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Environmental fate & pathways

Bioaccumulation: aquatic / sediment

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Bioaccumulation for cryolite is not to be expected as the substance dissociates into various ions. Data is available on uptake and metabolism of fluoride and aluminium ions. The availability of inorganic substances for uptake may vary depending on factors such as pH, hardness, temperature and redox conditions, all of which may affect speciation. BCF values will therefore be influenced by water chemistry. In general, only dissolved ions are potentially available for direct uptake.

Several authors have studied the bioaccumulation factor of aluminium in fish. Cleveland et al. (1986) exposed brook trout (Salvelinus fontinalis) eggs, larvae and juveniles to 300 µg/L total aluminium at three pH levels. At 30 days post-hatch for larvae and for an exposure period of 30 days for juveniles (37 to 67 days), significantly more aluminium was accumulated at pH 5.28 than at either pH 7.24 or 4.44. Aluminium levels at pH 5.28 were 398 and 112 mg/kg for the larvae and juveniles, respectively. At pH 7.24 residues were 12 and 33 mg/kg, and at pH 4.44, 71 and 17 mg/kg, respectively. The corresponding BCF values s were 1,327 and 373 L/kg at pH 5.28, 40 and 110 L/kg at pH 7.24 and 237 and 57 L/kg at pH 4.44.

In another study Cleveland et al. (1991) maintained brook trout in water containing 200 µg/L total aluminium at pH values of 5.0, 6.0 and 7.2 for 56 days. Estimated steady state bioconcentration factors for aluminium, which were inversely related to pH, were 215 L/kg at pH 5.3, 123 L/kg at pH 6.1 and 36 L/kg at pH 7.2. Elimination during the 28-day depuration phase was more rapid at pH 5.3 than at pH 6.1 or 7.2.

Karlsson-Norrgren et al. (1986) found that brown trout (Salmo trutta) accumulated significantly more aluminium in gill tissue at pH 5.5 than at pH 7.0 (60-160 µg/kg and 10-40 µg/kg dry weight, respectively) when exposed to 200-500 µg total aluminium/L. Skogheim et al. (1984) found a gill aluminium accumulation of 70 to 341 µg/g fresh weight in dying Atlantic salmon (Salmo salar) during an episodic fish kill in the river Ogna, Norway, at pH 5.4-5.5 and total aluminium and labile aluminium concentrations of 160 and 130 µg/L, respectively.

Segner et al. (1988) exposed young brown trout (Salmo trutta) to total aluminium (230 µg/L) at pH 5.0 in high calcium water at a temperature of 12°C for 5 days. Whole body aluminium concentrations were 230 mg/kg dry weight in aluminium-exposed fish, as compared to 75 mg/kg (pH 5.0) and 44 mg/kg (pH 7.2) for fish in aluminium-free water.

Also the bioaccumulation of fluoride in fish is extensively studied. In fish uptake occurs both in soft tissue and bone. As in other vertebrates, a higher level is found in osseous tissue than in muscles. Fish (Catla catla) exposed for 4 days to an effluent containing 4, 7 or 13 mg/L contained 3, 4 and 9 times more fluoride than control fish, respectively, on the basis of dry weights. BCF values were similar: 53 to 58 L/kg dw (Pillai and Mane, 1985). BCF for brown trout (Salmo trutta) were ≤2 L/kg ww after exposure for 1 week to 5, 10 or 20 mg/L (Wright, 1977). It is not clear whether or not equilibrium levels were reached in these accumulation studies.

In an experimental marine mesocosm study with fish, crustaceans and plants, F was found to accumulate in all species. The highest value, 149 L/kg, was found in fish. BCF values for crustaceans ranged from 27 to 62 L/kg, plants did not accumulate fluoride (Hemens and Warwick, 1972).

As extensive data is available for the dissolved ions that are potentially available for direct uptake, and which do not indicate that cryolite would be bioaccumulative a BCF test on cryolite itself does not seem necessary.