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Both sodium and bicarbonate are naturally present in aquatic ecosystems. The bicarbonate concentration are reported for a total number of 77 rivers and the sodium concentration for a total number of 75 rivers in North-America, South-America, Asia, Africa, and Oceania. For sodium the 10th- and 90th-percentile were 1.5 and 68 mg/l, respectively, for bicarbonate the 10th- and 90th-percentile were 20 and 195 mg/l, respectively (OECD SIDS on sodium bicarbonate (2002), pg. 19 -23). Because the natural pH, bicarbonate and sodium concentration (and also their fluctuations in time) varies significantly between aquatic ecosystems, it is not considered useful to derive a generic PNEC or PNECadded. To assess the potential environmental effect of a sodium bicarbonate discharge, the increase in sodium, bicarbonate and pH should be compared with the natural values and their fluctuations and based on this comparison it should be assessed if the anthropogenic addition is acceptable. The use of sodium bicarbonate could potentially result in an aquatic emission of sodium bicarbonate and it could locally increase the sodium and bicarbonate concentration in the aquatic environment. In contrast to sodium carbonate, sodium bicarbonate does not increase the pH of water to high and/or lethal levels (OECD SIDS on sodium bicarbonate (2002), pg. 19 -23). An addition of bicarbonate to water will converge the pH to a value of 8.34. The value of 8.34 is equal to (pKa1+ pKa2)/2. In other words, if the initial pH of the receiving water is for example 7.0 then an addition of bicarbonate will increase the pH but it will never be higher than 8.34. However, if the initial pH of the receiving water is for example 9.0 then an addition of bicarbonate will decrease the pH but it will never be lower than 8.34 (OECD SIDS on sodium bicarbonate (2002), pg. 19 -23).

Key aquatic toxicity studies are available and here summarised:

·     In a 96-hr acute flow-through test with bluegill sunfish (Lepomis macrochirus) a NOEC of 5,200 mg/l and a LC50 of 7,100 mg/l were determined (Machado, 1993).

·     A reliable publication (K2) is present exposing newly fertilised eggs of fathead minnow (Pimephales promelas) for 60 days to NaHCO3 at concentration range of 300-1,400mg/L. Results showed overall an LC50 at 37 days of 675 mg/L NaHCO3 and a NOEC of 400 mg/L NaHCO3 based on mortality (Farag et al, 2013).

·     In a 48-hr acute flow-through test with Daphnia magna a NOEC of 3,100 mg/L and a LC50of 4,100 mg/l were determined (Putt, 1993).

·     A weight of evidence approach was used for the long-term toxicity to invertebrates. A reproduction test with D. magna demonstrated that the 21-day Daphnia magna NOEC is higher than 576 mg/L (Leblanc and Surprenant, 1984). In addition, Farag et al. (2013) conducted a study exposing neonates of the water flea, C. dubia, for 7 days to a concentration range of 500-1500 mg/L of NaHCO3. Results showed a LC50 of 1192 mg NaHCO3/L and IC20 for reproduction of 359 mg NaHCO3/L. Furthermore, newly transformed freshwater mussels, L. siliquoidea, were also exposed in a separated experiment for 10 days to a concentration range of 500-2000 mg/L of NaHCO3. Results showed a EC50 and an IC20 for immobilization of 1061 mg NaHCO3/L and 952 mg NaHCO3/L, respectively.

·     In accordance with section 1 of Annex XI of the REACH Regulation, Algae toxicity tests don’t need to be conducted as in the aquatic environment sodium bicarbonate is dissociated into sodium and bicarbonate ions. Furthermore, bicarbonate ions are provided in high concentrations in algae growth medium, in order to ensure a sufficient carbon source for the organisms. Sodium ions are also present in high concentrations in the growth medium as essential ions. Indeed, two reliable studies (K 2) testing the increase of growth of algae with the addition of NaHCO3 are available. Nunez et al. (2016) exposed two marine diatoms, Phaeodactylum tricornutum and Nannochloropsis salina, to a concentration range of 0.5 to 5 g/L of NaHCO3 for 1-12 days during their growth phase, to assess their optimal growth condition. Indeed, with increasing test item concentration algae’s growth rate increased. Thus, a NOEC of 5000 mg/ L for inhibition effect was determined.

Differently, Zhou et al. (2016) exposed three marine red macroalgae, Gracilaria lemaneiformis, Gracilaria vermiculophylla and Gracilaria chouae, to a concentration range of 84 to 420 mg/L of NaHCO3 for 14 days to assess their optimal growth condition. Indeed, with increasing test item concentration algae’s growth rate increased up to the concentration of 420 mg/L (LOEC), when all the algae exhibited a significant grow rate inhibition compared with the control (NOEC 336 mg/l). Chl a, at the end of the experiment was also determined. A LOEC of 420 mg/L was determined for chlorophyll inhibition for G. lemaneiformis, G. vermiculophylla. G. chouae at the highest concentration tested showed a decrease but not significant decrease of Chl a compared with the control, thus a NOEC > 420 mg/L was determined.

Therefore, sodium bicarbonate has not to be classified for aquatic toxicity in accordance with CLP Regulation (EC) No 1272/2008.

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