Physicochemical Characterization of Air Particulate Matter
in Medellin City and Its Use in an In-silico Study of the Effect
of a PM Component on Cardiac Electrical Activity
R Buitrago-Sierra
1, *
, C Tobon
2
, L C Palacio
2
and J Saiz
3
1
MATyER, Facultad de Ingeniería, Instituto Tecnológico Metropolitano, Cll. 54 A
#30-01 Medellín, Colombia
2
MATBIOM, Facultad de Ciencias Básicas, Universidad de Medellín, Cra. 87 #30-65
Medellín, Colombia
3
CI
2
B, Universitat Politècnica de València, Camino de Vera s/n 46022 Valencia,
Spain
Abstract. Particulate matter (PM) is considered the most severe environmental pollution
problem due to its serious effects on human health associated with an increased risk of
cardiovascular morbidity and mortality. One of the most polluted cities in America is
Medellin. Physicochemical characterization of PM is necessary to understand its toxicology
in particular cities. The goal of this work is to perform a physicochemical characterization of
PM in the city of Medellin. Lead (Pb) was chosen between the major PM components to
perform an in silico study of the effect of Pb on cardiac electrical activity. Results evidence
the nature of the main components present in the PM and their wide range of sizes and
morphologies. Pb showed a pro-arrhythmic effect on cardiac electrical activity through
shortening of APD
90
, during normal electrophysiological conditions. In silico studies may
help to better understand the mechanism of how air pollution could trigger cardiac diseases.
1. Introduction
Environmental pollution is responsible for around 4.3 million premature deaths each year [1]. In
particular, air pollution increases the risk of mortality from cardiovascular disease by 76% [2].
Particulate matter (PM) is considered the most severe environmental pollution problem due to its
serious effects on human health [3,4]. PM air pollution is associated with an increased risk of
cardiovascular morbidity and mortality [5–10].
High levels of air pollution have been recorded in many countries around the world. In South
America, specifically in Colombia, Medellin appears as one of the most contaminated cities [11,12]
and some studies measuring the air quality in Medellin showed that PM concentrations are exceeding
the limits defined by the WHO [13,14].
It is well known that the nature of the PM (physical-chemical characteristics) is directly related to
its emission source, each region worldwide has specific characteristics associated with the type of
sources present in the emission of these particles. In this way, physicochemical characterization of
Buitrago-Sierra, R., Tobon, C., Palacio, L. and Saiz, J.
Physicochemical Characterization of Air Particulate Matter in Medellin City and Its Use in an In-silico Study of the Effect of a PM Component on Cardiac Electrical Activity.
In Proceedings of the International Workshop on Materials, Chemistry and Engineering (IWMCE 2018), pages 663-669
ISBN: 978-989-758-346-9
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
663

PM is necessary to understand its toxicity in a particular city [15], so a local characterization of PM
has a great importance for the understanding the effects related to the region particularities. In
Colombia there have been few studies of PM characterization, a study conducted in the city of
Bogotá, determined that the highest metals content in the PM was mainly related to lead (Pb) and
iron (Fe) [16].
Despite there are studies on the pollutants effects on the cardiovascular system, the
pathophysiological mechanisms of the PM effects on cardiac electrical activity remain largely
unknown. Nowadays, in silico studies (via computational simulation) have served to approximate,
among other aspects, the biophysics of cardiac activity in normal and pathological physiological
conditions [17–20].
In this context, the aim of this work is to perform a physicochemical characterization of PM in the
city of Medellin. Results were used in an in silico study of the effect of one of the most problematic
metal found in the PM components on cardiac electrical activity; contributing to the knowledge about
the physiopathological mechanisms by which atmospheric pollutants can affect human health,
specifically cardiovascular health.
2. Methods
2.1. Particulate Matter physicochemical characterization
PM was collected by extracting it the filters from sample of particles an environmental monitoring
station in the city of Medellin. Two samples of PM were collected in different climatic conditions at
a monitoring point in a residential area during a period of one month.
A physicochemical characterization of the obtained PM was carried out, through the scanning
electron microscopy technique SEM-EDS. Field emission scanning electron microscopy (FE-SEM)
and energy dispersive X-Rays spectroscopy (EDS) analyses were carried out in a JEOL JSM-7100F
electron microscope, equipped with a silicon drift detector for EDS (X-MaxN, Oxford). Previous to
the analyses, in order to improve the electrical conductivity of samples, they were coated with gold in
a sputter coating system (Q300TD, Quorum).
2.2. Human cardiac cell model
Courtemanche [17] membrane formalism was implemented to simulate the electrical activity of
human cardiac cell. The transmembrane voltage (V
m
) is given by:





+

+

=0 (1)
Where C
m
is the membrane capacitance (100 pF), I
ion
is the total membrane current, and I
st
is the
external stimulus current. The model is considered under normal electrophysiological conditions.
2.3. Model of PM component effect on cardiac electrical activity
Based on the results of the characterization shown in the "results" section, where lead (Pb) appears as
one of the main components, and according to the results of a study in ventricular myocytes, which
indicate that Pb affects the cardiac electrical activity by blocking the L-type calcium channels (I
CaL
)
[21], we developed a basic model of the Pb effect on I
CaL
using the steady state fraction of block
(b
Pb
). Hill equation has been used to fit the concentration-response relationships for ligand block. It
describes the fraction of the macromolecule saturated by ligand as a function of the ligand
concentration; it is used in determining the degree of cooperativeness of the ligand binding to the
receptor. In this model the kinetics of the channel would be considered unchanged in the presence of
the Pb.
IWMCE 2018 - International Workshop on Materials, Chemistry and Engineering
664



=










(2)
Where IC
50
is the half maximal inhibitory concentration for the current block by Pb, D
Pb
is the Pb
concentration. A Hill coefficient (h) of 1 indicates completely independent binding. For the IC
50
to
block I
CaL
we used 152 nM, this value was found by [21] in ventricular myocytes.
Following, the equations to calculate I
CaL
are given by:


=(1

)



(

65) (3)
Where g
CaL
is the maximum conductance of I
CaL
, d is the activation gate, f is the voltage-
dependent inactivation gate, f
Ca
is the calcium-dependent inactivation gate and 65 is the value of
equilibrium potential for calcium.
2.4. Simulation protocol
Unicellular model was implemented to simulate the sinus rhythm under physiological conditions,
using the Cellular Open Resource public CellML OpenCOR® software. Forward Euler method with
a time step of 0.001 ms was implemented to solve the equations. A train of 10 stimuli was applied at
a basic cycle length of 1000 ms. Pb concentrations from 0 to 300 nM were implemented. The APD at
90% of the repolarization (APD
90
), I
CaL
and the resting membrane potential were measured on the
10
th
beat using a program developed in MATLAB® software.
a) b)
c)
Figure 1. SEM images of filters with PM. a) X500, b) X5000 and c) X10.000.
Physicochemical Characterization of Air Particulate Matter in Medellin City and Its Use in an In-silico Study of the Effect of a PM
Component on Cardiac Electrical Activity
665

3. Results
3.1. Physicochemical characterization
SEM images of the PM are shown in Figure 1. From this, different particulate materials added to the
filter in form of fiber could be observed. Particles with a huge range of sizes could be identified in all
micrographs, from the images particles between 100 nm and 3 µm could be seen. In most of the cases
amorphous matter is observed from the micrographics.
EDS analysis is one easy and powerful tool in the chemical composition determination of
different materials, Figure 2 show the EDS spectrum and tabulated results obtained from the sample
(Wt is the weight), respectively.
From the EDS results, carbon (C), oxygen (O), silicon (Si) and lead (Pb), are the most abundant
elements present in all samples, probably all metals are in the form of oxides. Of these components
silicon and oxygen are associated with the filter material and carbonaceous materials have already
been widely studied. Reason why Pb has been chosen to conduct in silico studies of the effect of this
element on cardiac electrical activity.
Figure 2. EDS spectrum and compositional results.
Figure 3. Pb effect on action potential (top) and I
CaL
(botton) at different concentration.
IWMCE 2018 - International Workshop on Materials, Chemistry and Engineering
666

3.2. Pb effect on cardiac electrical activity
According to a study in ventricular myocytes, Pb affects the cardiac electrical activity by blocking
the L-type calcium channels (I
CaL
) [21]. Additionally, based on the results of the PM characterization
where Pb appears as one of the main components, we simulated the Pb effect on cardiac electrical
activity. Figure 3 shows the effects of different Pb concentrations on I
CaL
and action potential, under
normal electrophysiological conditions. It can be observed that I
CaL
without Pb effect shows a peak of
-456 pA, the current remains active during the plateau phase of action potential. The APD
90
has a
value of 291 ms under control conditions. First we applied different Pb concentrations. As the Pb
concentration increases, I
CaL
downregulation is observed, which causes an APD shortening and loss
of plateau phase. When the highest Pb concentration was applied (300 nM), the I
CaL
peak decreased
60% (-181 pA) and the APD
90
reached a value of 152 ms, which indicates a decrease of 48%. The
RMP did not show significant changes (-83 mV approximately).
4. Discussion
A total of two PM filters from an environmental monitoring station in a residential area of Medellin
were analyzed. The results of the PM characterization showed high concentrations of C, O, Si and
Pb, where the C and Si are part of the filter material. Pb was chosen to study its effect on cardiac
electrical activity by simulation, because carbonaceous materials have already been widely studied.
These results are in agreement with previously reported results of PM. A study in the city of Bogotá
[16] showed that the higher metal contents in the PM were mainly related to lead (Pb) and iron (Fe).
A study in the city of Medellin also showed the Pb as an important component of the PM [22].
After simulating the effect of Pb on cardiac activity based on experimental studies, our results
showed that Pb blocks the I
CaL
in a fraction greater as the concentration increases, prolonging its
action in time, which results in an APD shortening as was demonstrated experimentally [21]. This
analysis is consistent with an experimental study in ventricle myocytes of rats [21], where the Pb
blocked the L-type calcium channels. A study in ventricular myocardium of rats suggests that acute
Pb administration reduces the myocardial contractility by reducing sarcolemmal calcium influx and
the myosin ATPase activity [23]. In neurons has been observed that Pb may alter the bioelectrical
properties through blocking high voltage activated Ca
2+
currents, particularly L-type [24], and
differentially blocks the cloned T-type calcium channels [25]. There are not in silico studies of Pb
effect on human action potential.
In silico studies may contribute to a better understanding of the mechanisms by which air
pollutants have unhealthy effects on cardiac tissue, promoting cardiac diseases as arrhythmias.
5. Conclusions
Physicochemical characterization of air particulate matter in Medellin city, evidence the obtaining of
particulate material in a huge range of sizes from 100 nm until 3 um and different morphologies.
Carbon, oxygen, silicon and lead, were found as the major elements present in the PM. Lead was
found as one of the major elements in the particulate matter. Pb was chosen to study its effect on
cardiac electrical activity. Our results show pro-arrhythmic effect of Pb on expressed through
shortening of APD, during normal electrophysiological conditions. In silico studies may help to
better understand the mechanism of how air pollution could trigger cardiac diseases.
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