Dioxins
in Herbicides - A Primer
Most weedkillers for turf are
"phenoxy herbicides", which are commonly contaminated with dioxins.
Dioxin in the defoliant
Agent Orange was notorious, but what forms are being
spread today? What are the health effects of today's
herbicides? Are Canadians still suffering from
previous spraying?
What are Dioxins?
Dibenzo-para-dioxins
("dioxins") are toxic chemicals that break
down extremely slowly in the environment. They are
among the most toxic compounds made by man, and some
are targeted for elimination. Dioxins bioaccumulate -
they collect in fatty tissue, and become concentrated
in animals higher up the food chain. They are almost
exclusively man-made, and they are now everywhere in
our environment and in people's bodies - even before
birth and in mothers' milk.1,2
There are 76 different
chlorinated dioxins, distinguished by the number (0
to 8) and arrangement of chlorine atoms in the
labelled positions around dioxin's three-ring
structure. Other chemicals that cause
"dioxin-like" health effects include furans
and polychlorinated biphenyls (PCBs).
dioxin
furan
biphenyl
Where do dioxins come
from?
Dioxins are formed during
chemical manufacturing (especially pesticides),
chlorination and burning of waste in pulp and paper
making, and high temperature processes such as metal
sintering and waste incineration.
Why and how are dioxins
toxic?
Dioxins that have chlorine
atoms in at least the 2,3,7 and 8 positions bind to
the "aryl hydrocarbon receptor" (AhR) in
cells. This starts off a variety of reactions that
affect the immune, reproductive, endocrine and
neurological systems. Diseases associated with Agent
Orange contamination with
2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) include
many cancers, diabetes, birth defects, chloracne and
neurological problems.3 There are 17 such
dioxins, that are regulated internationally.
Virtually all the toxicity literature deals with the
strongest-binding one - 2,3,7,8-TCDD.
The other 58 dioxins are not
monitored or regulated, but they are toxic as well -
although there is little if anything published about
them. It is difficult to prepare and test this large
number of chemicals, but an entire family of very
similar chemicals (polynuclear aromatic hydrocarbons)
are biologically active and cause many illnesses.4
Dioxins also have toxic effects that do not involve
the AhR.5,6,7,8,9 Furthermore, the
toxicities (carcinogenicity, neurotoxicity,
immunological and reproductive toxicities) that had
been associated with 2,4,5-T continue to be reported
by independent researchers, in connection with other
phenoxy herbicides.10,11,12,13, 14,15
What about dioxins in
herbicides?
Dioxins are always produced
when making phenoxy herbicides. It is just a matter
of what kind and how much.
Agent Orange was a mixture of
the phenoxy herbicides 2,4,5-T and 2,4-D, used to
kill broad leaf plants. Crude manufacturing in the
1950's and 1960's meant that 2,4,5-T was heavily
contaminated with 2,3,7,8-TCDD. This was blamed for
illnesses and birth defects in the Vietnamese and
Vietnam war veterans, as well as in New Brunswick
power workers who used "Brushkill". 2,4,5-T
was banned world-wide in the 1970's early 1980's.
In 1990, Environment Canada
identified phenoxy herbicides (such as 2,4-D,
mecoprop and dicamba used to kill weeds) as the
second-largest chemical source of dioxins
contaminating the Canadian environment, after
contamination of pentachlorophenol wood preservative.16
Unlike the wood preservative contaminants,
today's phenoxy herbicide dioxins are not among the
17 regulated forms. 2,4-D is contaminated with
dioxins with two or three chlorine atoms, rather than
four,17,18 but these are not being
examined in the re-assessment of 2,4-D.19
Ottawa lawn care firms spread 3
tonnes of phenoxy herbicide active ingredients
annually.20 This does not include private
use, golf courses, or large properties. Canadian
pesticides sales and use data is not generally
available.
How are dioxins
regulated and monitored?
The 17 dioxins with four or
more chlorine atoms, which are toxic via the AhR, are
regulated internationally and are targeted for
elimination. In Canada they fall under the Canadian
Environmental Protection Act (CEPA), and numerous
other acts and regulations at the federal and
provincial level, including the Pest Control Products
Act. Track 1 Substances under CEPA also include
dioxins with 0 and 3 chlorine atoms, but dioxins with
1 and 2 chlorine atoms are not regulated. These
additional dioxins are generally not reflected in
other statutes.
Only 17 dioxins are measured
when using the US Environmental Protection Agency
(EPA) method used for analysis - it does not include
dioxins with fewer than 4 chlorine atoms. This is the
standard method called for by Canadian regulators as
well.
Dioxins are reported as
"toxic equivalents" (TEQ) - the mass of
2,3,7,8-TCDD that would bind the AhR in an equivalent
manner. 2,3,7,8-TCDD binds the AhR most strongly, and
is considered the most toxic dioxin. The other 16 are
pro-rated according to how strongly they bind the
AhR. This method assigns much lower values to the
other 16 regulated dioxins, and zero toxicity to the
59 dioxins that do not bind to the AhR. The TEQ is
much less than the mass of the regulated dioxins, as
seen in reports from Dow Chemical and the Chlorine
Council (the EPA recently required reporting of the
total mass of the 17 dioxins measured, as well as the
TEQ). 21,22
The TEQ scheme is based on a
relatively simple lab test. This easy way to
categorize toxicity of a large number of toxic
chemicals, including some PCBs and furans, left the
majority of similar toxic chemicals unregulated.
Although the 59 other dioxins
are not monitored, there is no reason to believe that
they are not at least as prevalent. Indeed, since
they have escaped the scrutiny of regulatory
agencies, manufacturers may not have made efforts to
decrease their production. Indeed, there may be an
incentive not to minimize dioxin contamination,
because during manufacturing of phenoxy herbicides
there is a trade-off between dioxin contamination and
speed of conversion and yield of herbicide. It was
the "quick and dirty" war-time
manufacturing of Agent Orange that led to high levels
of contamination with 2,3,7,8-TCDD.
What does this mean for
CFB Gagetown?
Veterans and neighbours of CFB
Gagetown are suffering ill health apparently related
to spraying of herbicides from the 1950's to the
1980's. Investigations
of dioxin contamination by the federal government are
only examining water, air, soil, vegetation and
sediment. Dioxin levels will be highest in the fat of
animals, such as fish, and wildlife (samples of moose
and deer could be donated during hunting season).
This is the usual way to sample the environment for
dioxins, but is not occurring at CFB Gagetown.
The only dioxins being analysed
for are the 17 AhR binding ones. The dioxin
contaminants of 2,4-D or other herbicides will not be
examined.
Twice as many analyses are
being done for the herbicides 2,4-D and 2,4,5-T
(these would be expected to have degraded decades
ago) as there are for dioxins. A large number of
"no detection" may be politically
expedient, but not informative.
Other toxic, persistent,
bioaccumulative substances that should be examined as
well include arsenic and hexachlorobenzene, and
doubtless others.
Wildlife, and human testing, of
blood, fat and breast milk, for the full range of
toxic pollutants are needed.
_________________________
Prepared by Meg Sears PhD -
please address concerns or comments to:
healthyottawa at hotmail dot com
References:
1 Environmental
Working Group. Body Burden
http://www.ewg.org/reports/bodyburden/es.php and
"The Pollution in Newborns". http://www.ewg.org/reports/bodyburden2/
2 Centers for Disease
Control, USA. National Report on Human Exposure to
Environmental Chemicals. http://www.cdc.gov/exposurereport/ (July 27, 2005)
3 United States
Veteran Affairs. VA's Guide on Agent Orange Claims. http://www.vba.va.gov/bln/21/benefits/Herbicide/AOno3.htm (June 13, 2005)
4 Agency for Toxic
Substances and Disease Registry. USA. Toxicological
Profile for Polycyclic Aromatic Hydrocarbons (PAHs).
August 1995 available via http://www.atsdr.cdc.gov/toxprofiles/tp69.html
5 Sulentic CE,
Holsapple MP, Kaminski NE. Putative link between
transcriptional regulation of IgM expression by
2,3,7,8-tetrachlorodibenzo-p-dioxin and the aryl
hydrocarbon receptor/dioxin-responsive enhancer
signaling pathway. J Pharmacol Exp Ther. 2000
Nov;295(2):705-16.
6 U.S Department of
Health and Human Services - Agency for Toxic
Substances and Disease Registry. Toxicological
Profile for Chlorinated Dibenzo-p-dioxins. Dec. 1998.
available via http://www.atsdr.cdc.gov/toxprofiles/tp104.html
7 De la Rosa P,
Barnett JB, Schafer R. Loss of Pre-B and Igm+ B Cells
in the Bone Marrow After Exposure to a Mixture of
Herbicides. J Toxicol Env Health.
2003;66(24):2299-2313.
8 Giesy JP, Kannan K.
Dioxin-like and non-dioxin-like toxic effects of
polychlorinated biphenyls (PCBs): implications for
risk assessment. Crit Rev Toxicol. 1998;28(6):511-69.
9 Nilsson CB,
Hakansson H. The retinoid signaling system--a target
in dioxin toxicity. Crit Rev Toxicol.
2002;32(3):211-32.
10 Schreinemachers D.
Mortality from Diabetes Mellitus and associated
diseases in four U.S. wheat-producing states.
Epidemiology. 2004;15(4)S182.
11 Sanbord M, Dr.
Donald Cole, Dr. Kathleen Kerr, Dr. Cathy Vakil, Dr.
Luz Helena Sanin, Dr. Kate Bassil. Pesticides
Literature Review. April 23, 2004 available at:
http://www.ocfp.on.ca/english/ocfp/communications/publications/default.asp?s=1#EnvironmentHealth
12 Daniels JL, Olshan
AF, Teschke K, Hertz-Picciotto I, Savitz DA, Blatt J,
Bondy ML, Neglia JP, Pollock BH, Cohn SL, Look AT,
Seeger RC, Castleberry RP. Residential pesticide
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Jan;12(1):20-7
13 Lerda D, Rizzi R.
Study of reproductive function in persons
occupationally exposed to 2,4-dichlorophenoxyacetic
acid (2,4-D). Mutation Res 1991;262:47-50.
14 Arbuckle TE, Savitz
DA, Mery LS and Curtis KM. Exposure to phenoxy
herbicides and the risk of spontaneous abortion.
Epidemiology 1999;10,752-760.
15 Schreinemachers DM.
Birth Malformations and Other Adverse Perinatal
Outcomes in Four U.S. Wheat-Producing States. Environ
Health Perspect 2003;111:1259-1264.
16 Boddington MJ,
Gilman AP, Newhook RC, Braune BM, Hay DJ, Shantora V.
Canadian Environmental Assessment Act. Priority
Substances List. Assessment Report no. 1:
Polychlorinated bibenzodioxins and polychlorinated
dibenzofurans. Minister of Supply and Services
Canada. Catalogue no. En 40-215/1E. ESBN
0-662-17644-8.
17 International
Programme on Chemical Safety, Environmental Health
Criteria 29, 2,4-dichlorophenoxyacetic acid (2,4-D).
World Health Organization, Geneva. 1984. http://www.inchem.org/documents/ehc/ehc/ehc29.htm
18 International
Programme on Chemical Safety Environmental Health
Criteria 84 2,4-Dichlorophenoxyacetic Acid (2,4-D) -
Environmental Aspects. Published under the joint
sponsorship of the United Nations Environment
Programme, the International Labour Organisation, and
the World Health Organization World Health
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19 Pest Management
Regulatory Agency. "Re-evaluation of the Lawn
and Turf Uses of (2,4-Dichlorophenoxy)acetic Acid
[2,4-D]" PACR2005-01, February 21, 2005. http://www.pmra-arla.gc.ca/english/pdf/pacr/pacr2005-01-e.pdf. (February 25, 2005).
20 City of Ottawa.
2004 year-end report on City of Ottawa pesticide
reduction strategy for private property. Ref.No:
ACS2005-PGM-POL-0029.
http://ottawa.ca/calendar/ottawa/citycouncil/hrssc/2005/05-05/ACS2005-PGM-POL-0029%20English.htm
(April 28, 2005)
21 The Dow Chemical
Company. Dioxin reports. TRI Dioxin Reporting (U.S.) http://www.dow.com/commitments/debates/dioxin/tri.htm
22 Chlorine Council
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Community Web.
