The Toxicity of Common Ions to Freshwater and Marine Organisms Whole effluent toxicity (WET) tests have become a common tool in the evaluation of effluent for discharge a cceptability. Recent investigations have indicated that deficiencies or excess es of “common” ions (inorganic ions that are nearly always present in most aquatic systems at nontoxic concentrations) can cause si gnificant acute or chronic toxicity in WET tests. This report presents the results of a re view of toxicological and physiological data on inorganic ions that have be en implicated in causing significant toxicity — bicarbonate, bo rate, bromide, calcium, chloride, fluoride, magnesium, potassium, strontium, and sulfate