Over the past two decades, much information has been assembled demonstrating that an organism’s trophic position in the aquatic food web can have an important effect on the magnitude of bioaccumulation of certain chemicals. 

In order to account for the variation in bioaccumulation that is due to the trophic position of the organism, the 2000 Human Health Methodology recommends that BAFs be determined and applied on a trophic level-specific basis. Hence, three national BAFs are derived; one for aquatic organisms in each of trophic levels 2, 3, and 4.

Accordingly the “FI times BAF” term in the equations is the sum of (FI_TL2 x BAF_TL2) + (FI_TL3 x BAF_TL3) + (FI_TL4 x BAF_TL4).

Guidance on trophic level-specific intakes is provided in the 2000 methodology on page 4-27.

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