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Understanding the Life Cycle Impact Assessment Process: Part II – Modeling Exposure: Intake and Bioavailability

Life Cycle Impact Assessment (LCIA) is a central element of Life Cycle Assessment (LCA) -- the point in the LCA process where potential environmental impacts of a product or service are identified and quantified.
Cause and Effect chain for modeling environmental impactsExhibit 1: Cause-effect chain for modeling environmental impacts
This is part two of a three-part series that reviews the three distinct phases of LCIA impact modeling (fate, exposure, and effect (Exhibit 1)), and explains how they build on one another to create a usable picture of environmental impacts for use in broader analyses.
As discussed in Part I, the LCIA process uses mathematical models to predict the possible outcomes of an upstream decision. These models can mimic the natural processes the emission will go through -- and the impact it will have on human health and plant and animal species.

We’ve already reviewed the use of fate modeling to account for the characteristics of an emission and the environmental concentration it forms once released. With this information in hand, we can move on to exposure modeling, which looks at the intake level of the emission by considering various routes and modes of intake; for ecosystems, exposure models consider the amount of the emission that becomes bioavailable. (Our upcoming Part III will look at modeling of effects of the intake by organisms.)

An exposure factor for a pollutant links the fate factor to the intake level (for humans) or the amount that becomes bioavailable (for other organisms) via a specific environmental medium (air, water or soil).

For humans, exposure can occur through various routes, including inhalation, ingestion and absorption through skin (Exhibit 2). Modeling of exposure through water and soil can be more complex than exposure through air, simply because of the large variety of food and drink that humans consume. Generally, exposure to pollutants in water occurs through direct consumption of the water, or indirectly through consumption of seafood. For pollutants in soil, exposure can occur through food or direct ingestion or inhalation of dust.

Human exposure routes

Exhibit 2: Exposure routes for humans


Exposure equation
Equation 1: Expressions for calculating human and ecosystem exposure
To model exposure pathways as accurately as possible, current toxicity models include a wide range of foods including most grains, fruits, vegetables, dairy products, meat and fish. The expressions in Equation 1 can be used to calculate exposure for humans and ecosystems.
We will wrap up our discussion of LCIA in the upcoming Part III of this series, with a look at effect modeling – the stage where we connect our exposure data to known toxicity data, and estimate the adverse effects at given exposure levels.

We hope you’re finding this discussion of LCIA useful; if you have questions or comments, please feel free to post them below!
For full information about sources referenced in this series, please visit our LCIA Bibliography.

For more information on impact assessment methods and models, please see the free online course on impact assessment and the free brown bag webinars offered by Earthshift Global.


Articles in This Series

Understanding Life Cycle Impact Assessment Process:  Part I – Overview and Fate
Understanding Life Cycle Impact Assessment Process:  Part II – Modeling Exposure: Intake and Bioavailability
Understanding Life Cycle Impact Assessment Process:  Part III - Modeling Effects and Conclusion


About the Authors

photo of Harnoor Dhaliwal, certified life cycle assessment consultant at EarthShift Global.Harnoor Dhaliwal is a certified LCA consultant at EarthShift Global. She holds a Bachelor’s degree in Botany from University of Delhi, India, and a Master’s degree in Environmental Policy Studies from New Jersey Institute of Technology. She did her graduate research work on sustainable remediation of contaminated sites. At EarthShift Global, Harnoor has carried out ISO-compliant Life Cycle Assessment studies on products including biofuels, packaging materials, food products, medical and pharmaceutical products, and industrial equipment. She has also developed and taught LCA courses. Her current focus is evaluating social Life Cycle Assessment and its application.

Pete Dunn is EarthShift Globals marketing consultant and a freelance strategist and writer.Pete Dunn, EarthShift Global’s marketing consultant is an entrepreneurial marketing and communications strategist and writer, serving clients in academia, technology and B-to-B marketing. His journalism background includes eight years as founder, editor and publisher of WaferNews, the leading news publication for the international semiconductor manufacturing community. He specializes in creative collaboration and translating complex subjects into clear messages that inform and inspire.


Goedkoop, M. and R. Spriensma (1999). The Eco-indicator 99. A damage oriented method for life cycle impact assessment. Methodology report and annex. Pré Consultants, Amersfoort, the Netherlands.

Hauschild M.Z., Huijbregts M., Jolliet O., Macleod M., Margni M., Dik van de Meent, Rosenbaum R.K., McKone T. E. (2008). Building a Model Based on Scientific Consensus for Life Cycle Impact Assessment of Chemicals: The Search for Harmony and Parsimony. Environmental Science &Technology, 2008, 42 (19), pp 7032–7037.

Huijbregts MAJ, Thissen U, Guinée JB, Jager T, Van de Meent D, Ragas AMJ, Wegener Sleeswijk A, Reijnders L. 2000. Priority assessment of toxic substances in life cycle assessment, I: Calculation of toxicity potentials for 181 substances with the nested multi-media fate, exposure and effects model USES-LCA. Chemosphere 41:541-573.

IPCC Fourth Assessment Report: Climate Change 2007 (AR4), 2007.

Kounina, A., Margni, M., Shaked, S., Bulle, C., Jolliet, O. 2014. Spatial analysis of toxic emissions in LCA: A sub-continental nested USEtox model with freshwater archetypes. Environment International 69 (2014) 67–89.

Van Jaarsveld, JA. 1995. Modelling the long-term atmospheric behaviour of pollutants on various spatial scales. PhD thesis. University of Utrecht, Utrecht, The Netherlands.