英语翻译

英语翻译
Samples were then dried in an oven
at 110?
C,sifted through a 2-mm sieve to remove extraneous
materials,and retained for further analysis.Two grams of the
sample were accurately weighed and digested for total heavy
metal analysis using the wet digestion procedure.The sample
was transferred to a polyethylene test tube and digested with
15 mL of a 1:1 mixture of nitric acid (HNO3):perchloric acid
(HClO4).The mixture was heated at 80?
C for 2–3 hours us-
ing a heating block.The contents were ltrated and transferred
through a simple ltration apparatus into a 25-mL polyethy-
lene volumetric ask.The lter paper was washed several times
with 1% HNO3,and the volume was completed to 25 mL with
1% HNO3.The solutions were stored in sealed plastic bottles
prior to analysis.The heavy metals (Pb,Cu,Zn,Ni,Fe,Al,Cr,
Co,Cd,Mo,and Mn) were determined in dust samples using
aPerkin Elmer Flame Atomic Absorption Spectrophotometer
model Analyst 300 (Perkin Elmer,Wellesley,MA,USA).Stan-
dard stock solutions of each metal (1,000 μg/mL) in 1% HNO3
were used to prepareworking standards.Calibration curveswere
built up for each metal where r > 0.995.Reagents blanks (two
per eight samples) were prepared by carrying out the whole ex-
traction procedure.All materials used for analysis (e.g.,bottles,
glassware) were washed thoroughly,rinsed with 1% HNO3,and
nally rinsed with distilled water.
The mineral constituents of the dry deposition samples were
determined using x-ray diffraction system(Philips-X` pertMpD,
PANalytical B.V.,Almelo,The Netherlands).The ne powder
samples were randomly mounted on special slides and then
scanned between
and 65?
2 θ,using Ni-?ltered Co Kα radia-
tion,40 kv/40mA,divergent and scattering slits of 0.02?
mm,a
receiving slit of 0.15 mm,with stepping of 0.01?
and scanning
speed of /min.
Results and Discussion
Heavymetals are naturally occurring constituents in the environ-
ment in low concentrations.Anthropogenic activities can cause
elevated levels of metal concentration in various parts of the
ecosystem.Heavy metals in river sediments,for instance,are
considered more sensitive than dissolved contamination as indi-
cators of contamination (Gaiero et al.,1997).The anthropogenic
sources of heavy metals in an urban environment could result
from multiple sources.Cu can result from electronic and metal-
lurgical industries,whereas Ni,Pb,Cd,and Zn can result from
fossil fuel combustion andmanufacturing industries such as that
for batteries,paints,printing and graphics,medicine,and met-
allurgy (Alloway and Ayres,1997).