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User's Guide and Technical Documentation
KABAM Version 1.0
(Kow (based) Aquatic BioAccumulation Model)
Appendix D
Selection of Mammal Species of Concern and Corresponding Biological Parameters
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Appendix D. Selection of Mammal Species of Concern and Corresponding Biological Parameters
Mammal species of concern were defined for use as default species in KABAM. Mammals were considered to be of concern for pesticide exposures through aquatic bioaccumulation if their diets incorporated freshwater aquatic animals. Specific species were identified using a Field Guide to Mammals of North America (Reid 2006). This guide contains information on the ranges, taxonomy, habits, feeding preferences, and habitats of mammals located in the continental United States, Canada, and Alaska.
A review of this source identified six species of mammals that consume aquatic animals. These include the American water shrew (Sorex palustris), the fog shrew (Sorex sonomae), the star-nosed mole (Condylura cristata), the marsh rice rat (Oryzomys palustris), the American mink (Mustela vison), and the Northern river otter (Lontra canadensis). Additional references were sought to obtain data on the body weights and feeding preferences of these mammals. These species are used in KABAM to represent mammals of concern for risks of pesticide exposures through aquatic bioaccumulation. Descriptions of these species are provided below. Information from these species descriptions were used to define the default parameters used to represent mammals in the KABAM tool.
D.1 Descriptions of Mammal Species
D.1.1. American Water Shrew (Sorex palustris)
The distribution of the American water shrew includes Canada, Alaska, and areas of the continental United States, including the West Coast, Rocky Mountains, Great Lakes, Appalachian, and New England areas. These shrews inhabit areas boarding fast and slow moving streams, marshes, creeks, and ponds. This species is primarily insectivorous, consuming aquatic invertebrates, such as stonefly nymphs, mayflies, caddisflies, and diptera. The American water shrew is also known to consume other animals, including fish, salamanders, leaches, and dead mice. Documented body weights range 0.008-0.018 kg, with males weighing more than females (Beneski and Stinson 1987).
D.1.2. Fog Shrew (Sorex sonomae)
Fog shrews inhabit parts of Oregon and California on the Pacific Coast in the "fog belt." This species is found in marshes, near streams, and in forests. Their diet includes insects, earthworms, centipedes, slugs, snails, and amphibians. Their weight ranges 0.0055-0.015 kg (Reid 2006, Smithsonian 2008).
D.1.3. Marsh Rice Rat (Oryzomys palustris)
Marsh rice rats are distributed in states along the Gulf of Mexico and East Coast of the United States. This species inhabits wetlands, marshes, swamps, meadows, and areas along streams. Its diet includes insects, fiddler crabs, snails, fish, clams, arthropods, wetland plants, seeds, fungus, baby turtles, bird eggs, and carrion (of mammals and birds). Their weight ranges 0.045-0.080 kg (Wolfe 1982).
Six subspecies of O. palustris have been recognized (Wolfe 1982). One of these subspecies, Oryzomys palustris natator has been federally listed as endangered since 1991. This subspecies is known to occur in Florida and has a designated critical habitat (USFWS 1993).
D.1.4. Star-nosed Mole (Condylura cristata)
The star-nosed mole is distributed throughout the Eastern and Great Lakes regions of the United States and Canada. It inhabits marshy areas and streams. The diet of this species includes aquatic annelids, aquatic insects, small fish, mollusks, crustaceans, grubs, and earthworms. Reported body weights range 0.034-0.085 kg. The weights of these animals do not differ by sex but by location within their geographic distribution range, with smaller animals being observed in the southern parts of the range (e.g., Tennessee) (Petersen and Yates 1980, Reid 2006, Smithsonian 2008).
D.1.5. American Mink (Mustela vison)
The American mink is distributed throughout the United States and Canada, except in the dry areas of Arizona, Nevada, California, Utah, and Texas. Mink inhabit wetlands and marshes. Their diet is composed mostly of fish, amphibians (frogs), crustaceans (crayfish and crabs), muskrats, and other small mammals. They will also consume squirrels, birds, bird eggs, reptiles, aquatic insects, earthworms, and snails if given the opportunity. Individual body weights vary based on range and sex, with females weighing less than males. Documented body weights of this species range 0.45-1.8 kg (Larivière 1999, USEPA 1993).
D.1.6. Northern River Otter (Lontra canadensis)
The historical distribution of the Northern river otter includes most of the United States and Canada. The current distribution of this species in the United States includes states bordering the Gulf of Mexico and Great Lakes, the East Coast, New England, the West Coast and Alaska, as well as Canada (Larivière and Walton 1998, Reid 2006). Northern river otters inhabit lakes, swamps, marshes, streams, and ponds. The diet of this species is primarily fish, but also includes frogs, crayfish, small mollusks, reptiles, birds, and fruits. Body weights range 5-15 kg, with males weighing more than females (USEPA 1993, Larivière and Walton 1998).
D.2 Determination of Mammalian Default Parameters for KABAM
Tables 7 and 8 of the KABAM tool allow the user to identify six mammal species of concern, their body weights and their diets. For the purpose of KABAM, mammalian species of concern include those that consume aquatic animals. Based on the information above, relevant species in the United States include the American water shrew, the fog shrew, the star-nosed mole, the marsh rice rat, the American mink, and the Northern river otter. A detailed version (with specific mammals identified) of the conceptual model of the aquatic ecosystem depicted in Figure I of the User's Guide is provided in Figure D1. Default values representing the body weights and diets of these mammals are described below.
Figure D1
Detailed conceptual model depicting aquatic food web, with mammals included.
Arrows depict direction of trophic transfer of bioaccumulated pesticides from lower levels to higher levels of the food web.
D.2.1. Identification of Default Body Weights for Mammalian Species
Body weight and diet are the parameters that distinguish one mammalian species from another within KABAM. Two pairs of species have similar body weights and diets, such that they can be grouped together. These pairs are
- the American water shrew and the fog shrew
- the star-nosed mole and the marsh rice rat.
The American mink and the northern river otter are sufficiently different in body weights to distinguish them as separate default species in the model.
The selected body weight value influences the estimates of pesticide exposure through consumption of contaminated food items, as well as dose-adjusted toxicity values. Therefore, the magnitude of the body weight parameter has an effect on the magnitude of the RQ. Since higher body weight values result in higher dose-based RQs, the higher body weight values were selected to represent the four groups of mammals used in KABAM. In order to bound risk estimates for the two heaviest species of mammals (i.e., American mink and Northern river otter), default parameters are set to the minimum and maximum body weights. The following values are suggested for inclusion in Table 7 of the KABAM tool to represent mammals 1-6:
Values Suggested for Inclusion in Table 7 of the KABAM Tool to Represent Mammals 1-6 Mammal # Name Body weight (kg) Mammal 1 Fog/Water Shrew 0.018 Mammal 2 Rice Rat/Star-nosed mole 0.085 Mammal 3 Small Mink 0.450 Mammal 4 Large Mink 1.800 Mammal 5 Small River Otter 5.000 Mammal 6 Large River Otter 15.000
D.2.2. Determination of Daily Food Intake
If the weight of a food item (i.e., aquatic trophic level) is less than that of the amount of food consumed by the mammal in one day, then the food item is a reasonable assignment. In order to determine whether or not a particular trophic level is relevant to a mammal, the daily food intake is estimated.
The dry food intake per day (Fdry, kg/day) for a mammal can be calculated according to Equation D1 (USEPA 1993). This value can be converted to represent food intake per day on a wet weight basis (Fwet, kg/day) by assuming that the diet of an organism is 75% water (Equation D2, see Appendix C for % water of aquatic organisms).
Equation D1
Fdry = 0.0687 * BW0.822
Equation D2
Fwet = Fdry / [1 - (% water of diet)]
The resulting wet food intakes per day for the mammalian species of concern for KABAM are provided in Table D1. This table presents food intake per day for each species based on the low and high ranges of the body weights. These wet food intakes can be used to assign appropriate aquatic animals to the default diets of these mammals.
Table D1
Low- and High-end Body Weights and Estimated Food Intake per Day of Mammals Which Consume Aquatic AnimalsSpecies Body Weight (kg) Dry Food Intake per day (kg) Wet Food Intake per day (kg) Percent Body Weight Consumed Daily Shrew (Water and Fog) 0.006 0.001 0.004 67% Shrew (Water and Fog) 0.018 0.003 0.010 56% Rice Rat, Star-nosed mole 0.034 0.004 0.017 50% Rice Rat, Star-nosed mole 0.085 0.009 0.036 42% Mink 0.450 0.036 0.143 31% Mink 1.800 0.111 0.446 25% River Otter 5.000 0.258 1.032 20% River Otter 15.000 0.636 2.545 17%
D.2.3. Definition of Default Diets of Mammals for use in KABAM
Water/fog shrew
The diets of the American water and fog shrews (see section D.1) include species that would be classified as benthic invertebrates (e.g., stonefly nymphs, mayflies, and snails) and fish (e.g., fish and amphibians) according to the trophic levels of KABAM. However, since these species are primarily insectivorous, the default diet is assigned as 100% benthic invertebrates.
Based on the daily food intake for these two species (Table E.1), it is reasonable to assume that these shrews can consume organisms in the small fish category. If interested in the potential acute risk to water/fog shrews from pesticides through consumption of fish/amphibians, the model user could define the diet of these mammals as 100% small fish. Since this represents a higher trophic level in the aquatic ecosystem than the benthic invertebrates, this assumption may result in a higher RQ.
Rice rat/star-nosed mole
The diets of the rice rat and the star-nosed mole (see section D.1) include species that would be classified as benthic invertebrates (e.g., arthropods, snails), filter feeders (e.g., clams) and fish according to the trophic levels of KABAM. Based on the daily food intake for these two species (Table E.1), it is reasonable to assume that individuals of these species could consume organisms in the small fish category. Since no data are available to define feeding preferences of these two species, for the purpose of KABAM, the default diet composition of these mammals is equally distributed among these three trophic levels (i.e., 34% benthic invertebrates, 33% filter feeders, and 33% small fish).
American mink
The diet of the American mink (see section D.1) includes species that would be classified as benthic invertebrates (e.g., crayfish) and small/medium-sized fish according to the trophic levels of KABAM. Based on the daily food intake for this species (Table E.1), it is reasonable to assume that these mammals could consume organisms in the small and medium fish category. The default diet for this mammal is 100% medium fish.
Northern river otter
The diet of the Northern river otter (see section D.1) is primarily fish, but also includes species that would be classified as benthic invertebrates (e.g., crayfish) according to the trophic levels of KABAM. Based on the daily food intake for this species (Table D.1), it is reasonable to assume that these mammals may consume organisms in the small, medium, and large fish categories. According to USEPA 1993, river otters have been documented as including various fish that would be classified in different trophic levels of KABAM, including sunfish and bass. Therefore, the default diet for this mammal is 100% medium fish for the small otter and 100% large fish for the large otter.