Zirconium bis(hydrogen phosphate)

Endpoint summary

Additional information

Two literature studies on accumulation of Zr are available.

Garnham et al. (1993) investigated the accumulation of zirconium by microalgae and cyanobacteria. They incubated the different microalgae and cyanobacteria for up to 4 h in the light and the dark and in the presence of metabolic inhibitors. The "uptake" was completed after 5 min and no further uptake was shown after 4 h. Nevertheless, since also the "uptake" values weren`t different in the tests using the metabolic inhibitor it can be stated that the accumulation was due to a single phase of metabolism independent "biosorption" with no apparent intracellular uptake being observed. Therefore, no bioaccumulation occurred and the uptake values are rather worst-case adsorption values. Furthermore, a desorption experiment has been conducted showing a fast removal of Zr from the microalgae and cyanobacteria giving another indication for adsorption instead of accumulation.

Additionally, ECHA Guidance on Information Requirements and Chemical Safety Assessment Chapter R.7c: Endpoint specific guidance states "Data on apparent accumulation in small organisms, such as unicellular algae, Daphnia and micro-organisms, can be confounded by adsorption to cell or body surfaces leading to higher estimates of bioconcentration than is in fact the case (e.g. cationic substances may adsorb to negatively charged algal cells). Adsorption may also result in apparent deviation from first order kinetics and may be significant for small organisms because of their considerably larger surface/volume ratio compared with that for larger organisms." and "BCF values determined for other invertebrates (e.g. algae) should not be used, since they are prone to high uncertainty". Nevertheless, the found values are low and since they represent worst-case values a bioaccumulation of Zr is not expected.

Additionally, Ferrand et al. (2006) investigated the phytoavailability of zirconium in relation to its initial added form and soil characteristics. In this study, transfer of Zr from soil to tomato and pea plants was studied during a 7-day exposure period in two soils (an acidic and a calcareous soil) spiked with either a soluble (ZrOCl2 or Zr acetate) or an insoluble Zr compound (Zr(OH)4). Zr adsorbed and accumulated mainly in the roots, with Zr adsorption to the root surface being of minor relevance. Translocation to aerial parts was limited. TF (translocation factor) values for roots were the highest for Zr acetate and the lowest for Zr(OH)4. They were all <= 0.1. TF (translocation factor) values for aerial parts were all <= 0.005 and were also generally the highest for Zr acetate and the lowest for Zr(OH)4. The added Zr form highly influences its absorption. The ZrOCl2 form is the most available form and is strongly absorbed by pea plants. Nevertheless, the TF values (can be compared to a BSAF value) are at least below 0.1 showing a minor transfer from the soil into the plant. Additionally, since Zirconium bis(hydrogenphospahate) Zr(HPO4)2 has a very low solubility and, therefore, a very low availability, the test results out of this study can be used as a worst-case consideration and show that a bioaccumulation and a transfer in organisms is assumed to be low.