Initial Estimate of Exposure Point Concentration for Total PCBs (Cont.)

As indicated earlier, the upper 95th-percent confidence limit of the arithmetic

average total PCB concentration in the sediments from the proposed dredging

project area is 1ug total PCB /g sediment.

The upper 95th-percent confidence limit of the arithmetic average of total PCB

in sediments at the reference site is 0.10 ug total PCB/g. The assessment assumes

that this is the exposure point concentration for winter flounder when foraging

away from the site and its area of influence.

The average fraction lipid of a flounder is 0.1, based on hypothetical data

provided by a fisheries agency.

Therefore, the average sediment exposure concentration of total PCB, Cs, at

the disposal site is:

(1 H 0.5) + (0.1 H 0.5) = 0.55 ug total PCB/g sediment

The state has also supplied data indicating that the fraction organic carbon in

sediments in the area is 0.05 (5 percent).

A locally calculated biota sediment accumulation factor (BSAF) is 3, based

on USEPA studies of PCB in flounder and sediment in this bay. The projected

body burden (weight wet), Ca, to a flounder exposed to this total PCB

concentration in sediments of 5 percent organic carbon is:

(0.55/Foc) H BSAF H (Fl)

(0.55/.05) H 3 H 0.1

3.3 ug total PCB/g wet weight flounder tissue

This body burden value can be used in both human health and ecological risk

assessments.

This example could have used a different species such as lobster. In that case,

the general method would remain the same, but parameters such as foraging area,

bioaccumulation factor, and fraction lipid would differ. Also, the example is

relatively simple in that it does not address differential uptake and storage of

PCB congeners among tissues. In some instances, it may be important to estimate

uptake in organs other than muscle. For example, lobster hepatopancreas has a

different fraction lipid than lobster muscle. In a human health risk assessment,

where some individuals in a population may consume the hepatopancreas, it

becomes important to calculate a separate concentration for that tissue based on

its particular lipid content.

F10

Appendix F Hypothetical Example