# Temporal Variations of Heavy Metal Sources in Agricultural Soils in Malta
## 1 Introduction  
Maltese soils are a natural resource with agricultural, environmental, and cultural value which have undergone human influence over time and due to intensive land-use are experiencing erosion, loss of organic matter, structural deterioration and chemical contamination from excess nitrates and salinity [1]. Desertification is another issue identified within Malta's ecosystem intensifying environmental problems resulting from changes in agricultural practices and increased urban development. Malta unfortunately ranks above the EU average for artificial land coverage with 23.6%, which correlates with a high percentage in population density [2]. The total cultivated area in Malta is around 10,000 hectares amounting to approximately 18.9% of the total land area [1]. An annual soil loss of 19.3% which equates to 10-25 tons per hectare per year indicates that Maltese north-western and Gozitan areas are at the risk of moderate to severe soil erosion [2]. This erosion is very typical of high inclination in arable land areas where poor management and conservation practices are used. The fragmentation of soil reduces its economic viability costing an average agricultural farmer in Malta \(\epsilon\) 1164.24 per 0.01 km\({}^{2}\) per year to replace eroded soils and artificially maintain the soil quality in eroded zones [2]. Malta has registered 135 zones that are undergoing potentially polluting activities in the issued JRC report in the EU and has remediated one registered site. According to the RUSLE2015 model, Malta has an average soil loss rate of 6.02 tons per hectare per year, which is high compared to the EU average of 2.46 tons per hectare per year [2]. Such data depends on the conditions of each individual country and proves that soil degradation is of high importance becauseof its role in carbon cycling and climate change. The pH level for 56% of Maltese soil lies between 8 and 8.5; thus, soil in Malta has a slightly alkaline pH [3]. There are three main soil types in Malta: Terra Rossa soil, Xerorendzina soil, and Carbonate Raw soil [3]. These have been subdivided into subgroups according to the area of location. As reported by [PERSON] in 1960 [3], the soil types found in the sampling zone are Terra Rossa, Xerorendzina, and the L-Iklin and Tad-Dawl complexes. Terra Rossa soil is a red clay-like soil resulting from both types of coralline limestone existing on the island. Its reddish color is derived from the high iron oxide content and has a calcium carbonate content of 2-15%. Xerorendzina soil ranges from a whitish to red soil with a calcium carbonate content of 58-80%. It is a constituent of Globigerina limestone which is made up of clay and lime [3]. Calcisol soil is characterized by calcium carbonate concentrations which are found as coatings on the soil structure faces. Such Calcisol horizons are present in the lower topsoil or subsoil horizons, are rich in lime and form in dry areas. If their dryness factor is adequately controlled through irrigation, drainage, and fertilization to prevent salinization, Calcisol soil is highly productive for crops [3]. A heavy metal is a dense metal with high atomic weight which is toxic at low concentration. Heavy metals are regarded as pollutants in soil because of their persistence and toxicity upon high concentration or unwanted presence. Since agricultural and industrial processes have changed over time due to modernization, several geo-chemical cycles, degradation processes, and ecosystem functions have been altered leading to significant concern over their polluting effects [4]. Trace elements accumulated in the soil are mainly due to industrial, mining, agricultural practices, and the disposal of waste from communal sources. Several trace elements have essential metabolic functions in living organisms, but some others influence the biological, chemical, and morphological traits in plants, animals and humans upon physical contact, inhalation, or ingestion [5].