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Small mammal heavy metal concentrations from mined and control sites
EnvironmentalPollution(SeriesA) 28 (1982) 121 134
SMALL
MAMMAL HEAVY METAL CONCENTRATIONS FROM MINED AND CONTROL SITES
GREGORY J. SMITH & ORRIN J. RONGSTAD
Department o f Wildlife Ecology, University of Wisconsin, 226 Russell Laboratories, 1630 Linden Drive, Madison, Wisconsin 53706, USA
ABSTRACT
Total body concentrations of zinc, copper, cadmium, lead, nickel, mercury and arsenic were determined for Peromyscus maniculatus and Microtus pennsylvanicus from an active zinc-copper mine near Timmins, Ontario, Canada, and a proposed zinc-copper mine near Crandon, Wisconsin, USA. Metal concentrations were evaluated with respect to area, species, sex and age groups. Metal concentrations in Peromyscus from the proposed mine site were not different from those collected in a third area where no mine or deposit exists. This is probably due to the 30 m of glacial material over the proposed mine site deposit. A statistical interaction between area, species, sex and age was observed for zinc and copper concentrations in small mammals we examined. Peromyscus from the mine site had consistently higher metal concentrations than Peromyscus from the control site. Greater total body cadmium and lead concentrations in adult--compared with juvenile--Peromyscus collected at the mine site suggests age-dependent accumulation of these toxic metals. Microtus did not exhibit this age-related response, and responded to other environmental metals more erratically and to a lesser degree. Differences in the response of these two species to environmental metal exposure may be due to differences in food habits. Nickel, mercury and arsenic concentrations in small mammals from the mine site were not different from controls. Heavy metal concentrations are also presentedJbr Sorex cinereus, Blarina brevicauda and Zapus hudsonicus without respect to age and sex cohorts. Peromyscus may be a potentially important species for the monitoring of heavy metal pollution.
INTRODUCTION
This paper describes differences in total body heavy metal concentrations in small mammals collected at an active zinc-copper mine site and at a site where a similar 121 Environ. Pollut, Ser. A. 0143-1471/82/0028-0121/$02-75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain
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GREGORY J. SMITH, ORRIN J. RONGSTAD
metal ore deposit has recently been discovered. The latter study area serves as a control site for current comparisons with the mined site, and also provides a temporal control for subsequent 'before' and 'after' comparisons when mining begins this decade. Small mammal heavy metal levels from the proposed mine site were also compared with an area where no mine or deposit is located. We also compared the responses of Peromyscus and Microtus to environmental metal exposure and determined the potential for using these small mammals to monitor heavy metal pollution. Total body heavy metal concentrations by species, from the active mine and proposed mine areas, are evaluated with respect to age and sex cohorts. Undesirable environmental effects of heavy metals have long been recognised. However, little information is available concerning the relationship between metalcontaminated environments and their indigenous fauna (Roberts et al., 1979). Metal concentrations in small mammals living in polluted environments and uncontaminated areas provide an insight into potential bioaccumulation, mobility within the ecosystem, response relationships and relative food chain transport (Johnson et al., 1978; Roberts & Johnson, 1978). Adverse biological impacts of heavy metals on mammals can occur in different ways including decreased reproduction, specific organ toxicity and carcinogenic, mutagenic and teratogenic effects (Beliles, 1975). The biological impact of a particular metal also depends on the metal's availability, toxicity, type of exposure (portal of entry) and the chemical state of the element (Beliles, 1975; Goldsmith & Scanlon, 1977). Mobility and accumulation within the animal depend upon homeostatic mechanisms within the animal's body. Elements essential to animals, such as zinc and copper, tend to be better regulated in the vertebrate body than non-essential metals such as lead, cadmium, nickel, mercury and arsenic (Bellies, 1975: Roberts & Johnson, 1978). Several studies have examined lead concentrations in small mammals exposed to automobile emissions (Jefferies & French, 1972; Mierau & Favara, 1975: Goldsmith & Scanlon, 1977; Clark, 1979). Some studies have also examined selected metal concentrations in small mammals from metalliferous mine and control sites (Martin & Coughtrey, 1975; Johnson et al., 1978: Roberts & Johnson, 1978). However, few studies have evaluated the interaction of area contamination, species, age and sex when assessing the response of small mammals to environmental heavy metal exposure.
METHODS
Study areas The proposed mine site is located 9km south of Crandon, Wisconsin, USA (Forest County). This study area was selected to provide baseline data for comparisons after the development of the mine and for current comparisons with an
HEAVY METALS IN MAMMALS FROM MINES
123
actively mined area. The ore composition for this deposit is approximately 5 ~ zinc, 1. l ~o copper and 0.4 ~o lead with trace amounts of other metals. The deposit is a massive sulphide type overlain by about 30 m of glacial material and will require underground mining. Mining is scheduled to begin in the mid-1980s. Vegetation on the proposed mine site is principally aspen (Populus spp.)northern hardwoods-mixed conifer stands at different successional stages. The upland forests are characterised by aspen, sugar maple Acer saccharum, red maple A. rubrum, northern red oak Quercus rubra, white pine Pinus strobus, and red pine P. resinosa. Lowland forests are typically black spruce Picea mariana, balsam fir Abies balsamea, and tamarack Larix laricma. The actively mined study site selected is 21 km north of Timmins, Ontario, Canada. This area has a long history of metal ore mining. The specific site we chose was first mined as an open pit from 1966 to 1973. Since 1973, all mining operations have been underground. The ore deposit at this site is also classified as a stratiform, massive, base metal sulphide deposit with the ore composed of approximately 9.8 ~o zinc, 1.5 ~o copper and 0.4~/o lead, cadmium being removed as a by-product (Matulich et al., 1974). Vegetation at the active mine site is characteristic of northern disturbed areas. Much of the area we worked on had been revegetated to prevent erosion. Ground cover was predominantly of various grasses--Poaceae, purple loosestrife Lythrum salicaria and crown vetch Coronilla varia. Adjacent to the mine, typical boreal forest communities occurred including black spruce, tamarack and muskeg in low areas. Aspen, birch Betula spp., jackpine P. banksiana and northern hardwoods are found at well drained sites.
Sampling Small mammals were captured, during summer months, in baited mouse- and ratsize snap-traps. Traps were placed at stations spaced 10 m apart and each trapline consisted of 25- 100 stations. At each station, two mouse-traps were set and at every fifth station one rat-trap was set. Specimens were identified, weighed and stored frozen in separate polyethylene bags for later dissection and analysis. Sample preparation and laboratory analyses Each sample consisted of five individuals of the same species, sex and age cohort. Age was determined on the basis of weight class with heavier animals--often with signs of reproduction (e.g. uterine scars or embryos in females)--being classified as adults. Animals in the lighter weight classes were classified as juveniles. The five individuals per sample were simultaneously homogenised in a commercial Waring blender. Each sample was frozen in a sealed, metal-clean jar and later packed in dry ice and shipped via airfreight to Analytical Biochemistry Laboratories, Columbia, Missouri, USA. All glassware and instruments used in sample preparation were double-washed in reagent grade nitric acid and rinsed with metal-free deionised
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GREGORY J. SMITH, ORRIN J. RONGSTAD
water. A total of sixty, forty-three and five composite small mammal samples were analysed from the proposed mine, the active mine and a study area where no mine or deposit exists, respectively. In the control area, with no ore deposit at the site, all five samples were of Peromyscus. At the proposed mine site, we obtained composite samples of sixteen Peromyscus, thirty Microtus, seven Sorex, two Blarina and five Zapus. At the active mine site we obtained thirty Peromyscus, nine Microtus, two Blarina and two composite Zapus samples. Five Peromyscus samples from each of the proposed mine and active mine areas were analysed for mercury and arsenic concentrations in our first series of analyses. Subsequently, because of low concentrations at both sites, we did not analyse for either of these elements. All other samples were analysed for concentrations of zinc, copper, cadmium, lead and nickel. At Analytical Biochemistry Laboratories, samples were digested in doubledistilled nitric acid and brought to volume with deionised water. Samples were analysed by atomic absorption spectrophotometry using a Perkin Elmer model 305B atomic absorption unit with background correction. Zinc, copper and cadmium analyses were performed by flame atomic absorption. Lead and nickel concentrations were determined by flameless atomic absorption, using a graphite furnace for ashing. Arsenic analyses were performed by flame spectrophotometry in conjunction with a Perkin Elmer MHS-10 hydride generation system, and mercury concentrations were determined by cold vapour procedures. All results are reported as wet weight concentrations (pg g-1). Statistical comparisons were made by analysis of variance using a 24 completely crossed design to examine area, species, sex and age factors, as well as statistical interactions (Box et al., 1978). Statistical analyses were performed on log transformed data where the variance was found to be proportional to the mean.
RESULTS
Mean total body zinc, copper, cadmium, lead and nickel concentrations (+ 1 standard deviation) for the five composite samples of all sex and age groups of Peromyscus from the control area in Wisconsin, where no ore deposit or mine exists, were 34.1 + 1.3, 4.1 _ 0.2, 0.1 _ 0.0, 0.46 + 0.17 and 1.0 _ 0.3 #gg- l, respectively. Wet weight concentrations were similar to those we observed for Peromyscus from the proposed mine site (Table 1). A significant interaction between area, species, sex and age (p = 0.002) was determined for total body zinc concentrations in Peromyscus and Microtus from the mined and proposed mine areas. Although zinc concentrations were higher in specimens from the active mine site compared with those from the proposed mine site, the pattern of zinc concentrations for the sex and age cohorts differed between species and areas (Table 1).
TABLE 1
"Nffi5. b N=ll. "N=3.
Microtus
Peromyscus
Species
Ad.~ Ad. 9 Juv.~ Juv. 9 Ad.~ Ad. 9 Juv.~ Juv. 9
Cohort
5 5 4 2 4 12 7 7
N
31'6±2"3 32"3±2-0 30'0±1'3 29"2 31'9±1'3 29.4±1.4 31'6±2'2 31-4±3"0
Zn
4"1±0"5 4-5±0"5 4"4±0"2 3-8 3"8±1"6 3.6±0.7 4"1±0-8 4"0±0"9
<0-1 <0-1 <0'1 <0"1 <0-1 <0.1 <0"1 <0"l
Proposed mine site Metal eoncen. (llg g - 1 ) Cu Cd
0"5±0'1 0"9±1-1 0"4±0.1 0"5 0"4±0'2 0.4±0-3 0'7±0"4 0"6±0"3
Pb
I-9±1-1 2'8±2"6 1-5±0-5 1'5 0"9±0-7 1.0±0.8 1'7±1.0 I-7±0"5
Ni
7 5 12 6 4 3 I 1
N
63-9±15-1 a 67.7±6-4 c 61.8±15-4 b 64"6±9-8 ° 38'6±6.5 58-3±17-4 81"6 42"0
Zn
15"7±7"6 13'2±4"6 14"1±3.4 14-0±1"4 5"5±2"4 9.9±4.4 10.4 7"7
0"5±0"1 0"6±0"4 0"4+0.0 0'4±0"0 0-3±0'1 0.5±0.2 0'4 0"5
Active mine site Metal concert. (gg g 1) Cu Cd
4"9±2"3 5"0±2"2 3"8±2'6 4"0±1-6 0"7±0"3 0.6±0.1 0'6 0"8
Pb
1-7±0"6" 1.2±0.5 c 1.8±0.8 b 1.6±0-4 ~ 0"8±0"6 1.4±1.0 1"8 0'8
Ni
WET WEIGHT C O N C E N T R A T I O N S OF HEAVY METALS IN Peromyscus AND Microtus COLLECTED AT CONTROL (PROPOSED MINING) AND ACTIVE MINING AREAS DURING SUMMER PERIODS, 1978 79. SAMPLE SIZES REPRESENT POOLS OF FIVE INDIVIDUALS OF THE SAME SEX AND AGE (WEIGHT CLASS). MEAN METAL CONCENTRATION (/~gg-1)+ 1 SD
t,J q~
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>
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126
GREGORY J. SMITH, ORRIN J. RONGSTAD
Total body copper concentrations also showed a significant area, species, sex and age interaction (p = 0-027). As we observed for zinc concentrations, mean copper concentrations for each of the species compared did not overlap between areas (Fig. 1). However, again no consistent pattern of total body copper was observed for sex and age cohorts in either study area or species. A significant interaction of area and species was determined for total body lead concentrations for small mammals we examined (p = 0.001). Peromyscus at the active mine site had higher lead concentrations than Microtus. Microtus at the active mine had similar lead concentrations compared with both Peromyscus and Microtus collected at the proposed mine site (Fig. 1). Specimens collected at the active mine had significantly greater cadmium concentrations than did small mammals collected at the proposed mine site (p = 0.001). This revealed a clear response of both species to environmental cadmium exposure. An interaction between species and age (p = 0.046) may be attributed to adult Peromyscus from the active mine having higher cadmium concentrations than juvenile Peromyscus, while Microtus did not exhibit any concentration differences with age. Total body nickel concentrations were significantly greater in Peromyscus than in Microtus (p = 0.020). Nickel concentrations did not differ between areas in either species. Mercury and arsenic total body concentrations determined for five composite Peromyscus samples from the active mine site and five samples from the proposed mine site were less than 0-10 ktg g-1 (wet weight). The only sample with a greater concentration was a single Peromyscus with an arsenic concentration of 0.2 ~g g- 1. Total body zinc and cadmium concentrations in Sorex collected at the proposed mine site were slightly higher than those metal concentrations for Peromyscus and Microtus from the same area (Table 2). Copper and lead concentrations in Sorex were similar to, and nickel concentrations were lower than, levels we observed for Peromyscus and Microtus collected from the same area (Tables 1 and 2). Zapus collected at the active mine site also had higher concentrations of all metals compared with mine site Peromyscus and higher concentrations of zinc, copper and cadmium than mine site Microtus (Table 2). Two Blarina brevicauda composite samples (one of each sex) from each area were analysed. Blarina from the active mine site had higher zinc, copper, cadmium and arsenic concentrations than Blarina from the proposed mine site (Table 2). The arsenic concentration of 0.82 ~g g- 1 for a female Blarina sample from the mine area and the mean Blarina cadmium concentration of 2-0 #g g- 1 from the mine site were the highest for these metals that we observed in any of the total body specimens. This might be due to the carnivorous food habits of this species. Since sample sizes were small for Sorex, Zapus and Blarina, no statistical comparisons were made for these species. Instead, these data were combined without regard to sex or age class (Table 2) and presented for possible general comparisons with other studies where sex and age effects are not evaluated.
8OO ZINC 600
400
Jill ilil 160
COPPER 120
80 uJ
=
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,o iiil
m •
!: ._!
I'l
0.6
o
CADMIUM
"i
O4 z LU £) Z 0
i!11 Jirjlil, ilili il
02
50
LEAD C3 0 m
30
0 1.0 2:
,.
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~J,n
Is!l
30
NICKEL
,,,, ii[
i
| 20
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Microlus
ill.!
Peromyscus
A
Microlus
Peromyscus
B
Fig. 1. Mean wet weight concentrations of heavy metals in Peromyscus and Microtus collected at the control-proposed mine site (A) and at the active mine site (B) study areas. Mean concentrations are represented for four sex and age groups for each species. From left to right: double interrupted bar, juvenile females; bias interrupted bar, juvenile males; single interrupted bar, adult females; solid bar, •adult males.
35.53 _+ 4.03 4.11 4- 0.53 0.24 +_ 0-11 0.88 4- 0.25 1-46 4- 0-21
Zinc Copper Cadmium Lead Nickel Mercury Arsenic
34.42 3.54 < 0.46 0.71
_ 3.05 + 0.54 0q 1 4- 0.19 4- 0.25
Z a p u s (n = 5) b 30.9 3.4 0.28 5.84 1.2 < 0.1 < 0.1
Blarina ( N = 2) c
Q Includes three adult male, one a d u l t female, two juvenile m a l e a n d one juvenile female samples. b Includes one a d u l t male, one a d u l t female, one juvenile m a l e a n d two juvenile female samples. c Includes one adult male, one a d u l t female samples.
Sorex (n = 7) a
Metal
Control site (proposed mining) Species
42.10 5.30 0.20 1.34 0.62
Z a p u s (n = 2) c
60.6 4.3 2.00 0-90 0.41 < 0.1 0.62
B l a r i n a (N = 2) c
Active mining site Species
TABLE 2 WET WEIGHT CONCENTRATIONS OF HEAVY METAL LEVELS IN Zapus, Blarina AND Sorex COLLECTED AT CONTROL (PROPOSED MINING) AND ACTIVE MINING AREAS DURING SUMMER PERIODS, 1978 79. SAMPLE SIZES REPRESENT POOLS OF FIVE INDIVIDUALS OF THE SAME SEX AND AGE (WEIGHT CLASS). MEAN METAL CONCENTRATION ( ~ g g - 1 ) + 1 S D
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0
0 0
tO OO
HEAVY METALS IN MAMMALS FROM MINES
129
DISCUSSION
Total body zinc and copper concentrations Zinc concentrations for Peromyscus and Microtus were higher at the mined site than at the proposed mine site. Peromyscus zinc levels at the mined site were higher than Microtus. Specimens collected at the proposed mine site showed little variability between species, sex and age groups for total body zinc concentrations. Microtus collected at the active mine site had a wider range of zinc concentrations than Peromyscus; however, the highest and lowest Microtus zinc concentrations represented only one composite sample for each. Johnson et al. (1978) determined significantly greater total body zinc concentrations in two of the six comparisons they made between mine and control areas in Wales. Total body analysis for zinc provides a sensitive assay for zinc contamination because skeletal tissues have been found to be long-term zinc storage sites in laboratory animals (Macapinlac et al., 1966). The four-factor interaction we observed in total body copper concentrations requires that area and species effects be interpreted with sex and age effects. Copper concentrations between sex and age cohorts of both species did not vary widely in the proposed mine site sample. However, samples collected at the active mine site indicate that Peromyscus retained more environmental copper than did Microtus. The pattern of copper concentrations again differed by area, species, sex and age. Greater variability in copper levels in Microtus at the mined area may be due to variability in the homeostatic mechanisms in this species or to small sample sizes for two of the Microtus sex-age cohorts examined. Schlesinger & Potter (1974) reported a mean total body wet weight copper concentration in Peromyscus to be 3.6 ~g g- 1 for males and 2.8/~g g- 1 for females. These animals were collected downwind from industrial centres in an area that received atmospheric deposition of heavy metals. These copper concentrations are lower than levels we determined for Peromyscus from our control areas. The difference between our highest control value and the lowest mean they reported (2.8 l~g g- 1) was 1.7/lg g- 1. The differences between our controls and levels that Schlesinger & Potter (1974) reported could be accounted for by differences in analytical procedure and experimental error. Both zinc and copper are bio-essential elements which are probably well regulated in most mammals. However, little is known about the seasonal changes of these elements in mammals. Total body analysis may tend to integrate the response of small mammals to heavy metal exposure compared with renal or liver concentrations, which may be more regulated. Although zinc and copper have a relatively low potential for toxicity, compared with some other metals, high exposure to these metals may affect reproduction or have other adverse affects on small mammal populations. More integration of field and laboratory research will
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GREGORY J. SMITH, ORRIN J. RONGSTAD
help determine whether these metals can pose a serious problem to mammalian fauna.
Total body lead and cadmium concentrations Peromyscus responded to environmental lead exposure at the active mine site, while Microtus did not have lead concentrations different from those of the control groups. This resulted in an interaction between species and area. Mierau & Favara (1975) determined that Peromyscus exposed to lead from automobile emissions had significantly higher lead concentrations than did controls. Schlesinger & Potter (1974) concluded that Peromyscus accumulated lead with age, as determined from total body analysis. Clark (1979) also reported that juvenile Peromyscus had lower lead concentrations than adults. Research concerning the response of Microtus to lead exposure is more conflicting. Beardsley et al. (1978) concluded that the response of Microtus to heavy metal pollution was too small and too erratic for the species to be used as an indicator of heavy metal contamination. Conversely, accumulation of lead by Microtus exposed to automobile emissions was demonstrated by Jefferies & French (1972). Clark (1979) determined that shrews and mice had higher total body lead concentrations than Microtus. Johnson et al. (1978) determined that Microtus taken from a mine site had significantly greater bone, kidney and liver lead concentrations than controls. Total body lead concentrations in Peromyscus from an atmospherically polluted area (Schlesinger & Potter, 1974) were greater than our control samples, but lower than Peromyscus we sampled from the active mine site. Heavy metals in mammals collected from roadsides and mine sites may not always be directly comparable. Our results indicate that Peromyscus total body lead concentrations do reflect environmental lead exposure; however, Microtus show no such response. Adult Peromyscus from the mine site had higher lead levels than juveniles, which suggests possible age-dependent accumulation. Cadmium levels in Peromyscus and Microtus were higher at the active mine site than at the proposed mine. The area effect did not interact with species, sex or age. The response of Microtus to cadmium exposure was different from response to lead. Again, Beardsley et al. (1978) concluded that Microtus did not adequately reflect environmental heavy metal exposure. This conflicts with our findings for cadmium levels in Microtus, Our results are consistent with those of Johnson et al. (1978), who determined significantly higher cadmium concentrations in Microtus from a mine compared with a control site. A significant interaction between species and age was determined for cadmium concentrations in small mammals we examined. Peromyscus cadmium concentrations suggest an accumulation with age, as we observed for lead in Peromyscus. Microtus did not exhibit any age-related response to this metal. Schlesinger & Potter (1974) also found an age-dependent accumulation of cadmium
HEAVY METALS IN MAMMALS FROM MINES
131
in Peromyscus from a contaminated environment. Both Peromyscus and Microtus collected at the proposed mine site had cadmium concentrations of less than 0.1 # g g - 1 . We suggest that Microtus does exhibit a response in total body concentration to environmental cadmium exposure; however, Peromyscus exhibits a greater response which is also age-dependent. Therefore, we consider Peromyscus to be a more accurate indicator of environmental cadmium contamination than Microtus.
Total body nickel, mercury and arsenic concentrations Although nickel levels at the active mine were higher than at the proposed mine, these differences were not significant. The lack of a significant area effect or interaction for nickel concentrations indicates that either environmental nickel levels were not reflected in small mammals or that nickel levels at the mine site were low. We believe that the latter explanation is the most likely, as nickel is found at the active mine in extremely small amounts. Peromyscus had significantly greater total body nickel concentrations than did Microtus. This condition might be attributable to basic differences in physiology between these species. The analyses of the ten Peromyscus composite samples from the active mine and proposed mine areas indicated that mercury and arsenic conditions were very low at both sites. Because of the low concentrations of these elements in initial samples we examined, and the lack of an area effect, we did not determine mercury and arsenic levels for subsequent samples. These highly toxic elements probably do not pose a serious environmental problem in this zinc copper mining operation.
Ecological impacts oj heat,)' metals We doubt that any of the total body metal concentrations that we observed in small mammals reached toxic levels. However, it is possible that subtle environmental problems could occur with few noticeable symptons. Shortened life spans were reported for rats fed 5 ppm of lead or cadmium (Schroeder et al., 1965). The largest proportion of the total body metal burdens probably occurred in bone, hair and skin tissues. Storage of metals in these tissues makes them largely unavailable to carnivorous animals which utilise small mammals as food. In our study areas, coyotes Canis latrans, red foxes Vulpes vulpes and several raptors utilise small mammals for food and could potentially be chronically exposed to heavy metals through the food chain. Cadmium and lead have the potential for bio-accumulation and could have a serious impact on individuals that are chronically exposed to these metals. Cadmium concentrations in small mammals at the mine site were less than 1.0/~gg -1. Browning (1969) reported that cats Felix domesticus fed 1 - 4 p p m cadmium developed anaemia. Similarly, low dietary levels of lead can result in lethal toxicity in mammals (Venugopal & Luckey, 1978). Zinc is a relatively non-toxic metal due to efficient homeostatic mechanisms
132
GREGORY J. SMITH, ORRIN J. RONGSTAD
(Venugopal & Luckey, 1978; Beliles, 1979). It is likely that far greater concentrations would have to occur in the small mammals we examined before serious problems would occur with those species or with species at higher trophic levels. Conversely, copper has a much greater potential for toxicity than zinc. Chronic dietary copper exposure of 10-15 ppm caused hepatic accumulation and sudden haemolytic crisis in sheep (Venugopal & Luckey, 1978). We observed small mammal copper concentrations in this range ( 13.2-15.7 pg g - 1) for Peromyscus at the mine site. Therefore, copper toxicity could potentially occur in carnivores utilising small mammals for food, if exposure were chronic. More research is needed to determine the relationship between total body metal burdens, heavy metal toxicity and bio-accumulation in species at different trophic levels in the terrestrial food chain.
CONCLUSIONS
Total body concentrations of zinc, copper, cadmium and lead in small mammals were generally higher in all species collected at an actively mined site than at a control area where zinc-copper mining has been proposed, Peromyscus collected at the proposed mine site did not have heavy metal concentrations different from specimens taken at a control site where no mine or ore deposit exists. Therefore, specimens collected at the proposed mine site were probably not affected by the ore deposit, and specimens may be considered as controls for not only 'before' and 'after' comparisons, but also for comparisons with the active mine area. A complete separation of mean metal values was found between area comparisons for both Peromyscus and Microtus. However, nickel levels in small mammals did not differ significantly between areas. This is probably due to the small amount of nickel in the active mine ore deposit. Peromyscus had significantly greater nickel concentrations than Microtus. This may be attributable to differences in physiology. It is unlikely that any of the total body metal burdens we observed in either of the species at the active mine site reached near toxic levels. However, accumulation of heavy metals in small mammals represents a potential for transference and accumulation of metals at higher trophic levels. Predators which make small mammals a large portion of their diet may possibly receive chronic dietary exposure to heavy metals stored in tissues of these animals. Peromyscus total body metal concentrations showed a greater and more consistent response to environmental heavy metal exposure than did Microtus. This species difference in response to zinc, copper and lead exposure resulted in a significant interaction between area and species for these metals. However, a significant interaction between area, species, sex and age was determined for both zinc and copper analyses. Microtus total body concentrations did respond to cadmium exposure, and the main area effect for cadmium did not interact with
HEAVY METALS IN MAMMALS FROM MINES
133
species, sex or age. The greater response of Peromyscus to environmental heavy metal exposure than Microtus may be at least partially attributable to differences in food habitats. While Microtus rely almost entirely on vegetation, fruits and bark, Peromyscus also feed on insects and invertebrates (Walker, 1975), which may tend to accumulate certain metals (Roberts & Johnson, 1978). We conclude that Peromyscus is likely to be a more accurate indicator of environmental heavy metal contamination than Microtus. Generally, metal concentrations for both species collected at the active mine site had larger standard errors of the mean values than did samples from the proposed mine area. This is possibly due to greater heterogeneity in the distribution and absolute amounts of heavy metals at the mine site. Lead and cadmium levels in Peromyscus taken at the active mine site were higher for adults than juveniles. Both these metals are non-essential, highly toxic, and have been demonstrated to accumulate with age in certain small mammals. Agedependent accumulation of these metals probably occurred in Peromyscus at the mine site, whereas we did not observe this condition in Microtus. Mercury and arsenic total body concentrations in Peromyscus were low for both the proposed mine and active mine areas. Therefore, these metals probably do not pose an important environmental problem in mining operations at a massive sulphide zinc-copper deposit. We conclude that Peromyscus may be a potentially important species for the monitoring of heavy metal pollution. This genus has a large geographic distribution, usually occurs in sufficient numbers and is easily captured. Total body analyses of small mammals do reflect gross differences in environmental heavy metal exposure; however, the model which describes the response relationship is not known. More research is needed to determine the physiological and behavioural correlates of specific total body heavy metal concentrations.
ACKNOWLEDGEMENTS
We thank M. Backes, M. Foy, E. Haug, C. Morgan and R. Rolley for assistance with field collections. Research was supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, USA, and by the Patuxent Wildlife Research Center (US Fish and Wildlife Service).
REFERENCES
BEARDSLEY,A., VAGG,M. J., BECKET,P. H. T. & SANSOM,B. F. (1978). Use of the field vole (M. agrestis) for monitoring potentially harmful elements in the environment. Environ. Pollut., 16, 65-71.
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BELILES, R. P. (1975). Metals. In Toxicology, ed. by L. J. Casarett and J. Doull, 454-502. New York, Macmillan. BELILES, R. P. (1979). The lesser metals. In Toxicity of heavy metals in the environment, Part 2, ed. by F. W, Oehme, 547-615. New York, Marcel Dekker. Box, G. E. P., HUNTER, W. G. & HUNTER, J. S. (1978). Statistics for experimenters. New York, John Wiley. BROWNING, E. (1969). Toxicity of industrial metals. London, Butterworth. CLARK, D. R. (1979). Lead concentrations: Bats vs. terrestrial mammals collected near a major highway. Environ. Sci. & Technol., 3, 338-41. GOLDSMITH, C. D. & SCANLON, P. F. (1977). Lead levels in small mammals and selected invertebrates associated with highways of different traffic densities. Bull. environ. Contain. & To xicol., 17, 311 - 16. JEFFERtES, D. J. & FRENCH, M. C. (1972). Lead concentrations in small mammals trapped on roadside verges and field sites. Environ. Pollut., 3, 147-56. JOHNSON, M. S., ROBERTS,R. D., HUTTON, U. K. M. & INSKIP, M. J. (1978). Distribution of lead, zinc, and cadmium in small mammals from polluted environments. Oikos, 30, 153-9. MACAPlNLAC, M. P., PEARSON,W. N. & DERBY, W. J. (1966). Some characteristics of zinc deficiency in the albino rat. In Zinc metabolism, ed. by A. S. Prasad, 142-68. Springfield, II1., Charles Thomas. MART1N, M. H. & COUGHTREY, P. J, (1975). Preliminary observations on the levels of cadmium in a contaminated environment. Chemosphere, 3, 155-60. MATULICH, A., AMOS, A. C., WALKER, R. R. & WATKINS, J. J. (1974). The Ecstall story--The geology department. Can. Mining Metall. Bull., 67, 56-69. MIERAU, G. W. & FAVARA,B. E. (1975). Lead poisoning in roadside populations of deermice. Environ. Pollut., 8, 55-64. ROBERTS,R. D. & JOHNSON, M. S. (1978). Dispersal of heavy metals from abandoned mine workings and their transference through terrestrial food chains. Environ. Pollut., 16, 293-310. ROBERTS, R. D., JOHNSON, M. S. & HUTTON, M. (1979). Lead contamination of small mammals from abandoned metalliferous mines. Environ. Pollut., 15, 61-9. SCHLESlNGER, W. H. & POTTER, G. L. (1974). Lead, copper, and cadmium concentrations in small mammals in the Hubbard Brook Experimental Forest. Oikos, 25, 148-52. SCHROEDER,H. A., BALASSA,J. J. & V1NTON,W. H. (1965). Chromium, cadmium, and lead in rats: Effects on life span, tumors, and tissue levels. J. Nutr., 86, 51-66. VENUGOPAL,B. & LUCF,EY, T. D. (1978). Metal toxicity in mammals. Part 2. New York, Plenum Press. WALKER, E. P. (1975). Mammals of the world, 3rd edn. Baltimore, Johns Hopkins.
SMALL
MAMMAL HEAVY METAL CONCENTRATIONS FROM MINED AND CONTROL SITES
GREGORY J. SMITH & ORRIN J. RONGSTAD
Department o f Wildlife Ecology, University of Wisconsin, 226 Russell Laboratories, 1630 Linden Drive, Madison, Wisconsin 53706, USA
ABSTRACT
Total body concentrations of zinc, copper, cadmium, lead, nickel, mercury and arsenic were determined for Peromyscus maniculatus and Microtus pennsylvanicus from an active zinc-copper mine near Timmins, Ontario, Canada, and a proposed zinc-copper mine near Crandon, Wisconsin, USA. Metal concentrations were evaluated with respect to area, species, sex and age groups. Metal concentrations in Peromyscus from the proposed mine site were not different from those collected in a third area where no mine or deposit exists. This is probably due to the 30 m of glacial material over the proposed mine site deposit. A statistical interaction between area, species, sex and age was observed for zinc and copper concentrations in small mammals we examined. Peromyscus from the mine site had consistently higher metal concentrations than Peromyscus from the control site. Greater total body cadmium and lead concentrations in adult--compared with juvenile--Peromyscus collected at the mine site suggests age-dependent accumulation of these toxic metals. Microtus did not exhibit this age-related response, and responded to other environmental metals more erratically and to a lesser degree. Differences in the response of these two species to environmental metal exposure may be due to differences in food habits. Nickel, mercury and arsenic concentrations in small mammals from the mine site were not different from controls. Heavy metal concentrations are also presentedJbr Sorex cinereus, Blarina brevicauda and Zapus hudsonicus without respect to age and sex cohorts. Peromyscus may be a potentially important species for the monitoring of heavy metal pollution.
INTRODUCTION
This paper describes differences in total body heavy metal concentrations in small mammals collected at an active zinc-copper mine site and at a site where a similar 121 Environ. Pollut, Ser. A. 0143-1471/82/0028-0121/$02-75 © Applied Science Publishers Ltd, England, 1982 Printed in Great Britain
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GREGORY J. SMITH, ORRIN J. RONGSTAD
metal ore deposit has recently been discovered. The latter study area serves as a control site for current comparisons with the mined site, and also provides a temporal control for subsequent 'before' and 'after' comparisons when mining begins this decade. Small mammal heavy metal levels from the proposed mine site were also compared with an area where no mine or deposit is located. We also compared the responses of Peromyscus and Microtus to environmental metal exposure and determined the potential for using these small mammals to monitor heavy metal pollution. Total body heavy metal concentrations by species, from the active mine and proposed mine areas, are evaluated with respect to age and sex cohorts. Undesirable environmental effects of heavy metals have long been recognised. However, little information is available concerning the relationship between metalcontaminated environments and their indigenous fauna (Roberts et al., 1979). Metal concentrations in small mammals living in polluted environments and uncontaminated areas provide an insight into potential bioaccumulation, mobility within the ecosystem, response relationships and relative food chain transport (Johnson et al., 1978; Roberts & Johnson, 1978). Adverse biological impacts of heavy metals on mammals can occur in different ways including decreased reproduction, specific organ toxicity and carcinogenic, mutagenic and teratogenic effects (Beliles, 1975). The biological impact of a particular metal also depends on the metal's availability, toxicity, type of exposure (portal of entry) and the chemical state of the element (Beliles, 1975; Goldsmith & Scanlon, 1977). Mobility and accumulation within the animal depend upon homeostatic mechanisms within the animal's body. Elements essential to animals, such as zinc and copper, tend to be better regulated in the vertebrate body than non-essential metals such as lead, cadmium, nickel, mercury and arsenic (Bellies, 1975: Roberts & Johnson, 1978). Several studies have examined lead concentrations in small mammals exposed to automobile emissions (Jefferies & French, 1972; Mierau & Favara, 1975: Goldsmith & Scanlon, 1977; Clark, 1979). Some studies have also examined selected metal concentrations in small mammals from metalliferous mine and control sites (Martin & Coughtrey, 1975; Johnson et al., 1978: Roberts & Johnson, 1978). However, few studies have evaluated the interaction of area contamination, species, age and sex when assessing the response of small mammals to environmental heavy metal exposure.
METHODS
Study areas The proposed mine site is located 9km south of Crandon, Wisconsin, USA (Forest County). This study area was selected to provide baseline data for comparisons after the development of the mine and for current comparisons with an
HEAVY METALS IN MAMMALS FROM MINES
123
actively mined area. The ore composition for this deposit is approximately 5 ~ zinc, 1. l ~o copper and 0.4 ~o lead with trace amounts of other metals. The deposit is a massive sulphide type overlain by about 30 m of glacial material and will require underground mining. Mining is scheduled to begin in the mid-1980s. Vegetation on the proposed mine site is principally aspen (Populus spp.)northern hardwoods-mixed conifer stands at different successional stages. The upland forests are characterised by aspen, sugar maple Acer saccharum, red maple A. rubrum, northern red oak Quercus rubra, white pine Pinus strobus, and red pine P. resinosa. Lowland forests are typically black spruce Picea mariana, balsam fir Abies balsamea, and tamarack Larix laricma. The actively mined study site selected is 21 km north of Timmins, Ontario, Canada. This area has a long history of metal ore mining. The specific site we chose was first mined as an open pit from 1966 to 1973. Since 1973, all mining operations have been underground. The ore deposit at this site is also classified as a stratiform, massive, base metal sulphide deposit with the ore composed of approximately 9.8 ~o zinc, 1.5 ~o copper and 0.4~/o lead, cadmium being removed as a by-product (Matulich et al., 1974). Vegetation at the active mine site is characteristic of northern disturbed areas. Much of the area we worked on had been revegetated to prevent erosion. Ground cover was predominantly of various grasses--Poaceae, purple loosestrife Lythrum salicaria and crown vetch Coronilla varia. Adjacent to the mine, typical boreal forest communities occurred including black spruce, tamarack and muskeg in low areas. Aspen, birch Betula spp., jackpine P. banksiana and northern hardwoods are found at well drained sites.
Sampling Small mammals were captured, during summer months, in baited mouse- and ratsize snap-traps. Traps were placed at stations spaced 10 m apart and each trapline consisted of 25- 100 stations. At each station, two mouse-traps were set and at every fifth station one rat-trap was set. Specimens were identified, weighed and stored frozen in separate polyethylene bags for later dissection and analysis. Sample preparation and laboratory analyses Each sample consisted of five individuals of the same species, sex and age cohort. Age was determined on the basis of weight class with heavier animals--often with signs of reproduction (e.g. uterine scars or embryos in females)--being classified as adults. Animals in the lighter weight classes were classified as juveniles. The five individuals per sample were simultaneously homogenised in a commercial Waring blender. Each sample was frozen in a sealed, metal-clean jar and later packed in dry ice and shipped via airfreight to Analytical Biochemistry Laboratories, Columbia, Missouri, USA. All glassware and instruments used in sample preparation were double-washed in reagent grade nitric acid and rinsed with metal-free deionised
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GREGORY J. SMITH, ORRIN J. RONGSTAD
water. A total of sixty, forty-three and five composite small mammal samples were analysed from the proposed mine, the active mine and a study area where no mine or deposit exists, respectively. In the control area, with no ore deposit at the site, all five samples were of Peromyscus. At the proposed mine site, we obtained composite samples of sixteen Peromyscus, thirty Microtus, seven Sorex, two Blarina and five Zapus. At the active mine site we obtained thirty Peromyscus, nine Microtus, two Blarina and two composite Zapus samples. Five Peromyscus samples from each of the proposed mine and active mine areas were analysed for mercury and arsenic concentrations in our first series of analyses. Subsequently, because of low concentrations at both sites, we did not analyse for either of these elements. All other samples were analysed for concentrations of zinc, copper, cadmium, lead and nickel. At Analytical Biochemistry Laboratories, samples were digested in doubledistilled nitric acid and brought to volume with deionised water. Samples were analysed by atomic absorption spectrophotometry using a Perkin Elmer model 305B atomic absorption unit with background correction. Zinc, copper and cadmium analyses were performed by flame atomic absorption. Lead and nickel concentrations were determined by flameless atomic absorption, using a graphite furnace for ashing. Arsenic analyses were performed by flame spectrophotometry in conjunction with a Perkin Elmer MHS-10 hydride generation system, and mercury concentrations were determined by cold vapour procedures. All results are reported as wet weight concentrations (pg g-1). Statistical comparisons were made by analysis of variance using a 24 completely crossed design to examine area, species, sex and age factors, as well as statistical interactions (Box et al., 1978). Statistical analyses were performed on log transformed data where the variance was found to be proportional to the mean.
RESULTS
Mean total body zinc, copper, cadmium, lead and nickel concentrations (+ 1 standard deviation) for the five composite samples of all sex and age groups of Peromyscus from the control area in Wisconsin, where no ore deposit or mine exists, were 34.1 + 1.3, 4.1 _ 0.2, 0.1 _ 0.0, 0.46 + 0.17 and 1.0 _ 0.3 #gg- l, respectively. Wet weight concentrations were similar to those we observed for Peromyscus from the proposed mine site (Table 1). A significant interaction between area, species, sex and age (p = 0.002) was determined for total body zinc concentrations in Peromyscus and Microtus from the mined and proposed mine areas. Although zinc concentrations were higher in specimens from the active mine site compared with those from the proposed mine site, the pattern of zinc concentrations for the sex and age cohorts differed between species and areas (Table 1).
TABLE 1
"Nffi5. b N=ll. "N=3.
Microtus
Peromyscus
Species
Ad.~ Ad. 9 Juv.~ Juv. 9 Ad.~ Ad. 9 Juv.~ Juv. 9
Cohort
5 5 4 2 4 12 7 7
N
31'6±2"3 32"3±2-0 30'0±1'3 29"2 31'9±1'3 29.4±1.4 31'6±2'2 31-4±3"0
Zn
4"1±0"5 4-5±0"5 4"4±0"2 3-8 3"8±1"6 3.6±0.7 4"1±0-8 4"0±0"9
<0-1 <0-1 <0'1 <0"1 <0-1 <0.1 <0"1 <0"l
Proposed mine site Metal eoncen. (llg g - 1 ) Cu Cd
0"5±0'1 0"9±1-1 0"4±0.1 0"5 0"4±0'2 0.4±0-3 0'7±0"4 0"6±0"3
Pb
I-9±1-1 2'8±2"6 1-5±0-5 1'5 0"9±0-7 1.0±0.8 1'7±1.0 I-7±0"5
Ni
7 5 12 6 4 3 I 1
N
63-9±15-1 a 67.7±6-4 c 61.8±15-4 b 64"6±9-8 ° 38'6±6.5 58-3±17-4 81"6 42"0
Zn
15"7±7"6 13'2±4"6 14"1±3.4 14-0±1"4 5"5±2"4 9.9±4.4 10.4 7"7
0"5±0"1 0"6±0"4 0"4+0.0 0'4±0"0 0-3±0'1 0.5±0.2 0'4 0"5
Active mine site Metal concert. (gg g 1) Cu Cd
4"9±2"3 5"0±2"2 3"8±2'6 4"0±1-6 0"7±0"3 0.6±0.1 0'6 0"8
Pb
1-7±0"6" 1.2±0.5 c 1.8±0.8 b 1.6±0-4 ~ 0"8±0"6 1.4±1.0 1"8 0'8
Ni
WET WEIGHT C O N C E N T R A T I O N S OF HEAVY METALS IN Peromyscus AND Microtus COLLECTED AT CONTROL (PROPOSED MINING) AND ACTIVE MINING AREAS DURING SUMMER PERIODS, 1978 79. SAMPLE SIZES REPRESENT POOLS OF FIVE INDIVIDUALS OF THE SAME SEX AND AGE (WEIGHT CLASS). MEAN METAL CONCENTRATION (/~gg-1)+ 1 SD
t,J q~
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>
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126
GREGORY J. SMITH, ORRIN J. RONGSTAD
Total body copper concentrations also showed a significant area, species, sex and age interaction (p = 0-027). As we observed for zinc concentrations, mean copper concentrations for each of the species compared did not overlap between areas (Fig. 1). However, again no consistent pattern of total body copper was observed for sex and age cohorts in either study area or species. A significant interaction of area and species was determined for total body lead concentrations for small mammals we examined (p = 0.001). Peromyscus at the active mine site had higher lead concentrations than Microtus. Microtus at the active mine had similar lead concentrations compared with both Peromyscus and Microtus collected at the proposed mine site (Fig. 1). Specimens collected at the active mine had significantly greater cadmium concentrations than did small mammals collected at the proposed mine site (p = 0.001). This revealed a clear response of both species to environmental cadmium exposure. An interaction between species and age (p = 0.046) may be attributed to adult Peromyscus from the active mine having higher cadmium concentrations than juvenile Peromyscus, while Microtus did not exhibit any concentration differences with age. Total body nickel concentrations were significantly greater in Peromyscus than in Microtus (p = 0.020). Nickel concentrations did not differ between areas in either species. Mercury and arsenic total body concentrations determined for five composite Peromyscus samples from the active mine site and five samples from the proposed mine site were less than 0-10 ktg g-1 (wet weight). The only sample with a greater concentration was a single Peromyscus with an arsenic concentration of 0.2 ~g g- 1. Total body zinc and cadmium concentrations in Sorex collected at the proposed mine site were slightly higher than those metal concentrations for Peromyscus and Microtus from the same area (Table 2). Copper and lead concentrations in Sorex were similar to, and nickel concentrations were lower than, levels we observed for Peromyscus and Microtus collected from the same area (Tables 1 and 2). Zapus collected at the active mine site also had higher concentrations of all metals compared with mine site Peromyscus and higher concentrations of zinc, copper and cadmium than mine site Microtus (Table 2). Two Blarina brevicauda composite samples (one of each sex) from each area were analysed. Blarina from the active mine site had higher zinc, copper, cadmium and arsenic concentrations than Blarina from the proposed mine site (Table 2). The arsenic concentration of 0.82 ~g g- 1 for a female Blarina sample from the mine area and the mean Blarina cadmium concentration of 2-0 #g g- 1 from the mine site were the highest for these metals that we observed in any of the total body specimens. This might be due to the carnivorous food habits of this species. Since sample sizes were small for Sorex, Zapus and Blarina, no statistical comparisons were made for these species. Instead, these data were combined without regard to sex or age class (Table 2) and presented for possible general comparisons with other studies where sex and age effects are not evaluated.
8OO ZINC 600
400
Jill ilil 160
COPPER 120
80 uJ
=
==
,o iiil
m •
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I'l
0.6
o
CADMIUM
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02
50
LEAD C3 0 m
30
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i
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Peromyscus
A
Microlus
Peromyscus
B
Fig. 1. Mean wet weight concentrations of heavy metals in Peromyscus and Microtus collected at the control-proposed mine site (A) and at the active mine site (B) study areas. Mean concentrations are represented for four sex and age groups for each species. From left to right: double interrupted bar, juvenile females; bias interrupted bar, juvenile males; single interrupted bar, adult females; solid bar, •adult males.
35.53 _+ 4.03 4.11 4- 0.53 0.24 +_ 0-11 0.88 4- 0.25 1-46 4- 0-21
Zinc Copper Cadmium Lead Nickel Mercury Arsenic
34.42 3.54 < 0.46 0.71
_ 3.05 + 0.54 0q 1 4- 0.19 4- 0.25
Z a p u s (n = 5) b 30.9 3.4 0.28 5.84 1.2 < 0.1 < 0.1
Blarina ( N = 2) c
Q Includes three adult male, one a d u l t female, two juvenile m a l e a n d one juvenile female samples. b Includes one a d u l t male, one a d u l t female, one juvenile m a l e a n d two juvenile female samples. c Includes one adult male, one a d u l t female samples.
Sorex (n = 7) a
Metal
Control site (proposed mining) Species
42.10 5.30 0.20 1.34 0.62
Z a p u s (n = 2) c
60.6 4.3 2.00 0-90 0.41 < 0.1 0.62
B l a r i n a (N = 2) c
Active mining site Species
TABLE 2 WET WEIGHT CONCENTRATIONS OF HEAVY METAL LEVELS IN Zapus, Blarina AND Sorex COLLECTED AT CONTROL (PROPOSED MINING) AND ACTIVE MINING AREAS DURING SUMMER PERIODS, 1978 79. SAMPLE SIZES REPRESENT POOLS OF FIVE INDIVIDUALS OF THE SAME SEX AND AGE (WEIGHT CLASS). MEAN METAL CONCENTRATION ( ~ g g - 1 ) + 1 S D
>
o:Z
0
0 0
tO OO
HEAVY METALS IN MAMMALS FROM MINES
129
DISCUSSION
Total body zinc and copper concentrations Zinc concentrations for Peromyscus and Microtus were higher at the mined site than at the proposed mine site. Peromyscus zinc levels at the mined site were higher than Microtus. Specimens collected at the proposed mine site showed little variability between species, sex and age groups for total body zinc concentrations. Microtus collected at the active mine site had a wider range of zinc concentrations than Peromyscus; however, the highest and lowest Microtus zinc concentrations represented only one composite sample for each. Johnson et al. (1978) determined significantly greater total body zinc concentrations in two of the six comparisons they made between mine and control areas in Wales. Total body analysis for zinc provides a sensitive assay for zinc contamination because skeletal tissues have been found to be long-term zinc storage sites in laboratory animals (Macapinlac et al., 1966). The four-factor interaction we observed in total body copper concentrations requires that area and species effects be interpreted with sex and age effects. Copper concentrations between sex and age cohorts of both species did not vary widely in the proposed mine site sample. However, samples collected at the active mine site indicate that Peromyscus retained more environmental copper than did Microtus. The pattern of copper concentrations again differed by area, species, sex and age. Greater variability in copper levels in Microtus at the mined area may be due to variability in the homeostatic mechanisms in this species or to small sample sizes for two of the Microtus sex-age cohorts examined. Schlesinger & Potter (1974) reported a mean total body wet weight copper concentration in Peromyscus to be 3.6 ~g g- 1 for males and 2.8/~g g- 1 for females. These animals were collected downwind from industrial centres in an area that received atmospheric deposition of heavy metals. These copper concentrations are lower than levels we determined for Peromyscus from our control areas. The difference between our highest control value and the lowest mean they reported (2.8 l~g g- 1) was 1.7/lg g- 1. The differences between our controls and levels that Schlesinger & Potter (1974) reported could be accounted for by differences in analytical procedure and experimental error. Both zinc and copper are bio-essential elements which are probably well regulated in most mammals. However, little is known about the seasonal changes of these elements in mammals. Total body analysis may tend to integrate the response of small mammals to heavy metal exposure compared with renal or liver concentrations, which may be more regulated. Although zinc and copper have a relatively low potential for toxicity, compared with some other metals, high exposure to these metals may affect reproduction or have other adverse affects on small mammal populations. More integration of field and laboratory research will
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GREGORY J. SMITH, ORRIN J. RONGSTAD
help determine whether these metals can pose a serious problem to mammalian fauna.
Total body lead and cadmium concentrations Peromyscus responded to environmental lead exposure at the active mine site, while Microtus did not have lead concentrations different from those of the control groups. This resulted in an interaction between species and area. Mierau & Favara (1975) determined that Peromyscus exposed to lead from automobile emissions had significantly higher lead concentrations than did controls. Schlesinger & Potter (1974) concluded that Peromyscus accumulated lead with age, as determined from total body analysis. Clark (1979) also reported that juvenile Peromyscus had lower lead concentrations than adults. Research concerning the response of Microtus to lead exposure is more conflicting. Beardsley et al. (1978) concluded that the response of Microtus to heavy metal pollution was too small and too erratic for the species to be used as an indicator of heavy metal contamination. Conversely, accumulation of lead by Microtus exposed to automobile emissions was demonstrated by Jefferies & French (1972). Clark (1979) determined that shrews and mice had higher total body lead concentrations than Microtus. Johnson et al. (1978) determined that Microtus taken from a mine site had significantly greater bone, kidney and liver lead concentrations than controls. Total body lead concentrations in Peromyscus from an atmospherically polluted area (Schlesinger & Potter, 1974) were greater than our control samples, but lower than Peromyscus we sampled from the active mine site. Heavy metals in mammals collected from roadsides and mine sites may not always be directly comparable. Our results indicate that Peromyscus total body lead concentrations do reflect environmental lead exposure; however, Microtus show no such response. Adult Peromyscus from the mine site had higher lead levels than juveniles, which suggests possible age-dependent accumulation. Cadmium levels in Peromyscus and Microtus were higher at the active mine site than at the proposed mine. The area effect did not interact with species, sex or age. The response of Microtus to cadmium exposure was different from response to lead. Again, Beardsley et al. (1978) concluded that Microtus did not adequately reflect environmental heavy metal exposure. This conflicts with our findings for cadmium levels in Microtus, Our results are consistent with those of Johnson et al. (1978), who determined significantly higher cadmium concentrations in Microtus from a mine compared with a control site. A significant interaction between species and age was determined for cadmium concentrations in small mammals we examined. Peromyscus cadmium concentrations suggest an accumulation with age, as we observed for lead in Peromyscus. Microtus did not exhibit any age-related response to this metal. Schlesinger & Potter (1974) also found an age-dependent accumulation of cadmium
HEAVY METALS IN MAMMALS FROM MINES
131
in Peromyscus from a contaminated environment. Both Peromyscus and Microtus collected at the proposed mine site had cadmium concentrations of less than 0.1 # g g - 1 . We suggest that Microtus does exhibit a response in total body concentration to environmental cadmium exposure; however, Peromyscus exhibits a greater response which is also age-dependent. Therefore, we consider Peromyscus to be a more accurate indicator of environmental cadmium contamination than Microtus.
Total body nickel, mercury and arsenic concentrations Although nickel levels at the active mine were higher than at the proposed mine, these differences were not significant. The lack of a significant area effect or interaction for nickel concentrations indicates that either environmental nickel levels were not reflected in small mammals or that nickel levels at the mine site were low. We believe that the latter explanation is the most likely, as nickel is found at the active mine in extremely small amounts. Peromyscus had significantly greater total body nickel concentrations than did Microtus. This condition might be attributable to basic differences in physiology between these species. The analyses of the ten Peromyscus composite samples from the active mine and proposed mine areas indicated that mercury and arsenic conditions were very low at both sites. Because of the low concentrations of these elements in initial samples we examined, and the lack of an area effect, we did not determine mercury and arsenic levels for subsequent samples. These highly toxic elements probably do not pose a serious environmental problem in this zinc copper mining operation.
Ecological impacts oj heat,)' metals We doubt that any of the total body metal concentrations that we observed in small mammals reached toxic levels. However, it is possible that subtle environmental problems could occur with few noticeable symptons. Shortened life spans were reported for rats fed 5 ppm of lead or cadmium (Schroeder et al., 1965). The largest proportion of the total body metal burdens probably occurred in bone, hair and skin tissues. Storage of metals in these tissues makes them largely unavailable to carnivorous animals which utilise small mammals as food. In our study areas, coyotes Canis latrans, red foxes Vulpes vulpes and several raptors utilise small mammals for food and could potentially be chronically exposed to heavy metals through the food chain. Cadmium and lead have the potential for bio-accumulation and could have a serious impact on individuals that are chronically exposed to these metals. Cadmium concentrations in small mammals at the mine site were less than 1.0/~gg -1. Browning (1969) reported that cats Felix domesticus fed 1 - 4 p p m cadmium developed anaemia. Similarly, low dietary levels of lead can result in lethal toxicity in mammals (Venugopal & Luckey, 1978). Zinc is a relatively non-toxic metal due to efficient homeostatic mechanisms
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GREGORY J. SMITH, ORRIN J. RONGSTAD
(Venugopal & Luckey, 1978; Beliles, 1979). It is likely that far greater concentrations would have to occur in the small mammals we examined before serious problems would occur with those species or with species at higher trophic levels. Conversely, copper has a much greater potential for toxicity than zinc. Chronic dietary copper exposure of 10-15 ppm caused hepatic accumulation and sudden haemolytic crisis in sheep (Venugopal & Luckey, 1978). We observed small mammal copper concentrations in this range ( 13.2-15.7 pg g - 1) for Peromyscus at the mine site. Therefore, copper toxicity could potentially occur in carnivores utilising small mammals for food, if exposure were chronic. More research is needed to determine the relationship between total body metal burdens, heavy metal toxicity and bio-accumulation in species at different trophic levels in the terrestrial food chain.
CONCLUSIONS
Total body concentrations of zinc, copper, cadmium and lead in small mammals were generally higher in all species collected at an actively mined site than at a control area where zinc-copper mining has been proposed, Peromyscus collected at the proposed mine site did not have heavy metal concentrations different from specimens taken at a control site where no mine or ore deposit exists. Therefore, specimens collected at the proposed mine site were probably not affected by the ore deposit, and specimens may be considered as controls for not only 'before' and 'after' comparisons, but also for comparisons with the active mine area. A complete separation of mean metal values was found between area comparisons for both Peromyscus and Microtus. However, nickel levels in small mammals did not differ significantly between areas. This is probably due to the small amount of nickel in the active mine ore deposit. Peromyscus had significantly greater nickel concentrations than Microtus. This may be attributable to differences in physiology. It is unlikely that any of the total body metal burdens we observed in either of the species at the active mine site reached near toxic levels. However, accumulation of heavy metals in small mammals represents a potential for transference and accumulation of metals at higher trophic levels. Predators which make small mammals a large portion of their diet may possibly receive chronic dietary exposure to heavy metals stored in tissues of these animals. Peromyscus total body metal concentrations showed a greater and more consistent response to environmental heavy metal exposure than did Microtus. This species difference in response to zinc, copper and lead exposure resulted in a significant interaction between area and species for these metals. However, a significant interaction between area, species, sex and age was determined for both zinc and copper analyses. Microtus total body concentrations did respond to cadmium exposure, and the main area effect for cadmium did not interact with
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species, sex or age. The greater response of Peromyscus to environmental heavy metal exposure than Microtus may be at least partially attributable to differences in food habitats. While Microtus rely almost entirely on vegetation, fruits and bark, Peromyscus also feed on insects and invertebrates (Walker, 1975), which may tend to accumulate certain metals (Roberts & Johnson, 1978). We conclude that Peromyscus is likely to be a more accurate indicator of environmental heavy metal contamination than Microtus. Generally, metal concentrations for both species collected at the active mine site had larger standard errors of the mean values than did samples from the proposed mine area. This is possibly due to greater heterogeneity in the distribution and absolute amounts of heavy metals at the mine site. Lead and cadmium levels in Peromyscus taken at the active mine site were higher for adults than juveniles. Both these metals are non-essential, highly toxic, and have been demonstrated to accumulate with age in certain small mammals. Agedependent accumulation of these metals probably occurred in Peromyscus at the mine site, whereas we did not observe this condition in Microtus. Mercury and arsenic total body concentrations in Peromyscus were low for both the proposed mine and active mine areas. Therefore, these metals probably do not pose an important environmental problem in mining operations at a massive sulphide zinc-copper deposit. We conclude that Peromyscus may be a potentially important species for the monitoring of heavy metal pollution. This genus has a large geographic distribution, usually occurs in sufficient numbers and is easily captured. Total body analyses of small mammals do reflect gross differences in environmental heavy metal exposure; however, the model which describes the response relationship is not known. More research is needed to determine the physiological and behavioural correlates of specific total body heavy metal concentrations.
ACKNOWLEDGEMENTS
We thank M. Backes, M. Foy, E. Haug, C. Morgan and R. Rolley for assistance with field collections. Research was supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, USA, and by the Patuxent Wildlife Research Center (US Fish and Wildlife Service).
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