Open Access
Highlights
- •
- Higher concentrations of p,p’-DDE, β-HCH, and lead among Mexican primiparous women.
- •
- PCB concentrations similar among Mexican and Canadian primiparous women.
- •
- Age, pre-pregnancy BMI, ethnicity group, and ever-smoked status were significant.
Abstract
Under
the North American Commission for Environmental Cooperation (CEC) and
its Sound Management of Chemicals (SMOC) program, a tri-national human
contaminant monitoring initiative was completed to provide baseline
exposure information for several environmental contaminants in Canada,
Mexico and the United States (U.S). Blood samples were collected from
primiparous women in Canada and Mexico, and were analysed for a suite of
environmental contaminants including polychlorinated biphenyls (PCBs),
dichlorodiphenyldichloroethylene(p,p′-DDE),beta-hexachlorocyclohexane
(β-HCH), mercury and lead. A multiple stepwise linear regression
analysis was conducted using data from Canadian and Mexican primiparous
mothers, adjusting for ethnicity group, age, pre-pregnancy BMI, years at
current city and ever-smoking status. Concentrations of p,p′-DDE,
β-HCH, and lead were found to be higher among Mexican participants;
however, concentrations of most PCBs among Mexican participants were
similar to Canadian primiparous women after adjusting for covariates.
Concentrations of total mercury were generally higher among Mexican
primiparous women although this difference was smaller as age increased.
This initial dataset can be used to determine priorities for future
activities and to track progress in the management of the selected
chemicals, both domestically and on a broader cooperative basis within
North America.
Keywords
- Primiparous women;
- Persistent Organic Pollutants (POPs);
- Metals;
- Canada;
- Mexico
1. Introduction
Prior to the initiation of the Trinational Biomonitoring study (CEC, 2011)
there was relatively limited biomonitoring data available across parts
of Canada and Mexico. In Canada, several targeted population and
community-based based studies have been conducted among Aboriginal
populations (Donaldson et al., 2010 and Wheatley and Paradis, 1995), and in specific regions including the Great Lakes (Cole et al., 2002) and the St. Lawrence region (St. Lawrence Vision, 2000), and in certain provinces (Alberta Health Wellness, 2008 and Institut national de santé publique du Québec, 2004).
More recently however, a number of comprehensive surveys have been
conducted such as the Canadian Health Measures Survey, and several
others described by Haines et al., (2012),
that provide a nation-wide level of information on contaminants present
in the population. In Mexico, biomonitoring data was relatively scarce
except for a few contaminants such as lead and DDT (López-Carrillo et al., 1996a and López-Carrillo et al., 1996b)
although more recently, studies have been conducted that focus on
environmental contaminants in suspected areas of higher levels (Domínguez-Cortinas et al., 2013, Meza-Montenegro et al., 2013, Trejo-Acevedo et al., 2012 and Trejo-Acevedo et al., 2009) at specific sites (Orta-Garcia et al., 2014) and at sites in proximity to point sources of contaminants (Soto-Jiménez and Fregal, 2011 and Soto-Ríos et al., 2010).
A
tri-national human contaminant monitoring initiative was developed by
the North American Commission for Environmental Cooperation (CEC) and
its Sound Management of Chemicals (SMOC) program, which is tasked with
implementing tri-national efforts to reduce the risks of exposure to
toxic substances related to human health and the environment in the
United States (U.S.), Canada and Mexico (CEC, 2011).
The initiative was developed with two main objectives: 1) to obtain an
initial profile of exposure to persistent organic pollutants (POPs) and
selected metals in primiparous women for Canada and Mexico, and women of
childbearing age in the U.S.; and 2) to enhance the capacity of Mexico
to monitor Stockholm Convention POPs and selected metals, establishing
the basis for the development of compatible and comparable databases of
human biomonitoring results for the three countries. The data collected
by this pilot biomonitoring study (Trinational Biomonitoring Study)
provides a baseline profile of human exposure to environmental
contaminants to help track progress in managing select chemicals in the
three countries (CEC, 2011) and assist in the prioritization of future monitoring activities.
The
POPs and metals contaminants measured in the Trinational Biomonitoring
Study are some of the most well studied contaminants and human health
effects associated with their exposure has been studied by numerous
researchers. Studies have linked lead exposure to neurodevelopmental (Boucher et al., 2012a, Boucher et al., 2012b, Cho et al., 2010 and Wang et al., 2008a), cardiovascular (Glenn et al., 2006, Glenn et al., 2003 and Yazbeck et al., 2009), renal (Muntner et al., 2005 and Muntner et al., 2003) and reproductive effects (Cantonwine et al., 2010). Mercury exposure has been associated with neurotoxic effects in adults (Harada et al., 2005 and Harada, 1995) and children (Grandjean et al., 2003), cardiovascular effects (Choi et al., 2009), and developmental effects in children from prenatal exposure (Boucher et al., 2012a and Boucher et al., 2012b).
In addition, several studies have identified a number of potential
health effects associated with exposure to persistent organic pollutants
(POPs), including exposure to dichlorodiphenyldichloroethylene
(p,p′-DDE) and PCBs (Dallaire et al., 2006 and Dallaire et al., 2004), PCBs and dioxins (Weisglas-Kuperus et al., 2004) with immune system effects, and exposure to PCBs with cardiovascular effects (Huang et al., 2006 and Sergeev and Carpenter, 2005), and neurodevelopment effects (Boucher et al., 2009, Grandjean et al., 2001, Jacobson and Jacobson, 2003 and Muckle et al., 2004).
An increasing number of studies are reporting increased risk of
developing type II diabetes associated with exposure to POPs, such as
PCBs and dioxins (Lee et al., 2006, Lee et al., 2010 and Wang et al., 2008b;) and p,p′-DDE (Rignell-Hydbom et al., 2009). Few studies have investigated health effects associated with exposure to polybrominated compounds (Kicinski et al., 2012), although several toxicology studies have documented developmental, neurotoxic, and endocrine disruption effects (Costa et al., 2008 and Darnerud, 2003).
Exposures
for young children and the developing fetus carry the most cause for
concern due to their rapid growth and physiological immaturity.
Environmental chemicals can be passed on from the mother to the
developing fetus through the placenta (Needham et al., 2011)
and some contaminants such as mercury have been detected at higher
concentrations in umbilical cord blood than in maternal blood (Ask et al., 2002, Sakamoto et al., 2004 and Soria et al., 1992).
Even after birth, when the body is still developing and young children
do not have a fully formed blood–brain barrier, further exposure to
contaminants can occur through breastfeeding (Anderson and Wolff, 2000 and Lakind et al., 2001).
For this reason, pregnant women were the target population for the CEC
Trinational Biomonitoring Study. Primiparous women in particular, are an
ideal population to study as they are not influenced by confounding
variables such as parity and breast-feeding (James et al., 2002 and Sarcinelli et al., 2003).
Several studies have investigated changes in maternal blood volume,
body mass index and other factors during pregnancy, however recent
studies indicate that the last weeks of the third trimester is the most
suitable time period for the measuring of organochlorines in blood
samples (Hansen et al., 2010).
Data
on concentrations of chemicals in human populations are required by
regulatory agencies to conduct risk assessments and for informing policy
decisions. The monitoring of contaminant levels in human populations
can provide information to track the effectiveness of regulations. In
Canada, for example, a decline in blood lead concentrations has been
observed over the last three decades, where 25% of Canadians aged 6 or
older were found to have blood lead concentrations above 10 μg/dL as
measured in the Canada Health Survey (1978–79), while less than 1% of
Canadians were above 10 μg/dl as measured in the Cycle 1 of Canadian
Health Measures Survey 30 years later (2007–2009; Wong and Lye, 2008). This may reflect the phase-out of leaded gasoline, lead-containing paints, and lead solder in food cans (Health Canada, 2004).
The concentrations of a number of organochlorines, such as DDT and
β-HCH, have also been measured to be declining in human breast milk in
Ontario and Quebec over several decades (Craan and Haines, 1998), the use of which has been reduced or eliminated due to either restricted use or production, voluntary bans or regulated bans.
Comparison
of biomonitoring datasets from different geographic areas and countries
can provide valuable information to compare and contrast contaminants
concentrations in human populations (a result of exposures from various
sources including consumer products, food and environmental media), as
well as to help evaluate the effectiveness of global regulations and
other risk management efforts. Challenges exist, however, when comparing
biomonitoring studies due to the potential for lack of consistency in
study design, sample populations, time period, laboratory analytical
methods, and interpretation of the data. To ensure comparisons for human
biomonitoring data are scientifically meaningful, it is essential to
evaluate the methodological components of the biomonitoring surveys and
their impact on the comparability of the data (LaKind et al., 2012).
The CEC biomonitoring data collected in this pilot study was conducted
using similar methods and designs in Canada and Mexico, which provides a
unique opportunity to make a meaningful statistical comparison between
these two populations. Due to the different recruitment/sampling
strategy used for the collection of US data, the analysis was restricted
to Canadian and Mexican data. A descriptive comparison of all three
countries is however presented in the original report (CEC, 2011).
The objective of this paper is to use statistical methods to compare
the concentrations of select POPs and metals in the blood of primiparous
women from Canada and Mexico after adjusting for covariates.
