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210Pb activities were analyzed in surface sediments from the Coatzacoalcos River (Gulf of Mexico) to evaluate its distribution according to sediment grain size and in different geochemical compartments by using sequential extraction techniques. The geochemical fractionation experiments provided compatible results: by using the Tessier’s method [1] more than 90% of the 210Pb activity in the samples was found the residual fraction (primary and secondary minerals) and the remaining (<10%) in the iron and manganese oxides fraction of the sediments; whereas using the Huerta-Diaz and Morse method [2] the 210Pb content was found in comparative amounts in the reactive, the silicate, and the pyrite fractions (accounting together for >80%), and the rest was found in the residual fraction. The grain size fractionation analyses showed that the 210Pb activities were mostly retained in the clay fraction, accounting up to 60–70% of the 210Pb total activity in the sediment sample and therefore, it is concluded that the separation of the clay fraction can be useful to improve the analysis of low 210Pb content sediments for dating purposes.
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Geochemical fractionation of
Pb in oxic estuarine sediments
of Coatzacoalcos River, Gulf of Mexico
J. F. Ontiveros-Cuadras A. C. Ruiz-Ferna
J. A. Sanchez-Cabeza L. L. Wee-Kwong
L. H. Pe
Received: 3 May 2011 / Published online: 18 February 2012
´miai Kiado
´, Budapest, Hungary 2012
Pb activities were analyzed in surface sedi-
ments from the Coatzacoalcos River (Gulf of Mexico) to
evaluate its distribution according to sediment grain size
and in different geochemical compartments by using
sequential extraction techniques. The geochemical frac-
tionation experiments provided compatible results: by
using the Tessier’s method [1] more than 90% of the
activity in the samples was found the residual fraction
(primary and secondary minerals) and the remaining
(\10%) in the iron and manganese oxides fraction of the
sediments; whereas using the Huerta-Diaz and Morse
method [2] the
Pb content was found in comparative
amounts in the reactive, the silicate, and the pyrite fractions
(accounting together for [80%), and the rest was found in
the residual fraction. The grain size fractionation analyses
showed that the
Pb activities were mostly retained in the
clay fraction, accounting up to 60–70% of the
Pb total
activity in the sediment sample and therefore, it is con-
cluded that the separation of the clay fraction can be useful
to improve the analysis of low
Pb content sediments for
dating purposes.
Pb Sequential extraction Grain size
Estuarine sediments Gulf of Mexico
Radionuclides are powerful tools which can provide
information about physical, chemical, biological, and sed-
imentological processes in aquatic systems. They are
especially useful because they include the time dimension
of processes, being like clocks associated to the system [3].
The most used tool to study processes spanning the past
100–150 years is the natural fallout radionuclide
Pb, a
member of the
U radioactive series with a half-live of
22.26 years. Unsupported
Pb is produced in the atmo-
sphere from the decay of
Rn emanated from continental
rocks and soils [4]. Atmospheric
Pb fluxes are known to
be predominantly regulated by climate features of a region
such as rainfall, and the oceanic or continental origin of the
dominant air mass. However, in low latitude regions
Pb concentration in air are low in com-
parison with northern mid latitudes (60N–30N) because
the low continent/ocean ratio (23%) and the atmospheric
zonal circulation [5].
Over the last decades the
Pb dating methodology has
been a basic tool to reconstruct recent chronologies of
lacustrine and marine coastal sediments, and to model
some aquatic processes. Humic acids are the major organic
fraction carrying unsupported
Pb (from atmospheric
fallout or produced in the water column) especially in lake
J. F. Ontiveros-Cuadras
Posgrado en Ciencias del Mar y Limnologı
´a, Universidad
Nacional Auto
´noma de Me
´xico (UNAM), Calz. Joel Montes
Camarena s/n, 82040 Mazatla
´n, Mexico
A. C. Ruiz-Ferna
´ndez (&)J. A. Sanchez-Cabeza
L. H. Pe
Instituto de Ciencias del Mar y Limnologı
´a, Universidad
Nacional Auto
´noma de Me
´xico (UNAM), Ciudad Universitaria,
04510 Coyoaca
´n, Me
´xico, D.F, Mexico
J. A. Sanchez-Cabeza
Institut de Cie
`ncia i Tecnologia Ambientals, and Departament de
´sica, Universitat Auto
`noma de Barcelona (UAB), 08193
Bellaterra, Spain
L. L. Wee-Kwong
Environment Laboratories, International Atomic Energy
Agency, 4 Quai Antoine 1er, 98000 Monaco, Monaco
J Radioanal Nucl Chem (2012) 292:947–956
DOI 10.1007/s10967-012-1668-3
and marine sediments where acidic conditions prevail,
whereas the supported
Pb (in equilibrium with its parent
Ra) is strongly bound to clay minerals [6,
7]. According to some studies [810] unsupported
activity increases with decreasing grain size, and the
degree of association with a particular grain size depend on
Fe and Mn-oxyhydroxides and organic material contents.
One of the best methods to study the partition of ra-
dionuclides in environmental matrices is the sequential
extraction or fractionation technique. Sequential extraction
procedures consist on subjecting a sediment sample to a
series of increasingly selective chemical reagents under
specified conditions [1,2,1113]. The basic assumption of
selective extraction techniques is that the reagents used are
able to selectively destroy one phase (specificity) without
solubilization of the others [14]. These studies have shown
that the designation of any extracted to a given substrate
does not necessarily reflect the whole scavenging action of
discrete sediment phases, but rather should be considered
as operationally defined by the method of extraction. The
objective of this paper is to contribute to a better under-
standing of the geochemical distribution of
Pb in surface
estuarine oxic sediments, which can be useful to improve
the analysis of
Pb for dating applications in areas where
Pb signal is characteristically low.
Materials and methods
Study area
The Coatzacoalcos River Estuary is located in the state of
Veracruz, southern Gulf of Mexico (Fig. 1) and has an
estimated length of 40 km. The Coatzacoalcos River
originates at more than 2,000 m elevation in Oaxaca State
and several smaller streams (Corte, Chichihua, Almoloya,
Malatango Sarabia, Jaltepec, Uxpanapa, and Calzada)
discharge waters into its main branch, draining an area of
21,120 km
, with an annual volume of discharge of 32
752 m
[15]. In the upper estuary, width and depth reach
213 and 18 m, respectively; in the river mouth, width and
depth reach 530 and 11 m, respectively. Several studies
show that the Coatzacoalcos River and wetlands sur-
rounding the Minatitla
´n-Coatzacoalcos industrial area are
contaminated by trace metals and petroleum hydrocarbons
due to the discharges of untreated wastes and oil spills [16,
17]. Discharges of untreated urban and industrial wastes
include, among other pollutants, 6.2, 1.5, and 25.3 ton per
day of suspended solids, heavy metals, and sulfates,
respectively [15]. The Coatzacoalcos River basin is com-
posed of different types of rock outcrops such as sand-
stones, siltstones, shale, and limestone [18]. The weather in
Fig. 1 Location of
Coatzacoalcos River sampling
stations: 1Calzadas River, 2
joint of Calzadas-Coatzacoalcos
River, 3San Francisco stream, 4
joint of San Antonio-
Coatzacoalcos River, 5joint of
Uxpanapa-Coatzacoalcos river,
6Coatzacoalcos River
948 J. F. Ontiveros-Cuadras et al.
the area is warm, with an average temperature of 24 C; the
area is characterized by heavy rains and hurricanes from
June to September and a dry season during spring (March
to May) when saline waters can be detected 45 km
upstream [19]. Northeastern trade winds prevail in the area;
however, strong cold winds from the north (NE, called
‘nortes’’), peaking at over 100 km h
, strike the region
from September through March; and hot–dry air masses
(SE, called ‘‘suradas’’) sweep in from the south toward the
coast, during the dry season [20]. Previous studies [21,22]
show that the coastal zone of the Gulf of Mexico has low
Pb fluxes. In the Coatzacoalcos River
catchment area the prevailing winds have an oceanic origin
and, therefore are especially depleted in
Pb [5].
Six samples of surface sediments were collected along the
Coatzacoalcos River bed in February 2008 (Fig. 1)by
using a Van Veen dredge. The sediment samples were
removed from the upper layer (1 cm) at the middle part of
the bulk sample, in such a way that sediments had no
contact with the metallic parts of the dredge. Sediments
were transferred to plastic bags and kept at 4 C until
Experimental and laboratory analysis
Grain size analysis was performed on fresh sample aliquots
by using the standard sieve and pipette method [23]. Other
sample aliquots were freeze-dried, ground to a powder with
a porcelain mortar and pestle, and stored in acid-washed
(2 M, HNO
) plastic bags. Total carbon (TC) was mea-
sured by using a TruSpec CN 630-100-100 and following
the method described by Van Iperen and Helder [24]. TC
was determined by analyzing 10 mg aliquots of dry and
ground sediment. For organic carbon (C
) analy-
sis,*500 mg of sediment (w
) was treated with 10 mL of
1 N HCl to remove carbonate content present in the sam-
ple, the residue was dried on a hotplate overnight (70 C)
and weighted (w
), and aliquots of 10 mg of this residue
(acidified sample) were analyzed with a TruSpec analyzer
org initial
). The C
value was estimated as follows:
Corg ¼Corg initial wf=wi
where w
is a correction factor for weight increase after
acidification, due to conversion of carbonate to chloride
and to hydration. The difference between TC and C
values was assumed to represent the contents of inorganic
carbon (C
). Values obtained from replicate analyses
(n=8) of the standard reference material EUROVECTOR
E1135-A showed good agreement with the certified carbon
content (accuracy =96%; precision =4.6%). Trace metal
element analyses were performed by X-ray fluorescence
(XRF) by using a Spectro X lab 2000 (Spectro Analytical
Instruments) at IAEA-MEL, Monaco. Pressed sediment
powder (4 g aliquots) was placed into a low-density
polyethylene cell, in which the bottom had been previously
wrapped up with ProleneT membrane film. The spectral
analysis and quantitative calculations were performed
using the systems software’s calibrated internal evaluation
method, by performing a combination of three measure-
ments with different X-ray targets, and enabled the deter-
mination of elemental concentrations of atomic numbers
ranging from 13 (Al) to 92 (U). Replicate analysis (n=6)
of the reference materials IAEA-158, IAEA-356, IAEA-
405, and IAEA-433 indicated good agreement between
certificated and analytical values for most metals, with
accuracies above 90% and uncertainties below 8% for most
of the analyzed metals (Table 1).
Pb determination
Pb was determined by alpha counting of
Po deposited
onto silver discs [25,26] assuming secular equilibrium
between both radionuclides. Sediment aliquots of 0.3 g
were spiked with
Po as yield tracer and then digested
using a 5:4:1 mixture of HNO
?HCl ?HF in Teflon
PFA containers hermetically closed and heated on a hot-
plate (150 C) overnight. The acid mixture was evaporated
and converted to a chloride salt by repeated evaporation
with 12 M HCl; the residue was resuspended in HCl 0.5 N
and separated by centrifugation. The solution was trans-
ferred to a glass beaker and 0.2 g of ascorbic acid was
added. A silver disc was placed into the solution to allow
Po isotopes to deposit spontaneously in orbital agitation at
room temperature overnight. The
Po levels were mea-
sured by a-particle spectrometry using Ortec-Ametek sili-
con surface barrier detectors (Model 920E) coupled to a PC
running under the Maestro
data acquisition software.
Replicate analyses (n=27) of the standard reference
material IAEA 300 confirmed good agreement with the
Pb activity (accuracy =84.3%, precision =
Pb in grain size fractions
Sediment bulk samples were gently disaggregated and
passed through a 63 lm sieve to separate the sand fraction
([63 lm) from the mixture of silt (2–63 lm) and clay
(\2lm). The mixture of silt and clay were collected and
homogenized with MilliQ water and were placed inside of
an ultrasonic bath during 10 min to induce the flotation and
separation of fine particles [27]. The suspension was dilu-
ted to 1 L and decanted in order to separate clays from
silts. The two fractions were dried at 40 C, ground to a
Geochemical fractionation of
Pb in oxic estuarine sediments 949
Table 1 Analysis of metals and radionuclides in certified reference materials (CRM)
Element IAEA-158
Certified value Measured value Certified value Measured value Certified value Measured value Certified value Measured value
Al (g kg
) 50.2 ±2.8 34.5 ±0.6 39.0 ±3.1 28.8 ±5.1 NA 71.7 ±4.0 78.2 ±4.2 66.8 ±2.0
Fe (g kg
) 26.3 ±1.4 28.2 ±0.1 24.1 ±0.6 26.7 ±0.1 37.4 ±0.3 40.4 ±0.1 40.8 ±1.9 43.5 ±0.5
Mn (mg kg
) 356 ±24 354 ±8 312 ±9 314 ±13 495 ±5 501 ±25 316 ±16 314 ±7
Br (mg kg
) 224 ±15 213 ±2 76.1 ±8.9 76.2 ±1.5 NA 85.4 ±1.1 67 ±16 62.8 ±0.9
Pb (mg kg
) 39.6 ±4.7 44.5 ±1.9 374 ±16 288 ±3 74.8 ±1.1 78.8 ±1.4 26.0 ±2.7 28.2 ±1.1
Th (mg kg
) 8.8 ±0.5 7.9 ±0.5 6.6 ±0.1 6.7 ±1.2 NA 12.2 ±1.2 9.7 ±0.5 8.7 ±0.6
U (mg kg
) 2.4 ±0.2 \5.9 3.2 ±0.2 \5.9 NA \5.9 2.4 ±0.2 \5.9
Radionuclide Certified value Measured value Certified 95% CI Measured median
Certified 95% CI Measured median
Certified 95% CI Measured median
Pb (Bq kg
) 201 ±12.7 181 ±6.1
Ra (Bq kg
) 307–379 372 (n=5) 2.0–2.9 2.2 (n=15) 21.6–22.4 23.5 (n=15)
NA not available
The IAEA reference materials are:
Trace metals and methylmercury in marine sediment (coastal UK)
Major, trace elements, and methylmercury compounds in polluted marine sediments (Venice Lagoon, Italy)
Trace elements and methylmercury in estuarine sediments (Tagus Estuary, Portugal)
Trace elements and methylmercury in marine sediments (coastal Algeria)
Radionuclides in the Baltic Sea sediments (Bothnian Sea)
f 226
Ra, Th and U in stream sediments (Sumatra, Indonesia)
Radionuclides in Fangataufa Lagoon sediment (French Polynesia)
Radionuclide in Irish Sea sediment
Data obtained from reference [28]
950 J. F. Ontiveros-Cuadras et al.
powder with a porcelain mortar and pestle and the activity
Pb was measured in the individual size fractions.
Ra determination
Ra was determined with the ultralow background liquid
scintillation system Quantulus 1220
(Wallac, Turku,
Finland) using alpha/beta discrimination [28]. Sediment
aliquots (0.2 g) were totally digested with a mixture 5:2:3
of HNO
?HCl ?HF in closed vessels at high pressure
using microwave heating. The extract was evaporated to
incipient dryness and small amounts of 0.5 M HCl were
added to dissolve the residue and eliminate HNO
. The
tracer solutions were prepared by gravimetrically spiking
Ra 2 M HNO
(NIST, SRM4967, U.S.A.) into known
amounts of deionized water contained in 20 mL low-dif-
fusion PE counting vials. The total volume was then
adjusted to 10 mL followed by the addition of 10 mL
OptiScint HiSafe cocktail to form two immiscible liquids.
The mixture was stored for 3 weeks in a dark temperature-
controlled area to allow in-growth and equilibrium of the
radioactive progenies. The background solutions were
prepared with 10 mL of deionized water, acidified to match
the standard solutions, to which 10 mL of the scintillation
cocktail was added. In all cases, quenching was changed by
adding different amounts of CCl
, ranging from 0 to
200 lL. All reagents used in the experiments were of
analytical grade (Fisher Scientific). Counting was per-
formed with Wallac OptiScint HiSafe III, diisopropyl
naphthalene based aqueous immiscible cocktail, and low-
diffusion PE counting vials (Packard BioScience) [29]. The
method accuracy was checked against recovery of certified
materials (IAEA-313, IAEA-384, and IAEA-385); results
are shown in Table 1.
Pb sequential extraction procedures
Aliquots of 5.0 g freeze-dried sediment were treated as
Method I [2]
(i) Reactive fraction. It comprises amorphous and crys-
talline iron and manganese oxyhydroxides, carbonates
and hydrous aluminosilicates. It was obtained after
digestion of the sediment sample with 40 mL of 1 M
HCl for 16 h at room temperature.
(ii) Silicate fraction. It comprises clay minerals, and was
extracted after two consecutive leachings of the
sediments with 60 mL of 10 M HF for 1 and 16 h
at room temperature, respectively. The precipitated
fluorides were redissolved with 10 g of H
(iii) Pyrite fraction. This fraction comprises pyrite and
associated trace metals. It was obtained after diges-
tion of the silicate fraction residue with 20 mL of
concentrated HNO
for 2 h at room temperature. In
the present study, the oxic conditions of the surface
sediments in Coatzacoalcos River would prevent
pyrite precipitation. Therefore, we considered that
this extraction corresponded to the organic matter
fraction since pyrite formation is primarily con-
trolled by the deposition of organic matter; and
reagents, normally used to dissolve pyrite, also
oxidize organic matter [30,31].
(iv) Remnant fraction. This is the solid residue after the three
previous fractions have been removed. Although this
was not considered in the original reference, we
considered important to analyze it since no complete
digestion is attained without using HF [32]. The residue
was digested with a mixture 5:4:1 of HNO
?HCl ?
HF and heated on a hotplate (150 C) overnight.
Method II [1]
(i) Exchangeable fraction. This chemical treatment step
changes the water ionic composition to promote the
remobilization of those metals adsorbed to the
exposed sediment surfaces. The sediment was
extracted at room temperature for 1 h with 80 mL of
magnesium chloride solution (1 M MgCl
, pH 7.0)
with continuous agitation.
(ii) Carbonates fraction. It comprises the components
incorporated to sediment carbonates by co-precipita-
tion reactions. The residue from fraction (i) was
leached at room temperature for 2 h under continuous
agitation with 160 mL of 1 M NaAc (CH
adjusted to pH 5.0 with HAc (HCH
(iii) Iron and manganese oxides fraction. These oxides
are important sinks and transport modes of heavy
metals in the environment because hydrous metal
oxides are pH sensitive and thermodynamically
unstable under anoxic conditions [33]. The residue
from the previous fraction was extracted with
100 mL of 0.04 M NH
OH-HCl in 25% (v/v) HAc
at 96 ±3C for 6 h with continuous agitation.
(iv) Organic matter fraction. This fraction comprises
colloidal and particulate organic material that has
the capacity to form organo-trace element complexes.
To the solid residue from fraction (iii) we added
15 mL of 0.02 M HNO
and 25 mL of 30% H
and adjusted to pH 2 with HNO
. The mixture was
heated to 85 ±2C for 2 h with occasional agitation.
A second aliquot of 15 mL of 30% H
(pH 2 with
) was added and the sample was heated again to
Geochemical fractionation of
Pb in oxic estuarine sediments 951
85 ±2C for 3 h with intermittent agitation. After
cooling, 25 mL of 3.2 M NH
20% (v/v) HNO
was added, the sample was diluted to
100 mL and agitated continuously for 30 min.
(v) Residual fraction. Once the previous four fractions
have been removed, the residual solid should contain
mainly primary (quartz, feldspars, micas) and sec-
ondary (detrital silicate minerals, resistant sulfides)
minerals and refractory organic material [34] which
may hold trace metals within their crystal structure.
These metals are not expected to be released in
solution over a reasonable time span under the
conditions normally encountered in nature. The last
solid residue was digested with a mixture 5:4:1 of
concentrated HNO
?HCl ?HF and heated on a
hotplate (150 C) overnight.
The residues from all the aqueous phases were centrifuged and
each supernatant were transferred to Teflon PFA containers,
where the solutions were evaporated to incipient dryness on a
hot plate at \80 C. The
Pb analyses of the dry residues
were performed following the methodology described in Sect.
Po was added as internal tracer to each supernatant of
the chemical extractions before acid digestion.
Results and discussion
Sediment characterization
In Table 2we present the geochemical properties and
activity concentrations of natural radionuclides in the
sediments samples from Coatzacoalcos River Estuary. The
samples were predominantly silt-sandy, with clay (\2lm)
contents \30%. The C
contents were low, ranging from
0.7 to 1.3%, whereas C
contents ranged from 0.09 to
0.45%. Aluminum and Fe showed rather small variation
between stations suggesting a relatively constant mineral-
ogical sediment composition and origin. Bromine contents
showed increased concentrations toward Coatzacoalcos
River mouth, showing an increasing influence of the
intrusion of sea water from the Gulf of Mexico; contrarily,
Th concentrations decreased in the same direction, indi-
cating a lower influence of terrigenous sources by runoff as
the water approached the river mouth [35]. Total activity
concentration of the radionuclides
Pb and
Ra ranged
from 20.4 to 31.5 Bq kg
and from 15.9 to 25 Bq kg
respectively. Sediment samples from stations 1, 3, 5, and 6
Pb concentrations very close to
Ra activities,
indicating that the
Pb present corresponded mainly to
Pb supported fraction, which is mostly controlled by
the mineralogy of the catchment bedrock and not the
atmospheric deposition of
Pb fractionation according to sediment grain size
The distribution of
Pb activities by grain size fractions is
presented in Fig. 2. The
Pb concentrations found in the
clay fractions (58.9 ±0.5 to 91.6 ±0.4 Bq kg
64–73%) were considerably higher than the activities in the
silt fraction (14.6 ±0.5 to 30.1 ±0.5 Bq kg
, 16–26%)
and the sand fraction (9.1 ±0.5 to 16.8 ±0.5 Bq kg
8–14%) thus reflecting the nature of radionuclide
Table 2 Chemical characterization and activity concentration of natural radionuclides in Coatzacoalcos River Estuary surface sediments
(uncertainty corresponds to 1r)
Magnitude Station
Distance to river mouth (km) 7.8 7.2 15.2 16.7 21.8 34.4
Al (g kg
) 62.9 ±5.6 55.0 ±5.8 50.5 ±4.8 74.7 ±6.9 47.9 ±8.4 77.5 ±7.9
Fe (g kg
) 35.2 ±0.1 45.4 ±0.1 32.2 ±0.1 41.6 ±0.1 36.6 ±0.1 44.2 ±0.1
Mn (mg kg
) 471 ±21 887 ±23 376 ±19 434 ±14 478 ±21 706 ±20
Br (mg kg
) 4.9 ±0.6 13.3 ±0.7 7.6 ±0.6 5.4 ±0.4 2.6 ±0.5 4.9 ±0.5
Pb (mg kg
) 7.7 ±1.6 12.8 ±1.6 10.7 ±1.6 15.1 ±1.3 10.8 ±1.6 15.2 ±1.5
Th (mg kg
) 3.3 ±0.9 4.1 ±0.8 4.8 ±0.9 5.7 ±0.8 8.2 ±1.0 7.8 ±0.9
U (mg kg
)\5.9 \5.9 \5.9 \5.9 \5.9 \5.9
(%) 0.72 ±0.003 1.14 ±0.004 1.3 ±0.005 0.9 ±0.003 0.93 ±0.004 1.1 ±0.004
(%) 0.09 ±0.001 0.19 ±0.003 0.45 ±0.007 0.3 ±0.004 0.3 ±0.004 0.15 ±0.002
Clay (%) 13.0 ±0.2 30.5 ±0.5 5.5 ±0.1 32.5 ±0.5 18.4 ±0.3 28.7 ±0.4
Silt (%) 11.7 ±1.5 43.9 ±5.7 36.6 ±4.7 39.2 ±5.1 36.2 ±4.7 36.9 ±4.8
Sand (%) 75.3 ±1.2 25.1 ±0.4 57.8 ±0.9 27.9 ±0.5 44.4 ±0.7 33.9 ±0.6
Pb (Bq kg
) 20.4 ±0.5 29.8 ±0.5 21.4 ±0.5 31.5 ±0.4 23.3 ±0.5 28.7 ±0.5
Ra (Bq kg
) 17.1 ±0.4 16.4 ±0.6 16.8 ±0.5 15.9 ±0.7 25.0 ±0.5 23.3 ±0.7
952 J. F. Ontiveros-Cuadras et al.
adsorption by sediment particles, i.e., when the adsorption
of ions by soil particles is associated with cation exchange
or similar processes, the specific surface area (or particle
size) of the particles exerts a primary control on the con-
centration adsorbed [36]. Also, heavy and transitional
metals (including Pb) are mainly related to the fine-grained
clayey sediments, while the coarse-grained sediments (first
of all, sand) are, on the contrary, depleted in these metals
because quartz, prevailing in sand and quartz silts, dilutes
the metal concentrations in sediments [37].
Pb activity of the sediment samples as a whole
was compared to the calculated
Pb activity (
distributed among the grain size fractions of each sample
clay content) ?(
content) ?(
sand content)] and were found
significantly equivalent (t-student test, P\0.05) at stations
1, 4, and 5 (Table 3); however, small differences were
observed for the rest of the stations, which were related to
heterogeneities of the sediment samples.
Fractionation of
Fractionation of
Pb: method I
Pb activities (Bq kg
) in the fractions defined for
method I, are compiled in Table 4. In stations 1, 2, 3, and 6,
the highest
Pb activities were found in the reactive and
silicate fractions in comparable ranges (between 28 and
41%, and from 31 to 45%, respectively) whereas the
activity ranges for pyrite (organic matter) and remnant
fractions were low, 11–25% and 12–15% correspondingly.
On the other hand, in stations 4 and 5, the
Pb activities
were associated to a greater extent to the silicate fraction
(31 and 47%, respectively), whilst the rest was distributed
among the pyrite (26 and 22%), the reactive (27 and 13%),
and the remnant (16 and 17%) fractions. The reactive
fraction comprises amorphous and crystalline iron and
manganese oxyhydroxides, carbonates, and hydrous alu-
minosilicates. Iron and manganese oxyhydroxides are
known to concentrate heavy metals on their surface [38]
and it is also known, that
Pb behavior is tightly coupled
to the reduction/oxidation cycle of manganese oxides
rather than iron oxides [39,40]. Regarding the silicate
fraction, it comprises clay minerals, which may form a
stable metal–ion binding, and behave as a template for
adsorption and chemical interactions [41]. Also, the total
decomposition method (5:4:1; HNO
?HCl ?HF)
applied in the remnant fraction, dissolves the silicates that
remain in the mineral matrix [2].
Fractionation of
Pb: method II
When using method II (Table 5) the
Pb radionuclide
activities in the fractions operationally defined as
exchangeable, carbonates and organic matter were below
the minimum detectable activity (MDA) of the technique
(1.6 910
to 2.3 910
Bq kg
). Similar results were
observed for the fractionation of
Pb in soils with dif-
ferent loads of organic matter, where the activities of the
radionuclide in the more labile fractions were below the
MDA [42]. The activity of
Pb in the fraction of iron and
manganese oxides was lower than 10%. The relative low
association of
Pb with the oxides fraction could be a
result of an incomplete extraction with hydroxylamine
hydrochloride (NH
OH–HCl 0.04 M), since it generally
attacks only the more labile fraction of Fe and Mn oxides
[12] but excludes other more resistant forms such as the Fe
Fig. 2
Pb activity distribution in clay, silt and sand fractions in
sediments from the Coatzacoalcos River
Table 3
Pb activity in the different grain size fractions
Station Size fraction (%)
Pb activity (Bq kg
) Total
Pb activity (Bq kg
Clay Silt Sand Clay Silt Sand Estimated Measured
1 13.0 ±2.6 11.7 ±2.3 75.3 ±15.1 77.0 ±1.4 30.1 ±0.1 9.1 ±0.7 20.3 ±2.1 20.4 ±0.2
2 30.5 ±6.1 43.9 ±8.8 25.1 ±5.0 79.9 ±0.7 18.9 ±0.1 13.8 ±0.2 36.2 ±1.7 29.7 ±0.8
3 5.5 ±1.1 36.6 ±7.3 57.8 ±11.6 6.9 ±4.2 14.7 ±0.1 10.6 ±0.2 15.2 ±1.5 21.3 ±0.5
4 32.5 ±6.5 39.2 ±7.4 27.9 ±5.6 91.6 ±0.7 23.1 ±0.3 16.8 ±0.7 43.5 ±1.9 31.5 ±2.9
5 18.4 ±3.7 36.2 ±7.2 45.0 ±9.0 58.9 ±2.4 19.9 ±0.6 12.8 ±1.4 23.7 ±1.7 23.3 ±0.5
6 28.7 ±5.7 36.9 ±7.4 33.9 ±6.8 74.7 ±2.6 24.4 ±0.7 14.1 ±0.1 35.2 ±2.1 28.6 ±1.0
Geochemical fractionation of
Pb in oxic estuarine sediments 953
attached to silicates [43]. The residual fraction showed the
highest concentration of
Pb in all the stations, with
values ranging from 92 to 98% of the total activity. The
closeness between the activity of
Pb and
Ra in all
sediment samples suggests that
Pb activities were
mainly related to the mineral matrix (supported fraction),
which comes from
Ra decay. The strong association of
Pb with the residual fraction is in agreement
with other studies [44,45].
Correspondence between both methods
According to the Pearson correlation test, there is a sig-
nificant correspondence between the
Pb contents in the
sediment fractions defined for both methods: (a) the iron
and manganese oxide fraction (method II) presented a
direct correlation (r=0.91; P\0.05) to the reactive
fraction (method I) which integrates amorphous and crys-
talline forms of Fe and Mn oxides; and (b) the residual
fraction (method II), which includes detrital sili-
cates ?sulfides ?refractory organic matter, was directly
correlated (r=0.88; P\0.05) to the silicate fraction
(method I), primarily composed by clay minerals. These
correlations suggest that there is consistency between the
geochemical components in both sequential extraction
Surface sediment samples from Coatzacoalcos River
Estuary are predominantly silt–sandy, with clay (\2lm)
contents less than 30%. The
Pb activities in the different
grain fractions were closely related to the particle specific
areas, as the radionuclide is preferentially adsorbed by finer
grain particles (clays), with activities ranging from
58.9 ±0.5 to 91.6 ±0.4 Bq kg
. The results of the
sequential extraction by method I indicated that
Pb was
mostly associated to both silicates and clays, and the
reactive fraction (Mn and Fe oxy-hydroxide ?carbon-
ates ?Al-silicates) accounted for up to 60–80% of the
Pb present in the samples. A non-negligible 10–25%
fraction appeared to be retained by the organic matter
fraction. The results of the sequential extraction of method
II indicated that
Pb in the sediments samples was mainly
associated with the residual fraction (detrital silicate min-
erals ?resistant sulfides ?refractory organic material)
with relative abundance between 92 and 98% and, to a
lesser degree, to the iron and manganese oxides fraction
(2.1–7.7%). The significant correlation between the
content in the sediment fractions defined for both methods:
(a) the iron and manganese oxide fraction and the reactive
fraction and (b) the residual fraction and silicate fraction,
confirmed that there was consistency between the
Table 4 Fractionation of
Pb (Bq kg
) by method I (Huerta-Dı
and Morse [2]), in surface sediments from Coatzacoalcos River
Estuary, Mexico
Station Fraction
* 210
Pb (Bq kg
) Ratio** (%)
1 1 2.94 ±0.27 18.41 ±3.68
2 7.18 ±0.71 45.01 ±9.00
3 3.92 ±0.33 24.56 ±4.91
4 1.92 ±0.06 12.02 ±2.40
2 1 5.27 ±0.72 26.71 ±8.01
2 6.19 ±1.56 31.37 ±9.41
3 5.12 ±0.23 25.96 ±7.78
4 3.15 ±0.21 15.95 ±4.78
3 1 2.47 ±0.20 13.03 ±1.30
2 8.92 ±0.37 47.17 ±4.71
3 4.24 ±0.21 22.40 ±2.24
4 3.29 ±0.27 17.40 ±1.74
4 1 7.37 ±1.01 28.34 ±5.66
2 10.69 ±0.16 41.13 ±8.22
3 4.39 ±0.24 16.89 ±3.37
4 3.55 ±0.34 13.64 ±2.72
5 1 6.60 ±0.27 38.09 ±3.80
2 6.63 ±0.01 38.26 ±3.82
3 1.82 ±0.08 10.51 ±1.05
4 2.28 ±0.15 13.13 ±1.31
6 1 9.88 ±0.55 41.13 ±4.11
2 7.56 ±0.02 31.47 ±3.14
3 3.58 ±0.33 14.92 ±1.49
4 3.00 ±0.14 12.48 ±1.24
Fraction 1: reactive; Fraction 2: silicates; Fraction 3: pyrite; Frac-
tion 4: remnant
The ratio is the percentage of
Pb activity in each fraction with
respect of the
Pb activity of the whole sample (
Pb in the frac-
Pb) 9100
Table 5 Fractionation of
Pb (Bq kg
) by method II (Tessier et al.
[1]), in surface sediments from Coatzacoalcos River Estuary, Mexico
Station Fe and Mn Oxides Residual
(Bq kg
Ratio* (%)
(Bq kg
Ratio* (%)
1 0.19 ±0.02 2.08 ±0.20 9.09 ±0.07 97.92 ±9.79
2 0.38 ±0.03 4.20 ±0.42 8.55 ±0.94 95.80 ±9.58
3 0.45 ±0.02 3.74 ±0.37 11.6 ±0.95 96.26 ±9.62
4 0.76 ±0.12 4.71 ±0.94 15.4 ±0.85 95.29 ±19.05
5 0.61 ±0.04 7.71 ±0.77 7.27 ±0.35 92.29 ±9.22
6 1.07 ±0.10 7.62 ±0.76 13.0 ±0.93 92.38 ±9.23
The ratio is the percentage of
Pb activity at each fraction with
respect of the
Pb activity of the whole sample (
Pb in the frac-
Pb) 9100
954 J. F. Ontiveros-Cuadras et al.
geochemical components in both sequential extraction
It is clear that the separation of the coarser fraction in
the sediment samples resulted in higher activities of
in the sample, and therefore, the analysis of the fine frac-
tion of the sediments could be useful to improve the
analysis of
Pb for dating purposes, especially in areas
where the atmospheric flux of
Pb is characteristically
low. This may improve the precision of
Pb chronologies
in these areas.
Acknowledgments This work was financially supported by the
program UNAM-DGAPA PAPIIT 105009 and the International
Atomic Energy Agency (IAEA) project RLA/7/012. The scholarship
of J.F. Ontiveros-Cuadras was provided by the Consejo Nacional de
Ciencia y Tecnologı
´a (CONACyT-Me
´xico). Thanks are due to F.
´ez-Osuna for his help in field work, to A. Abreu-Grobois for
reviewing the statistic section, and to M.C. Ramı
´uregui, G.
´ndiz, and H. Bojo
´rquez-Leyva for their technical
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... As time goes by, the activity of excess 210 Pb will decay until it reaches secular equilibrium with the supported 210 Pb fraction ( 226 Ra). The activity differences between the initial excess 210 Pb (at the surface of the sediment core) and the subjacent core sections can be used to estimate the time of when the sediment at this section was deposited (Aliev et al., 2007;Chakrabarty et al., 2006;Likuku, 2006;Sanchez-Cabeza and Ruiz-Fernández, 2012;Wan Mahmood et al., 2016). ...
... It has been shown that 210 Pb may be associated with biogenic particles and high 210 Pb activities may be derived from the lithogenic (detrital) inclusion (Bralower and Thierstein, 1987). As 210 Pb is a highly particle reactive and is readily scavenged by organic matter and clay size particles (Ontiveros-Cuadras et al., 2012), but under anoxic conditions, 210 Pb can be released back to the water (Benoit, 1988). ...
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Two sediments cores were collected from each Juru River and Perai River at the Penang's Perai Industrial Area during two different seasons and analyzed using nuclear techniques, with the purpose to evaluate the sediment accumulation rates at the study area. Radioactivities of 137Cs, 210Pb and 226Ra activity profiles were determined for each core by using gamma spectrometry system. However, due to the complexity of the excess 210Pb activity profiles obtained, it was not possible to obtain an age model from them. Nonetheless, preliminary apparent sediment accumulation rates were estimated, and were found to range between 0.94-4.91 cm/y and 1.79-4.83 cm/y for Juru and Perai River, respectively. As expected, the deposition rates were higher during rainy period where the value at Juru River almost five folds, and at Perai River, it was 2.5 times higher than that of the dry season. The highest sedimentation rate recorded was in the core collected at the Juru River (SP 03) during the rainy season.
... The determination coefficient found between 210 Pb and fine material content suggested that about 20 % of 210 Pb is scavenged by fine grained material in the EUL. The significant correlation between fine sediments content and 210 Pb activities has been also reported in other studies where the 210 Pb activity may be up to 8.5 times higher in clays than in sands (He and Walling 1996;Ontiveros-Cuadras et al. 2012). The latter reflects the increased adsorption capacity of the fine materials, explained by their high surface area compared with coarser materials (He and Walling 1996). ...
... The latter reflects the increased adsorption capacity of the fine materials, explained by their high surface area compared with coarser materials (He and Walling 1996). In fact, the limited absorption capacity of sandy sediments can cause a dilution effect of 210 Pb activities in sediments (Ontiveros-Cuadras et al. 2012), as demonstrated by the negative correlation between 210 Pb activities and the sand content. The correlation between 210 Pb and OM has been previously reported in other studies (e.g. ...
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The Estero de Urias Lagoon (EUL) is an inner shelf barrier coastal lagoon, located in the Mexican Pacific Coast (SE Gulf of California). It is surrounded by Mazatlan City, one of the most important international tourist areas of Mexico. To provide a comprehensive reassessment of the concentration levels and spatial variability of Hg and Pb-210 in the EUL, 40 surface sediment samples were analyzed for several geochemical variables (e.g. grain size distribution, organic matter and reference element concentrations) that could explain the observed variability of Hg and Pb-210. The Hg concentrations ranged from 23 to 214 ng g(-1), whereas Pb-210 activities varied from 20 to 56 Bq kg(-1). No defined distribution pattern was observed for Hg and Pb-210 concentrations in the lagoon and no evidence of a common atmospheric delivery route was observed. The sediments from EUL were found contaminated by Hg, and according to international guidelines 48 % of the sampling sites have concentrations that could be harmful to biota.
... The weather in the region is warm, with an average temperature of 24 °C. The Coatzacoalcos area is characterized by heavy rains and hurricanes from June to September and a dry season during spring (March to May) when saline waters can be detected 45 km upstream (Bahena-Manjarrez et al., 2002; Ontiveros-Cuadras et al., 2012). During fall and winter a broad surface-mixed layer forms due to the effect of the North winds, which decrease the surface (150 m) temperature (Monreal-Gómez and Leon, 1990). ...
... Northeastern trade winds generally prevail in the area. However, strong cold winds from the NE (called " nortes " ), peaking at over 100 km h À 1 , strike the region from September through March, and hot-dry air masses (SE, called " suradas " ) sweep in from the south towards the coast during the dry season (Buckles and Erenstein, 1996; Ontiveros-Cuadras et al., 2012). The Papaloapan River basin (17°–19° N and 95°–97° 40′ W) is the second largest hydrological basin in Mexico, drains 39,189 km 2 of catchment area before reaching the Gulf of Mexico with an annual volume of discharge of 39,175,000 m 3 (Tamayo, 1991). ...
The aim of this work is to constrain the provenance and depositional history of continental slope sediments in the Southwestern Gulf of Mexico (~1089–1785 m water depth). To achieve this, 10 piston sediment cores (~5–5.5 m long) were studied for mineralogy, major, trace and rare earth element geochemistry. Samples were analyzed at three core sections, i.e. upper (0–1 cm), middle (30–31 cm) and lower (~300–391 cm). The textural study reveals that the core sediments are characterized by silt and clay fractions. Radiocarbon dating of sediments for the cores at different levels indicated a maximum of ~28,000 year BP.
... Bq kg −1 , respectively. Ages and sedimentation rates were estimated from the 210 Pb (half-life 22.23 ± 0.12 years) activities by using the CRS model (Ontiveros-Cuadras et al., 2012). To check the 210 Pb dates, the samples were also analyzed for 137 Cs activity (half-life 30.05 ± 0.08 years), of which accumulation peak in sediments in 1963 is considered to be the important time mark (Ritchie & McHenry, 1990). ...
... Bq kg -1 and 98.1-312 Bq kg -1 , respectively. We estimated ages and sedimentation rates from the 210 Pb (half-life 22.23 ± 0.12 years) activities by using the CRS dating model (Ontiveros-Cuadras et al., 2012). The accumulation characteristics of 137 Cs in the cores of FX and DC were not obvious, and the recognized time markers were not present, so 137 Cs could not serve for dating in FX and DC. ...
... Bq kg −1 , respectively. Ages and sedimentation rates were estimated from the 210 Pb (half-life 22.23 ± 0.12 years) activities by using the CRS model (Ontiveros-Cuadras et al., 2012). To check the 210 Pb dates, the samples were also analyzed for 137 Cs activity (half-life 30.05 ± 0.08 years), of which accumulation peak in sediments in 1963 is considered to be the important time mark (Ritchie & McHenry, 1990). ...
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Plain Language Summary The impact of global warming on the environment is increasing, and previous research was mainly on the polar region, and there are relatively few studies on the impact on inland lake environments. In this paper, a typical organic pollutant, polycyclic aromatic hydrocarbons (PAHs), is taken as the starting point, and two lakes in eastern China, Luoma Lake, and Hongze Lake, are taken as the research objects. The sedimentary records of diatoms and bacteria were also analyzed to explore the interaction between diatoms and bacteria in the lake and PAHs. The results showed that diatoms had bioaccumulation effects on PAHs, especially HMW‐PAHs, and bacteria were the main contributors to the secondary productivity of the lake. In addition, changes in atmospheric temperature of Xuzhou and Bengbu recorded by weather stations near the lake show that the average annual atmospheric temperature has risen by nearly 2°C over the past 70 years, indicating a warming phenomenon in the region. Next, we analyzed the three factors related to algal growth in lakes, temperature, total nitrogen, and total phosphorus, and correlated them with PAH content and algal and bacterial biomarker content. There were significant positive correlations, especially for HMW‐PAHs, indicating that the increase in plankton productivity caused by climate warming promotes the accumulation of HMW‐PAHs in lake sediments.
... The present work did not split the region below 25 μm into smaller grainsize classes. Results from Aalto and Nittrouer (2012), Ontiveros-Cuadras et al. (2012), and Sun et al. (2018), suggest the possibility of using the clay fraction (< 4 μm) for normalization in 210 Pb-based radiometric dating models. Table 1. ...
Theoretical and experimental studies have shown that activity concentrations of fallout radionuclides (such as 137 Cs and excess 210 Pb) decrease with particles size in aqueous suspensions. This paper is aimed at reviewing the theoretical fundamentals for granulometric speciation of radionuclides, and at exploring its practical use in the analytical context of gamma spectrometry for the radiometric dating of recent sediments, with view to: i) improving the detection of 137 Cs (since its use as independent chronostratigraphic mark is challenging in the southern hemisphere because its low fallout rate), ii) supporting refined CIC models and normalization techniques in 210 Pb-based radiogeochronologies. The work uses surface sediments sampled from the Tinto Estuary (SW Spain), affected by mining and phosphate-fertilizer industries, and from the Ankobra Estuary (Ghana), affected by intensive artisanal gold-mining. Granulometric classes have been separated by a sieving column with decreasing mesh sizes and the obtained cumulative percentage of mass mathematically described by a Rosin-Rammler particle-size distribution. The target radionuclides for gamma spectrometry were 210 Pb, 226 Ra and 137 Cs, complemented with 40 K, 234 Th and 228 Ra. Results revealed that, far from ideal experiments, under actual environmental conditions the increase in activity concentrations with decreasing particle sizes is too moderate, and in general they are affected by larger counting uncertainties due to the small available amount of mass. Indeed, there was no correlation between grain-size and 137 Cs concentrations (p = 0.25), and similarly for excess 210 Pb (p = 0.53). No effect of the organic matter content was observed in 137 Cs (p = 0.58) and excess 210 Pb (p = 0.85) concentrations. Present results pose some concerns to the general use of granulometric spe-ciation in the context of gamma spectrometry for supporting the radiometric dating of recent sediments. A detailed discussion on the use of normalization methods is also presented.
... Esta es también la razón que explica las correlaciones positivas observadas entre la actividad de 210 Pb y la abundancia de limos y arcillas; la correlación negativa con el contenido de arenas. De hecho, estudios previos en sedimentos costeros han demostrado que la actividad del 210 Pb puede ser mayor hasta en un factor de 8.5 en la fracción más fina (< 2 μm) que en arenas (He y Walling, 1996;Ontiveros-Cuadras et al., 2012). ...
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This study analyzed the spatial-temporal distribution of Hg concentrations and 210Pb activities in different abiotic environmental compartments (atmospheric particulate matter, water, sediments and soil) at Estero de Urías Lagoon (EUL) in NW of Mexico. Hg concentrations in atmospheric particulate matter presented a range of 8-1395 pg m-3; the highest concentrations were found during spring-summer period and they were associated to the higher consumption of fossil fuel by a thermoelectric plant located in the surroundings, owing to the increased use of air conditioners during the warm months of the year. 210Pb activities in the atmospheric particulate were found within the range of 60-727 μBq m-3, no seasonal variation was found. In water, Hg concentrations ranged between<1-155 ng g-1in the suspended particulate matter and <3-218 ng L-1 in the dissolved phase, no spatial-temporal variation was observed. The wide range and high variability of Hg concentrations was associated to local wastewater discharges. In sediments, Hg concentrations showed a range of 4-239 ng g-1, the higher concentrations were observed towards the proximal areas to the sea, where port and industrial facilities are located. The 210Pb activities (13-50 Bq kg-1)no spatial-temporal variation was found. Three sediment cores were collected in EUL (not dredged area) with the aim to make a retrospective evaluation of the Hg contamination trends in the EUL, by using the 210Pb dating method. It was found that the sediment accumulation rates in the site are high (>1.1 cm year-1) and the sediments collected were relatively recent (28-46 years). It was observed Hg concentrations have regularly increased, most likely owing to unregulated releases of local wastes. The Hg concentrations observed in the sediments account for moderate to significant contamination levels; it was found that Hg concentrations could represent a risk to the aquatic biota of EUL, and to humans, through the consumption of contaminated seafood.
... On the other hand, the low amount of the 210 Pb in the western part (SAR4 and SAR6) show deficit of fine-grained sedimentary particles and organic matter displaying a high reactivity with radionuclides (San Miguel et al. 2003;Wan et al. 2005;Ontiveros-Cuadras et al. 2012). In comparison with other sites SAR4 and SAR6 have higher contents of SiO 2ter and sand as well as lower contents of aluminosilicates. ...
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Despite the fact that sediment dynamics in shallow coastal lakes strongly influences lake water quality and is crucial for preserving good quality paleo-records from coastal zones, the depositional processes in coastal lakes have not been thoroughly recognised so far. The present study aims at investigating the relationship between lake water circulation and the distribution of surface sediments, identifying the postdepositional physical mechanisms affecting lake deposits, and estimating the intensity of sediment mixing in a coastal lake on the Baltic coast. Our approach includes analyses of sediment grain size and chemical composition, hydrodynamic modelling and measurements of 210 Pb activity in sediment short-cores from various sections of the lake. We showed that the distribution of lithofacies in the lake is explained by hydrodynamic conditions. Enhanced water dynamics reduces spatial extent of organic-rich lacustrine deposits and results in the exposure of relic marine-lagoonal sediments. A major part of the lake sediments is prone to vertical mixing by wind waves to a depth of $ 40 cm. Hydrodynamic modelling and 210 Pb displayed overall agreement in predicting the depth of sediment mixing. At the same time the limitations of 210 Pb as a geochronologic marker in shallow coastal lakes are revealed. It appears that even exponential depth-wise 210 Pb distributions may be produced by storm redeposition.
Activity ratios (A.R.) of 234U/238U and activity concentration of 238+234U and 239+240Pu were measured in collected seawaters and sand beach samples from various locations along of littoral of Mexican state of Veracruz. Uranium and plutonium were separated and concentrated in a liquid-liquid partition chromatography, afterwards, detected and analyzed by means of alpha spectrometric technique. The 234U/238U activity ratio (AR) ranges from 0.72 to 1.11 in sand beach and from 0.77 to 1.22 in seawater. The activity concentration was found in sea water from 0.31 to 1.94 Bq/L for 234+238U and from 15 to 137 μBq/L for 239+240Pu, in sand beach samples was found to be from 0.64 to 3.86 Bq/kg for 234+238U and from 33 to 249 μBq/kg for 239+240Pu.
Technical Report
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This paper focuses on intensifying maize-based cropping systems in the Sierra de Santa Marta Region of Veracruz, Mexico. Following a description of the study area, the paper examines the historical forces that have shaped regional maize-based cropping systems, current maize production practices, and major productivity and sustainability constraints. Potential solutions to these constraints, some of which have been successfully tested in the area, are described and possible productivity and sustainability impacts are appraised in qualitative terms. The appraisal provides the basis for a quantitative analysis of the farm-level costs and benefits associated with the adoption of the alternative practices. A farmer-based approach to extension is described and implementation costs are estimated.
The Pocos de Caldas plateau is a weathered alkaline igneous intrusion where several radioactive anomalies (U and Th series) exist. Not only the local soils but also the edible vegetables produced in the region can present 226Ra concentrations up to 10 times higher than those from areas of normal radioactivity. The aim of this work is to evaluate through greenhouse experiments, the uptake of endogenous and exogenous 226Ra by carrots, brown beans and kale grown from four paired local natural and contaminated farm soils. Simultaneously, sequential selective extractions were performed to estimate the partitioning of 226Ra among six geochemical fractions. The results showed that concentration ratios (CRs), related to plant dry weight, for endogenous and exogenous 226Ra in soils, were of the order of 10-2 - 10-1 and 10-2 - 100 respectively. The averages of 226Ra exchangeable and residual fractions in soils were: 3.2% and 50.2% for endogenous and 15.4% and 6.0% for exogenous radium. The CRs calculated either in relation to total 226Ra or to the exchangeable fraction in soils showed about the same variability.
This book is a unified, condensed, and simplified version of the recently issued twin volumes, Fundamentals of Soil Physics and Applications of Soil Physics. Nonessential topics and complexities have been deleted, and little prior knowledge of the subject is assumed. An effort has been made to provide an elementary, readable, and self-sustaining description of the soils physical properties and of the manner in which these properties govern the processes taking place in the field. Consideration is given to the ways in which the soils processes can be influenced, for better or for worse, by man. Sample problems are provided in an attempt to illustrate how the abstract principles embodied in mathematical equations can be applied in practice. The author hope that the present version will be more accessible to students than its precursors and that it might serve to arouse their interest in the vital science of soil physics.
This contribution provides an overview of the use of radionuclides in aquatic sciences to study trace element-suspended particle and sediment-water interactions in the ocean and in lakes. Radionuclide involvement in geochemical processes is evaluated. The critical processes include the role of plankton and colloids in the vertical transport of stable and radioactive trace elements, the migration of radionuclides to and from horizontal boundaries, and the remobilization of solutes and particles from sediments. The matching of the time scale of the geochemical process to be studied by the radioactive half-life of the nuclide or by the other geophysical processes involved (such as the mixing or flow of water or the movement of particles) is of primary importance. The use of multiple tracers with either different radioactive decay times in the field, or with different chemical properties in experimental systems, is a very promising holistic approach that may constrain the effect of interrelated processes. These approaches are applicable to many current problems in limnological and oceanographic research.
A 210Pb database has recently been constructed and is now available. This base includes approximately 800 210Pb measurements of concentration in air at the Earth's surface, together with deposition flux both at the atmosphere-Earth and water-sediment interfaces. Here the data are analyzed and summarized. The atmospheric data (concentration and deposition flux) are presented for the different geographical areas when sufficient measurements are available. The trends are discussed in terms of mechanisms (sources, atmospheric circulation, and climate]. Water-sediment data are classified into four types of water reservoirs which differ in their sedimentation mechanisms or in their in situ 210Pb production. The corresponding histograms are compared with the air-surface flux histogram. This database points out the complete lack of information in some large areas of the planet.
It is well known that ultrasonic field is generally used in the cleaning of metal surfaces. Recently, there have been some attempts for the use of ultrasonic treatment in the mineral industry, especially in flotation and separation of fine particles from gases or liquids. Ultrasonic energy is used as a first time in the sedimentation of clay in this study. Laboratory scale sedimentation experiments are performed in natural and ultrasonic media in order to determine the sedimentation characteristics of clay samples in different settling environments. The effects of several parameters such as pulp density, flocculant addition and ultrasonic treatment on the sedimentation of clay are investigated and the optimum settling conditions are determined. It is found that ultrasonic treatment, applied during the sedimentation, positively affected the sedimentation of clay and increased the settling rates by lowering the settling time.
Lead-210 speciation was carried out on previously examined aquatic deposits of known ages and geochemical histories. The main separated fractions were fulvic, humic, humin and mineral-bonded humics. these organic components were wet-oxidized and their 210Po was extracted by coprecipitation with Fe3+, distillation at 450°C and self-deposition on silver-discs. The 210Po activities were determined by isotope dilution and alpha spectrometry techniques.Nineteen samples from three lakes and one ombrotrophic peat-hummock in southern Sweden; and three fjords of Skagerrak, North Sea, were investigated. Humic materials proved to trap and preserve aquatic unsupported 210Pb, especially in lakes and peats. Fulvic compounds, on the other hand, seem to enhance the mobility of unsupported 210Pb particularly under acidic conditions. However, the fulvic fraction of marine sediments showed higher amounts of unsupported 210Pb. Our results show that the supported 210Pb is incorporated with the organo-mineral complexes, the NaOH-insoluble fraction. The 210Pb activity of this fraction was found to converge to the expected supported 210Pb of sediment samples older than 100 years or so. Some younger sediments may also show the last mentioned observation. This might serve as an alternative for evaluating the supported 210Pb in 210Pb dating.