Mercury and behavior in wild mouse populations

EN”IRONMEN’1’4L

RESEARCH

Mercury

14, 30 - 34 (1977)

and Behavior

in Wild Mouse

Populations

GARY V. BURTON, ROBERT J. ALLEY, G. LYNN RASMUSSEN, PAL~L ORTON, VANCE Cox, PAUL JONES, AND DARRELL GRAFF Department

c?fzoology.

Weber State College. Ogden. Utah 84408

3750 Hnrrison

Bolrle,sard.

Received April 14. 1976 Various mouse populations on islands in the Great Salt Lake accumulate relatively high concentrations of mercury (3 = 10.8 ppm in hair) because of a unique diet of brine flies which are indigenous to the Great Salt Lake and, as a result, demonstrate several behavioral deviations when put under stressful situations (e.g., swimming and behavior field). Increased mercury levels (by hair analysis) resulted in decreased swimming ability in the mice, while behavior field observations demonstrated increased deviant behavior in the mice.

INTRODUCTION

Methylmercury, a widespread industrial waste product, has caused chronic and acute poisoning of various human and animal populations (Aaronson and Spiro, 1973; Kurland et ul., 1960; Goldwater, 1971: Bakir et al., 1973). The clinical symptoms and gross pathology of alkylmercury poisoning have been well documented (Kurland et nl.. 1961). Only recently have the subclinical effects of low-level mercury exposure been examined (Spyker et al., 1972; Burton and Meikle, 1976; Eye et al., 1970; Utidjian, 1973). Recent work has shown that offspring of mice injected with a low level of methylmercury had no readily observable dysfunction. However, when the offspring were subjected to stress (e.g. swimming and behavior field observations), they showed several behavioral deviations (Spyker et al., 1972). In this study, behavior and hair mercury levels were examined in Perornyscus rnnrziculatus (common white-footed deer mouse) trapped at selected Utah sites to determine if hair mercury levels correlate with mouse behavior and hair mercury levels that are associated with behavioral problems. Mercury forms mercaptides with the cysteine in growing hair (Bate and Dyer, 1965). This provides a possible stable site of deposition for analysis of long-term, low-level mercury exposure. METHODS

Adult male P. rnarziculatus were obtained using Sherman live traps’ at four similar habitats in Utah: Bird and Badger Island, in the Great Salt Lake; Magna, located near the Great Salt Lake; and Vernal, located near the Uintah Mountains in eastern Utah. Mice were maintained in metabolism cages with bedding, mouse chow, and water. The mice, which appeared overtly normal, were subjected, within 48 hours of capture, to two behavior tests: swimming and open field. ’ H. B. Sherman. P.O. Box 683. DeLand. Florida. 30 Copyright ‘0 1977 by Academx Pre\% Inc. All rights of reproductmn I” any form reserved.

MERCURY

AND

BEHAVIOR

IN

WILD

MICE

31

Swimming Mice were individually placed in a large glass-sided, water-filled tank (temperature 25°C) and observed for 1 minute by three independent observers. Mice were ranked either 1, 2, or 3 (good, fair, or poor swimmer, respectively) relative to their performances based upon ability to stay above water surface, either use or difficulty in using any extremities, and fatigue time. Number 1 swimmers showed no difficulties and did not sink below the water surface, while number 2 swimmers showed difficulties and sank beneath the water surface several times. Number 3 swimmers could not maintain themselves above water and required removal from the swimming tanks to prevent drowning before the completion of 1 minute. Agreement among observers differed only between number 2 and number 3 mice and then on only two animals. Observers were in complete agreement as to whether a mouse was a number 1 swimmer or demonstrated some swimming difficulties. Open Field (See Walker, 1959; Whimbey and Denenberg, 1968.) Mice were transferred to the open field (a large, enclosed, gridded, circular floor, 1 m in diameter) within a small light-proof box. After 15 seconds, the field was illuminated with bright lights, a loud buzzer activated, and the box removed from above the mouse. The activity and movements of the mouse inside the brightly illuminated, consistent acoustical environment were observed and recorded for 1 minute by three observers. Parameters recorded: (1) center latency (time for mouse to leave circle in center of field), (2) number of lines crossed and (3) backups (number of times mouse makes a definite backward movement). One observer recorded lines crossed while the other two observers each recorded both center latency and backups independently without disagreement. After behavior analysis, the mice were sacrificed and the dorsal hair was removed and analyzed for Hg by flameless atomic absorption using a Perkin-Elmer 303 Atomic Absorption Spectrophotometer (Hatch and Ott, 1968; Bouchard, 1973j.1 RESULTS

Bird Island and Badger Island mice had the highest mercury levels and the most behavior deviations (Table 1). Mercury levels found on Bird and Badger Island were 6 and 4 times greater than the mean mercury levels found at Magna and 35 and 25 times greater than those found at Vernal, respectively. The longest center latency and fewest lines crossed were demonstrated by Bird and Badger mice, which were also the only mice to demonstrate backing. A decrease in ambulatory activity (measured by center latency and lines crossed) and backing of mice are ” This method of analysis did not distinguish between methylmercury and inorganic mercury. However. because of the toxicity demonstrated in the mice and the demonstrated method of biological accumulation. the mercury was considered to be methylmercury.

32

ET AL.

RURTON

TABLE

Location Bird Badger Magna Vernal Unpaired

MERCURY

LEVELS

N

Hg (ppm)

Hair

AND

Swim

14 10.8 + 2.0*** 8 7.8 f 1.5 6 1.7 + 0.62* 7 0.31 2 0.064”* t-test

value

**P < 0.005. ***

BEHAVIORAL

2.0 1.6 1.3 1.0

comparisons rSEM

+ k 2 +

I

DATA

IN ADULT

Latency

0.25 0.26 0.16 O*”

with

Bird

29 25 8.3 4.9

t 2 i +

Island:

MALE

(set)

Lines

6.0 8.1 1.9* 1.2’%*

12.9 20.8 62.7 80.6

*

P.

MANICULATUS

crossed ? t 2 2

Number

3.5 9.1 8.2*” 8.7”*

P < 0.025,

backing II + 3 + 0 k 0 +

up

2.8 1.2 0.0” o.o*

Fisher Egart test comparisons with Bird Island,

*P < 0.002

thought to be signs of decreased stress tolerance (Whimbey and Denenberg, 1968; Walker, 1959). Vernal’s and Magna’s mean swim and behavior field scores differed significantly from Bird’s and Badgers. A direct correlation with hair mercury levels compared to swimming ability and number of lines crossed was found with all mice (Figs. 1 and 2). Vernal mice, which all had the lowest mercury levels, were all ranked as “number 1” swimmers. DISCUSSION

These results indicate that low levels of mercury as determined by hair levels have a behavioral effect on animals in the environment, and the level of mercury correlates well with the observed behavior. These mice, which appeared overtly normal, only demonstrated abnormal behavior when under stress (behavior field and swimming). These mercury levels are remarkably low and may suggest that many other animal populations, including humans, exposed to previously considered subtoxic levels of mercury, may be suffering from subtle effects of low-level mercury exposure. Our examinations for a possible source of the mercury in the mice living near the Great Salt Lake found that the Great Salt Lake water does not have a detectable level of mercury3 (with our instrumentation <0.005 ppm). However, mercury is detectable (0.5 ppm dry wt) in the brine fly (Ephydra spp.) which consumes algae in the lake water. Mice living along the shoreline of the islands of Great Salt Lake have up to a 60% diet of the dipterous insects4 (Rasmussen 1973). Therefore, through biological concentration, the mice accumulate relatively high levels of mercury and demonstrate subtle behavioral deviations. Although the Magna trapping site was at a sufficient distance from the Great Salt Lake to exclude the brine fly from the mouse diet, it was ‘/4 mile from a major highway and in close proximity to a large copper smelter.” This combination of 3 The mice

would

be unable

to drink

’ The islands (Bird and Badger) stable source of water. 5 Whether determined.

or not the smelter

this hypertonic

lack a fresh

is contributing

water mercury

water source.

regardless Possibly

in any form

of Hg content. the mice

use the brine

to the environment

fly as a

has not been

MERCURY

AND

BEHAVIOR

IN

WILD

22-

33

MICE

. .

2018-

I&

6-

4-

2-

I GOOD

FIG.

1. Relationship

KXI-

between

FL RAliK SWIM SCORES

hair mercury

levels

F&R

and swimming

ability

in P. maniculatus

. .

0

.

-0

zo-

. 0

FIG. 2. Relationship the open field.

‘, 2

. 4 between

I 6

. . .1

hair mercury

iAIR

1

.

tiq L&S PP:’ levels and number

. , 14

16

of lines crossed

18

. 20

(ambulatory

. 1 activity)

in

34

BURTON

ET AL

pollution might explain the slightly higher mercury levels found in Magna mice over Vernal mice, which were from an unpolluted environment. Industrial pollution of Bird and Badger Islands was considered to be insignificant. ACKNOWLEDGMENTS The Stacey

work was supported by the National for secretarial assistance.

Science

Foundation

SOS

Program.

We thank

Phyllis

REFERENCES Aaronson, R. M., and Spiro, H. M. (1973). Mercury and the gut. Amer. /. Dig. Dis. 18, 583-594. Bakir. F.. Damiuji. S. F., and Amin, Z. L. et N/. (1973). Methylmercury poison in Iraq. Scienca 181. 230-241. Bate, L. C., and Dyer, F. F. (1965). Trace elements in human hair. Nucleonics 23, 72. Bouchard. A. (1973). Determination of mercury after room temperature digestion by flameless atomic absorption. A. Ahsorpf. Nen~sl. 12. I I_(- 117. Burton, G. V., and Meikle, A. W. (1976). Adrenal insufficiency following chronic methylmercury poisoning. Clirz. Res. Eye. T. B., Wilcox. K. R.. Jr., and Reizen, M. S. ( 1970). Mercury, fish. and human health. Mic11. Med. 69, 873. Goldwater, L. G. (1971). Facts about mercury. Arch. Emiron. Health 22, 513-514. Hatch. W. R.. and Ott. W. L. (1968). Determination of submicrogram quantities of mercury by atomic absorption spectrometry. Anal. Chem. 40, 2085-2087. Kurland. L. T.. Faro. S. N., and Siedler, H. (1960). The outbreak of neurological disorder in Minamata. Japan, and its relationship to the ingestion of seafood contaminated by mercuric compounds. World Nertrol. 1. 370-395. Kurland, L. T., Faro, S. N., and Siedler. H. (1961). Minamata disease. P~lhlic Health Rep. 76, 671-672. Rasmussen. G. L., Hartog. B. .I.. Netschert. B. J., and Havertz. D. S. (1974). The brine fly as a food source for small vertebrates present on Antelope Island State Park. Lit&~ Acud. Sci. 51, 56-61. Spyker J. M., Sparber. S. B.. and Goldberg, A. M. (1972). Subtle consequences of methylmercury exposure: Behavioral deviations in offspring of treated mothers. Science 177, 621-623. Utidjian, H. M. 0. (1973). Criteria for a recommended standard. Occupational exposure to inorganic mercury. J. Occlcp. Med. 15. 909-914. Walker. W. I. (1959). Escape. exploratory, and food-seeking responses of rats in a novel situation. J. Camp. Physiol. Psycho/. 52, lO6- I I I. Whimbey. A. E.. and Denenberg. V. H. (1968). Two independent behavior dimensions in open-field performance. J. Camp. Phpsiol. Psycho/. 63, 500-504.