Bicarbonate toxicity to Ceriodaphnia dubia and the freshwater shrimp Paratya australiensis and its influence on zinc toxicity

Abstract

Bicarbonate is often a major ionic constituent associated with produced waters from methane gas extraction and coal mining, yet few studies have determined its specific toxicity. Currently, the environmental risk of bicarbonate anion in water discharges is assessed based on the toxicity of sodium chloride or artificial seawater and is regulated via electrical conductivity. Increased NaHCO(3) added to Ceriodaphnia dubia in synthetic or natural water gave similar 48-h 10% effective concentration (EC10) values of 1750 ± 125 mg NaHCO(3)/L (mean ± standard error) and 1670 ± 180 mg NaHCO(3)/L, respectively. Bicarbonate was toxic to C. dubia in both waters with conductivities above 1900 µS/cm. In contrast, when conductivity was elevated with NaCl, toxicity to C. dubia was observed only above 2800 µS/cm. Bicarbonate also impaired C. dubia reproduction with an EC10 of 340 mg NaHCO(3)/L. Major ion composition also influenced Zn bioavailability, a common co-occurring metal contaminant in coal mine waters, with sublethal concentrations of NaHCO(3) and elevated pH increasing Zn toxicity. Higher pH was the dominant parameter determining a 10-fold increase in the 48-h 50% effective concentration (EC50) for Zn toxicity to C. dubia at pH 8.6 of 34 µg Zn/L (95% confidence limit = 32-37 µg Zn/L) compared with the Zn toxicity at approximately circumneutral pH. Exposure of the freshwater shrimp Paratya australiensis (Atyidae) in natural water to increasing bicarbonate gave a mean 10-d 10% lethal concentration (LC10) of 850 ± 115 mg NaHCO(3)/L, associated with a mean conductivity EC10 of 1145 µS/cm, which is considerably lower than toxicity of NaCl and artificial seawater to this species reported elsewhere. Because toxicity was influenced by salt composition, specific ions should be regulated rather than conductivity alone in mine wastewater discharges.

Effects of environmentally relevant mixtures of major ions on a freshwater mussel

“…mechanism of toxicity reduction is thought to be complexation rather than competition for receptors and binding sites (Wang et al, 2009). In contrast, synthetic and natural waters produced similar EC 50 s for Ceriodaphnia dubia exposed to NaHCO 3 (Vera et al, 2014). The effect of natural water compared to reconstituted water on the toxicity of ion mixtures also requires further study.…”

Salinized rivers: degraded systems or new habitats for salt-tolerant faunas?

“…Our conceptual framework (figure 2) provides a guide to understanding the effects of salinization on rivers, regardless of ionic proportions. However, the ecological effects of a particular salinity will vary with ionic ratios because of different levels of toxicity on organisms, and species tolerant of one set of ionic proportions may be sensitive to another [80,83]. Organisms from marine/estuarine environments may be less likely to invade, and freshwater species recently evolved from estuarine/marine species may be less able to tolerate, or adapt to, non-NaCl-dominated saline waters.…”

Species of freshwater invertebrates that are sensitive to one saline water are mostly sensitive to another saline water but an exception exists

“…salts have been widely studied because they are generally representative of salinization from road de-icing with NaCl in cold regions in North America, and dryland salinity on the east coast of Australia, which tends to have ionic proportions more similar to seawater [15]. However, coal bed waters contain high proportions of other major ions, and they do not have proportions of ions similar to seawater [16]. In particular, these waters typically have significant concentrations (20 -80% of anions) of bicarbonate (HCO 3 2 ), which is much less abundant in seawater (about 0.3% of anions) [17,18].…”

“…In this paper, we determine if there is a direct linear relationship between the toxicity (as indicated by acute LC lethal concentration) values of SMS and that of sodium bicarbonate (NaHCO 3 ) in a sample of freshwater species. NaHCO 3 was chosen because it represents the primary compositional difference between natural surface salinity observed in many streams and the saline waters associated with coal beds in Australia [16]. If a relationship is found then, we will explore the possibility of using the extensive SMS toxicity database [8] in the literature to make effective management predictions.…”