Abstract
Chromium is naturally occurring, but emission from anthropogenic sources can lead to increased soil concentrations. Information on its toxicokinetics is essential in order to understand the time needed to reach toxicity and the mechanisms of uptake/elimination. In this study the toxicokinetics of Cr(III) was evaluated using the soil standard species Enchytraeus crypticus. The animals were exposed to 180 mg Cr/kg dry soil, a sublethal concentration, in LUFA 2.2 natural soil. OECD guideline 317 was followed, with a 14-day uptake phase in spiked soil followed by a 14-day elimination in clean soil. Exposure to Cr led to fast uptake and elimination, with Ku = 0.012 kgsoil/kgorganism/day and Ke = 0.57 day−1. The bioaccumulation factor was 0.022, and DT50 for elimination was 1.2 days. The concentration of Cr reached an internal equilibrium in the animals after 10 days. Transfer to clean soil allowed body Cr concentrations to return to background levels after approximately 7 days. E. crypticus seemed able to efficiently regulate internal Cr concentrations by actively eliminating Cr (an essential element). Although Ku and Ke deviated from the values reported in other studies for other soil invertebrates, the bioaccumulation factors were similar. These findings show the importance of toxicokinetic studies in evaluating toxicity based on internal metal concentrations that can more accurately represent the bioavailable concentration.
Highlights
The naturally occurring element chromium (Cr) is present in soils, plants, and animals, as well as in other environmental compartments [1,2]
The CaCl2 -extractable concentration in the spiked soil was 0.25 mg Cr/kg soil DW, which decreased by about 40% to 0.15 mg Cr/kg soil DW on day 1 and remained constant during the rest of the uptake phase (Table 1)
At the start of exposure, internal metal concentrations are dependent on both exposure concentration and time, but after equilibrium is reached, internal concentrations are only related to exposure concentration [29]
Summary
The naturally occurring element chromium (Cr) is present in soils, plants, and animals, as well as in other environmental compartments [1,2]. The main contributions to Cr contamination in the environment are anthropogenic sources like emissions from metal smelters, industrial wastes and spills, and landfills [2–6]. The anthropogenic use of Cr includes organic fertilizers, leather tanning, application of Cr-containing compounds such as pigments, chromates, and corrosion inhibitors, among others [1,7]. The use of Cr may result in high levels of Cr in soil, potentially affecting biota [8]. Chromium exists in different oxidation states [9,10]. Chemical speciation affects the biogeochemical cycle of Cr, with Cr(III) being less soluble, toxic, and mobile than
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