Untying the Knot – New EPA Guidance on Bound Residues in Environmental Fate Studies

Once chemicals enter soil, sediment, and/or water environments, whether purposefully, through responsible application; accidentally, through spills; or other means, they are subject to a variety of chemical and biological transformations or other forms of dissipation, including photodegradation, hydrolysis, volatilization, microbial breakdown, and others.

Each of these processes has importance in predicting or assessing environmental risk. Laboratory environmental fate studies allow for investigating these highly complex interactions and generate exposure model inputs.

Another important pathway is the formation of bound and non-extractable residues in soils and sediments.  There has been a long-standing debate over whether bound residues represent an environmental risk owing to potential chemical accumulation and persistence; a benefit as a route of removal and detoxification, or a combination of both.

Addressing bound residues has always been an important part of laboratory environmental fate studies, especially soil and aquatic metabolism studies.   Yet for years there has been limited (or no) guidance on how to approach this important aspect of chemical transformation in regulatory studies and the burden of proof was on the registrant that adequate efforts were made to “untie the knot” of bound residues in their studies.

Fortunately, in September 2014, the EPA issued its “Guidance for Addressing Unextracted Residues in Laboratory Studies.”

The guidance is important for registrants and collaborating laboratories in retrospectively assessing previously submitted studies for compliance, and prospectively aiding in study design and testing strategies to ensure compliance.

To learn more, I invite you to watch a webinar I conducted late last year to educate listeners on issues related to bound and non-extractable residues: evolving and competing definitions, extraction methodologies, analytical methodologies, the lack of previous guidance, and – especially - regulatory considerations and suggested best practices by walking the viewer through the new guidance.

You can access the webinar through our Resources portal, where you will also find other great information:

Webinar: "Strategies for Bound and Non-Extractable Residues in Laboratory Environmental Fate Studies"