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Lead concentrations in bullfrog Rana catesbeiana and green frog R. clamitans tadpoles inhabiting highway drainages
Environmental Pollution (Series A) 40 (1986) 233-247
Lead Concentrations in Bullfrog Rana catesbeiana and Green Frog R. clamitans Tadpoles Inhabiting Highway Drainages
Charles W. Birdsall, Christian E. Grue* & Allen Anderson US Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, Maryland 20708, USA
A BSTRA CT Lead concentrations were determined in sediment and tadpoles of bullfrogs R a n a catesbeiana and green frogs R. clamitans from drainages along highways with different daily average traffic volumes (range, 4272 to 108800 vehicles d a y - i ) andj~'om ponds >_ 0.4 km from the nearest highway. Lead concentrations (mg kg-1 dry weight) in sediment (7.8 to 940) were usually greater (4-5 times) than those in the tadpoles (bullfrog, 0"07 to 270; green frog, 0"90 to 2 4 0 m g k g - i ) . Lead concentrations in sediment (r = 0.63) and in both species of tadpoh, s (bullfrog, r = 0.69; green frog, r = 0.57) were positively correlated with average daily traffic volume. Lead concentrations in both species of tadpoles (bullfrog, r = O. 76; green frog, r = O"75) were also positively correlated with lead concentrations in sediment. At sites where both bullfrog and green frog tadpoles were collected, lead concentrations in the two species were closely related (r = 0"84). Lead concentrations in tadpoles living near highways may contribute to the elevated lead levels reported in wildlife that are potential tadpole predators. Dietary lead concentrations similar to those in our tadpoles have been associated with physiological and reproductive effects in some species of birds and mammals. However, additional data are needed to determine the hazards to predators o f lead concentrations in tadpoles. * To whom correspondence should be addressed. 233
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Charles W. Birdsall, Christian E. Grue, Allen Anderson
INTRODUCTION Tadpoles living in ponds and streams that receive runoff from roadbeds may be exposed to high concentrations of lead. In the United States, 106-118 million tonnes of lead entered the atmosphere from motor vehicle exhaust in 1975 (Provenzano, 1978). An estimated 22-58 % of the lead emitted in exhaust is deposited on the ground or vegetation on roadside verges (Little & Wiffen, 1978); accumulation is directly proportional to traffic density and inversely proportional to distance from the road surface (Wheeler & Rolfe, 1979). Today, less lead is probably emitted by motor vehicles because of the use of unleaded petrol and lead concentrations in roadside habitats may have declined (Byrd et al., 1983). However, lead concentrations within these habitats may still be an important source of lead pollution. Lead in freshwater ecosystems in the United States is widespread (Hem & Durum, 1973). Runoff from urban areas may contain large amounts of particulate lead (>_90% of total lead) which eventually settles on sediments (Hem & Durum, 1973; Wigington et al., 1983). Organisms that feed at the sediment-water interface may receive the greatest exposure to lead within aquatic ecosystems. For example, tadpoles feed on detritus and algae, incidentally ingesting fine sediments, and have been shown to accumulate metals adsorbed to sediment surfaces (Brungs, 1963; Hall & Mulhern, 1984). Tadpoles are prey of other amphibians, fish, birds and small mammals. Tadpoles living in aquatic habitats that receive runoff from roadbeds may accumulate lead to levels which may be hazardous to their predators. The objective of the present study was to determine lead concentrations in bullfrog R a n a catesbeiana and green frog R. clamitans tadpoles within highway drainages and to compare these concentrations with dietary lead levels that have been shown to affect adversely birds and mammals.
MATERIALS AND METHODS
Collection of samples We attempted to collect sediment and tadpoles from 24 highway drainages and 4 control sites (ponds 0.4-1.6km from the nearest highway) in Maryland and Virginia between 1 July and 9 December 1982.
Lead concentrations in tadpoles
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Study sites consisted of a single drainage, with one exception where we sampled three drainages at one location as a measure of intra-site variability. To obtain undisturbed sediment cores, we drove a 1 m section of 2.5 cm diameter acrylic tubing through the water into the sediment using rubber mallets. We corked the open end of the tubing, removed the tubing from the sediment and corked the bottom while the tubing was below the water surface. Both corks were then sealed with 0.6 cm wide strips of surgical tape. Three sediment cores were collected from each drainage. Sediment samples were transferred upright to the Patuxent Wildlife Research Center and allowed to settle overnight. They were then placed upright in a freezer and stored at - 15 °C. To prepare the frozen sediment samples for analysis, we used a stainless steel bone saw to remove a 2 cm section of the tubing (1 cm on either side of the sediment-water interface) since lead concentrations in sediment appear to be greatest within the top 1 cm (Getz et al., 1977). The tubing was removed from the sediment samples and the three cores from each drainage pooled and placed in chemically cleaned glass jars. After sediment samples were collected, nylon dip nets were used to capture bullfrog and green frog tadpoles at each site. A sufficient number of individuals was collected to obtain at least a 5 g sample of each species. The samples contained at least 9 tadpoles and weighed between 7 and 125g (wet weight). Tadpoles were immediately placed on ice (in chemically cleaned jars) to lower their metabolic rate and prevent them from evacuating their gut contents. Each tadpole was then rinsed with distilled water to remove any external debris and sorted by species. Each sample was weighed, placed in a chemically cleaned glass jar, and frozen ( - 15 °C).
Chemical analyses Sediment samples were dried in a convection oven overnight, and a 1 g portion was quartered out and dry-ashed for 2 h at 550 °C. The ash was cooled, digested in 20 ml 3:1 hydrochloric/nitric acids for 4 h, filtered, and diluted to 25 ml with distilled deionised water. Each tadpole sample was prepared using methods described by Haseltine et al. (1981). Lead concentrations were determined by comparison with aqueous standards using a Perkin-Elmer 5000 atomic absorption spectrophotometer (wavelength = 217 nm) with a fuel-lean air-acetylene flame and a
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Charles I4:. Birdsall, Christian E. Grue, Allen Anderson
TABLE I
Location of Study Sites, Average Daily Traffic Volumes (ADT) and Tadpole Species Collected Site
Location
Species ~
ADT b
A B C D
Harding Spring Pond, P W R C : 1.0km east of Rt 197 Goose Pond, PWRC, 0.9 km south-west of Rt 197 Island Marsh, PWRC, 1 km north of Rt 197 Pond, PWRC, 0.4km south-west (upstream) from Rt 197 and Bluegill Pond Bluegill Pond, adjacent to Rt 197 on PWRC, 2 km west of Powder Mill Rd Beaver Pond, Soil Conservation Rd, 2.2km south of Powder Mill Rd, Beltsville, Agricultural Research Center, Beltsville, MD Culvert below Rt 236E at Pickett Rd, Fairfax, VA Culvert below US 50 at Flatlick Run, VA Culvert adjacent to US 50 near Rt 609, 3.2 km west of Rt 28, VA Dammed culvert below the B-W Parkway at exit for NASA Goddard Space Flight Center, Greenbelt, MD Culvert below Rt 197, east of Foxhill Rd, Bowie, MD Pond adjacent to Rt 170 between Roberts Land and Watts Ave, Odenton, MD Pond adjacent to Rt 301 at Rt 4, MD Foxhill Pond adjacent to Rt 197 at Foxhill Rd, Bowie, MD Culvert below Powder Mill Rd, 0.2 km west of Rt 201, Beltsville, MD West side of culvert below 1-495, 2.4 km east of Rt 1, M D East side of culvert below 1-495, 2.4 km east of Rt 1, M D North-east side of culvert below 1-495, 2.4 km east of Rt 1, MD Pond adjacent to Rt 450 W at Rt 197, Bowie, MD Culvert adjacent to westbound Rt 197 at Cherry Lane, Laurel, MD
B,G G B,G
0 0 0
G
0
B
10 800
B,G B B,G
4 272 34050 13210
G
13210
G G
58 200 19 300
G G
10500 22000
B
19 300
G G G
11 900 108 800 108 800
G B,G
108 800 32 700
G
23 900
E F
G H I J K
L M N O Pl P2 P3 Q R
a B, bullfrog; G, green frog. b Maryland (MD), Prince George's County Department of Public Works and Transportation or Maryland State Highway Administration; Virginia (VA), Virginia Department of Highways and Transportation. c Patuxent Wildlife Research Center, Laurel, MD.
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237
deuterium arc background corrector. The detection limit was 0.1 mg k g wet weight. Recoveries from spiked material ranged from 79 % to 87 %. Residues were not corrected for percent recovery. Lead concentrations reported or discussed are on a dry weight basis unless noted otherwise. Statistical methods
The relationships between average daily traffic volume, sediment lead concentrations and tadpole lead concentrations were determined using linear regression (Neter & Wasserman, 1974). Lead concentrations and average daily traffic volume were transformed (log and square root, respectively) to meet the assumptions of regression analysis. Relationships were considered statistically significant if P < 0-05.
RESULTS We collected sufficient numbers of tadpoles at 16 of the highway sites and at all 4 control sites (Table 1). Bullfrog tadpoles were collected at 8 sites, whereas green frog tadpoles were collected at 17 sites. Both species of tadpoles were collected at 5 sites. Average daily traffic volumes at the highway sites in 1982 ranged from 4272 to 108 800 vehicles d a y (Table 1). Lead concentrations in sediment samples from control sites were 7.8 to 40 mg k g - 1; concentrations in sediment samples from highway drainages were 18 to 9 4 0 m g k g - 1 . Bullfrog tadpoles collected at control sites TABLE 2 Average Lead Concentrations in Sediment and Bullfrog and Green Frog Tadpoles from Highway and Control Sites
n Mean b 95~CI
Bullfrog a
Green frog a
Sediment Tadpoles
Sediment Tadpoles
8 8 57 14 16 200 2.5-72
17 17 66 14 35-120 7.3-25
Sites from which species was collected. bGeometric mean (mg kg- 1 dry weight). a
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Charles W. Birdsall, Christian E. Grue, Allen Anderson
1000
100
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I
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~000
1 O0
10
SEDIMENT
I 0
I 1
i 2
;
I 4
AVeA'D'~+ 100 Fig. 1. Square root of average daily traffic volume (ADT) and lead (Pb) concentrations ( m g k g - I dry weight) in sediment (r = 0.63) and bullfrog (r = 0'69) and green frog (r = 0.57) tadpoles. Correlation coefficients are statistically significant at P < 0.05.
Lead concentrations in tadpoles
239
contained 2.6 to 6.0 mgkg-1 lead; concentrations in bullfrog tadpoles collected at highway sites ranged from 0-70 to 270 mg kg-1. Green frog tadpoles collected at control sites contained 0.90 to 8-9mgkg -1 lead; those collected within highway drainages contained 4.8 to 240 mg kglead. Average lead concentrations in bullfrog and green frog tadpoles were about 20-25 % of those in the sediment (Table 2). Lead concentrations in the sediment (r = 0"63) and lead concentrations in both species of tadpoles (bullfrog, r = 0.69; green frog, r = 0"57) were positively correlated with average daily traffic volume (Fig. 1). Lead 1000
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SEDIMENT Pb (rag kg -1 dry wt) Fig. 2. Lead (Pb) concentrations (mgkg -1 dry weight) in sediment and lead concentrations in bullfrog (r =0.76) and green frog (r = 0-75) tadpoles. Correlation coefficients are statistically significant at P < 0 . 0 5 .
240
Charles W. Birdsall, Christian E. Grue, Allen Anderson 1000
T 100
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BULLFROG TADPOLEPb (mg kg -I dry wt)
Fig. 3. Lead (Pb) concentrations (mgkg-1 dry weight) in bullfrog and green frog tadpoles collected at the same sites (r = 0.84, P
concentrations in both species of tadpoles (bullfrog, r = 0"76; green frog, r = 0.75) were also positively correlated with lead concentrations in sediment (Fig. 2). At the 5 sites where both bullfrog and green frog tadpoles were collected, lead concentrations in the two species were closely related (r = 0.84, Fig. 3).
DISCUSSION Lead concentrations in tadpoles collected from highway drainages in Maryland and Virginia were less than those reported in tadpoles inhabiting drainages that received effluent from lead mines and smelters. Gale et al. (1973) reported lead concentrations of 1590mgkg -1 in tadpoles living in these habitats and Jennett et al. (1977) found lead concentrations exceeding 4100mgkg -1 in tadpoles and 6553 to 116 000 mg kg-1 in the sediment from these areas. The lower concentrations of lead in tadpoles inhabiting highway drainages compared to those exposed to effluent from lead mines and smelters undoubtedly reflect the lower amount of lead entering aquatic habitats from highway runoff as indicated by our sediment lead concentrations. Laboratory studies (Kaplan et al., 1967; Ireland, 1977)have shown that adult frogs and toads can accumulate lead. However, because of
Lead concentrations in tadpoles
241
differences in the feeding habits of larval and adult amphibians, tadpoles within highway drainages probably accumulate more lead than adult amphibians occupying similar habitats. In support of this hypothesis, lead concentrations in cricket frogs Acris crepitans and American toads Bujo americanus captured 5 m from a major highway (2-7-3-0 mg k g - 1) were lower than those (3.5 mg k g - 1) found in American toads captured in a marsh 50 m from any highway (Rolfe et al., 1977). Although tadpoles have the ability to accumulate lead to high concentrations, most of which is found in the gastrointestinal tract (Jennett et al., 1977), lead concentrations in tadpoles collected from highway drainages were 4-5 times lower than those found in sediments. These findings are in agreement with those of Gale et al. (1973), Drifmeyer (1975) and Getz et al. (1977) and suggest that biological magnification of lead does not occur in aquatic food chains. Algae, a food of tadpoles (Munz, 1920), appear to be an exception. Epipelic and epilithic algae (Phormidium sp. or Pithophora varia Wille, Oedogonium sp. and Oscillatoriasp.)accumulated an average of 189 and 404 mg k g - 1lead, respectively, from water containing about 8 7 m g k g -1 (Milne & Dickman, 1977). Vighi (1981) found that the alga Selenastrum capricornutum Prinz concentrated lead up to 1300 mg kg- 1 from water containing 2 4 - 4 4 # g k g -1 lead. Although algae were visible in the highway drainages we sampled, the results of our study tend to minimise the contribution of algal lead levels to those found in tadpoles. Average daily traffic volume accounted for only 32-48~o of the variation in sediment and tadpole lead concentrations (Fig. 1). The variation in lead concentrations in sediment and tadpoles that we observed among sites of similar traffic volume may have been due to several factors. Some of the variation may have been due to seasonal differences in lead inputs from runoff(Van Hassel et al., 1979; Lockery et al., 1983), because our sampling was conducted over a period of 6 months. The accumulation of lead on sediments also appears to be a function of microtopography and the resultant residence time of standing water (Wigington et al., 1983). Sediments in streams may contain significantly less lead than pond sediments; lead entering streams may be carried away from the source of pollution and the sediment may be scoured during storms. For example, lead concentrations in sediment samples from three drainages (P1, P2, P3) at our site with the highest average traffic volume (108 800 vehicles day- 1) varied between 86 and 310 mg kg- 1 and were lower than those in sediment at site Q (940 mg k g - 1) with an average daily
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Charles W. Birdsall, Christian E. Grue, Allen Anderson
traffic volume of 32 700. The drainages at site P were relatively still pools within a culvert (stream bed) periodically scoured by high water levels, whereas site Q was a pond without an outlet. The variation in lead concentrations in sediments at site P was probably caused by differences in the frequency of flooding; lead concentrations were highest at the most protected drainage (P3). The amount of particulate lead adsorbed to sediments within different highway drainages may also have been influenced by the composition of the substrate. Drifmeyer (1975) and Getz et al. (1977) found that fine sediments bind available lead better than coarse sediments. Because average daily traffic volume is only an index of lead levels to which tadpoles may be exposed, we would expect lead concentrations in tadpoles from highway drainages to be more closely related to lead levels in sediments than traffic volume. This was true in our study; sediment lead concentrations accounted for 56-58 ~o of the variation in tadpole lead levels. Why correlation coefficients between lead concentrations in tadpoles and those in sediment were not greater is unclear. Composition of the substrate may have been important. Lead concentrations in invertebrates and fish that feed at the sediment-water interface were influenced more by the amount of contact they had with silt than with other types of sediment (Getz et al., 1977). We would expect this also to be true for tadpoles. The amount of time our tadpoles spent in contaminated drainages and the amount of sediment in their gastrointestinal tracts at sacrifice may also account for some of the variation. Whether we sampled bullfrog or green frog tadpoles does not appear to have contributed to the variation observed in tadpole lead concentrations among sites. Lead concentrations in the two species were highly correlated at sites where they both occurred, probably because their feeding habits are similar, based on the morphology of their mouth parts (Dickerson, 1906). We do not believe that differences in the age of the tadpoles that we collected contributed to variation in tadpole lead concentrations among sites. Tadpoles of the genus R a n a are grazers. Grazing produces a suspension of food particles and sediments in the water which tadpoles subsequently assimilate by means of a complex and highly efficient filtration system (Wassersug, 1984). R a n a tadpoles maintain this mode of feeding until the stage of metamorphosis when their gills start to resorb (Stage 21; Taylor & Kollros, 1946). We collected only a few tadpoles
Lead concentrations in tadpoles
243
which were at this stage of development. Therefore, we believe that differences in feeding behaviour associated with age did not contribute to the variation in tadpole lead concentrations observed among sites. Nor do we believe that accumulation of lead in tadpole tissues with age can account for the observed inter-site variation in tadpole lead concentrations. The gut contents of Rana tadpoles may represent 50 ~ of their total body weight (Wassersug, 1984). In vertebrates, lead is not readily absorbed through the gut wall and that ingested is largely excreted in faeces (Bowen, 1966). Thus, lead concentrations in tissues of tadpoles before metamorphosis, irrespective of age, are probably only a small fraction of those in the gut. Lead concentrations in tadpoles living near highways may contribute to the elevated lead levels reported in wildlife that may be tadpole predators. For example, relatively high lead concentrations in raccoons Procyon lotor (> 1 4 ~ of diet = post-larval amphibians; Whitney & Underwood, 1952) have been reported by Sanderson & Thomas (1961) and Diters & Nielsen (1978). Neither Sanderson & Thomas nor Diters & Nielsen could determine the source of the lead present in the raccoons that they collected. The potential hazard to predators posed by the lead concentrations in our tadpoles cannot be adequately assessed at this time. To our knowledge, data on (1) the dietary lead levels associated with effects in tadpole predators, and (2) the consumption of tadpoles in highway drainages by predators, are lacking. For example, data on the effects of lead in adult frogs appear to be limited to those for Ranapipiens immersed in lead nitrate solutions. Kaplan et al. (1967) found that concentrations of lead nitrate of 25 mg k g - 1 or more caused a variety of anatomical and physiological disorders. The only study on the effects of dietary lead on fish appears to be that of Vighi (1981), in which guppies Poecilia reticulata fed Daphnia magna containing as much as 68 mg k g - 1 lead for 4 weeks accumulated whole body lead concentrations of as much as 24 mg k g - 1 without suffering any overt toxic effects. Since lead accumulation in fish depends, in part, on how closely they are associated with the sediment (Ney & Van Hassel, 1983), and because lead concentrations in our tadpoles were only a small fraction of those in the sediment, lead in aquatic habitats probably poses a greater hazard to benthic species of fish than to pelagic species, whether or not the latter consume contaminated tadpoles.
244
Charles W. Birdsall, Christ&n E. Grue, Allen Anderson
Diets with lead levels similar to those in our tadpoles have been associated with physiological and reproductive effects in some domestic and wild species of birds and mammals. 1 to 100 mg kg- 1 lead acetate in the diet of Japanese quail Coturnix coturnixjaponica resulted in reduced egg production and hatching success and delayed sexual maturity (Edens et al., 1976). In American kestrels Falco sparverius fed 104mgkg -~ metallic lead, the activity of red-blood cell (RBC) 6-aminolaevulinic acid dehydratase (ALAD), an enzyme essential for haemoglobin production, was reduced to 20 ~o of controls (Franson et al., 1983), but survival and reproduction were not affected (Pattee, 1984). Similarly, reproductive success of adult barn swallows Hirundo rustica living beneath the bridge of a major highway was comparable to that of rural populations, although their diet and that of their young contained 4-8-6-8 mgkg-1 lead and RBC ALAD activity was depressed by 14-34~o (Grue et al., 1984). In comparison, stomach contents of the nestling and adult European starlings Sturnus vulgar& from the verge of the same highway contained 84-94mgkg-1 lead, RBC ALAD activity in nestlings and adults was depressed by 46-60 ~ compared to controls, and haemoglobin concentrations and haematocrits of nestlings were reduced by 16 ~ and 10 %, respectively. Reproductive success and body weights of adults and nestlings were similar to controls, but brain weights in nestlings were lower (Grue et al., in press). Nestling American kestrels given the equivalent of about 289 mg kg- 1 lead in their diet suffered reduced RBC ALAD activity (-59~o), haemoglobin concentrations (27~o) and haelnatocrits ( - 14 ~o), and both body weights and brain weights were depressed (Hoffman et al., 1985a, b). On a wet weight basis, lead concentrations in our tadpoles (0.10-25-0 mg kg- 1) were similar to those found in the stomach contents of meadow voles Microtus pennsylvanicus (9"4 mg kg- 1) and white-footed mice Peromyscus leucopus (9.3 mg kg- 1) collected within the verge of a major highway (Clark, 1979). When transformed to milligrams of lead ingested per kilogram of body weight the concentrations of lead in the stomach contents of these voles and mice exceeded the minimum dosages of lead known to impair reproduction or cause mortality in five species of domestic mammals (Clark, 1979). In addition, our study and those of Brungs (1963), Gale et al. (1973), Jennett et al. (1977) and Hall & Mulhern (1984) suggest that tadpoles are good indicators of recent or ongoing metal contamination in aquatic habitats. Cooke (1981) suggested that tadpoles may also be useful as indicators of other pollutants.
Lead concentrations in tadpoles
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A C K N O W L E D G E M E N TS We thank Robert L. Almond Sr, US Department of Agriculture, Beltsville Agricultural Research Center, for permission to collect tadpoles on the Center, Dale G. Coppage and Dave Hall, Department of Public Works and Transportation, Prince George's County, Maryland, for conducting the traffic count on Soil Conservation Road, Clyde Vance for building the sediment sample storage rack, Douglas A. Berry for help in locating sampling sites and collecting tadpoles, Russell J. Hall for identifying tadpole species, Christine M. Bunck for statistical advice, Jeanne M. Grillo for help in preparing the figures, Lynda J. Garrett for obtaining m a n y of the references, and Marcia G. Holmes and Lynn M. T h o m a s for secretarial assistance. We also thank W. Nelson Beyer and Russell J. Hall for critical reviews of the manuscript.
REFERENCES Bowen, H. J. M. (1966). Trace elements in biochemistry. New York, Academic Press. Brungs, W. A. (1963). The relative distribution of multiple radionuclides in a freshwater pond. PhD thesis, Ohio State University. Byrd, D. S., Gilmore, J. T. & Lea, R. H. (1983). Effect of decreased use of lead in gasoline on the soil of a highway. Environ. Sci. Technol., 17, 121-3. Clark Jr, D. R. (1979). Lead concentrations: Bats vs terrestrial small mammals collected near a major highway. Environ. Sci. Technol., 13, 338~41. Cooke, A. S. (1981). Tadpoles as indicators of harmful levels of pollution in the field. Environ Pollut., Ser. A, 12, 123-33. Dickerson, M. P. (1906). The frog book. New York, Doubleday, Page & Co. Diters, R. W. & Nielsen, S. W. (1978). Lead poisoning of raccoons in Connecticut. J. Wildl. Dis., 14, 187-92. Drifmeyer, J. E. (1975). Lead enters food web of estuarine organisms. Worm Dredging, Nov., 41-3. Edens, F. W., Benton, E., Bursian, S. J. & Morgan, G. W. (1976). Effects of dietary lead on reproductive performance in Japanese quail, Coturnix coturnix japonica. Toxicol. Appl. Pharmaeol., 38, 307-14. Franson, J. C., Sileo, L., Pattee, O. H. & Moore, J. F. (1983). Effects of chronic dietary lead in American kestrels (Falco sparverius). J. Wildl. Dis., 19, i10-13. Gale, N. L., Wixon, B. G., Hardie, M. G. & Jennett, J. C. (1973). Aquatic organisms and heavy metals in Missouri's new lead belt. Water Res. Bull., 9, 673-88.
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Getz, L. L., Haney, A. W., Larrimore, R. W., Leland, H. V., McNurney, J. M., Price, P. W., Rolfe, G. L., Wortman, R. L., Hudson, J. L., Solomon, R. L. & Reinbold, K. A. (1977). Transport and distribution in a watershed ecosystem. In: Lead in the environment, ed. by W. R. Boggess, 105-34. Washington, DC, National Science Foundation. Grue, C. E., O'Shea, T. J. & Hoffman, D. J. (1984). Lead exposure and reproduction in highway-nesting barn swallows. Condor, 86, 383-9. Grue, C. E., Hoffman, D. J., Beyer, W. N. & Franson, L. P. Lead concentrations and reproductive success in European starlings Sturnus vulgaris nesting on roadside verges. Environ. Pollut., Ser. A., in press. Hall, R. J. & Mulhern, B. M. (1984). Are amphibians heavy metal accumulators ? In: Vertebrate ecology and systematies: A tribute to Henry S. Fitch, ed. by R. A. Seigel, L. E. Hunt, J. L. Knight, L. Malaret and N. L. Zuschlag, 123-33. Lawrence, Kansas, University of Kansas Museum of Natural History. Haseltine, S. D., Heinz, G. H., Reichel, W. L. & Moore, J. F. (1981): Organochlorine and metal residues in eggs of waterfowl nesting on islands in Lake Michigan off Door County, Wisconsin, 1977 78. Pestie. Monit. J., 15, 90-7. Hem, J. D. & Durum, W. H. (1973). Solubility and occurrence of lead in surface water. J. Am. Water Works Ass., 65, 562-8. Hoffman, D. J., Franson, J. C., Pattee, O. H., Bunck, C. M. & Anderson, A. (1985a). Survival, growth, and accumulation of ingested lead in nestling American kestrels ( Faleo sparverius). Arch. Environ. Contain. & Toxicol., 14, 89 94. Hoffman, D. J., Franson, J. C., Pattee, O. H., Bunck, C. M. & Murray, H. C. (1985b). Biochemical and hematological effects of lead ingestion in nestling American kestrels ( Falco sparverius). Comp. Biochem. Physiol., 80C, 431 9. Ireland, M. P. (1977). Lead retention in toads Xenopus laevis fed increasing levels of lead-contaminated earthworms. Environ Pollut., 12, 85-92. Jennett, J. C., Wixon, B. G., Bolter, E., Lowsley, I. H., Hemphill, D. D., Tranter, W. H., Gale, N. L. & Purushotaman, K. (1977). Transport and distribution around mines, mills, and smelters. In: Lead in the environment, ed. by W. G. Boggess, 135-78. Washington, DC, National Science Foundation. Kaplan, H. M., Arnholt, T. J. & Payne, J. E. (1967). Toxicity of lead nitrate solutions for frogs (Rana pipiens). Lab. Anim. Care, 17, 240-6. Little, P. & Wiffen, R. D. (1978). Emission and deposition of lead from motor vehicle exhausts. II. Airborne concentration, particle size and deposition of lead near motorways. Atmos. Environ., 12, 1331-41. Lockery, A. R., Gavailoff, T. & Hatcher, D. (1983). Lead levels in snow dumping sites along rivers in downtown Winnepeg, Manitoba, Canada. J. Environ. Mgmt., 17, 185-90. Milne, J. G. & Dickman, M. (1977). Lead concentrations in algae and plants grown over lead contaminated sediments taken from snow dumps in Ottawa, Canada. J. Environ. Sci. Health, A-12, 173-89. Munz, P. A. (1920). A study of the food habits of the Ithican species of Anura during transformation. Pomona College J. Entomol. Zool., 12, 33-56.
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Neter, J. & Wasserman, W. (1974). Applied linear statistical models. Homewood, Illinois, Richard D. Irwin. Ney, J. J. & Van Hassel, J. H. (1983). Sources of variability in accumulation of heavy metals by fishes in a roadside stream. Arch. Environ. Contain. & Toxicol., 12, 701-6. Pattee, O. H. (1984). Eggshell thickness and reproduction in American kestrels exposed to chronic dietary lead. Arch. Environ. Contain. & Toxicol., 13, 29-34. P,rovenzano, G. (1978). Motor vehicle lead emissions in the United States: An analysis of important determinants, geographical patterns and future trends. J. Air Pollut. Control Ass., 28, 1193-9. Rolfe, G. L., Haney, A. & Reinbold, K. A. (1977). Environmental contamination by lead and other heavy metals, 2: Ecosystem analysis. University of Illinois at Urbana-Champaign, Institute for Environmental Studies. Sanderson, G. C. & Thomas, R. M. (1961). Incidence of lead in livers of Illinois raccoons. J. Wildl. Mgmt., 25, 16(~8. Taylor, A. C. & Kollros, J. J. (1946). Stages in the normal development of Rana pipiens larvae. Anat. Rec., 94, 7 23. Van Hassel, J. H., Ney, J. J. & Garling, D. L. (1979). Seasonal variations in the heavy metal concentrations of sediments influenced by highways of different traffic volumes. Bull. Environ. Contain. & Toxicol., 23, 592-6. Vighi, M. (1981). Lead uptake and release in an experimental trophic chain. Ecotoxicol. Environ. Safety, 5, 177-93. Wassersug, R. (1984). Why tadpoles love fast food. Nat. Hist., 93, 60-9. Wheeler, G. L. & Rolfe, G. L. (1979). The relationship between daily traffic volume and the distribution of lead in roadside soil and vegetation. Environ. Pollut., 18, 265-74. Whitney, L. F. & Underwood, A. B. (1952). The raccoon. Orange, Connecticut, Practical Science Publishing Co. Wigington Jr, P. J., Randall, C. W. & Grizzards, T. J. (1983). Accumulation of selected trace metals in soils of urban runoff detention basins. Water Resour. Bull., 19, 709 18.
Lead Concentrations in Bullfrog Rana catesbeiana and Green Frog R. clamitans Tadpoles Inhabiting Highway Drainages
Charles W. Birdsall, Christian E. Grue* & Allen Anderson US Fish and Wildlife Service, Patuxent Wildlife Research Center, Laurel, Maryland 20708, USA
A BSTRA CT Lead concentrations were determined in sediment and tadpoles of bullfrogs R a n a catesbeiana and green frogs R. clamitans from drainages along highways with different daily average traffic volumes (range, 4272 to 108800 vehicles d a y - i ) andj~'om ponds >_ 0.4 km from the nearest highway. Lead concentrations (mg kg-1 dry weight) in sediment (7.8 to 940) were usually greater (4-5 times) than those in the tadpoles (bullfrog, 0"07 to 270; green frog, 0"90 to 2 4 0 m g k g - i ) . Lead concentrations in sediment (r = 0.63) and in both species of tadpoh, s (bullfrog, r = 0.69; green frog, r = 0.57) were positively correlated with average daily traffic volume. Lead concentrations in both species of tadpoles (bullfrog, r = O. 76; green frog, r = O"75) were also positively correlated with lead concentrations in sediment. At sites where both bullfrog and green frog tadpoles were collected, lead concentrations in the two species were closely related (r = 0"84). Lead concentrations in tadpoles living near highways may contribute to the elevated lead levels reported in wildlife that are potential tadpole predators. Dietary lead concentrations similar to those in our tadpoles have been associated with physiological and reproductive effects in some species of birds and mammals. However, additional data are needed to determine the hazards to predators o f lead concentrations in tadpoles. * To whom correspondence should be addressed. 233
234
Charles W. Birdsall, Christian E. Grue, Allen Anderson
INTRODUCTION Tadpoles living in ponds and streams that receive runoff from roadbeds may be exposed to high concentrations of lead. In the United States, 106-118 million tonnes of lead entered the atmosphere from motor vehicle exhaust in 1975 (Provenzano, 1978). An estimated 22-58 % of the lead emitted in exhaust is deposited on the ground or vegetation on roadside verges (Little & Wiffen, 1978); accumulation is directly proportional to traffic density and inversely proportional to distance from the road surface (Wheeler & Rolfe, 1979). Today, less lead is probably emitted by motor vehicles because of the use of unleaded petrol and lead concentrations in roadside habitats may have declined (Byrd et al., 1983). However, lead concentrations within these habitats may still be an important source of lead pollution. Lead in freshwater ecosystems in the United States is widespread (Hem & Durum, 1973). Runoff from urban areas may contain large amounts of particulate lead (>_90% of total lead) which eventually settles on sediments (Hem & Durum, 1973; Wigington et al., 1983). Organisms that feed at the sediment-water interface may receive the greatest exposure to lead within aquatic ecosystems. For example, tadpoles feed on detritus and algae, incidentally ingesting fine sediments, and have been shown to accumulate metals adsorbed to sediment surfaces (Brungs, 1963; Hall & Mulhern, 1984). Tadpoles are prey of other amphibians, fish, birds and small mammals. Tadpoles living in aquatic habitats that receive runoff from roadbeds may accumulate lead to levels which may be hazardous to their predators. The objective of the present study was to determine lead concentrations in bullfrog R a n a catesbeiana and green frog R. clamitans tadpoles within highway drainages and to compare these concentrations with dietary lead levels that have been shown to affect adversely birds and mammals.
MATERIALS AND METHODS
Collection of samples We attempted to collect sediment and tadpoles from 24 highway drainages and 4 control sites (ponds 0.4-1.6km from the nearest highway) in Maryland and Virginia between 1 July and 9 December 1982.
Lead concentrations in tadpoles
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Study sites consisted of a single drainage, with one exception where we sampled three drainages at one location as a measure of intra-site variability. To obtain undisturbed sediment cores, we drove a 1 m section of 2.5 cm diameter acrylic tubing through the water into the sediment using rubber mallets. We corked the open end of the tubing, removed the tubing from the sediment and corked the bottom while the tubing was below the water surface. Both corks were then sealed with 0.6 cm wide strips of surgical tape. Three sediment cores were collected from each drainage. Sediment samples were transferred upright to the Patuxent Wildlife Research Center and allowed to settle overnight. They were then placed upright in a freezer and stored at - 15 °C. To prepare the frozen sediment samples for analysis, we used a stainless steel bone saw to remove a 2 cm section of the tubing (1 cm on either side of the sediment-water interface) since lead concentrations in sediment appear to be greatest within the top 1 cm (Getz et al., 1977). The tubing was removed from the sediment samples and the three cores from each drainage pooled and placed in chemically cleaned glass jars. After sediment samples were collected, nylon dip nets were used to capture bullfrog and green frog tadpoles at each site. A sufficient number of individuals was collected to obtain at least a 5 g sample of each species. The samples contained at least 9 tadpoles and weighed between 7 and 125g (wet weight). Tadpoles were immediately placed on ice (in chemically cleaned jars) to lower their metabolic rate and prevent them from evacuating their gut contents. Each tadpole was then rinsed with distilled water to remove any external debris and sorted by species. Each sample was weighed, placed in a chemically cleaned glass jar, and frozen ( - 15 °C).
Chemical analyses Sediment samples were dried in a convection oven overnight, and a 1 g portion was quartered out and dry-ashed for 2 h at 550 °C. The ash was cooled, digested in 20 ml 3:1 hydrochloric/nitric acids for 4 h, filtered, and diluted to 25 ml with distilled deionised water. Each tadpole sample was prepared using methods described by Haseltine et al. (1981). Lead concentrations were determined by comparison with aqueous standards using a Perkin-Elmer 5000 atomic absorption spectrophotometer (wavelength = 217 nm) with a fuel-lean air-acetylene flame and a
236
Charles I4:. Birdsall, Christian E. Grue, Allen Anderson
TABLE I
Location of Study Sites, Average Daily Traffic Volumes (ADT) and Tadpole Species Collected Site
Location
Species ~
ADT b
A B C D
Harding Spring Pond, P W R C : 1.0km east of Rt 197 Goose Pond, PWRC, 0.9 km south-west of Rt 197 Island Marsh, PWRC, 1 km north of Rt 197 Pond, PWRC, 0.4km south-west (upstream) from Rt 197 and Bluegill Pond Bluegill Pond, adjacent to Rt 197 on PWRC, 2 km west of Powder Mill Rd Beaver Pond, Soil Conservation Rd, 2.2km south of Powder Mill Rd, Beltsville, Agricultural Research Center, Beltsville, MD Culvert below Rt 236E at Pickett Rd, Fairfax, VA Culvert below US 50 at Flatlick Run, VA Culvert adjacent to US 50 near Rt 609, 3.2 km west of Rt 28, VA Dammed culvert below the B-W Parkway at exit for NASA Goddard Space Flight Center, Greenbelt, MD Culvert below Rt 197, east of Foxhill Rd, Bowie, MD Pond adjacent to Rt 170 between Roberts Land and Watts Ave, Odenton, MD Pond adjacent to Rt 301 at Rt 4, MD Foxhill Pond adjacent to Rt 197 at Foxhill Rd, Bowie, MD Culvert below Powder Mill Rd, 0.2 km west of Rt 201, Beltsville, MD West side of culvert below 1-495, 2.4 km east of Rt 1, M D East side of culvert below 1-495, 2.4 km east of Rt 1, M D North-east side of culvert below 1-495, 2.4 km east of Rt 1, MD Pond adjacent to Rt 450 W at Rt 197, Bowie, MD Culvert adjacent to westbound Rt 197 at Cherry Lane, Laurel, MD
B,G G B,G
0 0 0
G
0
B
10 800
B,G B B,G
4 272 34050 13210
G
13210
G G
58 200 19 300
G G
10500 22000
B
19 300
G G G
11 900 108 800 108 800
G B,G
108 800 32 700
G
23 900
E F
G H I J K
L M N O Pl P2 P3 Q R
a B, bullfrog; G, green frog. b Maryland (MD), Prince George's County Department of Public Works and Transportation or Maryland State Highway Administration; Virginia (VA), Virginia Department of Highways and Transportation. c Patuxent Wildlife Research Center, Laurel, MD.
Lead concentrations in tadpoles
237
deuterium arc background corrector. The detection limit was 0.1 mg k g wet weight. Recoveries from spiked material ranged from 79 % to 87 %. Residues were not corrected for percent recovery. Lead concentrations reported or discussed are on a dry weight basis unless noted otherwise. Statistical methods
The relationships between average daily traffic volume, sediment lead concentrations and tadpole lead concentrations were determined using linear regression (Neter & Wasserman, 1974). Lead concentrations and average daily traffic volume were transformed (log and square root, respectively) to meet the assumptions of regression analysis. Relationships were considered statistically significant if P < 0-05.
RESULTS We collected sufficient numbers of tadpoles at 16 of the highway sites and at all 4 control sites (Table 1). Bullfrog tadpoles were collected at 8 sites, whereas green frog tadpoles were collected at 17 sites. Both species of tadpoles were collected at 5 sites. Average daily traffic volumes at the highway sites in 1982 ranged from 4272 to 108 800 vehicles d a y (Table 1). Lead concentrations in sediment samples from control sites were 7.8 to 40 mg k g - 1; concentrations in sediment samples from highway drainages were 18 to 9 4 0 m g k g - 1 . Bullfrog tadpoles collected at control sites TABLE 2 Average Lead Concentrations in Sediment and Bullfrog and Green Frog Tadpoles from Highway and Control Sites
n Mean b 95~CI
Bullfrog a
Green frog a
Sediment Tadpoles
Sediment Tadpoles
8 8 57 14 16 200 2.5-72
17 17 66 14 35-120 7.3-25
Sites from which species was collected. bGeometric mean (mg kg- 1 dry weight). a
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Charles W. Birdsall, Christian E. Grue, Allen Anderson
1000
100
J
10
GREEN
I
I
I
FROG
I
1000
100 "0
T E .Q O.
BULL FROG I
I
I
I
I
~000
1 O0
10
SEDIMENT
I 0
I 1
i 2
;
I 4
AVeA'D'~+ 100 Fig. 1. Square root of average daily traffic volume (ADT) and lead (Pb) concentrations ( m g k g - I dry weight) in sediment (r = 0.63) and bullfrog (r = 0'69) and green frog (r = 0.57) tadpoles. Correlation coefficients are statistically significant at P < 0.05.
Lead concentrations in tadpoles
239
contained 2.6 to 6.0 mgkg-1 lead; concentrations in bullfrog tadpoles collected at highway sites ranged from 0-70 to 270 mg kg-1. Green frog tadpoles collected at control sites contained 0.90 to 8-9mgkg -1 lead; those collected within highway drainages contained 4.8 to 240 mg kglead. Average lead concentrations in bullfrog and green frog tadpoles were about 20-25 % of those in the sediment (Table 2). Lead concentrations in the sediment (r = 0"63) and lead concentrations in both species of tadpoles (bullfrog, r = 0.69; green frog, r = 0"57) were positively correlated with average daily traffic volume (Fig. 1). Lead 1000
100
10
GREEN FROG
b
i
"0 I
"~
I
I I lllll
I
I
I I lllll
I
I
f .....
'
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100
10
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n
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n 100
n 1000
SEDIMENT Pb (rag kg -1 dry wt) Fig. 2. Lead (Pb) concentrations (mgkg -1 dry weight) in sediment and lead concentrations in bullfrog (r =0.76) and green frog (r = 0-75) tadpoles. Correlation coefficients are statistically significant at P < 0 . 0 5 .
240
Charles W. Birdsall, Christian E. Grue, Allen Anderson 1000
T 100
~e o CI
I0
z
W II1[
I
I
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I
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10
I
. . . . . . . .
1 O0
|
1000
BULLFROG TADPOLEPb (mg kg -I dry wt)
Fig. 3. Lead (Pb) concentrations (mgkg-1 dry weight) in bullfrog and green frog tadpoles collected at the same sites (r = 0.84, P
concentrations in both species of tadpoles (bullfrog, r = 0"76; green frog, r = 0.75) were also positively correlated with lead concentrations in sediment (Fig. 2). At the 5 sites where both bullfrog and green frog tadpoles were collected, lead concentrations in the two species were closely related (r = 0.84, Fig. 3).
DISCUSSION Lead concentrations in tadpoles collected from highway drainages in Maryland and Virginia were less than those reported in tadpoles inhabiting drainages that received effluent from lead mines and smelters. Gale et al. (1973) reported lead concentrations of 1590mgkg -1 in tadpoles living in these habitats and Jennett et al. (1977) found lead concentrations exceeding 4100mgkg -1 in tadpoles and 6553 to 116 000 mg kg-1 in the sediment from these areas. The lower concentrations of lead in tadpoles inhabiting highway drainages compared to those exposed to effluent from lead mines and smelters undoubtedly reflect the lower amount of lead entering aquatic habitats from highway runoff as indicated by our sediment lead concentrations. Laboratory studies (Kaplan et al., 1967; Ireland, 1977)have shown that adult frogs and toads can accumulate lead. However, because of
Lead concentrations in tadpoles
241
differences in the feeding habits of larval and adult amphibians, tadpoles within highway drainages probably accumulate more lead than adult amphibians occupying similar habitats. In support of this hypothesis, lead concentrations in cricket frogs Acris crepitans and American toads Bujo americanus captured 5 m from a major highway (2-7-3-0 mg k g - 1) were lower than those (3.5 mg k g - 1) found in American toads captured in a marsh 50 m from any highway (Rolfe et al., 1977). Although tadpoles have the ability to accumulate lead to high concentrations, most of which is found in the gastrointestinal tract (Jennett et al., 1977), lead concentrations in tadpoles collected from highway drainages were 4-5 times lower than those found in sediments. These findings are in agreement with those of Gale et al. (1973), Drifmeyer (1975) and Getz et al. (1977) and suggest that biological magnification of lead does not occur in aquatic food chains. Algae, a food of tadpoles (Munz, 1920), appear to be an exception. Epipelic and epilithic algae (Phormidium sp. or Pithophora varia Wille, Oedogonium sp. and Oscillatoriasp.)accumulated an average of 189 and 404 mg k g - 1lead, respectively, from water containing about 8 7 m g k g -1 (Milne & Dickman, 1977). Vighi (1981) found that the alga Selenastrum capricornutum Prinz concentrated lead up to 1300 mg kg- 1 from water containing 2 4 - 4 4 # g k g -1 lead. Although algae were visible in the highway drainages we sampled, the results of our study tend to minimise the contribution of algal lead levels to those found in tadpoles. Average daily traffic volume accounted for only 32-48~o of the variation in sediment and tadpole lead concentrations (Fig. 1). The variation in lead concentrations in sediment and tadpoles that we observed among sites of similar traffic volume may have been due to several factors. Some of the variation may have been due to seasonal differences in lead inputs from runoff(Van Hassel et al., 1979; Lockery et al., 1983), because our sampling was conducted over a period of 6 months. The accumulation of lead on sediments also appears to be a function of microtopography and the resultant residence time of standing water (Wigington et al., 1983). Sediments in streams may contain significantly less lead than pond sediments; lead entering streams may be carried away from the source of pollution and the sediment may be scoured during storms. For example, lead concentrations in sediment samples from three drainages (P1, P2, P3) at our site with the highest average traffic volume (108 800 vehicles day- 1) varied between 86 and 310 mg kg- 1 and were lower than those in sediment at site Q (940 mg k g - 1) with an average daily
242
Charles W. Birdsall, Christian E. Grue, Allen Anderson
traffic volume of 32 700. The drainages at site P were relatively still pools within a culvert (stream bed) periodically scoured by high water levels, whereas site Q was a pond without an outlet. The variation in lead concentrations in sediments at site P was probably caused by differences in the frequency of flooding; lead concentrations were highest at the most protected drainage (P3). The amount of particulate lead adsorbed to sediments within different highway drainages may also have been influenced by the composition of the substrate. Drifmeyer (1975) and Getz et al. (1977) found that fine sediments bind available lead better than coarse sediments. Because average daily traffic volume is only an index of lead levels to which tadpoles may be exposed, we would expect lead concentrations in tadpoles from highway drainages to be more closely related to lead levels in sediments than traffic volume. This was true in our study; sediment lead concentrations accounted for 56-58 ~o of the variation in tadpole lead levels. Why correlation coefficients between lead concentrations in tadpoles and those in sediment were not greater is unclear. Composition of the substrate may have been important. Lead concentrations in invertebrates and fish that feed at the sediment-water interface were influenced more by the amount of contact they had with silt than with other types of sediment (Getz et al., 1977). We would expect this also to be true for tadpoles. The amount of time our tadpoles spent in contaminated drainages and the amount of sediment in their gastrointestinal tracts at sacrifice may also account for some of the variation. Whether we sampled bullfrog or green frog tadpoles does not appear to have contributed to the variation observed in tadpole lead concentrations among sites. Lead concentrations in the two species were highly correlated at sites where they both occurred, probably because their feeding habits are similar, based on the morphology of their mouth parts (Dickerson, 1906). We do not believe that differences in the age of the tadpoles that we collected contributed to variation in tadpole lead concentrations among sites. Tadpoles of the genus R a n a are grazers. Grazing produces a suspension of food particles and sediments in the water which tadpoles subsequently assimilate by means of a complex and highly efficient filtration system (Wassersug, 1984). R a n a tadpoles maintain this mode of feeding until the stage of metamorphosis when their gills start to resorb (Stage 21; Taylor & Kollros, 1946). We collected only a few tadpoles
Lead concentrations in tadpoles
243
which were at this stage of development. Therefore, we believe that differences in feeding behaviour associated with age did not contribute to the variation in tadpole lead concentrations observed among sites. Nor do we believe that accumulation of lead in tadpole tissues with age can account for the observed inter-site variation in tadpole lead concentrations. The gut contents of Rana tadpoles may represent 50 ~ of their total body weight (Wassersug, 1984). In vertebrates, lead is not readily absorbed through the gut wall and that ingested is largely excreted in faeces (Bowen, 1966). Thus, lead concentrations in tissues of tadpoles before metamorphosis, irrespective of age, are probably only a small fraction of those in the gut. Lead concentrations in tadpoles living near highways may contribute to the elevated lead levels reported in wildlife that may be tadpole predators. For example, relatively high lead concentrations in raccoons Procyon lotor (> 1 4 ~ of diet = post-larval amphibians; Whitney & Underwood, 1952) have been reported by Sanderson & Thomas (1961) and Diters & Nielsen (1978). Neither Sanderson & Thomas nor Diters & Nielsen could determine the source of the lead present in the raccoons that they collected. The potential hazard to predators posed by the lead concentrations in our tadpoles cannot be adequately assessed at this time. To our knowledge, data on (1) the dietary lead levels associated with effects in tadpole predators, and (2) the consumption of tadpoles in highway drainages by predators, are lacking. For example, data on the effects of lead in adult frogs appear to be limited to those for Ranapipiens immersed in lead nitrate solutions. Kaplan et al. (1967) found that concentrations of lead nitrate of 25 mg k g - 1 or more caused a variety of anatomical and physiological disorders. The only study on the effects of dietary lead on fish appears to be that of Vighi (1981), in which guppies Poecilia reticulata fed Daphnia magna containing as much as 68 mg k g - 1 lead for 4 weeks accumulated whole body lead concentrations of as much as 24 mg k g - 1 without suffering any overt toxic effects. Since lead accumulation in fish depends, in part, on how closely they are associated with the sediment (Ney & Van Hassel, 1983), and because lead concentrations in our tadpoles were only a small fraction of those in the sediment, lead in aquatic habitats probably poses a greater hazard to benthic species of fish than to pelagic species, whether or not the latter consume contaminated tadpoles.
244
Charles W. Birdsall, Christ&n E. Grue, Allen Anderson
Diets with lead levels similar to those in our tadpoles have been associated with physiological and reproductive effects in some domestic and wild species of birds and mammals. 1 to 100 mg kg- 1 lead acetate in the diet of Japanese quail Coturnix coturnixjaponica resulted in reduced egg production and hatching success and delayed sexual maturity (Edens et al., 1976). In American kestrels Falco sparverius fed 104mgkg -~ metallic lead, the activity of red-blood cell (RBC) 6-aminolaevulinic acid dehydratase (ALAD), an enzyme essential for haemoglobin production, was reduced to 20 ~o of controls (Franson et al., 1983), but survival and reproduction were not affected (Pattee, 1984). Similarly, reproductive success of adult barn swallows Hirundo rustica living beneath the bridge of a major highway was comparable to that of rural populations, although their diet and that of their young contained 4-8-6-8 mgkg-1 lead and RBC ALAD activity was depressed by 14-34~o (Grue et al., 1984). In comparison, stomach contents of the nestling and adult European starlings Sturnus vulgar& from the verge of the same highway contained 84-94mgkg-1 lead, RBC ALAD activity in nestlings and adults was depressed by 46-60 ~ compared to controls, and haemoglobin concentrations and haematocrits of nestlings were reduced by 16 ~ and 10 %, respectively. Reproductive success and body weights of adults and nestlings were similar to controls, but brain weights in nestlings were lower (Grue et al., in press). Nestling American kestrels given the equivalent of about 289 mg kg- 1 lead in their diet suffered reduced RBC ALAD activity (-59~o), haemoglobin concentrations (27~o) and haelnatocrits ( - 14 ~o), and both body weights and brain weights were depressed (Hoffman et al., 1985a, b). On a wet weight basis, lead concentrations in our tadpoles (0.10-25-0 mg kg- 1) were similar to those found in the stomach contents of meadow voles Microtus pennsylvanicus (9"4 mg kg- 1) and white-footed mice Peromyscus leucopus (9.3 mg kg- 1) collected within the verge of a major highway (Clark, 1979). When transformed to milligrams of lead ingested per kilogram of body weight the concentrations of lead in the stomach contents of these voles and mice exceeded the minimum dosages of lead known to impair reproduction or cause mortality in five species of domestic mammals (Clark, 1979). In addition, our study and those of Brungs (1963), Gale et al. (1973), Jennett et al. (1977) and Hall & Mulhern (1984) suggest that tadpoles are good indicators of recent or ongoing metal contamination in aquatic habitats. Cooke (1981) suggested that tadpoles may also be useful as indicators of other pollutants.
Lead concentrations in tadpoles
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A C K N O W L E D G E M E N TS We thank Robert L. Almond Sr, US Department of Agriculture, Beltsville Agricultural Research Center, for permission to collect tadpoles on the Center, Dale G. Coppage and Dave Hall, Department of Public Works and Transportation, Prince George's County, Maryland, for conducting the traffic count on Soil Conservation Road, Clyde Vance for building the sediment sample storage rack, Douglas A. Berry for help in locating sampling sites and collecting tadpoles, Russell J. Hall for identifying tadpole species, Christine M. Bunck for statistical advice, Jeanne M. Grillo for help in preparing the figures, Lynda J. Garrett for obtaining m a n y of the references, and Marcia G. Holmes and Lynn M. T h o m a s for secretarial assistance. We also thank W. Nelson Beyer and Russell J. Hall for critical reviews of the manuscript.
REFERENCES Bowen, H. J. M. (1966). Trace elements in biochemistry. New York, Academic Press. Brungs, W. A. (1963). The relative distribution of multiple radionuclides in a freshwater pond. PhD thesis, Ohio State University. Byrd, D. S., Gilmore, J. T. & Lea, R. H. (1983). Effect of decreased use of lead in gasoline on the soil of a highway. Environ. Sci. Technol., 17, 121-3. Clark Jr, D. R. (1979). Lead concentrations: Bats vs terrestrial small mammals collected near a major highway. Environ. Sci. Technol., 13, 338~41. Cooke, A. S. (1981). Tadpoles as indicators of harmful levels of pollution in the field. Environ Pollut., Ser. A, 12, 123-33. Dickerson, M. P. (1906). The frog book. New York, Doubleday, Page & Co. Diters, R. W. & Nielsen, S. W. (1978). Lead poisoning of raccoons in Connecticut. J. Wildl. Dis., 14, 187-92. Drifmeyer, J. E. (1975). Lead enters food web of estuarine organisms. Worm Dredging, Nov., 41-3. Edens, F. W., Benton, E., Bursian, S. J. & Morgan, G. W. (1976). Effects of dietary lead on reproductive performance in Japanese quail, Coturnix coturnix japonica. Toxicol. Appl. Pharmaeol., 38, 307-14. Franson, J. C., Sileo, L., Pattee, O. H. & Moore, J. F. (1983). Effects of chronic dietary lead in American kestrels (Falco sparverius). J. Wildl. Dis., 19, i10-13. Gale, N. L., Wixon, B. G., Hardie, M. G. & Jennett, J. C. (1973). Aquatic organisms and heavy metals in Missouri's new lead belt. Water Res. Bull., 9, 673-88.
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