Assessing soil contamination and temporal trends of heavy metal contents in greenhouses on semiarid land

Information about the behavior and temporal evolution of heavy metals in agricultural soils is limited, particularly about greenhouse soils on semiarid lands, indeed it nonexistent. Western Almeria (Southern Spain) is a semiarid land where some 30,000ha are occupied by greenhouses with high productivity. As these greenhouses are fundamental to the socioeconomic development of this area, they should be maintained and well conserved. However, there are indications that long-term intensive agriculture with considerable agrochemicals use can deteriorate soil quality, which in turn, would reduce productivity and food quality. This study was conducted to investigate soil contamination and the temporal trends of heavy metal concentrations in greenhouse soils of western Almeria. Contamination level, availability, and sources of metals were evaluated by the extractable fraction percentage, by indices zinc equivalent, geoaccumulation, enrichment factor and pollution load, and by a correlation analysis between soil properties and metal contents. The results showed that the total contents of Cd, Cu, Ni, and Pb, and the available concentration of Cd, Cu, Pb, and Zn, were significantly higher than background levels. Temporal patterns indicated that these elements accumulate in greenhouse soils. After more than 20years of intensive agriculture, the available concentration of elements, and contamination, had clearly increased.