Acute and Chronic Effects of Sodium Tungstate on an Aquatic Invertebrate (Daphnia magna), Green Alga (Pseudokirchneriella subcapitata), and Zebrafish (Danio rerio)

Abstract

Although aquatic toxicity data exists for tungstate substances, insufficient data of high quality and relevancy are available for conducting an adequate risk assessment. Therefore, a series of acute and chronic toxicity tests with sodium tungstate (Na₂WO₄) were conducted on an aquatic invertebrate (Daphnia magna), green alga (Pseudokirchneriella subcapitata), and zebrafish (Danio rerio). Collectively, the data from these studies suggest that sodium tungstate exhibits a relatively low toxicity to these taxa under these test conditions. All studies were conducted in the same laboratory under good laboratory practice standards using Organisation for Economic Co-operation and Development guidelines with the same stock of test material and the same analytical methods. All results are reported as mg W/L. The following toxicity values were based on mean measured concentrations. For D. magna, the 21 day test no-observable effect concentration (NOEC) was 25.9 mg W/L, and the 48-h median effective concentration (EC₅₀) from the acute test was >95.5 mg W/L (the highest concentration tested). The P. subcapitata test yielded an ErC₅₀ of 31 mg W/L. A 38-day test with zebrafish resulted in an NOEC ≥5.74 mg W/L with no effects at any concentration. The 96-h LC₅₀ from the acute test with zebrafish was >106 mg W/L. The results of the current acute study for daphnids and fish are consistent with published literature, whereas the algae results are different from previously reported values. Transformation/dissolution (T/D) studies, which were conducted according to United Nations Globally Harmonized System of Classification and Labelling of Chemicals protocol, confirmed that the WO ⁻²₄ anion accounted for most of the tungsten in solution. For classification purposes, the algae ecotoxity reference value was then compared with T/D data and would not classify Na₂WO₄ as an aquatic toxicant under the European Union Classification, Labelling and Packaging scheme.