Urban activities release particles into the environment that can contain considerable amounts of metals and metalloids which may enter the trophic chain including humans, potentially negatively affecting health. In this sense, although the practice of Urban Agriculture is increasing as an ecological and economic alternative, it must be considered that urban contamination can represent a human health problem. 

In Mexico City, the practice of UA has been promoted by the local government since 2016 while making minimal or no mention of the
considerations required to prevent crops from being contaminated with metal(loid)s.

Soil to plant metal(loid) accumulation has been highly evaluated in recent years due to its significant impact on human health. A recent study reports the concentrations of 15 metal(loid)s in four vegetables (tomato, onion, chili, and lettuce) cultivated in one greenhouse, one top garden, and two roof gardens, rooftop urban gardens in four locations within the metropolitan area of Mexico City.

In this experiment, the contribution of metals and metalloids due to atmospheric deposition and irrigation may be negligible. It is considered that the concentration of metals depends only on transfer from the soil.

Soil analysis indicates that only vanadium in one location (a rooftop garden in V. Carranza) exceeds the permissible limits recommended by the Mexican government. For most metals, lettuce shows the highest concentrations and transfer factors compared to the other vegetables studied. The transfer factors were exceptionally high for Cd (lettuce) and Hg (tomato), presenting values above 1.

The concentrations of As, Cd, Hg, and Pb were compared with permissible limit values recommended for vegetables by different international agencies. It was observed that, except for As, these values are exceeded in various vegetables harvested in this study. This information must be corroborated with more detailed studies evaluating the chemical species in which those metal(loid)s is present and identifying the physicochemical parameters of the soil that caused the enrichment of these metal(loid)s to exceed the permissible limit values.

Read the complete research here.

Alonso-DurĂ¡n, Ivonne & Alvarez-Hernandez, Elizabeth & Morton-Bermea, Ofelia & Castro-Larragoitia, Javier & Ortega, Margarita. (2021). How Healthy Are Horticultural Plants Grown in Polluted Cities? The Case of Mexico City. 10.21203/rs.3.rs-526187/v1.