Commission for Environmental Cooperation

Trinational Biomonitoring Study

Assessment of Persistent Organic Pollutants and

Selected Metals in the Blood of First‐Birth Mothers

in Southern Canada and Mexico and in Women of

Reproductive Age in the United States
Commission for Environmental Cooperation ii

This study was prepared by the Secretariat of the Commission for 

Environmental Cooperation. See Acknowledgments for detailed 

information about contributions to this study. The information 

contained herein does not necessarily reflect the views of the 

CEC, or the governments of Canada, Mexico or the United States 

of America. 

The material herein may be reproduced without seeking 

permission, provided that it is accurately reproduced, is not used 

for commercial purposes, and includes an acknowledgement of 

the Commission for Environmental Cooperation. 

Except where otherwise noted, this work is protected under a 

Creative Commons Attribution‐Noncommercial‐No Derivative 

Works License. 

Commission for Environmental Cooperation, 2011 

Publication Details

Publication type: Report

Publication date: October 2011

Original language: English

QA08.34 

Please cite as : 

CEC. 2011. Trinational Biomonitoring Study: Assessment of Persistent

Organic Pollutants and Selected Metals in the Blood of First‐Birth

Mothers in Southern Canada and Mexico and in Women of

Reproductive Age in the United States. Montreal: Commission for

Environmental Cooperation.

For more information: 

Commission for Environmental Cooperation

393, rue St‐Jacques ouest 

Bureau 200 

Montreal (Quebec) Canada H2Y 1N9 

t 514.350.4300 f 514.350.4372 

info@cec.org / www.cec.org
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation iii

Table of Contents

Acknowledgements .................................................................................................................. iv

Acronyms.................................................................................................................................. vi

Executive Summary ................................................................................................................... 1

Study design .....................................................................................................................................1

Results ..............................................................................................................................................2

Capacity‐building..............................................................................................................................3

Conclusion ........................................................................................................................................4

1. Introduction ....................................................................................................................... 5

1.1 Purpose.......................................................................................................................................5

1.2 Background.................................................................................................................................5

2. Study Outline ..................................................................................................................... 7

2.1 Study Framework .......................................................................................................................7

3. Study Design....................................................................................................................... 9

3.1 Population Selection and Recruitment.......................................................................................9

3.2 Study Implementation and Samples Collected ........................................................................11

3.3 Analytical Issues .......................................................................................................................12

4. Statistical Analysis............................................................................................................ 18

5. Results.............................................................................................................................. 19

6. Discussion......................................................................................................................... 22

6.1 Concentrations of Persistent Organic Pollutants .....................................................................22

6.2 Concentrations of Dioxins in Pooled Blood ..............................................................................22

7. Capacity Building.............................................................................................................. 25

7.1 Training and Quality Assurance Exercises ................................................................................25

7.2 Recommendations on Improving Proficiency ..........................................................................26

8. Conclusions ...................................................................................................................... 29

8.1 Population Exposure Assessment.............................................................................................29

8.2 Capacity Building ......................................................................................................................30

8.3 Recommendations for Future Work.........................................................................................30

9. Bibliography ..................................................................................................................... 33
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation iv

Acknowledgements

The Commission for Environmental Cooperation wishes to 

recognize the dedicated experts responsible for developing 

this Trinational Blood Biomonitoring study: Assessment of 

Persistent Organic Pollutants and Selected Metals in the 

Blood of First Birth Mothers in Southern Canada and Mexico 

and in Women of Reproductive Age in the United States:  

 Mauricio Hernandez, Instituto Nacional de Salud Pública,

Secretaría de Salud

 Leonora Marro, Health Canada 

 Larry Needham, co‐author, Centers for Disease Control 

and Prevention 

 Horacio Riojas, co‐author, Instituto Nacional de Salud

Pública

 Sandra Rodriguez, Instituto Nacional de Salud Pública

 Jay Van Oostdam, co‐author, Health Canada 

 Jean‐Philippe Weber, co‐author, consultant 

 Lee‐Yang Wong, Centers for Disease Control and 

Prevention 

The Commission for Environmental Cooperation also 

wishes to recognize the valuable contributions of the 

following individuals and institutions in the development of 

this study: 

 The heads and staff of: Hospital de Especialidades del

niño y la mujer Querétaro, Hospital General de Cuautitlán,

Centro de Salud de la Cabecera Municipal de Tultitlán

Centro, Hospital Materno Infantil Mérida, Hospital

General Coatzacoalcos, Hospital Universitario Monterrey,

Hospital Integral Hermosillo, Hospital Zona “Yanga,”

Hospital General Ciudad Obregón, and Hospital Civil

Guadalajara.

 The lead researchers (Drs W. Foster, A. Chung, G. Graves, 

J. Jarrell, M. Walker, and K. Davis) and their staff at the 

following medical centers, respectively: McMaster 

University, University of British Columbia, Dalhousie 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation v

University, University of Calgary, University of Ottawa, 

and Health Canada. 

 The contributing mothers without whom this study 

could not have taken place. 

This study was made possible through the support of 

officials from Environment Canada, Health Canada, Instituto

Nacional de Salud Pública, Secretaría de Salud, Secretaría de

Medio Ambiente y Recursos Naturales, Instituto Nacional de

Ecología – Centro Nacional de Investigación y Capacitación

Ambiental, the Centers for Disease Control and Prevention, 

the United States Environmental Protection Agency and the 

World Bank.  

This report was prepared with the aid of the CEC 

Secretariat, including Luke Trip, Program Manager for 

Sound Management of Chemicals, Lucie Robidoux, 

Coordinator of the Environmental Monitoring and 

Assessment project of the Sound Management of Chemicals 

program, and Erika Hercules, program assistant. The 

publications staff, of Douglas Kirk, Jacqueline Fortson, and 

Johanne David, under the guidance of Jeffrey Stoub, carried 

out the demanding job of editing, translating and publishing 

the report, including a summary in three languages. 

It is with great sadness that the above contributors to this 

study wish to dedicate it to the memory and devotion of Dr. 

Larry Needham, co‐author and principal supporter of this 

work, who died in October 2010 after having seen it through 

its various stages. Larry's strong belief in the value of the 

study enabled him to surmount his personal tribulations 

and continue working on it until the last few weeks before 

his death. 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation vi

Acronyms

CCAYAC Comisión de Control Analítico y Ampliación de Cobertura

(Commission for Analytical Control and Extension of 

Coverage) 

CDC  Centers for Disease Control and Prevention 

Cenica Centro Nacional de Investigación y Capacitación Ambiental

(National Center for Environmental Research and Training) 

CHMS  Canadian Health Measures Survey 

Cofepris Comisión Federal para la Protección contra Riesgos

Sanitarios (Federal Commission for Risk Protection) 

EPW  expectant primiparous women (women in their first 

pregnancy) 

EQA  external quality assurance   

EQAS  external quality assessment scheme 

HCB  hexachlorobenzene 

HCH  hexachlorocyclohexane [either alpha‐, beta‐, or gamma‐ 

(lindane) forms] 

INE Instituto Nacional de Ecología (National Institute of 

Ecology) 

INSP Instituto Nacional de Salud Pública (National Institute of 

Public Health) 

INSPQ Institut national de santé publique du Québec (National 

Institute of Health of Quebec) 

LOD  limit of detection 

NHANES  US National Health and Nutrition Examination Survey 

OCP  organochlorine pesticides 

PAHO  Pan American Health Organization 

PBT  persistent, bioaccumulative, toxic chemicals 

PCB  polychlorinated biphenyls 

PCDD  polychlorinated dibenzo‐p‐dioxins 

PCDF  polychlorinated dibenzofurans 

POPs  persistent organic pollutants 

p,p'­DDE  p,p'‐dichlorodiphenyl‐dichloroethylene 

Proname Programa Nacional de Monitoreo y Evaluación de Sustancias

Tóxicas, Persistentes y Bioacumulables (National Monitoring 

and Environmental Evaluation Program) 

SMOC  Sound Management of Chemicals program 

TEF  toxic equivalency factor 

TEQ  toxic equivalent 

UASLP Universidad Autónoma de San Luis Potosí
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 1

Executive Summary

Human exposure to persistent organic pollutants (POPs) and 

certain toxic metals in our environment is a matter of serious 

concern because of their potential for causing deleterious effects 

on our health. An assessment of the degree of pollutant exposure 

in different sections of the three North American countries is 

thus of great importance. As women experiencing their first 

pregnancy or who are of reproductive age form categories of 

people most susceptible to ambient and ingestible pollutants, 

they were chosen as the subject group for developing an initial

profile of population exposure to such chemicals.  

This study was initiated under the Sound Management of 

Chemicals (SMOC) program of the Commission for 

Environmental Cooperation (CEC), a body established by the 

North American Agreement on Environmental Cooperation. The 

study had two main objectives:  

1. To obtain an initial trinational assessment of exposure to 

persistent organic pollutants (POPs) and selected metals in 

expectant primiparous women (EPW) in southern Canada 

and Mexico, and to present representative data on women of 

reproductive age who participated in the US National Health 

and Nutrition Examination Survey (NHANES); and  

2. To enhance the capacity of Mexico’s analytical facilities to 

monitor POPs listed in the Stockholm Convention on 

Persistent Organic Pollutants, as well as selected metals, 

thereby establishing the basis for the development of 

compatible, comparable databases of blood biomonitoring 

results for Canada, Mexico and the United States.  

Study design

To obtain exposure data on the desired study population, EPW 

were recruited from selected study sites across southern Canada

(five sites) and Mexico (10 sites). In the United States, women of 

reproductive age (defined here as 1544 years of age) were 

selected from NHANES 20032004; pooled samples from 
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Commission for Environmental Cooperation 2

NHANES 20012002 for women aged 2039 years were used for 

data on polychlorinated dibenzo‐p‐dioxins (PCDDs), 

polychlorinated dibenzofurans (PCDFs), and dioxin‐like 

polychlorinated biphenyls (PCBs). 

Blood collected from the study subjects was analyzed for metals

(lead, cadmium and mercury in all three countries, plus nickel in 

Canada and Mexico) and POPs (including 11 from the United 

Nations Environment Programme Stockholm Convention list, 

although endrin, dieldrin, and heptachlor epoxide were 

measured only in the United States), along with γ‐

hexachlorocyclohexane (γ‐HCH or lindane) and β‐

hexachlorocyclohexane (β‐HCH). Pooled samples were analyzed 

for PCDDs, PCDFs and PCBs, including dioxin‐like PCBs. The 

measurements were carried out in four laboratories: the Centre

de toxicologie du Québec at the Institut national de santé publique

du Québec (INSPQ) in Canada, the Centers for Disease Control 

and Prevention (CDC) in the United States, and in Mexico the 

Centro Nacional de Investigación y Capacitación Ambiental

(Cenica) for metals and the Universidad Autónoma de San Luis

Potosí (UASLP) for POPs. Mexican samples were split and 

analyzed by INSPQ and by the Mexican laboratories. Organic 

contaminant levels were expressed on a lipid‐weight basis, to 

account for differences in fasting status and stage of pregnancy 

among participants. Rigorous quality control/quality assurance 

procedures were carried out on the laboratory work to ensure 

the reliability of results. 

Mexican and Canadian sample designs were not nationally 

representative; instead, convenience samples were taken of EPW 

in selected geographical areas within these two countries. The 

United States supplied contaminant data for women of 

childbearing age from NHANES.  

Results

Cadmium, lead, total mercury, and nickel (not measured in the 

United States) among the metals, as well as selected PCB 

congeners, oxychlordane, β‐HCH and p,p’‐DDE (p,p'‐

dichlorodiphenyl‐dichloroethylene) were detected in at least 70

percent of the women in each country. The report presents, by 

country, the number of samples analyzed, the percent of each 

chemical detected, with detection limits, and the concentration

range and geometric means, including confidence intervals. 

PCDDs, PCDFs, and co‐planar PCBs were measured in composite 

or pooled samples and the mean results are presented. These 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 3

environmental chemicals enter the body via ingestion (generally

dietary), inhalation, and dermal absorption. For the general 

population, the predominant route is through dietary ingestion.

The highest concentrations in humans would be expected to be 

found in areas where these chemicals have been used or 

produced more recently and in higher quantities. They can, 

however, also be transported long distances, across borders, by

prevailing air currents and thus be found thousands of miles 

from their sources. POPs tend to be stable in the body and in the 

environment as well as being lipophilic; hence they 

bioaccumulate in the fatty and other lipid tissues of humans.  

The analyses conducted during the study reveal the predominant 

PCB congener in all population groups to be PCB 153, followed 

by 138, 180 and 118. This is in agreement with other 

biomonitoring studies that have shown PCBs 138 and 153 to be 

the major PCB congeners in North America and Europe. PCBs are 

technical mixtures used in a variety of products including 

transformers and capacitors and were widely used throughout 

the United States. Other POPs found in a high percentage of the

populations included p,p’‐DDE, beta‐HCH, and oxychlordane. The 

first of these is the major environmental degradate and human 

metabolite of p,p’‐DDT, which has been widely used in Mexico in

agriculture and as a mosquito repellant and insecticide. Beta‐

HCH is the most stable HCH isomer found in technical 

hexachlorocyclohexane formulations, which were banned in 

Mexico more recently than in the United States or in Canada. As

expected, cadmium, mercury and lead were detected at low 

concentrations in a high percentage of the women. Lead 

exposure can result from gasoline fumes and pottery glazing, 

among other sources. 

Capacity‐building

The North American capacity‐building initiative was useful in 

providing insights for necessary biomonitoring improvements. 

The training and quality‐assurance exercises, which took place 

primarily between the two Mexican laboratories and the 

Canadian laboratory from 2004 through 2006, were helpful in 

building analytical capacity in the two Mexican laboratories, and 

in improving the accuracy and reproducibility of their analytical 

results. It is important to note that biomonitoring of the general 

population for environmental contaminants is much different 

from occupational biomonitoring and especially different from 

environmental monitoring, both in the matrices of samples and 

in the concentrations of the analytes, which, in the case of 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 4

environmental chemicals, tend to be significantly higher and 

therefore easier to measure. Future capacity issues include 

instrumentation of the proper sensitivity to enable the two 

Mexican laboratories to conduct general population 

biomonitoring, and for the recruitment and training of key 

personnel to conduct such studies. The training should include 

continuing, active participation in external quality‐assessment

schemes, to allow personnel to demonstrate their proficiency 

objectively. The assessment schemes should include all the steps 

of population biomonitoring, from sample procurement, 

shipping, handling and storage, through analysis and data 

reporting. 

Conclusion

This study has produced an initial North American trinational 

profile of human exposure to environmental contaminants, 

including POPs and selected metals. This preliminary dataset 

will assist in setting priorities and tracking progress in the 

management of these chemicals, both domestically and on a 

broader, North American cooperative basis. This study should 

not be considered a national biomonitoring program for Mexico 

or for Canada, since such a program would require a much larger

and randomly‐selected population sample, similar to what has 

been done in the United States and is being implemented in 

Canada. In order for Mexico to plan and conduct a national 

biomonitoring program, its analytical facilities must be 

expanded and improved and qualified personnel trained and 

retained. The success of a nationwide biomonitoring program 

will depend upon the involvement of key personnel in other 

several disciplines and institutions, including epidemiologists, 

statisticians, and chemists. It will also require the necessary

administrative support. Only then will it be possible to generate 

data of sufficient quality for the program to play its role properly 

as a cornerstone of environmental health policy. 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 5

1. Introduction

1.1 Purpose

This study had two general objectives:  

1. To obtain an initial trinational profile of exposure levels to 

persistent organic pollutants (POPs) and selected metals in a 

particularly susceptible human population and  

2. To enhance the capacity of Mexico to monitor general 

population concentrations of Stockholm Convention POPs 

and selected metals, establishing the basis for the 

development of compatible, comparable databases of blood 

biomonitoring results for the three countries.  

Thus, this study is the first step towards the ultimate goal of

providing an integrated data set that could be used to determine 

priorities and track progress in the management of these 

chemicals, both domestically and on a broader, North American 

cooperative basis. The samples in Mexico and Canada were 

convenience samples collected from expectant primiparous 

women (EPW), and were analyzed by standard analytical 

techniques using accepted quality assurance and quality control

methodologies. The samples in the United States were collected 

as part of the National Health and Nutrition Examination Survey

(NHANES) to be representative of the United States general 

population; the data used in the study came from women of 

reproductive age (15–44 years of age).

1.2 Background

In 1995, in only its second year of existence, the Commission for 

Environmental Cooperation (CEC), by Council Resolution, 

initiated a Sound Management of Chemicals (SMOC) program to 

coordinate trinational efforts to reduce exposure to substances

toxic to human health and the environment in the three 

countries. Specifically named among these substances were 

persistent, bioaccumulative, toxic chemicals (PBTs) that may 

cross international borders, once released to the environment, 

and affect human populations far from their point of origin. 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 6

Transport of PBTs, generally through atmospheric air currents, 

can also pose an unacceptably high risk to the environment and 

to ecosystems upon which human life depends. (For the 

purposes of this report, the term PBTs comprises several classes 

of substances, including persistent organic pollutants (POPs) and 

some metals.) 

Convenient and dependable access to and dissemination of 

relevant, reliable and comparable monitoring information and 

sound interpretive assessments of that information are crucial to 

the confirmation and quantification of progress on reducing the

risk of exposure. Several of the substances are being addressed

by both the SMOC program and the Stockholm Convention on 

POPs. The availability of such information is important for risk 

analysis, risk assessment, risk management, and the 

communication of risks to targeted groups and the general 

population. These assessments will help to determine progress 

under these initiatives and to identify and explain important 

emerging issues related to PBTs in the North American 

environment.  

Under the auspices of the CEC SMOC program, an advisory body 

was created to initiate the study. It was composed of 

representatives from the appropriate agencies within the 

participating countries: i.e., the Department of Health (Health

Canada) for Canada, the Centers for Disease Control and 

Prevention (CDC) and the Environmental Protection Agency 

(EPA) for the United States, and the National Institute of Public 

Health (Instituto Nacional de Salud Pública—INSP), the 

Secretariat of the Environment and Natural Resources 

(Secretaría de Medio Ambiente y Recursos Naturales—Semarnat) 

and the National Institute of Ecology (Instituto Nacional de

Ecología—INE) for Mexicotogether with academics and 

experts who were active in POPs/metals biomonitoring research 

in North America, as well as representatives of the CEC itself. The 

participation of these agencies ensured the use of comparable 

sampling protocols and ensured that the laboratories would 

produce comparable analytical results. Representatives of the 

World Bank and the Pan American Health Organization (PAHO) 

were also invited to participate, upon the granting of funding 

requests.  
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 7

2. Study Outline

2.1 Study Framework

The study was established to enhance the capacity of Mexico to 

biomonitor Stockholm Convention POPs and selected metals, 

and to enable the country to work with the United States and 

Canada in establishing the basis for compatible, comparable 

databases of blood biomonitoring results. The POPs and metals 

data from Mexico and Canada were obtained by convenience 

sampling of expectant primiparous women (EPW) in those 

countries. The data in the United States are those of women of 

reproductive age who participated in NHANES 20032004, as 

well as of women aged 2039 years old selected from the pooled 

NHANES 20012002 samples. These quality‐assured data will 

assist in the further development and implementation of 

effective strategies for the management of POPs and metals. The

chemicals measured in at least one of the populations include 11 

of the 12 POPs listed in the Stockholm Convention (excluding 

toxaphene but including β‐HCH) and three of the metals 

(cadmium, lead and mercury) listed in the United Nations 

Economic Commission for Europe (UNECE) Convention on Long‐

range Transboundary Air Pollution and its Protocol on Heavy 

Metals, as well as nickel (of particular interest to Mexico, which 

until 2002 lacked a management plan for the safe disposal of 

nickel‐containing batteries). In addition, other POPs and metals 

were measured, although they are not addressed in this report. 

The population initially selected for biomonitoring from Canada

and Mexico was EPW from 18 to 30 years of age. The women 

selected were the first pregnant women attending the sampling 

sites who met the selection criteria (that is, a convenience 

sample). A search of the literature indicated that there exists an 

extensive comparative database in Canada for this population, 

particularly for northern Canada, including accepted protocols 

and patient‐consent models for maternal sampling during 

routine pre‐natal assessments. EPW also provide researchers 

with a consistent body burden of contaminant levels unaffected 

by lactation or by in utero transfer from mother to a previous 

infant. Working with pregnant women also enables outreach on 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 8

nutrition, the effects of lifestyle and pollutant exposure, and

health follow‐up to optimize the potential for infant health and 

development.  

The study was originally intended to last 12 months; however, 

difficulties in obtaining ethics‐board approvals from all 

participating hospitals and institutions and in the recruitment of 

study subjects meeting the inclusion criteria extended the time

required to collect, prepare and analyze the samples. There was

also some recruitment difficulty in Mexico because of the young

age at which many women have their first child; conversely, in 

Canada a similar sampling program found many women had not 

yet had their first child by age 30. Therefore, the participant age 

range was expanded to include women 14 to 43 years of age.  

The study incorporated additional quality‐assurance procedures.

First, sample collection, storage and analyses were monitored 

for consistency and quality. Second, chemical analyses of blood

samples were conducted by four different laboratories: one in 

Canada (Institut national de santé publique du Québec—INSPQ) 

which performed both metals and POPs measurements, two in 

Mexico (Cenica for metals and UASLP for POPs) and one in the 

United States (CDC) for POPs and metals. Third, analytical results 

and questionnaire responses were subjected to standardized 

quality‐control tests to ensure comparability and compatibility.  

The study specifically involved development of common 

biomonitoring methodology and capacity‐building in Mexico. 

Capacity‐building activities included analytical laboratory 

training exchanges, translation of guidance and survey 

questionnaire materials into Spanish, a training exercise 

regarding medical sampling procedures, and data interpretation 

and reporting. One of the more important aspects of the study 

was a quality‐assurance/quality‐control initiative to ensure that 

the reporting of analytical methodologies and analytical results 

were conducted in a consistent and comparable manner. 

Laboratories were provided with reference samples for which 

the concentration of a contaminant was known and results of the

analyses of these samples were compared to the known values. 

Any results consistently outside the acceptable range of values

resulted in an assessment of the laboratory’s procedural 

methodologies and analytical performance; considerable efforts 

were directed to locating the sources of the discrepancy and to

improving analytical precision and accuracy.  
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Commission for Environmental Cooperation 9

3. Study Design

The study uses a sampling protocol that produces a simple 

convenience sample of EPW in Canada and Mexico, although the 

countries used slightly different methods for population 

selection. In the United States, women of reproductive age were

included, whether pregnant or not. 

3.1 Population Selection and Recruitment

3.1.1 Inclusion and Exclusion CriteriaMexico and Canada

For Mexico and Canada, only EPW aged between 14 and 43 years 

and able to provide informed consent were to be included in this 

study. Exclusion criteria for this study included any disease that 

could significantly affect maternal or child health, specifically 

including pre‐eclampsia, diabetes or gestational diabetes, 

hypertension, epilepsy and endocrine disorders. 

3.1.2 Canada  

Study subjects were recruited from five southern Canadian cities 

between December 2005 and August 2007. The cities represent 

the East Coast (Halifax), the West Coast (Vancouver), Eastern 

Canada (Hamilton, mainly industrial, and Ottawa, primarily 

white‐collar), and Western Canada (Calgary) (Figure 1). EPW 

attending their first prenatal visit were approached to 

participate in this study until 25 women at each site had agreed 

to enroll in the study. Informed consent was obtained from each

woman. The study protocol was reviewed and approved by the 

research ethics boards of Health Canada and of each of the 

participating centers.  
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Commission for Environmental Cooperation 10

Figure 1. Sites selected for the study

3.1.3 Mexico

Between November 2005 and February 2006, 25 EPW in the last 

trimester of pregnancy were recruited from each of ten sites 

(Figure 1). The recruitments were made in one of the later 

prenatal visits, at which time the doctor in charge invited the

women to participate. If they agreed to participate, the women 

were directed to the study staff member who explained the 

study, after which the participants signed a consent form. The 

study protocol was reviewed and approved by the research, 

ethics and bio‐security commissions of INSP.  
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Commission for Environmental Cooperation 11

3.1.4 United States

For the United States, data come from NHANES, an ongoing 

national survey of the health, nutritional status and 

environmental chemical exposures of adults and children.  

Although the number of environmental chemicals monitored in 

NHANES increased from 27 in 1999 to more than 200 in 2003–

2004, POPs and metals have been continuously monitored. For 

this study, data on metals and POPs were obtained from the 

samples collected from women of reproductive age (15–44 

years), including analyses of the samples taken from pregnant 

women who had participated in NHANES 2003–2004 (the last 

years for which data were available at the time this report was

written) as well as from pooled samples from for women aged 

20–39 years taken during NHANES 2001–2002. During NHANES, 

blood was collected by mobile examination centers.  

3.2 Study Implementation and Samples Collected  

All blood collection tubes, needles and sample vials were pre‐

screened for the target metals by the CDC and were provided to 

each of the participating sites.  

3.2.1 Canada

EPW blood was collected in the third trimester, prior to delivery. 

Samples were collected according to the agreed sampling and 

laboratory protocols. Blood was collected from the antecubital 

vein into purple‐top, EDTA‐containing Vacutainer® tubes (two 7 

mL tubes for trace metal measurements and two 10 mL tubes for 

POPs measurements). Anticoagulated whole blood was stored at 

4°C until required for analysis. Plasma, obtained by 

centrifugation of POPs tubes, was decanted into pre‐cleaned 

vials and stored frozen. Duplicate samples were collected to 

allow follow‐up analyses. All plasma samples were shipped 

frozen to the analytical laboratory.  

3.2.2 Mexico

EPW blood was collected toward the end of the third trimester, 

according to the agreed sampling and laboratory protocols. 

Samples were collected by trained field workers coordinated by 

the National Institute of Public Health. Duplicate samples from

Mexico were collected so that analyses could be completed by 
TRINATIONAL BIOMONITORING STUDY

Commission for Environmental Cooperation 12

one or the other of the national laboratories (Cenica or UASLP)

and by the Canadian reference laboratory. Blood collection and 

storage was carried out as described in section 3.2.1.  

3.2.3 United States

Approximately 90 mL of blood were collected from each subject 

for a variety of clinical chemistry tests, nutritional status tests 

and measurements of environmental chemicals in either the 

whole blood (metals) or harvested serum (POPs, among others). 

The serum and whole blood were sent frozen on dry ice to the 

CDC laboratory and stored at no more than ‐70oC until analysis.  

3.2.4 Dioxins and Furans: Pooled Samples

To avoid drawing large volumes of blood from the EPW and to 

limit analytical costs, it was decided at the outset of the study 

that pooled plasma samples would be analyzed for PCDDs, 

PCDFs and both dioxin‐like and non‐dioxin‐like PCBs. From 

these data, dioxin toxic equivalent (TEQ) concentrations and 

total PCB concentrations were calculated. In Mexico two 

composite plasma samples were prepared for each of the ten 

sites, for a total of 20 composite samples, while for the Canadian 

samples, three composites were prepared from each of three 

sites, two composites from one site and one sample for one other 

site, for a total of 12 composite samples. In the United States, 

seven pooled serum samples with balanced volume from women 

between 20 and 39 years of age participating in NHANES 2001–

2002, who may or may not have been pregnant, were analyzed 

for PCDDs, PCDFs and dioxin‐like PCBs, and TEQs were 

calculated. 

3.3 Analytical Issues  

3.3.1 Analytes and Matrices  

All metal concentrations are reported on a whole‐blood volume 

basis. The POPs data in serum and plasma are reported on a 

lipid‐adjusted weight basis. The total lipid concentration of each 

sample was calculated by summing the measured concentrations 

of plasma lipid components. All lipid components were 

measured by standard clinical chemistry enzymatic methods.  
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Commission for Environmental Cooperation 13

INSPQ measured four components: total cholesterol (TC), free 

cholesterol (FC), triglycerides (TG), and phospholipids (PL), then 

calculated the total lipid (TL) concentration as: 

TL = 1.677 * (TC‐FC) + FC + TG + PL (Akins et al. 1989). 

CDC measured total cholesterol and triglycerides and calculated

total lipids as: 

TL = 2.27 * TC+TG + 0.623 (Philips et al. 1989).  

Both formulas yield equivalent total lipid results (Bernert 2007).  

Even though blood samples were taken from both pregnant and 

non‐pregnant women, studies have shown that this is not a 

major issue if the POPs concentrations are adjusted for lipid 

content. 

The following analytes were measured: 

Metals: Mexican and Canadian whole‐blood samples were 

analyzed for lead, mercury (total and inorganic), cadmium, 

cobalt, nickel, selenium, thallium and tin. The US whole blood 

samples were analyzed for lead, mercury (total and inorganic), 

and cadmium. 

POPs: A total of 60 POPs were measured, including 11 non‐

dioxin‐like PCB congeners and 15 organochlorine pesticides, 

metabolites, or byproducts measured in the same individual 

blood samples as the metals, as well as the 17 2,3,7,8‐substituted 

PCDDs and PCDFs and 12 dioxin‐like PCBs measured in 

composite plasma samples (Tables 1 and 2). The composite 

samples were also analyzed for a total of 35 PCB congeners in 

order to calculate total PCB concentrations. It should be noted

that most of the mono‐ortho substituted PCBs are included in the 

total PCB concentrations, but the coplanar PCBs are not, because 

of their relatively low concentrations and because they are 

measured analytically with the PCDDs and PCDFs.  

Table 1. Stockholm Convention POPs measured in plasma (Canada, Mexico) and serum

(USNHANES)

Parent Chemical or

Chemical Class

Analyte(s)

Aldrin Aldrin, Dieldrin*

Endrin Endrin*

Dieldrin Dieldrin*

Chlordane Oxychlordane, cis‐Chlordane**, trans‐Chlordane**, cis‐
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Nonachlor**, trans‐Nonachlor

Heptachlor Heptachlorepoxide*

DDT p,p’‐DDT,  p,p'‐DDE (p,p'‐Dichlorodiphenyldichloroethylene)

Mirex Mirex

Hexachlorobenzene

(HCB)

Hexachlorobenzene

Polychlorinated

biphenyls (PCBs)

Congeners: Non‐dioxin like: 28, 52, 99, 101, 128, 138, 153, 170,

180, 183, 187. Dioxin‐like mono‐ortho chlorinated: 105, 114, 118,

123, 156, 157,167, 189. Dioxin‐like coplanar+: 77, 81, 126, 169

Polychlorinated dibenzo‐

p‐dioxins+

2,3,7,8‐TCDD,1,2,3,7,8‐PeCDD, 1,2,3,4,7,8‐ HxCDD, 1,2,3,6,7,8‐

HxCDD, 1,2,3,7,8,9‐HxCDD, 1,2,3,4,6,7,8‐HpCDD, OCDD

Polychlorinated

dibenzofurans+

2,3,7,8‐TCDF, 1,2,3,7,8‐PeCDF, 2,3,4,7,8‐PeCDF, 1,2,3,4,7,8‐

HxCDF, 1,2,3,6,7,8‐HxCDF, 12,3,7,8,9‐ HxCDF, 2,3,4,6,7,8‐HxCDF,

1,2,3,4,6,7,8‐HpCDF, 1,2,3,4,7,8,9‐HpCDF, OCDF

*   not measured in samples from Canada and Mexico

** not measured in samples from the United States

+   measured in sample pools from Canada, Mexico and the United States

Table 2. Other POPs measured in plasma (Canada, Mexico) and serum (USNHANES)

Parent Chemical Analyte(s)

Technical hexachlorocyclohexane  α‐HCH**, β‐HCH, γ‐HCH

Polybrominated biphenyls   Polybrominated biphenyl 153

** not measured in samples from the United States

3.3.2 Analytical Methods

3.3.2.1 Canada and Mexico

Biological samples from Canada and Mexico were analyzed by 

the INSPQ laboratory. Samples from Mexico for some analytes 

were also measured in‐country, but the results from the 

Canadian reference laboratory were utilized for the data 

analyses for both countries, with the exception of the composite 

samples, which were analyzed for PCDDs, PCDFs, and PCBs by 

the CDC laboratory. Metals were measured by either inductively‐

coupled mass spectrometry (lead and cadmium) or cold‐vapor 

atomic absorption (mercury) (Butler‐Walker 2006). Chlorinated 

pesticides and PCBs were measured using high‐resolution gas 

chromatography/low‐resolution mass spectroscopy (GC‐MS) 

using an in‐house, ISO‐17025 accredited method adapted from 

Mes (1990). Plasma samples (2 mL) were extracted on a solid 

phase extraction (SPE) column. The extracts were purified on a 

Florisil column, concentrated to a final volume of 100 L, and 

analyzed by gas chromatography‐mass spectrometry using 

electronic impact ionization (EI). 
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3.3.2.2 United States

Whole blood samples (50 μL) were analyzed for mercury (total), 

lead and cadmium by inductively‐coupled plasma dynamic 

reaction cell mass spectrometry (ICP‐DRC‐MS) with a Meinhard 

nebulizer, a cyclonic spray chamber and an AS‐93 autosampler. 

In this method blood samples are diluted with ≥18 M‐ohm‐cm 

water and diluent, containing 1 percent v/v 

tetramethylammonium hydroxide (TMAH), 0.5 percent disodium 

ethylenediamine tetraacetate (EDTA), 10 percent ethyl alcohol, 

0.05 percent Triton X‐100® and gold (100μg/L). Gold (Au is 

added to reduce intrinsic mercury memory effects. The internal 

standards used were rhodium (Rh) (5 μg/L) for cadmium and 

bismuth (Bi) (5 μg/L) for mercury and lead. The samples were 

prepared with the ratio of Sample : Water : Diluent = 1:1:48 

(Nixon et al. 1999).  

Serum/plasma samples (1 mL) were analyzed for POPs by 

extracting through solid phase extraction, then detecting and 

measuring by high‐resolution gas chromatography/isotope‐

dilution high‐resolution mass spectrometry (Barr et al. 2003). 

PCDDs, PCDFs and PCBs were measured in the composite 

samples by the same method for all three countries (Patterson et 

al. 1987, 1990). The limit of detection (LOD) for POPs varied 

with each sample, based on several factors, including volume of

serum used and percent recovery of the analyte.  

3.3.3 Quality‐Assurance and Quality‐Control Procedures  

3.3.3.1 Canada and Mexico

For metals, internal quality control was accomplished through 

the use of reference material from the INSPQ’s Interlaboratory 

comparison program (Programme de comparaisons

interlaboratoires, or PCI) external quality assessment scheme 

(EQAS) (Weber 1996). These materials were analyzed several 

times within each analytical run (after the calibration curve, 

after every 10 samples, and at the end). Results were plotted on 

control charts having predetermined acceptability limits and 

were required to comply with the Westgard rules for run results

to be accepted (Westgard 2001). Accuracy was verified by 

participation in several EQAS from Canada, Germany, and the 

United States (INSPQ 2007, Schaller 2001, Stanton 1993). 

For POPs, precision was monitored through the use of in‐house 

reference materials, analyzed with each analytical run, using the 

same procedure as for metals. Routine checks of accuracy were 

made using certified reference serum from the US National 
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Institute of Science and Technology. Also, accuracy was verified 

periodically through participation in two EQAS. The LOD for 

POPs varied between 0.005 and 0.09 μg/L, depending on the 

analyte. 

3.3.3.2 United States

For metals in blood, CDC used both low‐ and high‐level bench 

quality‐control materials (blood mercury, lead and cadmium), 

prepared in the CDC laboratory, as well as two levels of “blind” 

QC materials. Bench and blind QC materials consist of 1.8 mL of

blood material in 2 mL cryo‐vials stored at ≤‐70o C until use. 

Both the bench and blind QC materials were characterized in 

40+ analytical runs. In addition, National Institutes of Standards 

and Technologies (NIST) Standard Reference Material (SRM) 

966 and 955b were routinely used for method‐accuracy 

determinations. Analytical accuracy was also verified by 

participation in several EQAS programs from INSPQ, the New 

York State Health Department and the Wisconsin State Health 

Department. To evaluate the validity of results, QC data within

each analytical run were compared to predetermined control 

limits using the Westgard rules (Westgard 2002). 

For POPs, pooled serum was used for QC materials. No further 

filtration or preparation of the serum pools was performed prior 

to their use. The pooled serum was aliquoted into vials, capped

and stored at ‐20°C. All QC concentration levels were 

characterized to determine the mean concentrations and the 

95th (1.96σ) and 99th (2.58σ) control limits by consecutive 

analysis of 20 samples of each QC level. QC data within each 

analytical run were compared to the control limits to evaluate 

the validity of analyses using the Westgard rules, as above.  

3.3.4 Limits of Detection Issues

3.3.4.1 Determination of Limits of Detection

In the United States, the analytical method LOD for each analyte 

within the method was calculated as 3S0, where S0 is the 

estimated standard deviation of measured concentration values 

as the concentration approaches zero. With this technique, S0 is 

an extrapolated value equivalent to the y‐intercept of a 

regression line from the plot of the standard deviations of the

measured concentrations versus their nominal concentration 

values (Taylor 1987, 75–93). Alternatively, for analytes having a 

method blank, the LOD was calculated as 3Sb, where Sb is the 

estimated standard deviation of blank values (Keith 1991, 93–
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119). The LOD is adjusted according to the analyte recovery in 

each individual sample. LOD calculations are determined based 

on 20+ analytical runs. The LOD calculations for the blood metals 

were determined using multiple analysts and instruments on 

40+ analytical runs. 

In Canada, a similar approach to LOD determination was used by 

the INSPQ laboratory. For analytical signals in the form of peaks 

(e.g., chromatographic output), an initial LOD was estimated as:  

LODest = sample concentration/((observed signal/noise 

ratio)/3). 

For continuous or averaged analytical signals (e.g., ICP‐MS), an 

initial LOD was estimated as three times the standard deviation

of the blank. A real or matrix‐matched spiked sample having a 

concentration between 5 and 7 times the LODest was then 

analyzed 10 times. The LOD was defined as the standard 

deviation of these 10 measurements (S0) multiplied by 3. 

3.3.4.2 Comparison of Limits of Detection between the United States and

Canada

As shown in Tables 3 and 4, the LOD for selected POPs and 

metals results produced by CDC and INSPQ are not identical, and

in some instances are substantially different.  
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4. Statistical Analysis

The Canadian EPW population was divided into two subgroups 

(Canada‐by‐birth and Canada‐immigrant). This was not done for 

the US women of reproductive age. For the Mexico data the 

samples were considered to be homogenous, in that all the EPW 

were native‐born. 

Summary statistics, including sample size, LOD and percent of 

observations above LOD were reported for all contaminants in 

each group. The range, geometric mean (GM) and corresponding 

95 percent confidence interval were evaluated for each 

contaminant, except γ‐HCH. For γ‐HCH in Mexico, only the range 

was reported, given the low frequency of detection. The GM and 

corresponding 95 percent confidence interval were reported in 

place of the arithmetic mean and corresponding 95 percent 

confidence interval, because most of the contaminants were log‐

normally distributed, as shown by the Anderson‐Darling test for

normality. Values below the LOD were imputed with 1⁄2 the LOD. 
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5. Results

Table 3 reports summary statistics for 12 contaminants in the 

Mexican and Canadian populations and Table 4 reports similar 

data for the US population (with the exception of nickel). For the 

data analysis in Table 3, the more comprehensive set of results 

for Canada and Mexico from the Canadian reference laboratory 

were used. 

Table 3. Descriptive statistics and summary results for 12 contaminants in EPW in Canada

and Mexico

Contaminant Data Provenance N % Detects Detection

Limit (DL)

Range Geometric Mean  

(95% CI)

Canada‐immigrant 16 100 0.05 (0.25–2.02) 0.59 (0.42–0.83)

Canada‐by‐birth 77 100 0.05 (0.16–4.95) 0.46 (0.38–0.55)

Cadmium

(μg/L)

Mexico   233 100 0.05 (0.16–1.69) 0.36 (0.34–0.37)

Canada‐immigrant 16 100 0.21 (3.52–33.15) 7.84 (5.65–10.86)

Canada‐by‐birth 77 100 0.21 (2.69–12.02) 5.72 (5.34–6.13)

Lead

(μg/L)

Mexico   233 100 0.21 (5.59–227.93) 24.87 (22.87–27.04)

Canada‐immigrant 16 100 0.35 (0.59–4.05) 2.49 (1.95–3.18)

Canada‐by‐birth 77 100 0.35 (0.18–5.58) 2.14 (1.91–2.40)

Nickel

(μg/L)

Mexico   233 100 0.35 (1.29–6.46) 3.23 (3.13–3.33)

Canada‐immigrant 16 94 0.1 (0.05–4.21) 0.88 (0.55–1.41)

Canada‐by‐birth 77 92 0.1 (0.05–2.81) 0.40 (0.32–0.50)

Total Mercury

(μg/L)

Mexico   233 97 0.1 (0.05–18.05) 0.86 (0.75–0.97)

Canada‐immigrant   20 95 1.33 (0.81–7.27) 2.49 (2.03–3.06)

Canada‐by‐birth 103 89 1.29 (0.63–12.64) 2.15 (1.92–2.40)

PCB 118

(μg/kg Lipid)

Mexico   240 46 1.29 (0.42–57.75) 1.22 (1.11–1.33)

Canada‐immigrant 20 100 1.33 (2.17–22.00) 6.00 (4.71–7.65)

Canada‐by‐birth 102 100 1.29 (1.03–20.78) 3.69 (3.31–4.11)

PCB 138

(μg/kg Lipid)

Mexico   240   82 1.29 (0.52–50.70) 2.38 (2.15–2.62)

Canada‐immigrant 20 100 1.33 (4.35–49.00) 11.08 (8.63–14.22)

Canada‐by‐birth 103 100 1.29 (1.27–19.54) 5.67 (5.07–6.34)

PCB 153

(μg/kg Lipid)

Mexico   240 93 1.29 (0.52–72.50) 3.64 (3.30–4.01)

Canada‐immigrant 20 100 1.33 (1.70–32.00) 7.90 (5.93–10.53)

Canada‐by‐birth 103 89 1.29 (0.52–85.54) 3.44 (2.88–4.11)

PCB 180

(μg/kg Lipid)

Mexico   240 74 1.29 (0.51–43.62) 2.08 (1.87–2.30)

Oxychlordane Canada‐immigrant 20 100 0.67 (1.09–11.90) 2.85 (2.17–3.75)
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Contaminant Data Provenance N % Detects Detection

Limit (DL)

Range Geometric Mean  

(95% CI)

(μg/kg Lipid) Canada‐by‐birth 102 100 0.65 (0.83–10.00) 2.08 (1.90–2.29)

Mexico   240 89 0.65 (0.30–15.05) 1.62 (1.50–1.76)

Canada‐immigrant 20 95 1.33 (0.88–988.64) 7.74 (3.83–15.63)

Canada‐by‐birth 103 84 1.29 (0.42–25.64) 2.12 (1.85–2.43)

β‐HCH

(μg/kg Lipid)

Mexico   240 98 1.29 (0.63–209.68) 8.34 (7.31–9.53)

Canada‐immigrant 19 0 1.33 ND ND

Canada‐by‐birth 103 0 1.29 ND ND

γ‐HCH

(μg/kg Lipid)

Mexico   240 2 1.29 (0.33–

6.90)

ND

Canada‐immigrant   20 100 11.97 (33.33–

1704.55)

162.17 (107.09–

245.58)

Canada‐by‐birth 103 100 11.62 (14.49–

294.87)

52.77 (47.91–58.12)

p,p'‐DDE

(μg/kg Lipid)

Mexico   240 100 11.62 (46.51–

19753.09)

335.68 (295.08–

381.86)

Table 4. Descriptive statistics and summary results for 11 contaminants for reproductive

age women 1544 years old in the NHANES survey, 20032004

Contaminant N Weighted % Detects Detection

Limit  (DL)

Range Weighted

Geometric

Mean

(95% CI)

Cadmium

(μg/L) 1649 70.9 0.14 (0.1–7.4)

0.32

(0.30–0.35)

Lead

(μg/L) 1649 92.8 2.8 (2–239)

9.38

(8.66–10.16)

Total Mercury

(μg/L) 1649 84.6 0.2 (0.1–30.7)

0.79

(0.69–0.92)

PCB 118

(μg/kg Lipid) 490 100 0.6 (0.95–40.36)

4.45

(3.89–5.1)

PCB 138

(μg/kg Lipid) 491 100 0.4 (1.39–70.17)

8.89

(7.83–10.09)

PCB 153

(μg/kg Lipid) 490 100 1.1 (1.6–90.32)

10.95

(9.73–12.32)

PCB 180

(μg/kg Lipid) 491 99.6 0.4 (0.06–82.56)

7.26

(6.45–8.18)

Oxychlordane

(μg/kg Lipid) 500 63.6 7.8 (1.06–36.4)

5.83

(5.31–6.41)

β‐HCH

(μg/kg Lipid) 498 55.5 7.8 ND

γ‐HCH

(μg/kg Lipid) 499 0.6 7.8* ND

p,p'‐DDE

(μg/kg Lipid) 495 99.8 7.8* (16.4–15100) 150.42

(120.27–188.13)
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ND (non‐detect) means further calculations were not applicable due to the low percent of observations being detected

(<10%).

Table 5 presents the data on age of the four groups included in 

this study. The youngest women were found in Mexico, while the 

oldest were found in the Canadian populations. Because many of 

the POPs bioaccumulate in the lipids of the body (including 

blood lipids), older populations could now be experiencing 

similar degrees of exposure as younger populations, yet have 

higher blood POPs concentrations because of bioaccumulation. 

For the United States data, different one‐third subsets were used 

for measuring PCBs and for measuring organochlorine pesticides 

(OCPs); therefore, the number of women of reproductive age in 

the PCBs and OCPs groups differ slightly. 

Table 5. Summary of age in each group across all contaminants

Group N Mean Age Range

Canada‐immigrant 20 33.0 (25–41)

Canada‐by‐birth 101 28.6 (18–40)

Mexico 240 20.8 (15–33)

United States (NHANES

20032004)—Metals*   1649 26.1 (15,–44)

United States (NHANES

20032004)—PCBs† 491 26.4 (15–44)

United States (NHANES

20032004)—OCPs‡

   500 26.1 (15–44)

* NHANES women aged 1544 were selected from the full sample for metals.

† NHANES women aged 1544 were selected from a one‐third subsample for polychlorinated biphenyls (PCBs).  

‡ NHANES women aged 1544 were selected from a different one‐third subsample for organochlorine pesticides

(OCPs).
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6. Discussion

Data for POPs are presented in this report on a lipid‐adjusted 

basis (i.e., μg/kg lipid) while the metals are presented on a whole 

blood basis (μg/L). As lipid concentrations increase throughout

pregnancy and in response to meals, comparisons of POPs on a 

lipid‐weight basis would be more reasonable. 

6.1 Concentrations of Persistent Organic Pollutants  

Results for the four most highly‐detected PCB congeners (118, 

138, 153, 180) are presented in Tables 3 and 4. The 

predominant PCB congener in all population groups is PCB 153, 

followed by 138, 180 and 118. PCBs 138 and 153 have been 

shown to be the major PCB congeners in other North American 

and European biomonitoring studies (Needham et al. 2005, 

Becker et al. 2002). PCBs are technical mixtures used in a variety 

of products including transformers and capacitors and were 

widely used throughout the United States. Other POPs found in a

high percentage of the populations included p,p’‐DDE, Beta‐HCH,

and oxychlordane. p,p’‐DDE is the major environmental 

degradate and human metabolite of p,p’‐DDT, which has been 

widely used in Mexico in agriculture and as a mosquito repellant 

and insecticide. Beta‐HCH is the most stable HCH isomer found 

in technical hexachlorocyclohexane formulations, which were 

banned in Mexico more recently than in the United States or in 

Canada. As expected, cadmium, mercury and lead were detected 

at low concentrations in a high percentage of the women. Lead 

exposure can result from gasoline fumes and pottery glazing, 

among other sources.   

6.2 Concentrations of Dioxins in Pooled Blood

Table 6 shows the concentrations for lipid‐weight adjusted 

arithmetic means and ranges for the total dioxin TEQs as well as 

TEQs for PCDDs, PCDFs and dioxin‐like PCBs (coplanar PCBs and 

mono‐ortho substituted PCBs) from pooled plasma samples of 

EPW from Mexico and Canada, and from pooled serum samples 

of women aged 2039 from the United States.  
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Table 6. Toxic Equivalent Concentrations1 of polychlorinated dibenzo‐p‐dioxins,

polychlorinated dibenzofurans, co‐planar PCBs, mono‐ortho PCBs and Total TEQs

in pooled serum

PCDDs PCDFs Coplanar PCBs Mono‐ortho PCBs TOTAL TEQ

Country Mean* Range Mean

*

Range Mean

*

Range Mean

*

Range Mean

*

Range

Mexico 4.3 2.9–15 1.3 1.0–1.6 1.1 0.69–1.7 0.09 0.04–0.15 6.8 5.3–18

Mexico

(outlier

removed)

3.8 2.9–5.9 1.3 1.0–1.6 1.1 0.69–1.7 0.09 0.04–0.15 6.3 5.3–9.4

Canada 3.3 2.6–5.6 1.4 1.2–2.0 1.2 0.76–1.4 0.17 0.12–0.23 6.1 5.1–9.2

United States

(NHANES

2001–2002)

6.7 4.1–9.0 1.8 1.4–2.3 1.7 1.2–2.3 0.31 0.17–0.41 10.5 8.1–14

1. All results presented as 2,3,7,8 TCDD TEQs.

* Arithmetic mean

The World Health Organization’s 2005 Toxic Equivalency 

Factors (TEFs) were used to calculate the TEQs (Van der Berg et

al. 2006). The TEQs were calculated by multiplying the 

individual concentration (ng/kg lipid) of each of the PCDDs, 

PCDFs and dioxin‐like PCB congeners by that chemical’s TEF to 

provide the TEQ for each of these chemicals; these TEQs were 

summed to provide class‐specific TEQs (e.g., for PCDDs) and for

total TEQs.  

Table 7 shows arithmetic mean concentrations and ranges of 

the sum of 35 PCB congeners (total PCBs) for the pooled samples

from Mexico, Canada and the United States. For calculating total 

PCBs, if a given congener was not detected, its concentration was 

imputed to be its LOD/2.  

Table 7. Sums of PCB concentrations in serum pools

Total PCB (μg /kg lipid)

Mean* Range

Mexico 36.6 18.3–59.0

Canada 50.7 25.5–95.3

United States (NHANES 2001–2002) 83.2 50.5–109

* Arithmetic mean

Arithmetic means were computed instead of geometric means 

for all of the pooled data because of unequal numbers of samples 

per pool and unequal volumes for some pools in the Canada data.

Also, the Mexican data consisted of only two pools from each 

site, which limited the ability to estimate the variation among the 
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pools within each site. This variation is needed in order to 

convert pooled sample results to geometric mean (GM) 

estimates, although these could have been calculated from the 

NHANES pooled samples, but then any comparisons with the 

Canada and Mexico data would not be appropriate.  

By using arithmetic means rather than geometric means, the 

results are positively biased, and this bias may vary with 

concentration if the among‐subject variances of the compounds 

of interest tend to vary with increasing concentration (Caudill et 

al. 2007). As a result, caution is required in comparing arithmetic 

mean estimates across sites or across countries. Because only 

pooled data are available, providing no measure of individual 

variability, only descriptive results can be presented. Like the 

other POPs data presented in this report, data in Tables 6 and 7

are not age‐adjusted. 
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7. Capacity Building

7.1 Training and Quality Assurance Exercises

7.1.1 Introduction

An important component of the capacity building exercise was to

ensure the accuracy and comparability of results produced by 

the Mexican laboratories involved in the study. These 

laboratories are those of the UASLP for the measurement of 

POPs and Cenica for the measurement of metals. To this end, an 

Operational Plan for Quality Assurance/Quality Control was 

submitted by the reference laboratory INSPQ in 2004. The key 

features of this plan were: 

 Training of UASLP staff at the INSPQ lab for POPs 

measurements and familiarization with QA/QC procedures. 

 Method validation and external quality assurance (EQA) 

exercises for both laboratories, in which the target 

laboratories (Cenica and UASLP) were sent representative 

proficiency‐testing material (blood and plasma samples) 

containing the required analytes.  

In the case of Cenica, these analytes were metals (lead, cadmium 

and mercury) in blood. For UASLP, proficiency testing materials

consisted of plasma samples containing various PCB congeners 

and organochlorine pesticides. Chemical analyses for each 

sample were conducted by the different laboratories: INSPQ for 

metals and all POPs except dioxins, Cenica for metals and UASLP

for POPs. All were subjected to reference standard calibration 

verification. Dioxin and dioxin‐like compounds were all analyzed 

at the CDC laboratory.  

Both Mexican laboratories were invited to participate in the 

appropriate INSPQ external quality assurance schemes: UASLP 

in the AMAP Ring Test for POPs, and Cenica in the PCI for metals. 

7.1.2 Results
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Training of UASLP staff (two members) took place 19–30 April 

2004, at INSPQ’s toxicology laboratory in Quebec City. The 

training focused on methodology for the measurement of POPs 

in blood, including sample preparation, purification and 

instrumental analysis. The trainees were tested at the conclusion 

of the training period and demonstrated proficiency in 

conducting the analyses. 

For each laboratory, two quality‐assurance exercises were held,

one in 2004, the other in 2006. Several more exercises had been

planned; however, major difficulties were encountered in cross‐

border shipments to Mexico, which require specific import 

permits for each shipment of biological material. Nevertheless,

the two exercises were beneficial in uncovering problems and 

documenting improvements in the quality of results from both 

laboratories. 

Both laboratories were repeatedly encouraged to enroll in the 

relevant INSPQ external quality‐assurance schemes, resulting in

participation in mid‐2006. Again, forwarding of proficiency‐

testing samples was beset by delays and rejections of shipments

by Customs officials unfamiliar with this type of effort. Cenica 

completed only one round; UASLP completed none. 

Analytical results were compared by using split or co‐located 

samples analyzed in Mexico laboratories and INSPQ. CDC 

supplied statistical expertise to compare results provided by 

INSPQ and Cenica for metals and UASLP for POPs. Results show 

that UASLP had a preponderance of non‐detectable values for 

the organochlorine chemicals. Therefore comparability analyses 

were performed solely on p,p'‐DDE. 

Results are based on 219 pairs of data and showed that the DDE 

(log scale) data obtained by UASLP tends to give a higher 

reading, by between 0.03 and 0.12. However, only 5 percent of 

log DDE ratios (difference) exceeded limits of agreement. A 

paired t‐test was used to compare means on the log scale from 

both laboratories; the result showed that UASLP had 

significantly higher DDE means than INSPQ (p<0.01). 

7.2 Recommendations on Improving Proficiency

It is worth noting the potential for induced measurement errors

based on laboratory proficiencies and prior experience with the

testing of particular sample media (in this case, either whole 

blood or blood serum). The facilities at Cenica are routinely 
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involved in the measurement of selected toxicants, including 

metals, in environmental samples of air, water, soils and 

sediments. Measurement of these same toxicants in blood or 

blood serum presents a unique set of challenges for which the 

facility and the analysts themselves may not be prepared. Blood

and blood serum are potentially complex matricesquite 

different from the matrices expected in environmental samples. 

The challenges they represent were exemplified by the first 

round QA/QC testing in 2004. The laboratory showed good 

agreement with reference samples when the anticipated toxicant 

values were provided prior to the analysis. When the anticipated 

results were unknown, however, the measured values varied 

considerably from the reference values. This is not uncommon in

analytical laboratory round‐robin QA/QC proficiency testing. 

Subsequent to this validation exercise, discussions were held 

with the laboratory personnel and the analytical protocol expert 

contracted by the CEC. The discussions resulted in significant 

improvement in the analytical results of the laboratory and a 

much‐enhanced appreciation of the QA/QC aspects of good 

laboratory practices. Later rounds of analysis did validate the

results and contributed to a significant improvement in both 

precision and accuracy. 

In a similar vein, UASLP, in undertaking the POPs measurements 

on behalf of INSP, had anticipated that analyte concentrations 

would be in the range of previous work where levels associated 

with crop‐ or vector‐control application had been determined. In 

fact, it is now apparent that very low levels near the LOD of 

state‐of‐the‐art methodologies and equipment would be 

encountered. The reasons for this include the banning of DDT 

and lindane, as well as the general trend toward reduced 

application of organochlorine pesticides. In the past, UASLP 

facilities had reported results indicating higher levels of 

exposure. This study, in contrast, looked at a national 

distribution of samples, some in areas where pesticide residues

were likely to be low. As a result, the comparatively higher LOD 

of the UASLP laboratories caused many “non‐detect” entries to 

be recorded, as shown in Table 8. 

Table 8: Comparison of LOD for three organic analytes

Analyte Laboratory

UASLP INSPQ

DDT (μg/L) 0.55 0.05

γ‐HCH (μg/L) 0.72 0.01

HCB (μg/L) 0.11 0.04
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Results generally improved significantly with subsequent 

training and analytical testing exercises, thereby underlining the 

need for laboratory accreditation as well as enrollment and 

participation in interlaboratory quality‐assurance programs or 

schemes (EQAS). National accreditation bodies able to operate 

according to ISO 17025, the appropriate standard for analytical

laboratories, exist in all North American countries. EQAS, 

generally including technical assistance, are available through

such organizations as the INSPQ external quality‐assurance 

schemes described above, the CDC’s Lead and Multi‐element 

Proficiency (LAMP) Program (CDC 2008a) and the German 

External Quality‐Assurance Scheme for analyses of biological 

material (University of Erlangen‐Nuremberg 2008). 

It is recommended that an initiative be developed to overcome 

border obstacles to the transfer of biological proficiency testing 

samples into Mexico. It is also recommended that a continental 

laboratory testing and verification initiative be coordinated. 
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8. Conclusions

The two main purposes of this study were to obtain an initial 

profile of population exposure to POPs and selected metals and 

to enhance the capacity of Mexico to monitor Stockholm 

Convention POPs and selected toxic metals, thus enabling Mexico

to work with the United States and Canada in developing 

compatible, comparable databases of blood biomonitoring 

results. 

8.1 Population Exposure Assessment

This study has shown the feasibility of developing comparable 

protocols and assessing contaminant levels in populations from 

Canada, Mexico and the United States. This preliminary dataset 

can be used to assist in setting priorities for and tracking 

progress in management of the selected toxicants both 

domestically and on a broader cooperative basis within North 

America. This should not be considered a national biomonitoring

program for Mexico or Canada, since such a program would 

require a much larger and randomly‐selected population sample, 

as has been done in the United States and is underway in Canada. 

The US NHANES program involves collecting health information 

on 8,000 individuals and measuring contaminant levels in a 

random one‐third subset of about 2,500 individuals every two 

years (CDC 2008b), while the Canadian Health Measures Survey 

will measure environmental contaminant levels in 

approximately 5,000 individuals in representative communities 

across the country in 2008–2009 (StatCan 2008). A national 

biomonitoring program for Mexico which could address levels of 

contaminants in a range of age, gender and ethnic groups would 

be useful for further comparative work with the United States, 

Canada and other countries.  

While the statistical representativeness of this study was 

constrained by the small sample sizes, it is apparent that further 

work should be undertaken to account more precisely for the 

probable sources of the contaminants, and to evaluate these and

any subsequent study results with respect to exposure routes. 
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8.2 Capacity Building

The capacity building component of the study has been useful in

providing insights for improvements necessary to operations on 

a trilateral basis within North America. The training and quality‐

assurance exercises between 2004 and 2006 were helpful in 

building analytical capacity in the two Mexican laboratories, and 

in improving the accuracy and reproducibility of their analytical 

results. It is important that the Mexican laboratories continue to 

participate actively in external quality‐assessment schemes, to

ensure that they can objectively demonstrate their proficiency.

A crucial difficulty that must be overcome for successful 

participation concerns the importation of biological proficiency 

testing samples into Mexico, an issue that appears to be unique

to that country. In none of the other 32 countries participating in 

the INSPQ external quality‐assessment schemes have problems 

been encountered in sending biological proficiency testing 

samples across borders to recognized laboratories. The 

continued cooperation of Mexican authorities will be essential in 

achieving reliable cross‐border transmission of proficiency‐

testing material. 

Trilateral efforts such as this one also reveal the importance of 

rigorous data management. Best practices of data‐management 

procedures should be implemented where lacking, and 

rigorously applied everywhere. There is a need to develop and 

use data standards, referring to documented procedures to 

ensure that data are clearly understood and collected by uniform 

methodologies. Roles and responsibilities for data management 

must be established, implemented and documented. The 

development of detailed agreements specifying who is 

responsible for development of standards, collection, storage 

and maintenance of data, protocols for their access and use, and 

the systematization of quality‐assurance procedures. 

8.3 Recommendations for Future Work

Mexico

This trinational study has allowed description of concentrations 

of several environmental contaminants in maternal blood within 

Mexico and, for the first time, made them in the context of the

other two North American countries. This is a significant step 

forward in regional biomonitoring. However, it is important to 

point out that some of the study’s objectives were not fully 
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attained. One of these is the creation and improvement of 

analytical capabilities, including equipment, facilities, and 

trained personnel within Mexico, to enable the implementation 

of a permanent human biomonitoring system. From this study 

we conclude that the Mexican government needs to invest in 

establishing these analytical capabilities, perhaps with resources 

from the CEC and other relevant international funding 

institutions. It is important to include not only the laboratories 

that participated in this study, but also regional laboratories

within the areas where long‐range human biomonitoring of 

POPs will be carried out. Essential components of these 

enhanced analytical capabilities in Mexico include participation 

in internationally recognized quality‐assurance/quality‐control

programs and round‐robin testing. 

In Mexico, long‐range monitoring of POPs is part of the National 

Monitoring and Environmental Evaluation Program (Programa

Nacional de Monitoreo y Evaluación de Sustancias Tóxicas,

Persistentes y BioacumulablesProname), which includes a 

biological/human biomonitoring component. One of the 

objectives of Proname is to assess contaminant concentrations 

and monitor trends of these contaminants in vulnerable 

population groups. 

The success of Proname hinges on the participation of key 

institutions. We recommend that the following institutions be 

included: the National Institute of Public Health (INSP) that 

coordinated this first effort in the country, the National Institute 

of Ecology (INE), the National Center for Environmental 

Research and Training (Cenica), the Ministry of Health, 

represented by the Federal Commission for Risk Protection 

(Cofepris), which also includes the Commission for Analytical 

Control and Extension of Coverage (CCAYAC), the network of 

laboratories within the Ministry of Health. 

We also recommend follow‐up human biomonitoring in those 

cities where the highest POPs levels (including metals such as 

mercury and lead) were encountered in this initial study, 

regardless of the relevance to Proname.  

Canada, Mexico and the United States

Both Canada in the Canadian Health Measures Survey (CHMS) 

and the United States in the National Health and Nutrition 

Examination Survey (NHANES) have national human 

biomonitoring programs directly relevant to the proposed 

ongoing biomonitoring in Mexico. Canada and the United States 
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need to continue to provide population sampling expertise and 

analytical support for the follow‐up studies proposed by Mexico. 

Canada and the United States will be able to continue to 

collaborate with Mexico on trinational comparisons of other 

relevant population subgroups, such as children. Close 

collaboration on study design of new biomonitoring programs in 

Mexico must take place to ensure comparability of the 

population groups studied and the resulting data. 

Chemicals not included in this study, such as brominated flame 

retardants and perfluorinated chemicals, are being measured in 

the CHMS and NHANES. Only limited monitoring data for these 

chemicals are available in Mexico. Further sampling and 

analytical capacity building for human biomonitoring in Mexico 

must include these chemicals, as they are likely to be considered 

for addition to various international treaties to which Mexico,

Canada and the United States are or may become signatories. 

Quality assurance and quality control and participation in 

international round‐robins are essential components in the 

production of quality data. Canada and the United States must 

continue to participate with Mexico in the development and 

assessment of the QA/QC information developed under the 

proposed monitoring in Mexico. Canada and the United States 

should also provide analytical training, reference samples and 

access to various international analytical round‐robins as part of 

this trinational biomonitoring program.
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