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Sistema de Información Científica
Red de Revistas Científicas de América Latina y el Caribe, España y Portugal
Rev. Int. Contam. Ambient. 11
(Z),
95-98, 1995
MOUSE-ERYTHROCYTE MICRONUCLEUS (Mus-EMN) ASSAY ON THE CLASTOGENICITY OF
INDUSTRIAL WASTEWATER
Te-Hsiu MA', Xiaodong ZHOU1, G. Flavia LOARCA2, Gemma G. ARREOLA2 and Salvador U. LECONA2
'Laboratory
of
Environmental Mutagenesis, Department of Biological Sciences,
Western
Illinois University, Macomb,
L,
6 1455 USA.
2Centro de Estudios Académicos sobre Contaminación Ambiental, Universidad Autónoma de Querétaro, Querétaro, Qro., México.
(Recibido
enem
199.5,
aceptado julio 1995)
Keywords: mouse, erythrocytes, micronucleus, clastogenicity, wastewater
ABSTRACT
The Mouse-Erythrocyte-Micronucleus (Mus-EMN) assay is a modified mouse-micronucleus test which
conventionally
scom
the micronucleus
frequencies in bone marrow polychromatic etythrocyíes (PCE).
In
the
Mus-EMN assay, MN frequency is
scored
in mature normachromatic erythrocytes (NCE) in the circulating
blood obtained fmm the tail or the eye socket of the mouse. This simplifd
in
vivo Mus-EMN assay was used
to monitor the chronic clastogenicity of industrial wastewater throughout one
year
in the cumt study. Tweníy
four young (2 month old) CDl white mice were divided into 3 groups of 8, with 4 males and 4 females in
each group, and caged individually for this study. Two treated groups of animals were fed with industrial
wastewater cdlected weekly fmm the
down
stm of the Arena Canal (wastewater dispoal
system)
from the
Benito Juarez Industrial District of the Queretaro Ciíy of Mexico.
In
order
to reduce the toxicity, wastewater
samples were diluted with tapwater at
1:s
ratio (wastewater: tapwater) for treated group 1 and a 1:2 ratio for
treated group 2. Animals of the control group drank the tapwater. Red blood samples were collected monthly
from the tail and blood smears were double stained with hernatoxylin and
Giemsa,
and about 10,000 mature
red blood cells were scored from each of the 8 slides of the experimental groups to derive the means and
standard emrs. Results of this year-mund study showed a significant increase
in
MN
frequencies (5.08
-
9.80
MN11000
cells)
in the treated groups during the months of Octuber through January of the following year, the
dry
season
of this
area
of Mexico. The
MN
frequencies of the treated mice declined to the control level (1.29
-
3.20 MN/1000 cells) afier 6-7 months of continuous exposure. Results of this study indicate that the Mus-
EMN assay is adequate for chronic clastogenicity tests of water pollutants with the maximum time limit
around 6 months which is abwt 20% of the youthful life of the mouse.
RESUMEN
El ensayo de Micronúcleos (MN) en Eritrocitos de Ratón, es una prueba
modificada que registra
wnvencionalmente las frecuencias de micronúcleos
(MN)
en los eritrocitos policromaticos (EPC) de la
médula osea. En
esta
prueba se registra la frecuencia de MN en eritrocitos normocromlticos (ENC) maduros
de la sangre circulante obtenida de la cola o de la cavidad del ojo de ratón. Esta prueba simplificada
in
vivo
fue usada como monitor de la clastogenicidad crónica de las aguas de desecho industrial a través de todo el
aíío. Veinticuatro ratones blancos CDl jóvenes de 2 meses, se dividieron en 3 grupos de 8
mi
4 machos
y 4 hembras y fueron enjaulados individualmente para este estudio.
Dos
de los grupos de animales fueron
alimentados con agua de desecho industrial colectada semanalmente de la corriente baja del Canal Arena
(sistema de eliminación de agua de desecho) del Distrito Industrial Benito Juárez de la Ciudad de Querétaro
de México. Para reducir la toxicidad, las muestras de agua residual fueron diluidas con agua comente en
proporción 1:5 (agua de desecho: agua comente) para el
grupo
tratado 1 y de 1:2 para el grupo tratado 2.
Los animales del grupo testigo bebieron agua corriente. Las muestras de sangre fueron colectadas
mensualmente de la cola y los frotis fueron tefiidos doble con hematoxilina y Giemsa y alrededor de 10,000
células rojas maduras de la sangre se registraron de cada 8 preparaciones de los grupos experimentales
para obtener las medias y los errores estándar.
Los
resultados de este estudio de todo el año mostraron un
incremento signifmtivo en las frecuencias de
MN
(5.08
-
9.80 MNi1000 células) en los grupos tratados
durante los meses de octubre a enero del aíío siguiente, la estacibn seca de esta área de México. Las
frecuencias de MN de los ratones tratados disminuyeron a nivela testigos (1.29
-
3.20 W1000 células)
después de 6 a 7 meses de exposición continua. Los datos obtenidos indican que el ensayo de
MN
en los
eritrocitos de ratón es adecuado para las pruebas de clastogenicidad crónica de las aguas contaminadas con
tiempo límite máximo de alrededor de 6 meses, que corresponde al 20% de la juventud del ratón.
T.H. Ma
el
al.
INTRODUCTION
The
Mouse-Eq%hmcyte-Micronucleus
(Mus-EMN) assay is
a modifíed clastogenicity testing system (TvíacGregor
et al.
1980,
Salamone
et al.
1980) from the mouse bone marrow erythrosrte
micronucleus
test
(Heddle 1973,
Schmid
1975). IntheMus-EMN
test, the blood samples
can
be collected from the eye socket or
the
tail
of the animal repeaay for an extended period. Thus
the
test
can
be applied to the same
animai
under the chronic or
subchronic exposure to chemical agents
(Salamone
e! al.
1980,
Barale
et al.
1985, Choy
et al.
1985,
Ma
et al.
1985, Rithidech
et al.
1988) or
X-rays
(Harris
et al.
1984, 1985). Schlegel
and
MacGregor (1982) demonstrated that mimnuclei induced by
chronic treatment with triethylenemelanine could persist in
nonnachromatic erythrocyte (NCE) for 30-40 days in the
circulating blood of mice. The Mus-EMN test
was
conducted
to
test the clastogenicity of drinking water from a shallow
well
of
a
rural community
(Ma
et
al. 1987) at the monthly intervals for 6
months. Increased
MN
frequencies in the
treated
group
over
the
control were
observed
3 months after feeding the mice with the
polluted shallow well water. This demonstrated that
the
Mus-
EMN assay
was
ef6cient for detecting clastogenicity of water
pollutants at very low concentration under the chronic exposure.
The current study is one year long project to monitor the
clastogenicity of wastewater samples oollected fmm
the
Arena
Canal containing effluents from the Benito Juarez industrial
district
of the Queretaro City
in
Mexico
(Fig.
1).
We also intended
to detect the possible seasonal variation of
ihe
clastogenicity,
and the eficacy of this test for long range monitoring of
clastogenicity of water pollutants.
MATERLALS AND METHODS
The Mus-EMN assay with a double staining procedure
(Harris hematoxylin and Giemsa) was used throughout this
study. The double stained perrnanent slides enhanced the
Ng.
1.
The
&,of watasample collecti011
aííhe
Arena Canal
whi&
&ves
ths
~ofíheBenitoJuarczmdustrialzoneoftheQuerdaroCity.
clarity of the micronuclei and allowed more time for careful,
repeated scoring. Twenty four young (about 2 month old)
CD-
1 white mice were divided into three groups of 8, with 4 males
and 4 females in each group for this in
vivo
study. Each one
of these mice was caged individually for repeated blood
sampling and data collection. Two treated groups were fed
either with 1
:5 (wastewater: tapwater) ratio (treated group
1)
or 1:2 (wastewater: tapwater) ratio (treated group 2) of
wastewater collected from the Arena Canal diluted with
iapwater, ami
the
control group was fed with clean water which
was
obtained from the tapwaier supply of the City of Queretaro.
100
m1
of the diluted wastewater or tapwater were supplied to
each cage bery week, and the blood samples were collected
from a small puncture on the tail of the mouse at monthly
intervals beginning on September 19, 1986 and ending on
August 18, 1987 with the exception of the month of March.
About 3
pL
of peripheral blood collected fiom each mouse
was immediately mixed with 3%ethylene diamine tetraacetic
acid (EDTA) solution in a cell-well and smeared onto a clean
slide. The erythrocytes were fvred in 100% methanol for 1
rninute and allowed to dry in an high temperature (40°C)
incubator ovemight. The micronuclei
(Fig.
2) in the fixed
erythrocytes were double stained with Harris hematoxylin (10
minutes) and 0.1% Giemsa (15 minutes). Usually 3 slides
were made and repeatedly double scored by two different
observers. The scoring procedure involves counting of the
number of evenly distributed eqthrocytes under a lOOOX
magnification field of view with the help of a cross-hair reticle
in the ocular lens. Generally, the counts were made from 10
typical slides with even-spread erythrocytes in order to
establish an average number of erythrocytes per field for a
given series of experiments.
The
number of MNs was actually
counted from a number of fields (generally in the
neighborhood of 350-500 cells) totalling around 10000
erythrocytes (NCE) from each slide. The means and standard
deviations and standard errors of the micronuclei frequencies
were derived from 8 slides of each of the experimental
groups. The data were statistically analyzed with F-test and
Dunnett-t statistics (Dunnett 1955) for the difference (0.05
significance) among two treated against a negative control
gr0UP.
RESULTS AND DISCUSSION
The monthly micronucleus frequencies of two treated and
one control groups through the year are given in Table 1.
The MN frequencies of the treated groups of mice which
drank
two different dilutions of wastewater in the months of
October of 1986 through January of the following year were
~ig~cantly
higher than that of the control. This indicates
the clastogenicity of these diluted wastewaters (Table 1).
Preliminary tests on undiluted wastewater were fatal to the
animals. During this 4 month period, the MN frequencies of
two different treated groups showed similar patterns of
Mus-EMN ASSAY IN WASTEWAER
Ng.
2. Photomimgraphs ofthe nonnachrdc
erythrocytts
with micronuclei,
a)
erythrocytes
under high
dry
magnification,
and
b) under oil immersion.
fluctuation and then fe11 to the background level after the
month of April. The
MN
frequencies induced by the higher
concentration of wastewater (group 2) were relatively higher
than that induced by the lower concentration (group 1). This
pattern
of
fluduation and
relative
difference in MN frequencies
of these two treated groups could serve as the signs of
seasonal
variation of the clastogenicity of the wastewater and the
clastogenicity may be preferentially elevated during the
dry
season of this
area
of Mexico. We regret that no chemical
analysis data of the water samples were available to
substantiate this postulation. The MN frequencies of the
control group stayed at the steady rate except the month of
January. Whether this was due to elevated clastogenicity of
tapwater in this month requires further contirmation with
bioassay and chemical analysis. The elevated
MN
frequencies
of the treated groups in the current study began at
the
end of
the
first
month after treatment as compared with the earlier
tests on the shallow well water
(Ma
et al.
1987) which began
at the end of the third or fourth month after continuous
exposure. The
MN
frequencies of the current study which
reached the significantly higher level in a relatively short
time is the sign of higher clastogenicity of wastewater
than the shallow well water.
The decline of the MN frequencies after 6-7 months
of drinking the diluted wastewater followed a general
trend which was demonstrated in earlier tests on shallow
well water (Ma
et al.
1987).
A
study on low concentrations
of formaldehyde (5-15 mglkg, i.p. injections) treated 0-1
mice (Loarca
et al.
1989) reached the peak MN frequencies
two weeks after treatment and the MN frequencies started
to decline 60 days after treatment. A similar decline of
TABLE
1.
RESULTS OF A YEAR-LONG MONITORING OF THE CLASTOGENICITY OF INDUSTRIAL
WASTEWATER WiTH THE Mus-EMN ASSAY
Montha
Contml
T-l(1:5 diiution)
T-2 (1:2 dihith)
Tapwater: waíer
W~iewatcr:Tapmtcr
Wistmitcr: Tapwater
MNIlOOO NCE
MNllOOO NCE
MN11000 NCE
Mrin
*
SE.
Mcui
+
SE.
Mrin
+
SE.
Sep.
1986
3.3
0.53
3.0
0.25
4.5
0.25
Oct.
1.5
0.04
5.4.
0.81
8.2*
0.50
Nov.
3.0
2.47
7.0*
0.25
7.0.
0.32
Dec.
3.2
0.18
8.1.
0.42
9.6.
0.46
Jan
1987
4.4
0.50
9.0.
0.53
10.0.
0.56
Feb.
3.4
0.25
7.5
1.60
7.6
1.10
Mar.
poot
slides
m
2.8
0.43
3.8
0.42
3.3
0.35
M~Y
2.4
0.21
3.8
0.53
5.0
0.84
Jun.
2.0
0.25
2.2
0.11
2.9
0.21
Jul.
2.6
0.18
2.5
0.18
3.6
0.11
Aug
2.0
0.15
3.0
0.28
2.0
0.18
The
mean
MN frequencies ofthe months of Odober, November, December and January
are
C
=
3.0,
T-1
=
7.4,
and
T-2
=
8.7,
which
are
reldively
higher
than the
okr
montks
ofthe year
and
are significantly
@ <
0.05)
higher
than
control
values
*
Significant, p
<
0.05
T.H. Ma
ef
01.
MN frequencies was observed after 42 or 60 days of
continuous treatment with benzene (Barale et al. 1985,
Rithidech et al. 1988). The two-year continuous treatment of
B6C3F 1 mice with benzene (Choy et al. 1985) showed a linear
increase of MN frequencics under the dose range of 25-600
mglkg in blood samples collected on the 120th day. Progressive
decline of MN frequencies was observed at the end of one and
tnro years. By comparing the Mus-PEMN test results of these
chronic or subchronic continually treated mice, the onset of
the
peak
MN frequency and the time ofdecline of MN frequency
depend upon the magnitude of clastogenicity of the agents.
There is a trend that the higher the potency of the treating
agent, the quickcr it reaclies the peak, and also the sooner it
starts to decline. This general trend of non-linear increment
and decline of MN frequencies after a relatively long
duration of chronic or subchronic exposure to the
clastogens could be the result of overdose and toxic effect
in this test system. For this season, the Mus-EMN assay
has the limited effective duration for chronic or subchronic
clastogenicity testing of different chemical agents. The
eficient duration falls between 1 and 6 months after the
continuous esposures to various agents. Considering the
two and one half years of the average life span of the
laborato- mice, this 6-month youthful diiration in chronic
tests of water pollutants covers as much as 20% of their
useful life. The eficacy of the Mus-EMN test on chronic
effects of water pollutants is well justified. For chemical
tests. the Mus-EMN is suitable for subchronic esposiire
within two-month duration. The current study did not show
ses dependent sensitivity as demonstrated in benzene
studies (Baralc et al. 1985. Choy et al. 1985).
A report by Parton et al. (1989) indicated that the
in
vi\~o
induced MN could be expelled from polychromatic
enthrocytes in the bone marrow of the mouse. Whether or
not this could indirectly contribute to the decline of the
MN frequency in the peripheral blood erythrocytes requires
further investigation. At least. so far, there is no report
available for such espulsion process in pcripheral blood
cqthrocges.
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