Chromium

Bioaccumulation: aquatic / sediment

Description of key information

As underlined in the risk characterization document: “Environmental Risk Assessment Report – Metallic Chromium and Trivalent Chromium Compounds” (2008) one aspect to consider in this section is that chromium (III) is an essential element, needed for growth and development of micro-organisms, animals and humans. The chromium hazard potency is also defined by the homeostasis as micro-element and summarized in the same document as follows:

“Natural chromium levels, available for animals living in a specific environment, depend on the natural geological and physico-chemical characteristics of the water, sediments and soils. To ensure appropriate chromium tissue levels without causing toxicity from chromium excess, it is expected that internal chromium levels are homeostatically regulated by all living organisms. Homeostatic regulation of chromium allows organisms, within certain limits, to maintain the physiologically required levels of chromium in their various tissues, both at low and high chromium intakes.”

 

Several parameters are taken into consideration to define the bioaccumulation potential as Bioaccumulation potential is part of the assessment of PBT/vPvB properties. Bioaccumulation refers to uptake from all environmental sources including water, food and sediment. Bioaccumulation is defined by bioconcentration which is the accumulation of a substance dissolved in water by an aquatic organism. The bioconcentration factor (BCF [l/kg]) is defined as the ratio of the concentration of a substance in an organism to the concentration in water once a steady state has been reached.

 

Bioaccumulation is also impacted by the Biomagnification concept which refers to accumulation through the food chain. It can be defined as an increase in the internal (fat normalized) concentration of a substance in organisms at consecutive trophic levels in a food chain.

 

The poor solubility of chromium (III) is expected to determine its behavior and fate in the environment, and subsequently its potential for ecotoxicity. Indeed, a transformation/dissolution test (OECD Series on Testing and Assessment Number 29, 2001) of Chromium metal powder at a loading of 1 mg/L at pH 6 and pH 8 resulted in total Chromium and Cr6+ concentrations below the respective reporting limits (Cr: 0.5 µg/L, Cr6+: 0.05 µg/L) for all measured timepoints (24h, 7d, 28d). Therefore, the extent to which Chromium metal powder can produce soluble available ionic and other metal-bearing species in aqueous media, is limited.

 

This means that rate, soluble (bio)available ionic & other chromium-bearing species in environmental media is limited.

This endpoint includes several published studies that calculated BCF (Bioconcentration Factors), BAF (Bioaccumulation factor) and BSAF (Biota-sediment accumulation factors) for several species at different trophic levels in situ. All considered studies are Klimisch 2 quoted.

 

From sediment to cyanobacteria, algae and fishes, the studies demonstrate the absence of biomagnification in the food chain (Dsikowitzky et al., 2013; Hsieh et al. 2013; Cheng et al., 2013; Di Veroli et al., 2014; Milošković et al., 2016) and confirm the conclusion established by WHO n 2009.

 

The absence of biomagnification across the aquatic food chain was already established by WHO (2009) in the “Concise International Chemical Assessment Document 76 INORGANIC CHROMIUM(III) COMPOUNDS” report and summarized as follows:

“Chromium is not expected to biomagnify in the aquatic food-chain.”

 

Additional information

The solubility of metallic chromium is negligible. The amount of dissolved ionic species is so low that it does not significantly contribute to the environmental chromium concentrations in air, water, sediment or soil. The resulting levels are also far below toxic concentrations.