# Petkau effect

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The **Petkau effect** is an early counterexample to linear-effect assumptions usually made about [radiation](/source/Radiation) exposure. It was found by Dr. [Abram Petkau](https://en.wikipedia.org/w/index.php?title=Abram_Petkau&action=edit&redlink=1) at the [Atomic Energy of Canada](/source/Atomic_Energy_of_Canada) [Whiteshell Nuclear Research Establishment](/source/Whiteshell_Nuclear_Research_Establishment), [Manitoba](/source/Manitoba) and published in Health Physics March 1972.[1] The Petkau effect was coined by Swiss nuclear hazards commentator Ralph Graeub in 1985 in this book *Der Petkau-Effekt und unsere strahlende Zukunft* (The Petkau effect and our Radiating Future).[2]

Petkau had been measuring, in the usual way, the radiation dose that would rupture a simulated artificial [cell membrane](/source/Cell_membrane). He found that 3500 [rads](/source/Rad_(unit)) delivered in 2+1⁄4 hours (26 rad/min = 15.5 Sv/h) would do it.[3] Then, almost by chance, Petkau repeated the experiment with much weaker radiation and found that 0.7 rad delivered in 11+1⁄2 hours (1 millirad/min = 0.61 mSv/h) also ruptured the membrane. This was counter to the prevailing assumption of a linear relationship between total dose or dose rate and the consequences.[4]

The radiation was of ionizing nature, and produced negative [oxygen](/source/Oxygen) [ions](/source/Ion) (free radicals). Those ions were more damaging to the simulated membrane in lower [concentrations](/source/Concentration) than higher (a somewhat counter-intuitive result in itself) because in the latter, they more readily recombine with each other instead of interfering with the membrane. The ion concentration directly correlated with the radiation dose rate and the composition had [non-monotonic](/source/Non-monotonic_logic) consequences.

## Radio-protective effects of superoxide dismutase

Petkau conducted further experiments with simulated cells in 1976 and found that the enzyme [superoxide dismutase](/source/Superoxide_dismutase) protected the cells from free radicals generated by ionizing radiation, obviating the effects seen in his earlier experiment.[5][6] Petkau also discovered that superoxide dismutase was elevated in the [leukocytes](/source/Leukocytes) (white blood cells) in a sub-population of nuclear workers occupationally exposed to elevated radiation (*ca*. 10 mSv in 6 months), further supporting the hypothesis that superoxide dismutase is a radioprotective agent.[7] Thus, Petkau's original 1972 experiment apparently revealed the potential effects of ionizing radiation on cells without natural radioprotective mechanisms in place.

## References

1. **[^](#cite_ref-Petkau_1-0)** Petkau, A. (1972). "Effect of 22Na+ on a phospholipid membrane". *Health Physics*. **22** (3): 239–244. [doi](/source/Doi_(identifier)):[10.1097/00004032-197203000-00004](https://doi.org/10.1097%2F00004032-197203000-00004). [PMID](/source/PMID_(identifier)) [5015646](https://pubmed.ncbi.nlm.nih.gov/5015646).

1. **[^](#cite_ref-Graeub_2-0)** Graeub, Ralph (1985). *Der Petkau-Effekt und unsere strahlende Zukunft*. Zytglogge. [ISBN](/source/ISBN_(identifier)) [978-3729602229](https://en.wikipedia.org/wiki/Special:BookSources/978-3729602229).

1. **[^](#cite_ref-Petkau2_3-0)** Petkau, A. (1971). ["Radiation Effect with a Model Lipid Membrane"](https://doi.org/10.1139%2Fv71-196). *Canadian Journal of Chemistry*. **49** (8): 1187–1196. [doi](/source/Doi_(identifier)):[10.1139/v71-196](https://doi.org/10.1139%2Fv71-196).

1. **[^](#cite_ref-4)** Djurovic, Branka, MD, PhD, "Biological Effects of Ionizing Radiation", Slide 15, [Military Medical Academy, Belgrade, Serbia](/source/Military_Medical_Academy_(Serbia))

1. **[^](#cite_ref-Petkau4_5-0)** Petkau, A.; W.S. Chelack (1976-05-21). "Radioprotective effect of superoxide dismutase on model phospholipid membranes". *Biochimica et Biophysica Acta (BBA) - Biomembranes*. **433** (3): 445–456. [doi](/source/Doi_(identifier)):[10.1016/0005-2736(76)90272-8](https://doi.org/10.1016%2F0005-2736%2876%2990272-8). [ISSN](/source/ISSN_(identifier)) [0005-2736](https://search.worldcat.org/issn/0005-2736). [PMID](/source/PMID_(identifier)) [945071](https://pubmed.ncbi.nlm.nih.gov/945071).

1. **[^](#cite_ref-Petkau5_6-0)** Petkau, Abram (1978-04-03). "Radiation Protection By Superoxide Dismutase". *Photochemistry and Photobiology*. **28** (4–5): 765–771. [doi](/source/Doi_(identifier)):[10.1111/j.1751-1097.1978.tb07015.x](https://doi.org/10.1111%2Fj.1751-1097.1978.tb07015.x). [ISSN](/source/ISSN_(identifier)) [1751-1097](https://search.worldcat.org/issn/1751-1097). [PMID](/source/PMID_(identifier)) [366641](https://pubmed.ncbi.nlm.nih.gov/366641).

1. **[^](#cite_ref-Petkau3_7-0)** Petkau, A. (June 1987). ["Role of superoxide dismutase in modification of radiation injury"](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2149491). *The British Journal of Cancer. Supplement*. **8**: 87–95. [ISSN](/source/ISSN_(identifier)) [0306-9443](https://search.worldcat.org/issn/0306-9443). [PMC](/source/PMC_(identifier)) [2149491](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2149491). [PMID](/source/PMID_(identifier)) [3307878](https://pubmed.ncbi.nlm.nih.gov/3307878).

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Adapted from the Wikipedia article [Petkau effect](https://en.wikipedia.org/wiki/Petkau_effect) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Petkau_effect?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.