The Effect Of Metal Content On Different Trophic Levels

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The significant variations of metal content in species of the same and different trophic levels (Table 3.2) imply that species, more than the trophic category, was the factor which best explained the variability observed in the concentration of metals in terrestrial organisms. This may be bound up their species-specific ability of active excretion of heavy metal ions and/or their ecological characteristics (Van Straalen and Van Wensem 1986; Grodziniska et al. 1987). This find is conforming to Mackay et al. (1997), who stated that “it may be the physiology of an organism, and not the trophic level which determines the internal concentration of heavy metals”. Likewise, this find, to some extent, accords with the observations of Hernández et…show more content…
However, these bioaccumulation factors increased in case of Cu (from the secondary consumers) of El-Manzala, and Pb of Al-Tebbin until the fourth trophic level of the food web. In relation to the bioaccumulation factors of metals along trophic levels, Zn shows the most consistent trend in both regions (Table 3.3). Although the higher bioaccumulation factors for all metals were noted for primary consumers at the second trophic level, bioaccumulation factors for Pb in El-Manzala (3.7) and in Al-Tebbin (1.4) were higher at the third and fourth trophic levels, respectively. Lead of the two investigated food webs had the highest frequency of biomagnification factors that are more than 1.0, whereas the lowest frequency of bioaccumulation factors that are more than 1.0 was noted for Cd and Zn. Among 46 bioaccumulation factors calculated for Pb, 26 were above 1.0, but at the same time, as many as 18 were lower than 1.0. The minimum bioaccumulation value (Cd) reached as low as 0.001, and the maximum one (Cd) reached as high as 50.0 in El-Manzala.

Calculation of bioaccumulation factors values indicated that accumulation of heavy metals was more frequent in arthropods and other taxa at lower trophic levels of the food web. In contrast, concentrations of metals decreased in animal species at higher trophic levels, suggesting that the transfer of trace metals along the vertebrate
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