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Ambient Air Measurements of Polycyclic Aromatic Hydrocarbons (PAH),
Polychlorinated Dibenzo-p-Dioxins (PCDD) and Polychlorinated
Dibenzofurans in Canada (1987-1997)
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Executive Summary
As a component of the National Air Pollution Surveillance (NAPS)
network, the Analysis and Air Quality Division (AAQD), Environmental
Protection, Environment Canada operates an ambient air measurement
program for polycyclic aromatic hydrocarbons, polychlorinated
dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF).
With the co-operation of provincial and municipal environment agencies
and Environment Canada regional offices, samples have been collected
at thirty-nine urban and rural monitoring sites across Canada.
This reports summarizes available results for the period 1987 to 1997
(most data were collected between 1995 and 1997).
The category of compound known as PAH has received a good deal of
attention over the last thirty years because some species of PAH are
known human carcinogens. Because PAH result from the incomplete
combustion of fossil fuels they are ubiquitous in the atmosphere.
Based on an inventory of Canadian emissions of PAH for 1990 the primary
anthropogenic sources of PAH are aluminum smelting, residential wood
combustion, open air burning and diesel motor vehicles. Forest fires
account for 46% of total emissions in the inventory, but their impact
on average measured ambient PAH concentration is generally small.
PAH appeared on the Canadian Environmental Protection Act (CEPA)
priority substances list (PSL) and five species (benzo(a)pyrene,
benzo(b)fluoranthene, benzo(j)fluoranthene, benzo(k)fluoranthene and
indeno(1,2,3-cd)pyrene) were designated ‘toxic’ as defined in Section
11c (constituting a danger to human life or health) of the Act.
Nine PAH (acenapthene, fluorene, phenanthrene, anthracene, fluoranthene,
pyrene, benz(a)anthracene, benzo(a)pyrene and naphthalene) were found
to be toxic under Section 11a (having a harmful effect on the
environment).
Numerous assessments of PCDD/PCDF have recognized that because of
their toxicity to animals, their persistence and their ability to
bio-accumulate, they represent a significant danger to human health
and to the environment. Of the 210 possible PCDD/PCDF congeners, it
is the 2,3,7,8 substituted PCDDs and PCDFs that are of most concern
from a health and environmental effect perspective. Of these, the
2,3,7,8-TCDD isomer has been shown to be the most toxic to mammals.
There is no intentional production or use of PCDD/PCDF.
They are released into the environment as contaminants or by-products
associated with the production or combustion of chlorinated organic
substances. The recently released Federal Provincial Advisory Committee
for the Canadian Environmental Protection Act (CEPA-FPAC) inventory for
dioxins, furans and hexachlorobenzene shows that incineration accounted
for ~60% of PCDD/PCDF emissions in 1990.
Data from approximately 2,200 daily PAH samples collected at 35 sites are available.
For 1994-1997 data, mean PAH concentrations vary by more than three orders of magnitude
from the rural-remote Jasper Park sites to the industrial influenced Jonquière site (the
range of means is 0.9 to 801 ng/m³ and the range of 90th percentile values is
4.8 to 2,650 ng/m³). For the urban sites (with more than 10 sampling days of data) mean
total PAH concentrations ranged from 10 to 65 ng/m³ with 90th percentile
concentrations ranging from 14 to 115 ng/m³. In general, the larger population areas
experienced the highest mean and 90th percentile PAH concentrations. The sites
with industrial emission sources (or wood smoke in the case of the Whitehorse site) nearby
recorded the highest mean and 90th percentile concentrations. The most abundant
species were phenanthrene, fluoranthene, pyrene and benzo(b)&(k)&(j) fluoranthene
with frequencies of detection ranging from 94 to 99.9%. In contrast the species with the
lowest frequency of detection were 3-Me-cholanthrene and 7-Me-Benz(a)anthracene. Overall,
vapor phase species account for most of the PAH mass with particulate phase species found
in much lower concentrations.
For sites with the longest data records (Jonquière, Montréal, Toronto, Hamilton and
Windsor) yearly variations in the sum of the CEPA toxic (health) PAH were determined. For
Jonquière, median concentrations decreased substantially through the period with smaller
decreases in 75th and 90th percentile values. The Hamilton site
shows substantial year to year variation but the median concentration for 1996 was the
same as for 1989. The Montreal site appears to be experiencing an upward trend whereas
median concentrations at the Toronto site show a significant decline between 1994 and
1996.
Over 500 daily samples were collected for PCDD/PCDF analysis from 34 monitoring sites
with 344 samples collected between 1994 and 1997. For many sites, however, only 2 or 3
days of data are available. The only sites with long data records are Windsor-University
Ave. (1989 to 1995), Windsor-College and Prince (1990-1997) and Walpole Island
(1989-1995). Overall, mean TEQ concentrations (using 0.5-DL substitution) ranged from 105
fg/m³ at the Toronto site to 10 fg/m³ at St. Andrews, N.B. For sites with more than ten
sampling days, ninetieth-percentile TEQ values ranged from 326 fg/m³ at the Jonquière
site to 16 fg/m³ at Kejimkujik. Octa-PCDD is the most abundant isomer and was detected in
all samples, followed by hepta-PCDD and hepta and octa-PCDF. Maximum concentrations of 73
pg/m³ of total PCDD, 37 pg/m³ of total PCDF and 1.95 pg/m³ TEQ were recorded during the
program. The isomer 2,3,7,8-T4CDD was detected in 28% of the samples with a
median concentration of 3 fg/m³ and a maximum of 61 fg/m³. Although the octa and hepta
congeners are most abundant they are also the least toxic and make only a small
contribution to TEQ. Four isomers, 2,3,4,7,8-P5CDF, 2,3,7,8-T4CDF,
1,2,3,7,8-P5CDD and 1,2,3,4,7,8-H6CDF, account for 65% of computed
TEQ.
Polycyclic aromatic hydrocarbons, polychlorinated dibenzo-p-dioxins and
dibenzofurans are ubiquitous in air samples collected in rural and urban locations in
Canada. Mean total PAH concentrations vary by almost three orders of magnitude between
remote rural sites and source impacted urban locations while mean PCDD/PCDF concentrations
(expressed as 2,3,7,8-T4CDD toxic equivalents vary by a factor of 20. While
there has been some apparent reductions in air concentrations over the past ten years, it
is clear that there are still numerous sources of these toxic substances in Canada. These
sources create both immediate and long range impacts. Additional efforts are required in
characterizing and quantify emission releases of PAH and PCDD/PCDF and in determining the
impact of specific sources on measurement sites. Because of the many known harmful effects
of these classes of substance, it would be prudent to accelerate efforts to reduce
environmental exposures.
For full transcript please contact:
e-mail: Tom Dann
phone: (613) 991-9459.
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