The acute toxicity of major ion salts toCeriodaphnia dubia: I. influence of background water chemistry : Water chemistry effects on acute ion toxicity toCeriodaphnia

Abstract

<p class="first" id="P1">The ions Na ⁺, K ⁺, Ca ²⁺, Mg ²⁺, Cl ⁻, SO ₄ ²⁻, and HCO ₃ ⁻/CO ₃ ²⁻ (referred to here as “major ions”) are present in all fresh waters and are physiologically required by aquatic organisms, but can increase to harmful levels from a variety of anthropogenic activities. It is also known that the toxicities of major ion salts can vary depending on the concentrations of other ions, and understanding these relationships is key to establishing appropriate environmental limits. In this paper we present a series of experiments with <i>Ceriodaphnia dubia</i> to evaluate the acute toxicity of twelve major ion salts and to determine how toxicity of these salts varies as a function of background water chemistry. All salts except CaSO ₄ and CaCO ₃ were acutely toxic below saturation, with the lowest LC50s found for K salts. All ten salts that showed toxicity also showed some degree of reduced toxicity as the ionic content of the background water increased. Experiments that independently varied Ca:Mg ratio, Na:K ratio, Cl:SO ₄ ratio, and alkalinity/pH demonstrated that Ca concentration was the primary factor influencing the toxicities of Na and Mg salts, while the toxicities of K salts were primarily influenced by the concentration of Na. These experiments also indicated multiple mechanisms of toxicity and suggested important aspects of dosimetry: the toxicities of K, Mg, and Ca salts were best related to the chemical activity of the cation, while the toxicities of Na salts also reflected an influence of the anions and were well correlated with osmolarity. Understanding these relationships between major ion toxicity and background water chemistry should aid in the development of sensible risk assessment and regulatory standards. </p>