Metal uptake in a peri-urban Lactuca sativa cultivated area

Abstract

In this study, two Lactuca sativa crops grown in a net-protected site and an unprotected site were compared. The results showed metals were accumulated by Lactuca sativa. Higher metal accumulation in lettuce grown in the unprotected parcel was established, and the only significant differences in their physicochemical properties were cation exchange capacity and exposure to sunlight. Exposure to the sun may translate into higher soil–plant flux of water and/or higher decomposition rate of organic matter, which may augment the mobilization of metals into the plant, and therefore lead to higher noxious metal accumulation on the crops. Also, EDTA was explored as a possible extractant that could predict the bioavailablity of metals to the lettuce. Our results did not show a good agreement between the metal transferred from soil to leaves and the EDTA extracted metals, although some tendencies were found for the metal transfer from soil to roots. It is predicted that many developing countries will continue and/or increase the use of waste water for the irrigation of crops despite the health risks. Different solutions have been explored to diminish the availability of the metals in the soils. Our study shows that an action as simple as placing a net over the parcel could help diminish the accumulation of metals into the crops of a rapidly expanding peri-urban agricultural system.

Keywords:

• Metals
• bioaccumulation
• Lactuca sativa
• evapotranspiration
• peri-urban agriculture

Notes

*Significant differences between the inprotected and protected parcels (P < 0.05).

*Significant differences at P < 0.05 between the protected and unprotected parcels.

^a Values recommended by the Mexican Secretary of Environment and Natural Resources.^{[ 47 ]}

^b Values recommended by Canadian Environmental Quality Guidelines for Agricultural Soils.^{[ 48 ]}

^c Values found in lettuce leaves by the Food and Drug Administration.^{[ 25 ]}

*Significant correlation; + positive correlation; − negative correlation.