Have you noticed that a restricted-entry interval (REI) has become much longer on a key crop protection product lately? You’re not alone. Re-evaluation decisions in recent years by the Pest Management Regulatory Agency (PMRA) have, at times, resulted in much longer REIs being applied to some products and tasks. For example, want to apply mancozeb to an apple crop? Currently an REI of 24 hours is needed prior to hand thinning apples after application. When the new label changes take effect over the next two seasons, that interval will be increasing – to 35 days.

There are several reasons for such big shifts in REIs, including new toxicology information, the fact that many of these recent decisions applied to “old” products registered before 1995, and a revised Pest Control Products Act coming into force in 2006. Suffice to say, how we got to longer REIs is a subject for another day. However, what can be done about it is a more pragmatic discussion at this time. One surprisingly simple solution is already in practice in some cases: working with gloves.

Estimating potential exposure to persons entering an area that was treated with a crop protection product remains an important part of PMRA’s risk assessments. The purpose of an REI is to ensure that agricultural workers in treated crops do not face unacceptable potential risks to human health. The conditions of product registration, including label directions such as REIs, mean that potential risks have been determined to be acceptable to human health.

The length of an REI is based on several factors including toxicological data and estimated exposure to the product. Estimated exposure considers possible residues on the crop, duration and frequency of labour activities, and a factor for the degree of crop contact. The latter especially can have a major impact on the duration of REIs.

Residues that are on plant surfaces and are available for transfer are called dislodgeable foliar residues. Generally, residues are highest immediately after an application and decline over time due to various mechanisms including transformation into smaller compounds and mechanical removal due to rain. As the degree of potential exposure is related to the amount remaining on the foliage, potential exposure should decrease over time.

Duration and frequency of an activity such as hand harvesting is based on agronomic practices for a crop. This includes consideration for each task for hours per day, days per year, interval between repetition, crop stage, and calendar date range of the activity. Essentially it is how often and how long do workers perform these tasks in a crop. 

The crop contact factor – known as a transfer coefficient – is a measure of residue transferability from the foliage of plants to the body of a worker. Transfer coefficients can be determined for any given crop or, potentially, each crop stage and activity combination (for example hand harvesting peaches or scouting young celery plants) from post-application worker exposure monitoring studies. The transfer coefficient represents primarily a function of the degree of body immersion in treated foliage. Hand harvesting sweet corn, for example, has about eight times the transfer coefficient of hand harvesting field-grown strawberries, a far smaller statured crop.

Studies that are used currently to estimate post-application worker exposure are based on workers wearing long-sleeved shirts, long pants, socks, and footwear. This represents the baseline personal protective equipment (PPE) that workers performing hand labour tasks are expected to be wearing. Importantly, gloves are not considered – and hands are a key potential route of exposure.

Be it for comfort, protection, or food safety, some workers are commonly wearing gloves to perform activities in the field. Hand harvesting broccoli, cucumbers, or grapes already sees common use of gloves for example. Even some tasks requiring a bit more finger dexterity such as hand thinning apples are being done with gloves on in some cases. Some studies suggest gloves can significantly reduce exposure – but this protection is not currently being accounted for on product labels.

A multi-stakeholder working group is hoping to address this gap. The Post-Application Exposure Working Group is comprised of representatives from Health Canada’s PMRA, Agriculture and Agri-Food Canada, CropLife Canada, and the Canadian Horticultural Council. The group has already determined that gloves are indeed possible mitigating PPE that can reduce potential exposure. Now what is needed is data to understand how the use of gloves affects the degree of crop contact. This will require field studies to generate new transfer coefficients under these conditions. Using representative crops from major types of horticultural production, the group ideally hopes to be able to propose a default “glove protection factor” in the future that could apply broadly to most crops and tasks. 

What does this mean for REIs? Well good news. A glove protection factor should result in reduced transfer coefficients and lower potential exposure. Shorter REIs will be the direct outcome of these developments. As for workers, the current regulation already requires that REIs be acceptable under barehanded conditions. Accounting for the added factor of gloves will only help to make these occupational scenarios more realistic.