2.
Materials
and
methods
2.1.
Subjects
Sixty
subjects
who
volunteered
for
the
study
were
divided
into
three
groups:
(i)
exposure
group
I
consisted
of
20
workers
exposed
to
organic
BPs
from
a
small
fac-
tory;
(ii)
exposure
group
II
was
composed
of
20
workers
exposed
to
organic
BPs
from
another
small
factory;
(iii)
control
group
included
20
healthy
subjects
unexposed
to
harmful
agents.
The
two
factories
producing
organic
bentonite
were
located
in
Zhe-
jiang
province
of
east
China.
The
characteristics
of
three
groups
are
listed
in
Table
1.
Controls
were
matched
with
exposed
workers
on
the
basis
of
age,
gender
and
smok-
ing
habit.
All
subjects
were
male.
There
were
no
significant
differences
in
age
and
smoking
habits
among
three
study
groups
(P
>
0.05).
The
mean
year
of
exposure
in
group
I
was
3.95
±
0.55
years,
which
was
significantly
higher
than
that
(2.20
±
0.17
years)
in
group
II
(P
<
0.01).
The
working
hours
in
both
group
I
and
group
II
were
the
same,
i.e.
8
h
per
day.
All
subjects
were
informed
of
the
objective
of
this
study,
and
consented
to
participate
in
this
investigation.
The
ethical
committee
of
Zhejiang
Provincial
Center
for
Disease
Control
and
Prevention
(CDC)
approved
the
research
schedule
used
in
this
investigation