Ionising Radiation, Low Dose, Radiation Hormesis

Radiation science is dominated by a paradigm based on an assumption without empirical foundation. Known as the linear no-threshold (LNT) hypothesis, it holds that all ionizing radiation is harmful no matter how low the dose or dose rate. Epidemiological studies that claim to confirm LNT either neglect experimental and/or observational discoveries at the cellular, tissue, and organismal levels, or mention them only to distort or dismiss them. The appearance of validity in these studies rests on circular reasoning, cherry picking, faulty experimental design, and/or misleading inferences from weak statistical evidence. In contrast, studies based on biological discoveries demonstrate the reality of hormesis: the stimulation of biological responses that defend the organism against damage from environmental agents. Normal metabolic processes are far more damaging than all but the most extreme exposures to radiation. However, evolution has provided all extant plants and animals with defenses that repair such damage or remove the damaged cells, conferring on the organism even greater ability to defend against subsequent damage. Editors of medical journals now admit that perhaps half of the scientific literature may be untrue. Radiation science falls into that category. Belief in LNT informs the practice of radiology, radiation regulatory policies, and popular culture through the media. The result is mass radiophobia and harmful outcomes, including forced relocations of populations near nuclear power plant accidents, reluctance to avail oneself of needed medical imaging studies, and aversion to nuclear energy—all unwarranted and all harmful to millions of people.

Sono riportati in letteratura risultati di irraggiamenti di specie vegetali con radiazione ‘ultravioletta C’ (UV-C), che evidenziano una drastica riduzione della presenza di patogeni e di malattie pre- e post-raccolta delle colture. Si tratta di una promettente tecnologia alternativa ai pesticidi, l’uso dei quali deve essere ridotto perché contribuisce all’inquinamento di suolo, acqua,  aria, e rappresenta un rischio per la salute di operatori e consumatori. I migliori effetti germicidi UV-C sono stati ottenuti usando lampade a mercurio a bassa pressione, che emettono radiazione alla lunghezza d’onda di 254 nm. Viceversa, i tentativi di ottenere effetti di ormesi usando lo stesso tipo di lampade hanno prodotto risultati incerti. Per ormesi intendiamo la stimolazione -tramite radiazione UV-C- di metaboliti in grado di aumentare le difese immunitarie naturali delle piante e quindi la resistenza ai patogeni.
In questo Rapporto si descrive l'efficacia dei raggi UV-C alla lunghezza d’onda di 277 nm, emessi da matrici di Light Emitting Diodes (LED), per generare una risposta ormetica in piante di basilico, frutti di mele, fragole e limoni dopo irraggiamento ed esposizione ai patogeni fungini Botrytis cinerea e Pennicillium digitatum. I LED sono sorgenti di radiazione a stato solido che offrono diversi vantaggi rispetto alle lampade: sono più compatti, hanno maggiore resistenza agli urti, tempo di accensione immediato, possibilità di scegliere la lunghezza d’onda della radiazione UV-C tale da accordarsi sullo spettro di assorbimento dei patogeni senza
generare ozono, ed un’alimentazione elettrica più semplice, a basso voltaggio.

Abstract
Excellent results have been reported on ultraviolet C (UV-C) radiation to limit pre- and post-harvest diseases of fruit and vegetable crops. UV-C radiation appears a promising and sustainable technological substitute for pesticides, the use of which must be reduced because it damages the environment, and the health of operators and consumers. The best germicidal effects have been obtained using lowpressure mercury lamps, which emit radiation at a wavelength of 254 nm. Conversely, attempts to obtain hormesis effects using mercury lamps have produced uncertain results. Here for hormesis we mean a stimulation -through UV-C electromagnetic radiation- designed to increase the natural immune defenses, and therefore, resistance to pathogens. We have explored the effectiveness of a different UV-C wavelength (277 nm) emitted by Light Emitting Diodes (LED) to stimulate hormesis in basil plants, apples, strawberries, and lemons, after irradiation and exposure to the fungal pathogen Botrytis cinerea and Pennicillium digitatum. The LED are solid-state UV-C radiation sources that offer several advantages vs. the lamps: LED are much more compact, have greater resistance to shocks, shorter ignition time, a simpler electrical circuitry with a lower working voltage.

The paper presents the concept of balance equation as a result of jostling process between detrimental and beneficial factors due to ionising radiation impact on the human population. The Lotka-Volterra equation was used to describe the evolution process of the population in low-dose radiation environment. The balance equation, which is a result of Lotka-Volterra's equation stabilisation over time, describes correctly most of the human population, wherein the probability of detrimental (cancerous) processes equals the probability of beneficial (hormetic) processes. It concludes that most of people respond via threshold dose-response curve, while radiosensitive people respond using linear model and radioresistant people respond using hormetic one.

The paper is composed of two parts: a review of a group of experiments among irradiated plants and own search for radiation hormesis in a single experiment. In the first part the Bayesian analysis of the hormetic-like data published so far shows that the NOAEL (no observed adverse effect level) point, above which adverse effects appear, may be located between 30 and 100 Gy. In the second part the influence of low doses of ionizing radiation was tested on the particularly fast growing plant, namely the cress (Lepidium sativum L.). Two experimental scenarios were used: in the first one the cress was irradiated during the growth (maximal dose 2.3 Gy), while in the second scenario dry seeds were irradiated (maximal dose 100 Gy). The experiment indicates that the NOAEL point lies above 100 Gy and statistically insignificant hormetic effect can be seen between 0.1 and 14 Gy. No linear reaction is observed in the full range of doses.