Proposed Re-evaluation Decision PRVD2016-07, Thiram

Pest Management Regulatory Agency
29 February 2016
ISSN: 1925-0967 (PDF version)
Catalogue number: H113-27/2016-7E-PDF (PDF version)

Summary

Table of Contents

• What is the Proposed Re-evaluation Decision?
• What Does Health Canada Consider When Making a Re-evaluation Decision?
• What is Thiram?
• Health Considerations
• Environmental Considerations
• Value Considerations
• Proposed Measures to Minimize Risk
• Next Steps

What is the Proposed Re-evaluation Decision?

After a re-evaluation of the fungicide thiram, Health Canada's Pest Management Regulatory Agency (PMRA), under the authority of the Pest Control Products Act and Regulations, is proposing the cancellation of all thiram uses in Canada.

An evaluation of available scientific information found that, under the current conditions of use, thiram products pose potential risks of concern to human health and the environment. Based on the health and environmental assessments, risks of concern were identified for both workers and the general public in addition to birds, mammals and aquatic organisms.

This proposal affects all end-use products containing thiram registered in Canada. Proposed Re-evaluation Decision PRVD2016-07, Thiram is a consultation document that summarizes the science evaluation for thiram and presents the reasons for the proposed re-evaluation decision.

The information in Proposed Re-evaluation Decision PRVD2016-07, Thiram is presented in two parts. The Summary describes the regulatory process and key points of the evaluation, while the Science Evaluation provides additional technical information on the assessment of thiram.

PMRA will accept written comments on Proposed Re-evaluation Decision PRVD2016-07, Thiram up to 60 days from the date of publication of Proposed Re-evaluation Decision PRVD2016-07, Thiram. Please forward all comments to Publications.

What Does Health Canada Consider When Making a Re-evaluation Decision?

PMRA's pesticide re-evaluation program considers potential risks as well as the value of pesticide products to ensure they meet modern standards established to protect human health and the environment. Regulatory Directive DIR2001-03, PMRA Re-evaluation Program, presents the details of the re-evaluation activities and program structure. Re-evaluation draws on data from registrants, published scientific reports, information from other regulatory agencies and any other relevant information.

What is Thiram?

Thiram is a contact protectant fungicide registered in Canada for both food and nonfood uses. It is registered to control diseases as seed treatment (cereal, oilseed, pulse, vegetable, fruit and feed crops), foliar spray application on tree fruits (apple, peach and plum), strawberry and celery (plant beds), root dip of sweet potato, and as an animal repellent to protect dormant outdoor ornamentals and young fruit trees. Thiram is applied by growers, farm and nursery workers and professional applicators.

Health Considerations

Can Approved Uses of Thiram Affect Human Health?

Based on the human health risk assessment, all uses of thiram are proposed for cancellation.

Exposure to thiram may occur through diet, when handling the product or by entering treated sites. When assessing health risks, two key factors are considered:

• the levels at which no health effects occur and
• the levels to which people may be exposed.

Toxicology studies in laboratory animals describe potential health effects from varying levels of exposure to a chemical and identify the dose at which no effects are observed. Unless there is evidence to the contrary, it is assumed that effects observed in animals are relevant to humans and that humans are more sensitive to effects of a chemical than the most sensitive animal species. For thiram, toxicology endpoints from a developmental neurotoxicity study in rats were used for risk assessment. Based on the weight of evidence from the available studies, a cancer unit risk value was also established for thiram.

The risk assessment compares the estimated level of human exposure to the no-effect doses identified in the animal tests. The reference values used to assess risks are established to protect the most sensitive human population (for example, children and nursing mothers). The estimated exposure to thiram from domestically produced and imported food commodities exceeded the acute, chronic and cancer reference values established from the toxicology database. Potential risks of concern were identified for workers handling thiram products during mixing/loading and application as well as from planting treated seeds and re-entering treated sites following application. Potential risks of concern were also identified for handlers of the domestic-class product as well as for individuals coming into contact with treated fruit trees in residential settings.

The thiram health risk assessment has considered the currently registered use pattern and label directions as well as additional mitigation measures to reduce exposure such as additional personal protective equipment, engineering controls, reduced application rates and cancellation of certain uses.

Environmental Considerations

What Happens When Thiram Is Introduced Into the Environment?

The use of thiram poses potential risks to birds, mammals and aquatic organisms that cannot be fully mitigated.

Thiram can enter nontarget terrestrial and aquatic habitats through spray drift and can enter aquatic habitats through runoff. Thiram is soluble in water and does not vaporize when sprayed on crops and is not expected to enter the atmosphere and be transported long distances from where it is used. Thiram is non-persistent in soil and water, breaking down quickly and is not likely to accumulate in fish tissues. Thiram has the potential to move through the soil profile and contaminate groundwater in some types of soil.

When exposed to high enough concentrations, thiram is toxic to birds and mammals, which may be at risk if they consume food sources that have been sprayed with this pesticide. Aquatic organisms are also potentially at risk due to exposure to thiram. The environmental risk assessment considered the currently registered use pattern as well as mitigation in the form of spray buffer zones and label statements highlighting the risk of runoff, however, risks to birds and aquatic organisms cannot be fully mitigated.

Value Considerations

What is the Value of Thiram?

Thiram is important for the control of several fungal root diseases on many cereal, oilseed, pulse, vegetable, fruit and feed crops; for the control of several fungal diseases on apple, peach, plum, strawberry and celery; and as an animal repellent to protect dormant outdoor ornamentals and young fruit trees. It is a contact protectant fungicide with multi-site mode of action. It is most often used in coformulation with single-site fungicides for broader disease control, and resistance management, thereby prolonging the effective life of these fungicides which are highly prone to the development of resistance. According to proprietary pesticide usage data, thiram is most often applied as a seed treatment, with the highest use on canola, dry beans, rye, flax and wheat.

Proposed Measures to Minimize Risk

Based on the available data and current risk assessments, Health Canada is proposing cancellation of all uses of thiram. Consequently, all maximum residue limits are proposed for revocation.

Next Steps

The PMRA is inviting stakeholders to submit comments on this document, as well as detailed proposals to further refine the risk assessment and mitigate risks. The PMRA will accept comments and proposals for a period of 60 days from the date of publication of on Proposed Re-evaluation Decision PRVD2016-07, Thiram. Please forward all comments to Publications.

Before making a final decision on thiram, the PMRA will consider all comments or proposals received from the public in response to on Proposed Re-evaluation Decision PRVD2016-07, Thiram. A science-based approach will be applied in making a final decision on thiram. The PMRA will then publish a re-evaluation decision document, which will include the decision and the reasons for it, a summary of the comments and proposals received on the proposed decision and the PMRA's response to these comments and/or proposals.

If no proposals to refine the risk assessment are received, or if those received are inadequate, then the PMRA will proceed to finalize the re-evaluation decision to cancel all thiram uses in Canada.