Sustainability 2023, 15, 4022. https://doi.org/10.3390/su15054022 www.mdpi.com/journal/sustainability Review Graffiti Paint on Urban Trees: A Review of Removal Procedures and Ecological and Human Health Considerations † Valentina Roviello 1,‡ , Melinda Gilhen-Baker 2,‡ and Giovanni N. Roviello 3, * 1 Department of Chemical, Materials, and Industrial Production Engineering (DICMaPI), University of Naples Federico II, Piazzale V. Tecchio 80, 80125 Naples, Italy 2 National Trust, Bowe Barn, Borrowdale Road, Keswick CA12 5UP, UK 3 Institute of Biostructures and Bioimaging, Italian National Council for Research (IBB-CNR), Area di Ricerca Site and Headquarters, Via Pietro Castellino 111, 80131 Naples, Italy * Correspondence: giroviel@unina.it; Tel.: +39-08-1220-3415 † Dedicated to the Memory of Frank Nigel Hepper, botanist at the Royal Botanic Gardens, Kew, UK. ‡ These authors contributed equally to this work. Abstract: Mature trees play a fundamental role in nature and are crucial to maintaining good air quality in the urban ecosystem where they reduce air pollution, lower the surface temperature, and emit medicinal volatile organic compounds which combine to improve human health and mental wellbeing. From an aesthetic and cultural point of view, they are true living monuments to be pre- served. In both rural and city environments, it takes numerous years for trees to become mature enough to have a significant impact on our health and the current global climate changes together with high levels of pollution in urban environments and other anthropic factors such as vandalism constitute important obstacles to new tree growth. This clearly makes existing trees, especially old growth, far more valuable than we often realize. Regardless of their artistic quality and in some instances their positive messages, graffiti are still unacceptable on living organisms, especially older urban trees. They also have a significant environmental impact due to the emissions related to graf- fiti that are primarily based on anthropogenic volatile organic compounds (VOCs) which contribute to the formation of ground-level ozone. We reviewed the literature on graffiti and paintings applied on tree bark and ultimately found that oil-based paints in particular can damage tree life support systems. We herein also discuss graffiti prevention, the potential impact on human health related with graffiti removal, as well as methods for tree bark cleaning including, as suggested by different urban forestry specialists, the application of citrus-based products for 20–60 min before rubbing and rinsing or multiple 1–2 h treatments, in the case of recent or old graffiti, respectively. Keywords: graffiti; tree-bark: paintings; vandalism; nature conservation; volatile organic compounds; old-growth trees 1. Introduction By the word ‘graffiti’ one usually indicates messages, scribbles, patterns, or drawings written, carved, or painted on different types of surfaces including walls, monuments, and tree bark. Consequently, a ‘graffitist’ is a person who creates graffiti [1]. Graffiti has existed as long as human society but has become a public issue in recent decades, being often considered as a recurrent and unacceptable form of vandalism. The engravings and paintings of wild fauna in the Lascaux caves in the Dordogne region, France and the Ro- mito grotto in Papasidero, Italy are said to date from more than 10,000 years before the Common Era [2,3]. Similar representations realized thousands of years ago on boulders, rock faces, and cave walls still exist in Australia, Africa, and Asia [4]. Ancient graffiti of various natures are found on the walls of the city of Pompeii, and on Egyptian monu- ments, to cite just a few examples [5]. Through the centuries, numerous people have left Citation: Roviello, V.; Gilhen-Baker, M.; Roviello, G.N. Graffiti Paint on Urban Trees: A Review of Removal Procedures, and Ecological and Human Health Considerations. Sustainability 2023, 15, 4022. https://doi.org/10.3390/ su15054022 Academic Editor: Asterios Bakolas Received: 10 January 2023 Revised: 17 February 2023 Accepted: 20 February 2023 Published: 22 February 2023 Copyright: © 2023 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and con- ditions of the Creative Commons At- tribution (CC BY) license (https://cre- ativecommons.org/licenses/by/4.0/).