Example 13: 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 an 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 an NOAEL as well as an LOAEL.

Black et al. 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."

Gas Research Institute (GRI) approach for developing toxicity

factors

The Gas Research Institute (GRI 1996) has developed a protocol for selecting or

developing toxicity factors for a COC. It includes the following:

a. Select a value if an appropriate state or Federal agency has proposed it.

b. In the absence of a proposed value and if data are available on NOAELs for

the receptor species or for species that are phylogenetically and ecologically

similar to the selected receptor species (e.g., from the same family of birds

or mammals), select the lowest NOAEL.

c. If NOAELs for phylogenetically similar species are unavailable, the

assessment adjusts NOAEL values for other species (as closely related as

possible) by dividing by a factor of 10 to account for extrapolations

between families or orders. The lowest NOAEL is used whenever several

studies are available. This interfamily extrapolation is similar to EPA's

derivation of human health reference dose (RfD) values, where animal

studies are extrapolated to humans by dividing by a factor of 10.

d. In the absence of appropriate NOAELs, if LOAELs (the lowest concentra-

tion, dose, or body burden available in the literature at which an effect

occurs) are available for phylogenetically similar species, divide these by a

factor of 10 to account for an LOAEL-to-NOAEL conversion. The LOAEL

to NOAEL conversion is similar to EPA derivation of human health RfD

values, where LOAEL studies are adjusted by a factor of 10 to estimate

NOAEL values.

e. For calculating chronic toxicity values from data for subchronic tests (e.g.,

acute data), the resultant LOAEL or NOAEL values are divided by an

Chapter 3 Ecological Exposure Assessment