7    A NEED FOR ENVIRONMENTAL QUALITY GUIDELINES
BASED ON BIOAVAILABILITY IN NATURAL WATERS:
CASE STUDY "ZINC"
Ralph J. Magliette, Chemical Engineer
D. McKinney, Chemical Engineering Technician
E. S. Venkataramani, Research Fellow
S. Bacher, Director, Developmental Technology
Merck & Co., Inc
Rahway, NJ 07065-0900
F. G. Doherty, Manager, Aquatic Toxicology
Syracuse Research Corporation
Syracuse, NY 13210
INTRODUCTION
The U.S. Environmental Protection Agency (EPA) has formulated surface water quality criteria to
protect aquatic life from toxic concentrations of 14 metals. Many states have adopted these criteria,
carte blanche, with little modification to represent site/state-specific conditions. This despite that
under Section 303 of the Clean Water Act, state-specific surface water quality standards were to be
implemented by each state.
The 1987 Clean Water Act Amendments required the EPA and the states to emphasize the attainment of water quality standards and designated water uses, especially for toxic pollutants in all
freshwater systems. As a result there has been increased emphasis on establishing NPDES permit
limits for metals (including zinc) based upon state water quality standards. Many states adopted the
EPA criteria for metals. These water quality criteria for metals have been developed from laboratory
data, generated by the EPA at the Environmental Research Laboratory in Duluth, Minnesota. Several
publications from Mount and Norberg (1984)1 and Norberg and Mount (1985)2 for effluent testing
provided the basis for the testing protocols and discharge limits. The procedures and scope of aquatic
toxicity evaluations were formalized in two documents, namely the EPA "Methods for Measuring the
Acute Toxicity of Effluents to Freshwater and Marine Organisms" (1985)3 and the Quality Criteria for
Water (1986)4. The aim was to conduct aquatic toxicity tests under controlled conditions using
synthesized reconstituted water which is essentially free of suspended solids and organic constituents
that could interact with the metals being tested.
Use of the laboratory-based water quality criteria to establish surface water quality standards, and
the subsequent application of these standards to calculate water quality-based limits for NPDES
permits results, in some cases, in permit limits that are so low as to be technically unachievable. The
criterion continuous concentration (CCC) for zinc is 47 mcg/L. Surface water data that has been
collected and analyzed have indicated that EPA criteria for zinc are exceeded in many natural surface
waters. Faust and Ally (1983)5 have found zinc (3-2000 mcg/L) in drinking water. Brown, et al.
(1983)6 has found that most U.S. soil contain between 10-300 mg/L zinc. These references indicate
that exceeding the EPA CCC for zinc by a several fold factor does not appear to affect the ecosystem
health of the particular surface water under evaluation. The discrepancy between the toxic effects of
zinc in laboratory tests on daphnia and fathead minnows as reported in the literature and seen in
surface waters is due in large part due to differences in the physical and chemical forms of zinc in the
two environments. When viewed in the context of toxicity of a metal to aquatic organisms, the
bioavailable fraction of the metal induces the adverse response. Zinc complexes which are in a non-
bioavailable form will not contribute to the toxicity to aquatic life and are irrelevant in the protection
of an aquatic ecosystem as long as the aquatic community is healthy.
The laboratory tests that are used by the EPA to develop the aquatic life criteria typically contain
the substance being tested in a bioavailable form. This approach is used to minimize the uncertainty in
47th Purdue Industrial Waste Conference Proceedings, 1992 Lewis Publishers, Inc., Chelsea, Michigan 48118.
Printed in U.S.A.
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