Abstract
Freshwater mussel taxa are severely imperiled and among the most sensitive to several contaminants, including chloride. Relatively little is known of the toxicity of major ions to glochidia (larvae), particularly for rare species, or the effects of hardness on major ion toxicity to glochidia. Therefore, the primary objectives of this work were to: (1) determine the acute toxicity of major ion salts to glochidia, (2) compare chloride sensitivity of glochidia from common and rare species, and (3) evaluate the relationship between water hardness and chloride toxicity to glochidia. We assessed 24 h EC50s for fatmucket (Lampsilis siliquoidea) glochidia exposed to NaCl, KCl, MgCl2, CaCl2, Na2SO4, MgSO4, CaSO4, and NaHCO3 in moderately hard water. We determined NaCl EC50s for four species and KCl EC50s for glochidia of three species. Toxicity of chloride was generally consistent among the various chloride salts except for KCl, which was more toxic than all others by 1–2 orders of magnitude. Our results suggest that commonly tested species may be generally representative of rare species. Water hardness ameliorated the toxicity of chloride for all species to varying degrees. Results of this work indicate that some existing water quality criteria that do not include mussel toxicity data may not be protective of freshwater mussels.
Highlights
In North America and elsewhere, water pollution from major ions (Na+, K+, Ca2+, Mg2+, Cl−, SO4−, HCO3−) stems largely from anthropogenic activities such as mineral mining, oil and gas extraction, irrigation, industrial effluents, and road deicing [1,2]
Water quality parameters were within acceptable ranges for all toxicity tests: temperature ranged from 19.7–20.2 °C, dissolved oxygen ranged from 7.68
Acute toxicity tests with salts of chloride and sulfate revealed that freshwater mussel glochidia are sensitive to these major ions, consistent with results from previous glochidia ion toxicity research [5,9,12] as well as ion testing with juvenile mussels [16]
Summary
In North America and elsewhere, water pollution from major ions (Na+, K+, Ca2+, Mg2+, Cl−, SO4−, HCO3−) stems largely from anthropogenic activities such as mineral mining, oil and gas extraction, irrigation, industrial effluents, and road deicing [1,2]. Major ion pollution can cause osmotic stress and increased metabolic costs in freshwater organisms [3,4], posing a threat to fish and aquatic invertebrates such as freshwater mussels [5–. Freshwater mussels (family Unionidae) are well documented among the most imperiled of aquatic species [11] and toxicity studies with early life stages of freshwater mussels exposed to major ions have demonstrated that glochidia (larvae) and juveniles are among the most sensitive of all species tested [5,10,12,13,14,15,16]. Field studies corroborate lab toxicity testing; in the Clinch and Powell River systems in Tennessee, USA, declining mussel richness and density has been connected with rising concentrations of major ions from coal mining operations [15]. In Ontario, Canada, stream salinization from road salt application during the winter resulted in elevated glochidia mortality [5,9]
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