**1. Introduction**

Soils in urban environments are strongly influenced by man, whose activity is based in these environments. The anthropogenic influence alters the processes of soil formation, often changing the direction of soil evolution. The human perturbation may vary in intensity, giving rise to a wide range of urban soils from quasi-natural to strongly disturbed soils. Human influence can interfere more or less intensely with the natural processes of soil formation, can provide exogenous materials, including pollutants, and can eventually build new soils by providing organic or mineral materials from which new processes of soil formation will start. Urban soils usually show a high vertical and horizontal variability, often contain artefacts, and are classified in the WRB [1] as Technosols.

On the other hand, urban soils provide considerable ecosystem services, such as supporting plant growth, including urban agriculture; taking part in biogeochemical cycles; contributing to the hydrological cycle; storing carbon and regulating greenhouse gases; modulating urban climate and air quality; contributing to urban biodiversity; supporting human activities; and intercepting and immobilizing or decomposing contaminants [2,3]. Therefore, having healthy urban soils is of paramount importance to enhance the quality of the urban environment and foster urban sustainable development.

The presence of high levels of trace elements and heavy metals is a major threat to the quality of urban soils, being of special concern in those involved in urban agriculture. A number of published articles studied potentially toxic elements (PTEs) in urban and peri-urban soils around the world [4–17]. Virtually all of them reported concentrations of heavy metals in urban soils higher than in natural soils.

The Cuban urbanization process is one of the oldest in the Americas. The urban population (8,637,568 inhabitants) constitutes 77% of the total residents of Cuba in 2018. Of this urban people, 2,131,480 inhabitants reside in the province of Havana [18]. One hundred percent of the province of Havana is urbanized. Given the size of the urban population, urban agriculture, which emerged in Cuba in 1987 as a programme of the Cuban Government, contributes significantly to local food self-sufficiency and to the country's food security [19]. Urban agriculture uses locally produced organic fertilizers with agro-ecological pest control and local seed production, avoiding the use of petrochemicals [19,20]. Along with urban agricultural soils, soils of parks and gardens, urban groves, and vacant areas constitute the urban soils of Havana.

This paper aims to study the concentrations and forms of PTEs in urban soils in the province of Havana, as a contribution to the knowledge of the quality of these soils, and to identify the possible origin of these elements. For such purposes, 35 urban soils were selected having a variety of uses (including urban agriculture) and intensity of human intervention.
