The Coalition for a Healthy Ottawa

Fact Sheet on PAR III (PAR 3) herbicide

PAR III is a mixture of toxic synthetic herbicides used by lawn pesticide application companies attempting to suppress or kill broadleaf weeds.

PAR III contains:

  1. 2,4-D
  2. Mecoprop
  3. Dicamba

PAR III also contains proprietary formulants.

There are currently two versions of PAR III allowed for use in Canada by the Pest Management Regulatory Agency (PMRA):

1) An old version (Reg. number 19810) which contains the racemic form of Mecoprop. Here is its product label and Material Safety Data Sheet (MSDS).

2) A new version (Reg. number 27884) which contains Mecoprop-p. Here is its product label and Material Safety Data Sheet (MSDS).


On May 13, 2004, the PMRA identified significant data gaps for racemic mecoprop that would have to be addressed in order to bring the supporting database up to modern standards. Rather than generate the required data to support continuing registration, the registrants of racemic mecoprop decided to discontinue sales of the technical active ingredient. However, it may still be sold in stores until December 31, 2009.

PAR III also includes "inert" formulants, and may include some which are deemed likely carcinogens by the International Agency for Research on Cancer (IARC).

Some forms of 2,4-D are more toxic than others; hence unequal study results.

A breakdown product of 2,4-D is 2,4-dichlorophenol (2,4-DCP). It is associated with the unpleasant smell of the product. The PMRA subsume human exposure under "Mammalian toxicity," which they claim is low. However, a report of US Centers for Disease Control (CDC) maintains that monitoring shows that only in animals is 2,4-D excreted largely unchanged. Humans are much more heavily contaminated with 2,4-DCP than with 2,4-D. 2,4-DCP is considered a possible carcinogen by the International Agency for Research on Cancer (IARC).

In evaluating the risk of pesticides, the PMRA measures exposures to one chemical at a time in animals (often rats) and does not account for the cumulative and comprehensive effect of the chemical. In other words, the PMRA does not consider the toxicities of these mixtures.

In April 2004 the genome of the rat was published in the prestigious journal "Nature". An important finding was that rats have genes that do not exist in people for detoxification of chemicals, and therefore are a poor model for toxicity testing. (There is a reason that rats can live in sewers and garbage dumps, and people cannot.) Dogs are much more sensitive to 2,4-D, but the dog data was put aside in favour of the more robust rats.

Exposure to herbicide-treated lawns and gardens increases the risk of bladder cancer in Scottish terriers (source).

A study in the peer-reviewed journal "Environmental Health Perspectives", noted that the commercial, off-the-shelf mixture of 2,4-D, Dicamba and Mecoprop may pose serious reproductive risks. (source)

Herbicide health effects reported in recent peer-reviewed literature include cancers, type 2 diabetes, and reproductive and neurological problems.

2,4-D, was recently found to be persuasively linked to cancers, neurological diseases and reproductive problems (Sears et al., Paediatrics and Child Health, April 2006) (source). Since then, very recent research greatly strengthened the scientific links between non-Hodgkin's lymphoma and 2,4-D.

In a cohort study of 139,000 farm workers, the incidence of non-Hodgkin lymphoma (NHL) was almost 4x greater on farms where 2,4-D was used.1

The age-standardized incidence rates of NHL in Canada and the United States are among the highest in the world (source), with the number of cases and age adjusted incidence rates for NHL rising steadily in Canada from 1992-2002 (source).

Non-Hodgkin lymphoma (NHL) with a particular genetic change is correlated with herbicide exposure, while the subset without this genetic trait is not.2  The increases of NHL have been greater for the subtype associated with exposure to pesticides. Furthermore, this subtype is more difficult to treat in its advanced stages.

The PMRA released their 2,4-D draft re-assessment document in 2005 without examining the likely connection between pesticide exposure and childhood cancers. A PMRA document 3 noted: "The issue goes beyond the re-evaluation of 2,4-D...a separate assessment is more appropriate to address the issue of pesticide exposure and childhood cancer." Children's health was thus put on the back burner.

What the spokespeople for the PMRA are now admitting to is that they went ahead and re-assessed 2,4-D without fully taking into account the consequences of children's exposure, yet children are the most precious and vulnerable population group.

By nature of the way the herbicides are synthesised, they are inevitably contaminated with chlorinated dioxins. These persistent, bioaccumulative toxic substances are passed onto the next generation, and are linked to cancers, particularly non-Hodgkin's lymphoma, and to reproductive, immunological and neurological problems. The dioxins that are known to contaminate 2,4-D should be at least measured and the toxicities of those dioxins should be tested. This hasn't been done. No dioxin analyses were submitted in support of the PMRA's re-registration of 2,4-D.

Developmental neurotoxicity testing for 2,4-D has also not been carried out in the PMRA's re-evaluation of 2,4-D.

The Pest Management Regulatory Agency (PMRA) has placed a condition of registration on 2,4-D such that the 2,4-D registrant(s) must provide the PMRA with a required developmental neurotoxicity study by September 20, 2009.

 Meanwhile, in the United States, California's Office of Environmental Health Hazard Assessment classifies 2,4-D as a developmental toxicant.

"2,4-D is far from safe. It can affect women's ability to bear healthy children, and epidemiological studies show strong links between use of 2,4-D products and cancer," noted Dr. Susan Kegley, Senior Scientist at PAN. (source)

In June 2008, Meg Sears, Ottawa Adjunct Investigator, Children's Hospital of Eastern Ontario (CHEO)'s Research Institute, notes that an objection to the PMRA was filed, stating that the Agency was premature in re-registering 2,4-D due to lack of important studies.  For more information, please click here to read her comments.


CHO has serious concerns relating to the PMRA's approval of PAR III. CHO therefore does not recommend the use of PAR III. Much safer alternatives exist to PAR III and its like (Trillion, Killex and Tri-Kill), so CHO believes that the precautionary principle should prevail. Please check out CHO's tips for a natural lawn without using synthetic pesticides.Up


1  Mills PK, Yang R, Riordan D.  Lymphohematopoietic cancers in the United Farm Workers of America (UFW), 1988-2001.  Cancer Causes Control. 2005 Sep;16(7):823-30.

2  Chiu BCH, Dave B, Blair A, Gapstur SM, Zahm SH, Weisenburger DD.Agricultural pesticide use and risk of t(14;18)-defined subtypes of non-Hodgkin lymphoma.  Blood First Edition Paper, prepublished online April 18, 2006; DOI 10.1182/blood-2005-12-008755.

3. PMRA "Speaking Points: Paediatric and Child Health Article PMRA Position." May 2006. Prepared by Edith Lachapelle.Up



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Last updated: September 29, 2008

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