Chronic toxicity of uranium to three benthic organisms in laboratory spiked sediment

Abstract

Due to mining activities, concentration of uranium (U) in the environment nearby former and operating sites can be higher than in other areas. The derivation of quality criteria for U in freshwater ecosystems, rivers and lakes includes the consideration of contaminated sediments and the associated risk to the benthic life. Therefore, the derivation of a quality criteria for sediment has been viewed as a logical and necessary extension of the work already done to establish water quality criteria. In order to contribute to the determination of a Quality Standard for sediment (QS_sediment) according to the European recommendations, this study focuses on the acquisition of a new toxicity dataset, to enrich the few rare existing data, most often unsuitable. A basic set of organisms, including three complementary benthic organisms (Chironomus riparius, Hyalella azteca, Myriophyllum aquaticum), was chronically exposed to U spiked to a standard laboratory-formulated sediment, according to the related bioassay guidelines (ISO/FDIS16303, OECD 218/9, ISO/DIS 16191). We looked to determine when possible both NOEC and EC₁₀ values for each organism. For C. riparius, a NOEC (emergence rate) value was estimated at 62 mgU, kg^-1, dm and the EC₁₀ value reached 188 mgU, kg^-1, dm (CI_95% 40-885 mgU kg^-1, dm). For H. azteca, a NOEC (survival rate) value of 40 mgU kg^-1, dm was observed while the EC₁₀ value at 296 mgU kg^-1, dm (CI_95% = 155-436 mgU kg^-1, dm) was slightly higher than for growth at 199 mgU kg^-1, dm (CI_95% = 107-291 mgU kg^-1 dm). Finally, the less sensitive organism seemed to be the plant, M. aquaticum, for which we determined a NOEC value of 100 mgU kg^-1, dm. Results obtained regarding the toxicity of U made it possible to suggest a preliminary QS_sediment value of 4 mgU kg^-1, dry mass. This value was shown conservative compared to U sediment quality criteria derived by other jurisdictions.

Keywords: Benthic organisms; Bioassay; Quality standard; Sediment; Toxicity; Uranium.