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Environmental fate & pathways

Bioaccumulation: terrestrial

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In general, cobalt is not largely concentrated from soil into plant or soil into invertebrate or vertebrates, with BCF/BSAFs or trophic ratios less than 5. Six studies were of sufficient quality to meet data quality objectives. With a BSAF of 0.0586, the terrestrial earthworm study by Crossley et al (1995) indicates that earthworms assimilate only small amounts of cobalt from mineral soil, and that any assimilation of cobalt must be from the organic fraction of soils. The study of He et al. (2015) reported a BCF of 5L/Kg in an annelid worm Echytraeus crypticus exposed to cobalt in quartz sand. The review by Gal et al (2008) reiterates this finding, with a BCF <<0.5 for most plants. This has been further demonstrated in empirical data of food crops e.g. tomato with reported BCF of >0.0036 to < 0.102 (Gitet et al. 2016), mean BSAF of 10 tobacco varieties of 0.44 (Liu et al. 2019), and slightly higher whole body BCF of 1-1.5 m3/Kg in tropical evergreen shrub Acalypha wilkesiana (Lya et al. 2018). Plant hyperaccumulators have been identified that have the ability to accumulate especially high concentrations of cobalt (concentrations ranging from 0 to 1400 ppm). The distribution of cobalt in plants is species dependent and cobalt availability is associated with cobalt bioavailability from soil being a function of soil pH and MnO2levels. In a review of vertebrate metals bioaccumulation with a number of elements, Sample et al (1998; Environmental Sciences Division Publication No. 4783, prepared for the U.S. Department of Energy, Office of Environemental Policy and Assistance, Air, Water, and Radiation Division) showed that uptake ratios from soil to organism for cobalt is < 0.2, even accounting for dietary variability, i.e.herbivore (diet consisting primarily of plant material), and omnivore (diet consisting of both animal and plant material).