)

Topics in environmental health
Volume 6
1983
ELSEVIER
AMSTERDAM · NEW YORK · OXFORD
Biological and environmental effects
of arsenic
Editor
BRUCE A. FOWLER
Laboratory of Pharmacology
National Instititute of Environmental Health Sciences
National Institutes of Health
Research Triangle Park, North Carolina, U.S.A.
1983
ELSEVIER
AMSTERDAM · NEW YORK · OXFORD
© Elsevier Science Publishers Β. V., 1983
All rights reserved. No part of this publication may be reproduced, stored in a retrieval
system, or transmitted in any form or by any means, mechanical, photocopying, recording
or otherwise, without the prior permission of the copyright owner.
ISBN for the series: 0 444 41597 1
ISBN for volume 6: 0 444 80513 3
PUBLISHED BY:
Elsevier Science Publishers B.V.
P.O. Box 211
1000 AE Amsterdam
The Netherlands
SOLE DISTRIBUTORS FOR THE U.S.A. AND CANADA:
Elsevier Science Publishing Company, Inc.
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Library of Congress Cataloging in Publication Data
Main entry under title:
Biological and environmental effects of arsenic
(Topics in environmental health ; v« 6)
Bibliography: p.
Includes index«
1. Arsenic poisoning—Addresses, essays, lectures.
2. Arsenic--Environmental aspects--Addresses, essays,
lectures. 3. Arsenic—Metabolism—Addresses, essays,
lectures. I. Fowler, Bruce Α. II. Series. [DNLM:
1. Arsenic--Poisoning. 2. Arsenic--Toxicity.
3. Environmental exposure, h. Environmental pollutio
Wl T0539LM v.6 / QV 29k B615]
RA3231.A7B56 I983 628.5 83-II503
ISBN 0-^-80513-3
Printed in The Netherlands
Preface
Arsenic is one of the most common and important trace elements whose toxic and
medicinal properties have been known for centuries. An understanding of processes
which generate the various chemical species of this element in the environment and
biological organisms, however, is only now beginning to occur due to the advent of
improved analytical methodologies. During the next several decades, massive
mobilization of this element may occur as a result of increased utilization of fossil-
fuel energy conversion processes but the environmental and human health risks
associated with these technologies are presently unknown. An understanding of
these potential problems is crucial to the safe and effective long-range development
of these technologies.
This book is intended as a current summary of our present knowledge concerning
the emission sources, environmental chemistry, metabolism, epidemiological data,
and mechanisms of toxicity for the various chemical species of arsenic. It differs
from most other works on toxic metals or agents in two general respects. First, each
of the authors has been asked to provide not only a current review of the literature
on arsenic in his/her specific area of expertise but also to make a prospective assess-
ment of future research needs so that evolving problems may be hopefully iden-
tified. In this regard, emphasis has been placed on expanding sources of arsenical
mobilization such as fossil-fuel energy technologies. An effort has been made to ex-
amine both the expected quantities of total arsenic released by these various pro-
cesses as well as the chemical species formed where this is known, since knowledge
of the species formed is essential to understanding the bioavailability of this ele-
ment.
A second feature of this volume is the attempt to integrate the knowledge from
vi Preface
the various areas of research so that the reader will be able to derive some overall
assessment of our current knowledge of arsenic as an environmental agent.
This has been approached by keeping the number of chapters to a minimum and
by including a summary chapter which attempts to pull together major thoughts and
research needs from the various chapters.
Bruce A. Fowler
Fowler (ed.) Biological and environmental effects of arsenic
© Elsevier Science Publishers Β. V., 1983
CHAPTER 1
Mobilization of arsenic by natural and
industrial processes
WARREN T. PIVER
National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle
Park, NC 27709, U.S.A.
1.1. Introduction
The cycling of arsenic through the environment is accomplished by a combination
of many different processes that are occurring simultaneously and continuously.
However, because there is confusion about the meanings of terms such as cycling,
mobilization, and emissions of arsenic from natural and industrial activities, it is im-
portant to start with definitions of these terms as they will be used throughout this
chapter.
Cycling is an all-inclusive term that requires functional statements on
macroscopic and microscopic transport phenomena describing the movement of
substances through all phases of the environment. Along with these statements on
transporting mechanisms, statements are required that describe the chemical
transformation of arsenic while it is transported through the different phases of the
environment. And finally, descriptions and characteristics of emissions of arsenic
from natural and industrial activities are required to complete the picture. Because
in this review we are mainly concerned with the relative rates of emissions, the term
mobilization is used to define both natural and industrial activities that emit arsenic
in different chemical forms to different phases of the environment. Although this
chapter is about the mobilization of arsenic by natural and industrial processes,
most of the discussion will focus on industrial mobilization. The rationale is
twofold. The details of natural processes are discussed more fully elsewhere in this
monograph and there is a high probability of developing control measures for
arsenic emissions in industrial processes if the phenomena can be understood from
a fundamental standpoint.
2 W. T. Piver
In developing our definitions of cycling and mobilization, frequent use of the
term phases of the environment has been made. The impression given by this term
is that the phases of the environment exist as separate and distinct compartments.
This is a false impression because the phases of the environment neither exist as
homogeneous isotropic media, nor can they be considered to have rigidly fixed
boundaries. It is impossible to find a fixed boundary between the atmosphere and
the lithosphère for example, because they exist within each other and the
phenomena which describe cycling of arsenic require that this situation be recogniz-
ed. When reference is made to a particular phase of the environment, it is being used
as an identifier for a portion of the environment that is dominated by a particular
set of characteristics, but in which heterogeneous multiphasic transfers can occur.
Quite clearly, descriptions of all of these processes whether they occur on a
macroscopic scale of time and distance, or on a microscopic or localized scale, are
incomplete. In many instances, it is only possible to account for the movement of
arsenic in the environment in a qualitative manner. Part of this inability of quantify-
ing arsenic movement on an absolute basis is the difficulty of assigning observed
concentrations of arsenic in different phases of the environment to specific natural
or industrial activities. Another reason is our incomplete understanding of the com-
plex heterogeneous processes that occur between the solid, liquid, and gaseous com-
ponents of the environment and the difficulty in deriving predictive expressions ex-
cept for very simplified situations.
Even with these uncertainties, there is a practical need to control arsenic because
of its demonstrated toxicity and its mobility in the environment. Much of the
mobility of arsenic in the environment as compared with other elements can be at-
tributed to its chemical characteristics. As a group V element, arsenic exhibits a very
wide range in chemical reactivity. It is able to form alloys with other elements as
well as form both ionic and covalent bonds with carbon, hydrogen, and oxygen.
Arsenic can readily participate in oxidation-reduction, methylation-demethylation,
and acid-base reactions. In the environment, this chemical reactivity makes many
pathways available for transport and transformation.
It would be incorrect to conclude from this statement, however, that because
there are so many diverse reaction pathways available for arsenic, environmental
levels are not reached that can produce harmful effects in exposed plants and
animals. In these situations, even though removal by one or more reactions or
transport mechanisms can occur, the net rate of entry into a particular locality may
greatly exceed the rate of removal. The net result is the accumulation of significant
concentrations of arsenic. Too often there is confusion between what constitutes
localized events and macroscopic events and how natural processes, industrial pro-
cesses, macroscopic events, and localized events interact. On a localized scale, cycl-
ing and partitioning of arsenic are strongly related to the characteristics of the en-
vironment in which it is found. It would not be uncommon in a specific locality for
important reaction pathways that would contribute to a reduction in arsenic concen-
tration to be nonexistent.
Mobilization of arsenic by natural and industrial processes 3
T
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Fig. 1.1. Arsenic cycling in the environment.
4 W. T. Piver
In Fig. 1.1, an attempt has been made to illustrate how macroscopic and localized
cycling of arsenic by different pathways in the environment is thought to occur. The
diagram also presents the idea of the heterogeneous nature of the processes that
cycle arsenic through the environment, e.g. weathering of minerals and adsorption
to sediments. Superimposed on this cycling scheme is a representation of major
natural and industrial processes that introduce arsenic into the environment. Within
this context, cycling of arsenic as it is defined here, is the sum total of macroscopic
and local events that transform and move arsenic in its different chemical forms
through the environment. They include processes that occur over a large scale of
time and distance such as wind motion and precipitation, as well as processes that
occur on a smaller scale such as methylation of arsenic in lake sediments and com-
bustion of coal in electrical power plants. In an attempt to make a distinction bet-
ween natural and industrial activities that mobilize arsenic in the environment,
natural cycling mechanisms are grouped on the left and industrial activities on the
right. It is evident, however, that mobilization by industrial processes must include
appropriate mention of processes that are in the domain of natural macroscopic
transport processes that describe movement in air, water, and soil. Clearly there is
no definitive way to make a sharp distinction among the rates of cycling of arsenic
by natural and industrial processes except that, as a rule, industrial activities greatly
accelerate the mobilization of arsenic and have a much greater rate of movement
of arsenic within a smaller geographic area.
1.2. Mobilization of arsenic by natural processes
An understanding of geochemical principles is essential to an explanation of the
mobilization of arsenic by natural processes. Geochemical mobilization of elements
includes two distinctly different activities (Brooks, 1977). In the first, referred to as
hypogene mobilization, geochemical processes occurring over hundreds to
thousands of years are still important in the formation of the earth's crust and result
in the solidification of magma and the distribution of elements among the different
rock types. The second natural process is supergene mobilization and relates to in-
teractions that occur at the interfaces of rocks with the atmosphere and
hydrosphere. These latter weathering processes, which are heterogeneous because
they involve the interactions between dissimilar phases and include the interphase
mass transfer of an element, happen over tens to hundreds of years and provide a
steady supply of elements to the environment. Supergenic processes represent one
of the principle methods by which the soil is formed and replenished with elements
essential for plant growth.
Along with supergenic mobilization of elements, elements such as arsenic are also
transferred from one phase to another or within a heterogeneous phase such as soil
by microbially mediated processes. Aerobic and anaerobic microorganisms, prin-
cipally bacteria and fungi, transform the elements into coordination complexes and
organometallic compounds. Generally, anaerobic bacteria methylate arsenic to
5
Mobilization of arsenic by natural and industrial processes
form organometallic compounds that have measurable vapor pressures and other
properties different from inorganic arsenic. Aerobic bacteria and fungi often
transform arsenic into coordination complexes that are more mobile in soil water
than the uncomplexed cation.
Environmental characteristics also strongly influence arsenic movement in soils.
Movement is a strong function of speciation and soil type. For a non-adsorbing soil
such as sand, the mobilities of As(III) and As(V) in groundwater are dependent
upon the dispersion coefficient and permeability for solute transport. As(III),
however, is 5 - 8 times more mobile in sandy soil than is As(V) (Gulens et al., 1979).
Soil pH also influences arsenic mobility. At a pH of 5.8, As(V) is slightly more
mobile than As(III). As pH changes from acidic to neutral to basic, As(III) tends
to become the more mobile species, though the mobility of both increases with in-
creasing pH (Gulens et al., 1979). In strongly adsorbing soils, transport rate and
speciation are influenced by organic carbon content and microbial population
(Holm et al., 1979). Both As(III) and As(V) are transported at a slower rate in a
strongly adsorbing soil as compared to the sandy soils.
Arsenic is also mobilized by forest fires and volcanic action. During these ac-
tivities, arsenic is transported by wind. In addition to the macroscopic motion of
the atmosphere, arsenic is widely dispersed by the motion of rivers and oceans.
1.3. Mobilization of arsenic by industrial activities
It has long been recognized that the smelting of non-ferrous metals together with
the production of energy from fossil fuel resources are the two leading industrial
processes that transfer arsenic from the ground to the air and water at significant
rates. In most instances, arsenic is present as a trace constituent. While the mobiliza-
tion of arsenic by these processes is unintentional, this is an important pathway for
movement of arsenic in the environment.
To avoid confusion, processes that result in the intentional mobilization of
arsenic are separated from those that are unintentional. Combustion of fossil fuels
and smelting of non-ferrous metals are unintended methods leading to arsenic
mobilization. The manufacture and use of arsenic pesticides and wood preservatives
are processes that intentionally mobilize arsenic. Several examples of activities that
unintentionally and intentionally cycle arsenic are presented in Table 1.1 (NAS,
1977). All of these activities represent intensive mass transport within a small por-
tion of the environment. Because of this intensive mass flux, the potential for
substantial human exposure is high.
The data of this table provide an important perspective for the examination of
industrial activities that mobilize arsenic in the environment. Since these data were
published, however, developing energy technologies using fossil fuels have emerged
that can represent significant future sources of arsenic emissions. As much as is
possible, the emission data from these developing energy technologies are presented
and analyzed in the same manner as the data for existing energy production
technologies.