The use of a simultaneous multiple species acute toxicity test to compare the relative sensitivities of aquatic organisms to mercury

Abstract

Recently there has been concern in the scientific community about observed declines in some amphibian populations. These population declines may be reflecting a global phenomenon or may be part of a natural cycle. Both viewpoints suggest that the observed declines are due to the general sensitivity of amphibians to their environment and to contaminants in their environment. To begin to determine if amphibians are more sensitive to environmental contaminants than other aquatic organisms, a simultaneous, multi‐species toxicity test was conducted. By simultaneously exposing several species of aquatic organisms to a series of mercury concentrations, the relative sensitivities of the organisms could be determined. Six aquatic species were used in the toxicity test: three amphibians, Rana catesbeiana (bullfrog), R. clamitans (green frog), and R. sphenocephala (southern leopard frog); two fish, Gambusia qffinis (mosquitofish) and Notemigonus crysoleucas (golden shiner); one aquatic oligochaete, Lumbriculus variegatus (aquatic earthworm). The organisms were exposed to a series of five test concentrations (1.4, 3.9, 12.0, 110.0, and 487.0 μg Hg/L). The resultant 96hr‐ LC₅₀ values produced the following rank order: R. sphenocephala, 6.59 μg Hg/L; R. clamitans, 14.7 μg Hg/L; N. crysoleucus, 16.75 μg Hg/L; L. variegatus, 43.72 μg Hg/L; G. affinis, 52.62 μg Hg/L; R. catesbieana, 63.36 μg Hg/L. No general organism class sensitivity trend was developed from the data, contrary to the implicit suggestions of some researchers.

Key words:

• Amphibians
• Mercury
• Toxicity
• Multiple‐species toxicity testing

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