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Bioconcentration and bioaccumulation are considered to be the partitioning of compounds between the lipid phase of an organism and water (Veith, 1979).Chemicals accumulate in organisms when they were taken up and stored in tissues of organism faster than were metabolised or excreted. Fatty acids occur naturally in all aquatic organisms and are ubiquitous any dynamic in the aquatic environment, where fatty acids are readily biodegraded in an aerobic environment by microorganisms.

Microbial metabolism is the primary route of degradation in aquatic environment. As nutritional energy source, fatty acids are absorbed by different uptake mechanisms in mammals depending on the chain length. Short- and medium chain fatty acids (C1 - C12) are rapidly absorbed via intestine capillaries into the blood stream. In contrast, long chain fatty acids (>C12) are absorbed into the walls of the intestinevilli and assembled into triglycerides, which then are transported in the blood stream via lipoprotein particles (chylomicrons). In the body, fatty acids are metabolised by various routes to provide energy. Besides this, fatty acids are stored as lipids in adipose tissue and as  precursors for signalling molecules and even long chain fatty. In addition fatty acids are an integral part of the cell membranes of every living origanism from bacteria and algae to higher plants. Fatty acids are known to be easily metabolised. The rate of metabolism of fatty acids was considered to vary in proportion to their water solubility (Lloyd, 1957).  Odle (1989) investigated the utilisation of triglyceride containing medium chain (C8, C9 and C10) and long chain (> C16) of fatty acids in pigs within 48 h. The results showed that the medium chain fatty acids may be better utilized than long chain fatty acids, where the maximum concentrations of 3-OH-butyrat (BHBA) in blood and plasma medium chain fatty acids reached 2 hours after forced-feeding.

To understand how muscle lipid metabolism is regulated in fish, using sarcolemmal vesicles isolated from both red and white muscle fibers and palmitate as a representative long chain fatty acid (LCFA), Richards et al. were able to demonstrate that LCFA uptake by both trout red and white muscle is via a protein mediated carrier, which may share some similarities with the mammalian counterpart (e.g., SSO sensitivity). Although the maximal uptake rate of vesicles from red fibers was about twice that of white fibers, the affinities of the two for palmitate were similar. However, in contrasts with what is seen in mammals, as palmitate uptake by vesicles from both red and white muscle was not increased with the enhance of lipid use.

A non-GLP but well documented fish accumulation study is available on a C12 fatty acid –sodium laurate (van Egmond, 1999), in which showed negligible evidence of bioaccumulation potential in fish tissue with an estimated BFC of 255 L/kg after 28 days exposure. Furthermore, of various fatty acids tested, uptake is highest with the long-chain acids (G-G), with no marked difference due to unsaturation. Un-saturated acids (oleic and linoleic) and a short-chain acid (caprylic) are partly adsorbed to fish muscle proteins so strongly that they cannot be extracted with acid isopropanolheptane (Czub, 2007).

Although the range of logKow values given suggests that fatty acids with chain length greater than C12 may be expected to have tendency of a higher bioaccumulation. However, this takes into account of the physicochemical properties of chemicals and only indicates intrinsic potential of the substance, but not of its behaviour in the environment, for instance, biodegradation, and in living organism, for example, metabolism. Whereas, a bioconcentration derived from experiments using radiolabelled compounds, in which differentiation between parent compounds and metabolites or other breakdown products is not possible. Furthermore, as fatty acids are the end products of carbohydrate metabolism in living organisms muscle tissues, an evaluation of anthropogenic distribution of fatty acids based on the concentrations determined in the organs and tissues of aquatic organisms may overestimated.

 

In conclusion, fatty acids are considered no real risk to aquatic organisms from their bioconcentration and biomagnification properties. The bioconcentration factors of fatty acids are generally below the level of concern. Hence, no classification to chronic hazardous to environment needs to be assigned.

 

Lloyd, L. E. and Crampton, E. W. (1957). The relation between certain characteristics of fats and oils and their apparent digestibility by young pigs, young

guinea-pigs and pups. J. Anita. Sci. 16:377.

 

Veith GD., De Foe DL, Bergstedt BV (1979) Measuring and estimating the bioconcentration of chemicals in fish. J. Fish. Res. Bd. Can. 36, 1040–1048.Mancha, 1997

 

Odle J., et. al. (1989). Utilization of Medium-Chain Triglycerides by Neonatal Piglets: Effects of Even- and Odd-Chain Triglyceride Consumption over the First 2 Days of Life on Blood Metabolites and Urinary, J Anim Sci 1989. 67:3340-3351.

 

Czub, G., et. al. (2007) Influence of the temperature gradient in blubber on the bioaccumulation of persistent lipophilic organic chemicals in seals. Environ. Tox. Chem., Vol. 26, No. 8, pp. 1600–1605,