California EPA approach

additional factor of 10. This is consistent with what is done in deriving

human health RfD values.

f. In cases where NOAELs are available as a dietary concentration (e.g.,

milligram contaminant per kilogram food), a consumption rate for marine

birds or marine mammals may be estimated based on various food intake

summaries (e.g., USEPA's Wildlife Exposure Factors Handbook

(USEPA/Office of Research and Development 1993)) and a corresponding

NOAEL may be calculated. This consumption rate is expressed as a

percentage of the animal's body weight on a wet weight basis or in units of

kilogram of food (wet weight) per kilogram of body weight per day

(kg/kg/day).

g. Some NOAEL values may be over conservative because they provide

information on which dose produces no effect, but not how much higher the

concentration has to be to produce an effect. Where the lowest NOAEL

available in the literature is so low that background concentrations will

produce a dose that exceeds it, reject the lowest NOAEL and use the next

highest NOAEL.

California EPA approach

The following description is adapted from the California EPA approach for

calculating toxicity factors (adapted from California EPA 1996).

a. Use toxicity data for representative species and members of the same

taxonomic family in estimating toxicity to representative species.

b. If data are lacking or judged inappropriate, use data for surrogate species

following application of one or more uncertainty factors (UFs). These UFs

may be based on data when available or, in the absence of data, on the

default values provided below.

(1) Apply a UF of 500 to adjust from less sensitive end points, such as

mortality, to a chronic NOAEL (e.g., LD50 to NOAEL Chronic).

(2) Apply a UF of 10 to adjust from an acute LOAEL to a chronic NOAEL

(e.g., LOAEL Acute to NOAEL Chronic).

(3) Apply a UF of 5 to adjust from LOAEL to NOAEL.

(4) Apply a UF of 1 for interspecies extrapolations within the same

taxonomic family (e.g., beagle to fox - canidae to canidae).

(5) Apply a UF of 5 for interspecies extrapolation within the same

taxonomic order.

(6) Apply a UF of 10 for interspecies extrapolation between taxonomic

orders.

Chapter 3 Ecological Exposure Assessment