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Bioaccumulation: aquatic / sediment

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No fully reliable bioaccumulation studies are available, so measured data from different aquatic organisms have been used to calculate tentative BCF values. For those studies which included measured data for both water and organism samples the BCF varies between 2.9 - 28.6 for freshwater and <5 - 114 for marine water.
The diantimony trioxide risk assessment relied upon studies in which the concentrations measured in aquatic organisms were compared to monitoring data from other studies. The BCF reported varied between 40 and 15000 for marine fish, whereas for freshwater fish the BCF values were lower, with the highest being 14. For invertebrates tentative BCFs in the range of 4000 - 5000 were calculated.These values were also used in OECD (2008).
As there is a considerable uncertainty in these BCF values the risk characterisation for secondary poisoning in the EU RAR for diantimony trioxide was performed using both a BCF of 40 and a BCF of 15000. The BCF of 15000 gave very unrealistic results, whilst the BCF of 40 predicted concentrations similar to those observed in the environment. The EU RAR for diantimony trioxide therefore concluded that a BCF of 40 was appropriate for use in the assessment of both fresh and marine water. A BCF of 40 is very similar to the BCF calculated from studies which monitored concentrations in both the water and exposed organisms so will also be used in this risk assessment.The bioaccumulation potential of antimony in natural ecosystems is considered to be low. It is therefore concluded that antimony does not meet the bioaccumulation criteria (BCF >2000 l/kg) as set out in the definitive criteria for PBT assessment and listed in Annex XIII of REACH.

Key value for chemical safety assessment

Additional information

There are no standard laboratory studies designed to measure the bioaccumulation of antimony. Tentative bioconcentration factors can be estimated using results from monitoring studies where the concentration of antimony has been measured in different aquatic organisms.

The EU RAR for diantimony trioxide largely relied on studies that compared measured concentrations in sampled organisms with concentrations in water measured by other researchers.

One study calculated bioconcentration factors for a number of elements, including antimony, for fish, invertebrates and plants in both marine and freshwater environments based on literature data. The concentration factors were based on the concentration of the elements expressed in ppm (in water) and ppm of wet weight (in aquatic organisms). When elemental concentrations were reported otherwise (i.e. as units of dry or ash weight of an aquatic organism), the value was converted to wet weight with the assumption that wet weight values are 10 percent of values reported as dry weight and one percent of values reported as ash weight. The concentration of the element in seawater was selected from the literature to be representative of the continental shelf or estuarine waters, since the majority of seafood is harvested from these inshore waters. The representative concentration of antimony was chosen to be 0.5ug/l.

A study calculated a bioconcentration factor for antimony of 16,000 (8/0.0005) in oyster, using the concentration 8 mg Sb/kg ww . In another study, six samples each of the three species of bivalves,Ostrea sinuate,Pecten novae-zelandiaeandMytilus edulis aoteanus,were sampled 18 km north of Nelson, New Zealand, at a depth of 22 m in the Tasman Bay. The content of trace elements, among them antimony, was determined i) in the whole animal excluding shells, ii) in the shells, iii) in the individual dissected organs and also iv) in sediment. Antimony was below the detection limit of 30 mg Sb/kg dw in all samples, except for the muscle of the oysterOstrea sinuate, where a concentration of 80 mg/kg dw was measured.

For marine fish, a bioconcentration factor of 40 was derived using a concentration of 0.02 mg Sb/kg ww derived from literature . In a report the chemical composition of marine organisms was reported for a number of species and elements. A value of 0.2 mg Sb/kg dw in this book is given for both the spiny dogfish (Squalus acanthias) (eviscerated) and Goldsinny (Ctenolabrus rupestris) (whole).

In a large survey trace element levels, including antimony, were determined in tissues of finfish, molluscs and crustaceans taken from 198 sites around the US coast, including Alaska and Hawaii. Muscle was analysed from 159 species of finfish, liver from 82, whole fish from 17, molluscs from 18, and crustaceans from 16 species. The mean levels of antimony in most finfish muscles and livers fell in the range 0.5-0.9 mg/kg. Most species of whole finfish had antimony levels between 1.0 and 3.0 mg Sb/kg. Most shellfish species displayed mean antimony levels between 0.8 and 1.0 mg Sb/kg. The report does not clearly state on what basis (dry weight, wet weight etc.) the reported concentrations are given. It is assumed that they are given on a wet weight basis. Tentative BCF values for whole finfish and shellfish would be in the range of 5000-15000, and 4000-5000, respectively, using a concentration of antimony in marine waters of 0.2 µg Sb/l.

A study measured the concentration of a number of metals, including antimony, in freshwater fish from a lake free of major industrial development (Moose Lake) and from lakes in a highly industrialised area (Lower Great Lakes basin). All samples were composite samples consisting of at least 2.5 kg or three fish. In the majority of samples the number of fish used was larger than three. Samples were prepared as follows: headless dressed fish (at least three) were ground and thoroughly mixed and stored at -40 ºC until analysis. Antimony was analysed using Neutron Activation. The concentration of antimony in the water of the lakes was not measured in the study. Tentative BCFs were calculated in the EU RAR using an estimated antimony concentration in surface water of 0.3 µg Sb/l. The resulting BCF values are presented above.

In addition to these studies, the EU RAR also reported two studies which had measured concentrations in both the exposed organisms and the water.

A study measured antimony in marine organisms and waters from South Eastern Australia using HG-AAS. Water was filtered through a 0.45 μm filter. Samples of macroalgae were washed with distilled water to remove salts, freeze dried and ground to pass a 200 μm sieve. Animals were separated into component tissues and composites prepared by combining the tissues of five freeze dried specimens of each sample. The concentration measured in the marine water (140ºE, 51.5ºS) was 0.17 ± 0.02 μg Sb/l. Tentative bioconcentration factors were calculated using the concentrations in biota and in water, and a conversion factor of 10 between concentrations in dry weight and wet weight. The resulting bioconcentration factors for algae, mollusc tissues, crustacean tissues, and fish muscle are 55 - 114, 18 - 35, 11 and 68, and < 5-6, respectively.

A study evaluated the relationships between concentrations accumulated by specimens of the amphipodHyalella aztecaand concentrations in water for 27 metals (including antimony) in a field deployment in two metal-contaminated rivers in northwestern. The amphipods were placed along with natural food items in small acrylic cages and left in six riverine sites for 17 days. Based on the findings of another study, which showed that the dissolved phase was the dominant route of metal accumulation for 24 (including antimony) of the 27 metals, the authors concluded that biouptake of metals in nature byHyalellais mainly due to bioconcentration and therefore adequately represents a field BCF. The use ofHyalellafor deriving a BCF is supported by the findings of another study who developed a mechanistically based saturation model for bioaccumulation of metals inHyalella aztecain the laboratory. Although this results in a BCF that decreases with increasing concentrations of metal in the water, a background-corrected BCF at low water concentration can be calculated from the slope of the bioaccumulation curve at metal concentrations in water approaching 0 . The BCFs in a field study could not be determined using the full bioaccumulation curve because none of the transplant sites had enough metal concentrations to reach the plateau region of bioaccumulation corresponding to maximum uptake.

Presently, no criteria exist for the measurement of BCFs and BAFs in the field. However, the approach taken in a study included key characteristics of methodologies for deriving BCF values, namely:

- the requirement of at least three low exposure (i.e. substantially below acute toxicity) treatment levels per metal for the test species. The authors used three deployments per river.

- for a given metal the requirement to obtain an absorption isotherm with a slope of approximately 1; this isotherm is defined as the log-log relationship between the chemical concentration in the test organism and that in the water. This condition is equivalent to reaching steady-state between organism and water “compartments” for the metal studied.

However, for all sites, except one, the measured concentration of antimony in theHyalellaor in the water, or both, was below the detection limit. The BCF value calculated for the only remaining site where the mean measured concentration of both theHyalellaand the water was above the detection limit, is 5.6. Although not fully reliable, the study indicates that the bioaccumulation of antimony inHyalellais low.

An additional study has since been identified that investigates the bioaccumulation of antimony. The authors exposed caged brown trout (Salmo trutta) to water contaminated with various metals downstream of a firing range. Fish were exposed for up to 23 days with concentrations in the water and fish gills and liver determined on days 2, 4, 7, 9, 11 and 23. The concentrations of antimony remained relatively stable throughout the exposure period (2.1 -3.1 µg Sb/l). The concentrations of antimony measured in the fish gills and liver were variable over the exposure period. The authors note that the measured concentrations were close to the analytical limit of detection, which makes them subject to greater uncertainty. In addition, the concentrations in the fish are reported in graphical format only. However, the BCF based on data reported in this study ranges from 4.5 - 28.6, indicating a low potential for bioaccumulation.