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Administrative data

Link to relevant study record(s)

Description of key information

Short description of key information on bioaccumulation potential result: 
A toxicokinetic assessment of bentonite acid leached has been written based on the available data

Key value for chemical safety assessment

Additional information



TEST MATERIAL: Bentonite acid leached


The test material bentonite acid leached (EC no 274-324-8) is a UVCB substance which consists of the following mineralogy: smectite (montmorillonite), amorphous silica, feldspar, sepiolite, kaolinite, and quartz. It is an off white solid which can compose of fine, medium and coarse grades.   


In a water solubility study with bentonite acid leached the nominal loading rate of 1.0 g/l confirmed that bentonite acid leached was essentially insoluble in water, with less than 1.0 mg/l of each element being detected in solution with the exception of calcium (1.6 mg/l) (O’Connor & Woolley 2010a).  


Solubility of bentonite acid leached was also assessed in artificial gastric fluid and simulated alveolar fluid. Analytical verification of the following elements sodium, magnesium, aluminium, silicon, potassium and calcium) equated to a total solubility of ~ 1% (O’Connor & Woolley 2010b).  


Particle size analysis of a typical sample of medium grade sample showed that 75.5% of particles were smaller than 100µm only 0.14% of particles were smaller than 10 µm (O’Connor & Woolley 2010c).  


In the acute inhalation study the 4 hr LC50of bentonite acid leached was calculated to be 50 mg/L (Nitka 1988). As such although bentonite acid leached has the potential to be inhaled due to its particle size distribution it doesn’t exhibit inhalation toxicity at a high dose in the rat.Since the test material has a low solubility in artificial alveolar fluid it is considered the inhaled test material will not be absorbed. 


The acute oral median lethal dose (LD50) of the test material was estimated to be > 5000 mg/kg bw (Nitka 1985). As such, the test material has a very low potential for toxicity by oral absorption. The LD50 in the dermal toxicity study was > 2000 mg/kg (Bradshaw 2010). In conclusion, the test material has a low potential for any absorption by oral ingestion and dermal absorption.


Since the test material has a low potential for absorption by any route it means that the test material will not be readily bioavailable. The majority of any test material that is ingested orally is likely to pass through the gastrointestinal (GI) tract unchanged and be excreted in the faeces. Any small amount of constituents from the test material that are absorbed by the gut will enter the essential elemental pool along with those that are absorbed from the daily nutritional requirement of elements and therefore are not considered to be of any toxicological significance.  


The following conclusion is taken from the UNEP (2004) report for synthetic and amorphous silicas regarding absorption, disposition and elimination which may be considered relevant for the test material which also contains amorphous silica and quartz:


Analytical data on the kinetics of silica deposition in the lung of experimental animals during and after prolonged exposure to silica are largely consistent. The initial uptake phase is characterized by relatively high deposition followed by a phase of low increase. Synthetic amorphous silicas are rapidly eliminated from the lung tissue, whereas crystalline silica exhibits a marked tendency to accumulate. No disproportionate deposition of synthetic amorphous silica occurs in the lymph nodes.


After oral ingestion, there is no accumulation of synthetic amorphous silica in body tissues. Upon cessation of exposure rapid elimination occurs. Intestinal resorption appears to be insignificant in animals and humans the human test, the small apparent increases in the urine output of human volunteers were remarkably low as compared with the high dose of 2500 mg SiO2applied subcutaneously are subjected to rapid dissolution and removal.




O’Connor & Woolley 2010a Bentonite acid-leached: Determination of general physico-chemical properties Harlan Laboratories Ltd, Project no 2881/0001


O’Connor & Woolley 2010b Bentonite acid leached: Determination of solubility in simulated gastric fluid and simulated alveolar lung fluid Harlan Laboratories Ltd, Project no 2881/0015


O’Connor & Woolley 2010c Bentonite acid-leached: Determination of general physico-chemical properties Harlan Laboratories Ltd, Project no 2881/0001


Nitka S (1988) Acute inhalation toxicity in rats, Consumer Product Testing, Report no 88047-2.


Nitka S (1985) Acute oral toxicity in rats, Consumer Product Testing, Report no 85365-4.


Bradshaw (2010) Bentonite acid-leached: Acute dermal toxicity (limit test) in the rat, Harlan Laboratories Ltd, Project no 2881/0003


UNEP(2004) Synthetic amorphous silica and silicates - SIDS Initial Assessment Report for 19. UNEP