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Sediment toxicity

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One reliable long-term toxicity study (Klimisch 2) of vanadium substances to sediment organisms was identified: In a chronic sediment toxicity test acc. to US EPA test method 100.4, Hyalella azteca (7-14 d old) were exposed to vanadium in field-contaminated sediments or in spiked natural sediment collected from Lake Catherine (Arkansas, USA) for 28 days and effects on survival and growth were assessed (Bennett, 2016). In the spiked sediment toxicity test, 28-d LC10 and LC50 values of 417 and 742 mg V/kg sediment dw (measured) were determined, respectively. Effects on the relative growth rate of H. azteca were observed only at the measured concentration of 626 mg V/kg (LOEC) but not at 1269 mg V/kg. However, a 28-d NOEC of 498 mg V/kg sediment dw (measured) could be derived for growth rate.

Contrary to effects observed in spiked sediments, effects on mortality or growth of H. azteca could not be observed in the same study with field-contaminated sediments with substantially higher measured sediment V concentrations of up to 1826 mg V/kg. Field sediments were collected from 9 different sites at Lake Catherine (including control) in June and October 2015. Measured V concentrations of 12 out of 18 collected sediment samples were > 417 mg V/kg sediment d.w. (i.e. LC10 of H. azteca in laboratory spiked sediments). The absence of effects in field-contaminated sediments with substantially higher vanadium concentrations suggests that the bioavailability and toxicity of vanadium is much lower in field contaminated than in laboratory-spiked sediments (equilibrated for 14 days). The corresponding pore water analysis confirmed that measured V(V) concentrations of pore water of site sediments were < 1 µg/L for all sites, whereas pore water concentrations of spiked sediments were significantly higher (e.g. at the LC10: 371 µg V/L). Furthermore, significantly higher iron and organic carbon levels were determined in field sediments compared to spiked sediments, which also supports the assumption that vanadium was more bioavailable in laboratory-spiked sediments. Results from field-contaminated sites are thus considered more relevant for the hazard assessment of vanadium, since equilibrium was presumably not reached in laboratory-spiked sediments so that bioavailability and consequently toxicity were thus overestimated.

A reliable short term-toxicity test (Nedrich et al. 2018; Klimisch 2), in which 7-9 day old Hyalella azteca were exposed to vanadium in two field-collected sediments with respective background V concentrations of 807.45 and 1124.72 mg V/kg dry weight. Significant effects on survival and growth compared to a control sediment (31.24 mg V/kg) and a reference-site sediment (118.16 mg V/kg) were not observed in a sediment-filled microcosm after 7 days.

Additionally, significant toxic effects on growth and survival to Hyalella azteca were not observed in a 10-day test in field-contaminated sediments enriched with V up to 503 and 1590 mg V/kg dry weight and molybdenum by metallurgical activities (supporting study by Conestoga-Rovers & Associates, 2009; Klimisch 3).

All three studies on the toxicity of vanadium in field-contaminated sediments with high background V concentrations can be considered as supporting studies for the hazard assessment of vanadium since mixture toxicity of field-collected sediments cannot be excluded.

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