85    EVALUATING TOXICITY OF SPECIATED METALS FROM
METAL DISCHARGING INDUSTRIES
Mujde Erten, Project Engineer
Malcolm Pirnie Inc.,
Newport News, Virginia 23606
Jerome L. Pitt, Environmental Engineer
U.S. EPA Region VII
Kansas City, Kansas 66101
Nord L. Gale, Chairman
Life Sciences Department
University of Missouri-Rolla
Rolla, Missouri 65401
Bobby G. Wixson, Dean
College of Sciences
Clemson University
Clemson, South Carolina 29634
Resit Unal, Assistant Professor
Old Dominion University
Norfolk, Virginia 23529-0456
INTRODUCTION
The aquatic toxicity of metals is a complicated phenomena involving interactions between the
environment and the metal pollutants of concern. Predicting the toxic effect that metals have in
natural waters requires evaluating the bioavailability of the metal pollutants. The term "bioavailability" reflects the premise that for some heavy metals organisms may be exposed to less than the total
amount present in their habitat.1
Earlier studies to determine the toxicity of lead,2,3 cadmium,4"8 and zinc9"'2 to fish indicated that
water quality characteristics such as pH and hardness affect bioavailability and toxicity. Further
investigations13"15 showed that evaluation of the toxic bioavailability of metals is dependent on the
chemical complexation and speciation. The toxicity of heavy metals to aquatic biota is immensely
influenced by the physicochemical factors of the specific environment. Many chemical characteristics
of the water are important in defining both the chemical species of the metal present and physiological
status of the organism being tested.14
The fractionation of metal species has been recognized as an essential step in the assessment of the
potential biological uptake, and predicting the toxicity is dependent on understanding the limitations
of laboratory toxicity tests and the effects of physicochemical variables at the field site. In recent
years, increasing effort has been made to identify the ligands which dominate heavy metal speciation
in natural waters, and to develop a speciation scheme for measuring the fraction of the trace metal
concentration which is toxic to aquatic biota.16 For a speciation scheme to be useful, however, it must
reliably detect all the important toxic forms of the metals present. Also, information must be available
about the relative toxicity of the various forms measured by the scheme.
The lack of precise and definitive information about the various chemical species of lead, cadmium
and zinc which might be present or the relative toxicity of various compounds of these metals have
frustrated the development of appropriate and adequate water quality standards. Because of the
different species of metals occurring in the environment and the lack of definitive information about
their relative toxicities, there is no ideal analytical measurement available for expressing aquatic life
criteria for metals of lead, cadmium and zinc. A criterion or a standard for a metal that is based on
only one set of environmental variables will be unnecessarily stringent for one type of environment
45th Purdue Industrial Waste Conference Proceedings, © 1991 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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