Selection of a Toxicity Factor for Exposure of Winter Flounder to Total PCBs

Selection of a Toxicity Factor for Exposure of Winter

Flounder to Total PCBs

Black et al. (1998) assessed the effects of PCBs on the reproduction of a fish

using Fundulus heteroclitus (marine minnow) as an experimental organism. They

measured a Lowest Observed Adverse Effect Level (LOAEL) at 3.8 ug PCB/g

wet weight and a No Observed Adverse Effect Level (NOAEL) of 0.76 ug PCB/g

wet weight. The risk assessor chose a body burden of 0.76 ug PCBs/g wet weight

as the toxicity factor. This is an appropriate toxicity factor because:

a. It addresses toxicity to total PCBs, the COC.

b. It is from a study which includes the measurement of a NOAEL as well

as a LOAEL.

Black et al. (1998) describe the end points in the study as female mortality

and decreased egg production, therefore, the toxicity factor relates to the

assessment end point "Health and Maintenance of the Local Flounder

Population."

Risk to Flounder

The appropriate method to assess risk to flounder is to compare a measured

effect level for body burden of PCBs in flounder to the calculated flounder body

burden. As indicated earlier, the selected toxicity factor is 0.76 ug PCB/g wet

weight. This is less than the 3.3 ug PCB /g body tissue concentration calculated

for winter flounder in this example. Therefore, the assessment shows that there is

potential for risk to the selected receptor, winter flounder. At this point, the risk

assessor and risk mangers can:

a. Accept the initial conclusion and employ risk management activities.

b. Employ more complex fate and transport models and perhaps a more

complex food chain model and recalculate risk.

The conclusion of risk from the initial estimates has various sources of

uncertainty including:

a. Uncertainty concerning the actual foraging area of a flounder.

b. Uncertainty concerning the BSAF - the assessment used the

recommended BSAF of 3 which may be overly conservative. A more

sophisticated food chain model may give a more realistic estimate of

body burden.

c. Uncertainty associated with possible interspecies differences between the

experimental organism, Fundulus heteroclitus, and the flounder.

F11

Appendix F Hypothetical Example