Annals of Tropical Medicine and Public Health
Home About us Ahead Of Print Instructions Submission Subscribe Advertise Contact e-Alerts Editorial Board Login 
Users Online:421
  Print this page  Email this page Small font sizeDefault font sizeIncrease font size
 


 
Table of Contents   
ORIGINAL ARTICLE  
Year : 2017  |  Volume : 10  |  Issue : 1  |  Page : 82-89
Total serum IgG and respiratory symptoms as determinants of occupational exposure to the microbial contaminants in metalworking fluids among machining industry workers


1 Department of Environmental and Occupational Health, Universiti Putra Malaysia, Serdang, Selangor, Malaysia
2 Department of Medical Microbiology and Parasitology, Universiti Putra Malaysia, Serdang, Selangor, Malaysia

Click here for correspondence address and email

Date of Web Publication5-May-2017
 

   Abstract 

Background: Metalworking fluids (MWFs) are commonly used during metalworking processes in the machining industry. Aims: This study was to determine the relationship between total serum immunoglobulin G (IgG) levels with the exposure to microorganisms among workers using MWFs and also to study associations between health symptoms with total IgG. Setting and Design: This cross-sectional study was carried out on 138 machine workers who were exposed to MWFs. Materials and Methods: Respondents were invited to participate in blood sampling for the total serum IgG level analysis. The microbial assessments were carried out on the MWF bulk samples and the aerosols in the air. The data were analyzed using the Statistical Package for the Social Sciences version 22.0. Results: The findings showed significant difference between work sections for serum IgG level (p value = 0.04). The environmental bacteria level had a significant correlation with the total serum IgG level (p value = 0.003). There were also significant relationships between body mass index (BMI) (p value = 0.044), work duration (p value = 0.014), smoking (p value = 0.014), and environmental contaminants (p value = 0.049), with the total serum IgG levels. Health symptoms, such as cough (p value = 0.031), wheezing (p value = 0.043), skin itching (p value = 0.033), and skin redness (p value = 0.005), also related with the total serum IgG levels. Conclusion: There were significant correlations between the total serum IgG levels with microbial contaminants of MWF in metalworking processes. Work duration, smoking, BMI, and environmental contaminants, and health symptoms of cough, skin itching, and inflammation significantly influenced the total serum IgG levels. Total serum IgG antibodies may serve as an indicator of occupational exposure to the microbial contaminants in MWF.

Keywords: Metalworking fluids, microbial contamination, respiratory symptoms, skin symptoms, total serum IgG

How to cite this article:
Hashim NM, Hashim Z, Hamat RA. Total serum IgG and respiratory symptoms as determinants of occupational exposure to the microbial contaminants in metalworking fluids among machining industry workers. Ann Trop Med Public Health 2017;10:82-9

How to cite this URL:
Hashim NM, Hashim Z, Hamat RA. Total serum IgG and respiratory symptoms as determinants of occupational exposure to the microbial contaminants in metalworking fluids among machining industry workers. Ann Trop Med Public Health [serial online] 2017 [cited 2019 Nov 20];10:82-9. Available from: http://www.atmph.org/text.asp?2017/10/1/82/205545

   Introduction Top


Metalworking fluids (MWFs) are frequently known as coolants, lubricants, machining fluids, and cutting oil (NIOSH, 2011) National Institute of Occupational Safety and Health. MWFs comprise four major categories, which are straight oil, soluble oil, semisynthetic fluids, and synthetic fluids. Straight oil contains highly refined petroleum, marine, vegetable, animal, or synthetic oil and is not diluted with water. Soluble oil is the combination of highly refined lubricant-based oil and emulsifiers. Soluble oil is diluted with water. Semisynthetic fluids are water-soluble and contain lower amounts of highly-refined lubricant-based oil. Synthetic fluids are water-soluble and contain no petroleum oil.[1]

MWFs are commonly used in the machining industry during metalworking processes, such as cutting, turning, milling, drilling, and grinding. These fluids are extensively used as industrial lubricants to facilitate the lubricating and cooling of metalworking operations by reducing friction at the tool-workpiece interfaces, thus reducing heat. MWFs are also used to wash away waste metal debris, consequently improving the machining performance, and as a result, prolonging the life of the cutting tool.[1]

Exposure to MWFs may lead to adverse health risks, such as skin and respiratory problems. Dermatitis is the most common complaint associated with MWFs. Respiratory effects, such as upper respiratory irritation, asthma, and hypersensitive pneumonitis are caused by exposure to diluted MWFs, microbial, and chemical contaminants of the fluids.[2]

The most frequently used MWFs in the machining industry are water-based; thus, the primary concern is the presence of contaminants that encourage the growth of bacteria and fungi. Biological agents present in the MWF liquids are emitted in the form of droplet bioaerosols during rapid rotation of the working metal tools. This, when inhaled by machine operators, can result in adverse health effects mainly on the respiratory system.[3] The most common contaminant in MWFs is the gram-negative bacteria.[4]

Specific immunoglobulin G (IgG) antibodies serve as an excellent indicator and tool in assessing exposure to microbial contaminants. There is significant elevation of specific IgG antibodies in response to bacterial antigens.[4] The aim of our study was to determine the relationship between total serum IgG levels with the mould and bacteria levels in the workplace air and in the MWF bulk samples. Besides that this study also aims to study the associations between skin and respiratory symptoms with the total IgG level of MWF workers. Equations should be numbered consecutively beginning with [1] to the end of the paper. The number should be enclosed in parenthesis and set flush right in the column on the same line as the equation. An extra line space should be left above and below a displayed equation or formula.


   Materials and Methods: Top


Study population

The cross-sectional study was conducted at a bearing factory located in Negeri Sembilan, Malaysia. At this factory, MWFs were extensively used during the metalworking process. Simple random sampling method is used in this study. Subjects are randomly chosen from a list of workers that matched with the inclusion criteria. However, the participation of respondents is voluntary-based. Selected machining workers who refused to participate will not be forced to take part in the study and will be replaced by another randomized selected respondent. After screening, 138 workers who fulfilled the inclusion criteria were randomly selected to participate in this study. The inclusion criteria in this study were workers ranging in age between 20 and 58 years old, mentally healthy, and had been employed for more than 6 months. Approval from the factory and written consents from all participants were also obtained. The study was approved by the Medical Research Ethics Committee, Universiti Putra Malaysia prior to data collection [FPSK (FR14) P002].

Workplace and MWFs

There were four main sections in the factory based on the production of products, namely, the self-aligning ball bearing (SABB), deep groove ball bearing (DGBB), spherical roller bearing (SRB), large size roller (LSR), and 12 subsections, which were SABB 1, SABB 2, SABB 3, DGBB 1, DGBB 2, DGBB 3, SRB 1, SRB 2, SRB 3, SRB 4, SRB 5, and LSR. All of the sections except for the SRB used similar types of MWF. The distribution of MWFs used in each section is shown in [Table 1].
Table 1: Types of MWFs used in each section

Click here to view


Data and Blood Collection

The self-administered questionnaires were distributed to all respondents and interviews were conducted simultaneously. The questionnaire included questions related to sociodemographic data, recent work information, work history, health problems, and lifestyle information.

Written informed consent form was obtained from the respondents before the blood sampling procedure. Information and procedures were orally explained with clarity and precision to the respondents before blood sampling was conducted. A total of 2 mL of blood were drawn from the cubital fossa of the respondents and collected into Li-heparin blood collection tubes by an experienced physician. Then, the blood samples were transported to the Pathology Laboratory, Universiti Putra Malaysia and analyzed. The total serum IgG levels were analyzed using an Automated Chemistry Analyzer (Roche Cobas C501), a system with in vitro test for the qualitative determination of IgG in human serum and plasma, which is based on the principle of immunological agglutination.

Environmental Sampling

The microbial air samplings were conducted using a DUO SAS SUPER 360™ in order to identify the bacteria and fungus concentrations in the environment. Two different types of agar plates were used in this sampling, which were tryptic soy agar (TSA) for bacteria and sabouraud dextrose agar (SDA) for fungus. The airflow speed was selected at 200 L/min for 2 min. Three air samples were taken at each work section environment, in the morning, afternoon and evening. An average was taken from the three air samples reading. Both of the agar plates were incubated at 25°C and then the colonies were counted to estimate the bacteria and fungus concentrations.

Bulk Sampling (MWF)

Bulk samples were collected in sterile containers from 12 MWF tanks in various work sections. These were serially diluted to tenfold dilution in 0.85% NaCl and inoculated into 2% SDA for fungus and into TSA for bacteria. All plates were incubated at 25°C for 2-7 days. The colonies were counted to estimate the bacteria and fungi concentrations at the various work sections.


   Results Top


The demographic details of the respondents are shown in [Table 2]. Most of them were in the age range 20-29 years old. A substantial percentage of respondents were overweight and most of them were smokers. Their education levels were generally high since most of them were educated at the tertiary level. A large percentage of the respondents had been working at the factory for 6 months to 5 years and most of them worked as long as 8 hours a day. The majority of the selected respondents were working at DGBB 3.
Table 2: Sociodemographic characteristics of the respondents

Click here to view


The SABB section had 10 machines, which was the highest number of MWF machines in a particular section. The distance between MWF machines in each section was also an important finding in this study. The distance of machines was divided into two ranges consisting of less or more than three metres [Table 3]. The information on reported health symptoms consisting of respiratory and skin symptoms during the past 6 months were obtained during the interview with the respondents [Table 4].
Table 3: Workplace information

Click here to view
Table 4: Health symptoms reported

Click here to view


Level of Microbial Contaminants and Total Serum IgG Levels in Different Job Sections

The levels of microbial contaminants were measured in the different job sections. Microbial levels were obtained by measuring the bacterial and fungus concentrations in the environment and from the MWF. [Table 5] shows the level of microbial contaminants in the different job sections. Section SABB 2 had the highest bacterial and fungus levels in the environment. The mean value of the total serum IgG levels of the respondents from job section SABB 2 was also the highest compared with other job sections. [Table 6] also shows that the mean value of the total serum IgG levels of the respondents from job section SABB 2 and SABB 3 exceeded the normal range, which is between 7.0 and 16.0 g/L.
Table 5: Levels of microbial contaminants in various job sections

Click here to view
Table 6: Total serum IgG level in workers' blood at various job sections

Click here to view


Correlation between the Total Serum IgG Level with Microbial Contaminants

[Table 7] shows the correlation between the total serum IgG levels and the microbial forming unit. The results showed that environmental bacteria had a significant correlation with the total serum IgG level (p = 0.002).
Table 7: orrelations between the total serum IgG level with environmental and MWF microbial contaminants

Click here to view


The Relationship between Selected Variables with the Total Serum IgG and Microbial Contaminants Level

[Table 8] shows the relationship between selected variables with total serum IgG levels. On the basis of [Table 8], the significant factors that influenced the total serum IgG levels was body mass index (BMI) (p = 0.044), work duration (p = 0.014), smoking factor (p = 0.014), and bacteria concentrations in the environment (p = 0.049). All had a significant relationship with the total serum IgG levels. Referring to [Table 9], the number of machines in each section had a significant relationship with the environmental bacteria levels (P = 0.004).
Table 8: The relationships between selected variables with total serum IgG level

Click here to view
Table 9: The relationships between selected variables with the microbial levels in the environment

Click here to view


The Relationship between Personal Factors and Total Serum IgG Level with Reported Health Symptoms

There was a significant relationship between cough (p = 0.031), wheezing (p = 0.043), skin itching (p = 0.033), and skin redness (p = 0.005) with the total serum IgG levels [Table 10]. Personal factors, such as BMI and smoking, were also correlated with cough and wheezing, respectively.
Table 10: The relationships between personal factors and total serum IgG level with reported health symptoms

Click here to view



   Discussion Top


Sections

The exposure of workers to microbes can be extensive when microbe contaminated MWFs are used in machining plants. In this study, the concentrations of microbial contaminants from different job sections using MWF were measured. Job section SABB 2 had the highest concentration of bacteria and fungus in the environment at 665 CFU/m³ and 350 CFU/m3, respectively, which, generally, is considered to be high. This may be due to many factors, one of them being the high number of machines present in the section. It was noted that job section SABB 2 had the highest number of water-based MWF machines in the factory. This may indicate that higher the number of MWF machines present in a section, higher would be the environmental contaminants.

In addition, the distance of MWF machines at the SABB section was within 3 m or less, which is considered close to each other. The bacteria and fungus levels in the air decreased when the distances between the MWF machines were increased. In another study, the findings showed that the total number of bacteria collected with a Reuter centrifugal sampler in the air surrounding the machines was inversely related to the distances from the machines.[4]

MWF samples from each section contained high levels of microbial contaminants. The total mean values for microbial contamination in MWF were 37916.7 CFU/mL (bacteria) and 38833.3 CFU/mL (fungus). These concentrations were generally low. According to some studies, the average concentrations of viable bacteria in MWF were from 105 to 108 CFU/mL, with the highest level being 108 CFU/mL.[4] The low levels of microbial contaminants in bulk samples of MWF were due to the addition of antibacterial agents (biocides) to the MWF in most of the machines. However, even if biocides were added to the fluids, they can easily be contaminated by microbes, since microbes can remain on the surface of water tanks. Even when old fluids were replaced by fresh ones, the fresh fluids would also become contaminated.[5]

Furthermore, the wrong technique used for the topping up of the coolant was also one of the factors, which contributed to the presence of microbial contaminants in bulk samples. Most machinists added coolant when it was depleted in their machines. When the machinist added coolant to the sump, they did not add biocides; hence, bulk samples were still contaminated by microorganisms.

Total Serum IgG Level in Blood for Different Job Sections

The levels of total IgG in the serum of the 138 respondents from the different job sections were measured. It was noted that the majority of the respondents in section SABB 2 had a high level of total IgG in their serum, which exceeded the normal range of total IgG levels. The normal range of total IgG levels for adult men is between 7.0 and 16 g/L.[6] The results from the serology tests showed that the mean of the total serum IgG levels of the respondents from job section SABB 2 was the highest at a level of 17.27 g/L, when compared with the rest of the respondents from the other job sections. The high total serum IgG levels of respondents were probably due to the high concentration of microbial contaminants in the environment of job section SABB 2.

Moreover, all job sections were in enclosed air-conditioned spaces with central heating, ventilation, and air-conditioning (HVAC) systems. Insufficient ventilation resulted in a lack of incoming fresh air with contaminated air circulating in the room. According to a study, microorganism contamination of air-handling units is a widespread phenomenon in buildings with central HVAC systems and is a potential source of contamination for occupied spaces. Fungi have been found growing on air filters, insulation, and cooling coils, as well as in ducts. This contamination often contributes to building-related diseases, including both infectious diseases and hypersensitivity diseases, such as allergic rhinitis, asthma, and hypersensitivity pneumonitis.[7] On the basis of findings in this study, there was a significant correlation between environmental bacteria with the total serum IgG levels. There seemed to be a tendency for workers in the same workplace to have the same kind of antibody profiles, depending on the type of MWF and its dispersion in the air. Based on the literature, the total IgG antibody responses were associated with the microbial concentrations in the air of the corresponding workplaces.[4]

Correlation between the Total Serum IgG Level Antibodies and Microbial Contaminants

Most of the respondents in section SABB Channel 6 also had high total serum IgG levels, which exceeded the normal range. The high total serum IgG levels were due to the high environmental microbial contaminant levels in section SABB 2. Based on the results obtained, the environmental bacteria level had a significant correlation with the total serum IgG level (p = 0.002). Very few studies are available concerning the immune response to antigens in MWFs.[7] According to a study, it can be concluded that environmental bacteria constituted the most prominent source of a worker's exposure when working with MWFs, and that exposure to other airborne microbes was also primarily related to the environment.[4]

The Relationship between Selected Variables with the Total serum IgG Level and the Microbial Contaminants

A significant factor that influenced the total serum IgG level is BMI (P = 0.044). Overweight and obese individuals were commonly associated with chronic diseases. Thus, their total serum IgG levels were higher than that of normal individuals. The results also showed that work duration had a significant relationship with the total serum IgG level (p = 0.014). The longer the work duration, the higher the exposure to microbial contaminants, and, hence, the higher the total serum IgG levels. Smoking (p = 0.014) and environmental bacteria levels (p = 0.049) also had a significant relationship with the total serum IgG levels, respectively. This is because, generally, smokers had higher total serum IgG levels compared with nonsmokers; therefore, smoking was associated with total IgG levels.

There are studies that investigated the serum Ig concentrations in relation to demographic factors, common habits, such as smoking and alcohol intake. Age was also positively associated with the total serum IgA and IgG levels. It was concluded that sex, age, alcohol consumption, smoking, and common metabolic abnormalities should be taken into account when interpreting the total serum levels of IgA, IgG, and IgM.[8] Based on the findings in this study, the number of machines in each section had a significant relationship with the environmental bacteria levels (p = 0.004). This finding was similar to Laitinen et al.[4], who found that the total number of bacteria collected with a Reuter centrifugal sampler in the air surrounding machines was related to the distances between the machines.

The Relationship between Personal Factors and Total Serum IgG Level with Reported Health Symptoms

The highest reported respiratory symptom was cough (42%), and there was a significant relationship between cough, wheezing, itching, and skin redness with the total serum IgG levels. This means that respiratory symptoms, such as cough, as well as skin symptoms, such as itching and skin redness, were influenced by the total serum IgG levels. A study in Poland indicated that there were increased risks of cough and acute symptoms suggestive of pneumonia found among respondents who were exposed to microbial contaminants in their workplace.[9] In addition, based on the Center for Disease Control and Prevention in the USA, the findings in a report that represented one of the largest reports on the outbreak of work-related respiratory illness and health implications in the machining environment in the United States estimated that one million workers were exposed to MWFs. All of these studies and findings indicated that there were significant relationships between respiratory symptoms (cough and wheezing) with the total serum IgG levels. The presence of cough and wheezing symptoms was due to high total serum IgG levels.

Another serious health concern associated with MWF is dermatitis. Every year, around 200 cases of contact dermatitis related to exposure to cutting oils and coolants are reported to European Prevention Initiative for Dermatological Malignancies. This figure was undoubtedly a very substantial underestimate of the true incidence of skin disease.[10] Based on the findings in a study, a high level of exposure to allergens was associated with increased prevalence of allergy and appreciably higher total serum IgG levels.[11] Thus, it is concluded that skin symptoms, such as skin itching and skin redness, were due to high total serum IgG levels.

In addition, the type of MWF used in the section is also one of the factors that may contribute to the skin and respiratory symptoms. As stated in material safety data sheet (MSDS), most of the types of MWF used in the section induced both of the symptoms. The comparison of total serum IgG levels between work units showed that there were significant differences of total serum IgG levels between the work unit B (SRB) and work unit A (SABB, DGBB, and LSR). Work unit B had a higher mean value of total serum IgG levels compared with the other work units. This is due to the different types of MWF used in work unit B (SRB) as compared with work units A (SABB, DGBB, and LSR). Hyspin AW 68, Hydraulic VG22 MI, P3-Neutrapon 5088, and Rustilo DWX 88 are the MWFs that were only used by work unit B. All of these MWF have greater health effects with chronic exposure and may induce skin and respiratory symptoms among respondents in work units B, which will eventually raise the total serum IgG levels. The MSDSs for a total of six different MWFs were reviewed for reported evidence of skin and respiratory symptoms. Some of the reviewed MSDS were Hysol x,[12] Ilocut 603,[13] Hydraulic VG22 MI,[14] Rustilo DWX 88,[15] and Hyspin AW 68.[16]

Acknowledgement

This research study was supported by the EScience Research Fund, Project No. 06-01-04-SF1203 from Ministy of Science, Technology and Innovation (MOSTI), Malaysia

Financial source of support

This research study was supported by the EScience Research Fund, Project No. 06-01-04-SF1203 from Ministy of Science, Technology and Innovation (MOSTI), Malaysia.

Conflicts of interest

There is no conflict of interest.

 
   References Top

1.
OSHA U.S Department of Labour. “Metalworking Fluids: Safety and Health Best Practices Manual”. 1999;Available from: http:/www.osha.gov/SLTC/mmetalworkingfluids/metalworkingfluids_manual.html. [Last accessed on 2014 Mar 17].  Back to cited text no. 1
    
2.
Cohen H, White EM. Metalworking fluid mist occupational exposure limits: a discussion of alternative methods. J Occup Environ Hyg 2006;3:501-7.  Back to cited text no. 2
[PUBMED]    
3.
Cyprowski M, Piotrowska M, Zakowska Z, Szadkowska-Stanczyk I. Micobial and endotoxin contamination of water-soluble metalworking fluids. Int J Occup Med Environ Health 2007;20:365-71.  Back to cited text no. 3
    
4.
Laitinen S, Linnainmaa M, Laitinen J, Kiviranta H, Reiman M, Liesivuori J. Endotoxins and IgG antibodies as indicators of occupational exposure to the microbial contaminants of metal-working fluids. Int Arch Occup Environ Health 1999;72:443-50.  Back to cited text no. 4
[PUBMED]    
5.
Mattsby-Baltzer I, Sandin M, Ahlström B, Allenmark S, Edebo M, Falsen E, et al. Microbial growth and accumulation in industrial metal-working fluids. Appl Environ Microbiol 1989;55:2681-9.  Back to cited text no. 5
    
6.
Wolfgang H, Volker E, References for adults and children 2008: Pre-analytical consideration. 2008;122.  Back to cited text no. 6
    
7.
Estelle L, Richard S, Christine AR, Robert S. Effectiveness of germicidal UV radiation for reducing fungal contamination within air-handling units. Appl Environ Microbiol 2001;68:3712-5.  Back to cited text no. 7
    
8.
Gonzalez-Quintela A, Alende R, Gude F, Campos J, Rey J, Meijide LM, et al. Serum level of immunoglobulins (IgG, IgA, IgM) in a general adult population and their relationship with alcohol consumption, smoking, and common metabolic abnormalities. Clin Exp Immunol 2008;151:42-50.  Back to cited text no. 8
[PUBMED]    
9.
Krogulska A, Bialek J, Funkowicz M. The prevalence of IgG-dependent food allergy in asthmatic children. Clin Translat Allergy 2013;61:2045-7022.  Back to cited text no. 9
    
10.
Lillienberg L, Burdorf A, Mathiasson L, Thörneby L. Exposure to metalworking fluids aerosols and determinants of exposure. Ann Occup Hyg 2008;52:597-605.  Back to cited text no. 10
    
11.
Chapman MD, Rowntree S, Mitchell EB, Di Prisco de Fuenmajor MC, Platts-Mills TAE. Quantitative assessments of IgG and IgE antibodies to inhalant allergens in patients with atopic dermatitis. J Allergy Clin Immunol 1983;72:27-33.  Back to cited text no. 11
    
12.
Castrol, Hysol X material safety data sheet. 2008;Available from: http://www.lubricantsonline.co.za/uploads/548443011_Hysol_X.pdf. [Last accessed on 2014 Apr 15].  Back to cited text no. 12
    
13.
Castrol, ILOCUT 603 material safety data sheet. 2003;Available from: http://msdspds.bp.com/ussds/amersdsf.nsf/0/D50F3658B113467680257B2C0057F414/$file/190333Ilocut%20603.pdf. [Last accessed on 2014 Apr 15].  Back to cited text no. 13
    
14.
Brad Penn. Hydraulic VG22 MI material safety data sheet. 2012;Available from: http://www.amref.com/CMSFiles/File/bp_msds/7362_BP_R_O_ISO_VG_22_Turb_Hyd_Oil.pdf. [Last accessed on 2014 Apr 15].  Back to cited text no. 14
    
15.
Castrol, Rustilo DWX 88 IV material safety data sheet. 2014;Available from: http://msdspds.castrol.com/ussds/amersdsf.nsf/0/8CB5438E88E568ED80257C77005809A4/$file/282055Rustilo%20DWX%2088%20IV.pdf. [Last accessed on 2014 Apr 15].  Back to cited text no. 15
    
16.
Castrol. Hyspin AW 68 material safety data sheet. 2004; Available from: http://theoilnet.com/Atlantic-States-Lubricants/msds/Industrial-Lubricants/Castrol-Hyspin-AWS-68.pdf. [Last accessed on 2014 Apr 15].  Back to cited text no. 16
    

Top
Correspondence Address:
Dr. Zailina Hashim
Department of Environmental and Occupational Health, Faculty of Medicine and Health Sciences, Universiti Putra Malaysia, Serdang, Selangor
Malaysia
Login to access the Email id

Source of Support: None, Conflict of Interest: None


DOI: 10.4103/ATMPH.ATMPH_79_17

Rights and Permissions



 
 
    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]



 

Top
 
  Search
 
    Similar in PUBMED
   Search Pubmed for
   Search in Google Scholar for
 Related articles
    Email Alert *
    Add to My List *


    Abstract
   Introduction
    Materials and Me...
   Results
   Discussion
    References
    Article Tables

 Article Access Statistics
    Viewed928    
    Printed43    
    Emailed0    
    PDF Downloaded18    
    Comments [Add]    

Recommend this journal