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How much of an impact does pesticideherbicide use have on aquatic life?

Submitted by: Hileaeyesus Solomon


Expert response from holmquist1x

Friday, 11/05/2018 10:16

Believe it or not, I jump at opportunities to talk about aquatic life, so thank you for your interest. I developed a passion for aquatic animals early on and remain grateful that I have managed to explore my passions in ecotoxicology for over 25 years!

Many different short-term and long-term aquatic studies are required for pesticides during the registration process and these studies are used to evaluate if there are potential impacts to aquatic life. These required studies test for potential toxic effects to aquatic plants and animals. Aquatic plants include marine and freshwater algae and freshwater vascular plants. Studies on animals include both freshwater and marine vertebrate and invertebrate species. Regulatory authorities such as the Environmental Protection Agency (EPA) in the U.S. and the Pesticide Management Regulatory Authority (PMRA) in Canada have developed specific guidance to conduct these studies and how to evaluate the reliability of these toxicity studies before they can be used in an environmental assessment.

The results from these toxicity studies are then used along with predictions of aquatic exposure to the pesticide to determine if there will be a risk to aquatic ecosystems, including threatened and endangered aquatic plants and animals. The ecological risk assessment process performed by the regulatory agencies follows well defined guidance. If the Agency determines that there is an unacceptable risk to aquatic ecosystems for a pesticide, or for a specific use of a pesticide, then the Agency will address that risk by requiring specific mitigations that minimize risk. For example, if there is a potential risk to aquatic life with a pesticide seed treatment, the Agency may require treated seeds to be planted in a manner that would minimize [or “reduce” if minimize is too affirmative] the pesticide’s ability to reach a water body, such as by requiring the seed to be planted at a minimum depth in the soil.

Another effective approach to reduce pesticide run-off to aquatic ecosystems employs the use of vegetated strips of land, known as “buffer strips”, which are placed between the edge of the field and aquatic waterbodies. These vegetated strips are sometimes required by the EPA to reduce pesticide run-off to levels that will not have short-term or long-term effects to aquatic organisms. For foliar applications, Agencies may also require a specified distance, known as a “buffer distance,” between the edge of the application and a waterbody to reduce aquatic exposures to no effect levels. In some cases, a regulatory authority may use water monitoring data, or require additional water monitoring data, to further assess if there is a realistic risk of impacts to aquatic ecosystems.

It is important to point out that ecological risk assessments are conducted to be protective of the most sensitive species in the ecosystem, thereby, protecting all aquatic organisms. For example, if an aquatic plant is the most sensitive species to a pesticide, the protections put in place to protect that species will therefore also be protective of the less sensitive aquatic species (e.g. amphibians, fish, invertebrates) by default. 

Additionally, pesticides are re-evaluated every 15 years in North America. During re-evaluation, pesticide assessments are typically updated with additional exposure and effects data. Furthermore, any adverse incidents caused by the pesticide’s use that have been reported to the Agency are considered in the new assessment. In some cases, investigations of these incidents can lead to changes in how the pesticide is applied to ensure safety to aquatic environments.


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