Essential and non-essential elements in lettuce produced on a rooftop urban garden in São Paulo metropolitan region (Brazil) and assessment of human health risks

Abstract

Urban agriculture is considered an important solution to food security. Rooftops are a new addition to possible places to grow vegetables due to urban land being limited and expensive. However, urban agriculture can be a risk in the case that vegetables are contaminated with heavy metals via atmospheric deposition because of traffic emissions. Among the vegetables, lettuce stands out as one of the most popular in Brazilian food and it is a very important vegetable for the human diet, but its consumption is the most common route for human exposure to toxic metals. The objective of this study was to evaluate the essential and non-essential elements in lettuce cultivated on a rooftop urban garden developed by Agronomy College within the metropolitan region of São Paulo, Brazil. In addition, to assess the human health risks associated with the potentially toxic metals based on the estimated daily intake (EDI) and the target hazard quotient (THQ), and to access the possible sources of heavy metal contamination by multivariate statistical. Instrumental neutron activation analysis, graphite furnace atomic absorption spectrometer, and inductively coupled plasma optical emission spectrometry were applied to determine the elemental concentration in lettuce leaves. This study demonstrated that lettuces grown on a rooftop are sources of essential macronutrients such as potassium, calcium, and magnesium and have lower concentrations of trace elements. The Cd, Cu, and Pb concentrations did not exceed the Brazilian legislation limit. The Ba, Co, Cr, Ni, and Pb presented low levels compared to oral reference dose (RfD). The results of the cluster analysis showed that Ni, Cr, Co, and Pb may be associated to vehicles emissions. Both EDI and THQ values suggested minimal risk upon consumption of lettuce.