Donald Mackay

1936 - 2023

Donald Mackay (1936 – 2023): The Architect of Fugacity in Environmental Chemistry

Donald Mackay was a visionary chemical engineer and environmental scientist whose work fundamentally transformed how humanity understands the movement of pollutants through the global environment. By translating complex thermodynamic principles into accessible mathematical models, Mackay provided the "Rosetta Stone" for predicting how chemicals distribute themselves between air, water, soil, and living organisms.

1. Biography: From the Clyde to the Otonabee

Donald Mackay was born on October 30, 1936, in Glasgow, Scotland. His early life in a major industrial and shipbuilding hub likely influenced his interest in engineering. He attended the University of Glasgow, earning his B.Sc. (1958) and Ph.D. (1961) in Chemical Engineering.

After a brief stint in the petrochemical industry with Imperial Chemical Industries (ICI), Mackay immigrated to Canada in 1967. He joined the Department of Chemical Engineering and Applied Chemistry at the University of Toronto. It was here that he began shifting his focus from traditional industrial engineering to the emerging field of environmental science.

In 1995, Mackay moved to Trent University in Peterborough, Ontario. There, he founded the Canadian Environmental Modelling Centre (CEMC). This move marked a prolific era where he synthesized decades of research into tools used by regulatory agencies worldwide. He remained active as a Professor Emeritus until his passing on October 20, 2023, just shy of his 87th birthday.

2. Major Contributions: The Fugacity Revolution

Mackay’s most significant contribution was the application of the thermodynamic concept of fugacity to environmental modeling.

The Fugacity Concept

In chemistry, fugacity (from the Latin fugere, "to flee") represents the "escaping tendency" of a substance. Before Mackay, scientists struggled to track chemicals as they moved between different phases (e.g., from a lake into the air). Mackay realized that while concentrations change wildly across different media, fugacity provides a "common currency." When two phases are in equilibrium, their fugacities are equal, even if their concentrations are vastly different.

The "Mackay Models" (Levels I–IV)

He developed a hierarchy of models to predict chemical behavior:

Level I: Simplest equilibrium distribution in a "unit world."
Level II: Includes equilibrium plus degrading reactions and advection (flow).
Level III: Describes a "steady-state" world where phases are not necessarily in equilibrium—the most widely used regulatory model.
Level IV: Dynamic models that account for changes over time (e.g., how long it takes for a lake to recover after a factory closes).

PBT Assessment

He was a pioneer in defining the criteria for Persistence (P), Bioaccumulation (B), and Toxicity (T), which are now the standard benchmarks for identifying "forever chemicals" like PFAS and PCBs.

3. Notable Publications

Mackay was a prolific author with over 600 peer-reviewed papers. His most influential works include:

Multimedia Environmental Models: The Fugacity Approach (1991, 2nd Ed. 2001): Often referred to as the "bible" of environmental modeling, this book translated complex thermodynamics into a practical handbook for scientists and regulators.
"Finding Equilibrium in the World of Fugacity" (1979): Published in Environmental Science & Technology, this paper introduced the fugacity concept to the broader scientific community.
"Global Fractionation and Cold Condensation of Low Volatility Organochlorine Compounds in Polar Regions" (1993): Co-authored with Frank Wania, this paper explained why chemicals used in the tropics end up in the bodies of Arctic polar bears (the "Grasshopper Effect").

4. Awards & Recognition

Mackay’s impact was recognized by both the scientific community and the Canadian government:

Order of Canada (2003): Appointed an Officer for his contributions to environmental chemistry.
The Honda Prize (2001): An international award for "Eco-Technology," often regarded as a prestigious precursor or equivalent to a Nobel for environmental engineering.
SETAC Founder’s Award: The highest honor from the Society of Environmental Toxicology and Chemistry.
Fellow of the Royal Society of Canada: Elected for his outstanding scholarly achievements.

5. Impact & Legacy: From Theory to Treaty

Donald Mackay’s work did not stay confined to textbooks; it shaped international law. His models were instrumental in the development of the Stockholm Convention on Persistent Organic Pollutants (POPs), a global treaty to eliminate or restrict chemicals that remain in the environment and climb the food chain.

Today, if a company wants to register a new pesticide or industrial chemical, they must provide data on its environmental partitioning—data that is processed using the "Mackay-type" models. He shifted environmental science from a reactive field (measuring damage after it happened) to a predictive field (preventing damage before a chemical is mass-produced).

6. Collaborations

Mackay was known for his "open-door" philosophy and mentored generations of scholars.

Sally Paterson: A long-time research associate at the University of Toronto who co-authored many of the foundational fugacity papers.
Frank Wania: A former student who became a leading expert on the global transport of pollutants and the "Grasshopper Effect."
The "Trent School": At Trent University, he collaborated with researchers like Tom Hutchinson and Chris Metcalfe, cementing the university's reputation as a global hub for environmental toxicology.

7. Lesser-Known Facts

The "Back-of-the-Envelope" Master: Despite his mathematical prowess, Mackay was famous for his ability to estimate a chemical’s fate on a napkin. He often told students:
"If you can't describe the problem simply, you don't understand the physics."
A Love for the Sea: Reflecting his Scottish roots, Mackay was an avid sailor. His understanding of fluid dynamics wasn't just academic; it was lived on the water.
The "Mackay Glass": He developed a physical laboratory device, known as a "thin-film personal sampler" or a variation of a "Mackay Glass," to physically measure how chemicals move between air and water, proving his theories with empirical hardware.
The "Unit World": To make his models work, he invented a hypothetical "Unit World"—a square kilometer containing specific proportions of air, water, soil, and sediment. This simplified "imaginary planet" allowed scientists to compare different chemicals on a level playing field.