Assessment of heavy metal pollution of drain sediments in the urban area of Mexicali, Mexico

The valley of Mexicali is one of the most important agricultural areas in the northwest of Mexico. Rapid urbanization has meant that parts of the agricultural channels and drains now lie within the urban area. To evaluate the concentrations of heavy metals in urban drain sediments, thirty-one samples were collected in the Mexicali urban area. Mean concentrations of Cd, Cu, Cr, Fe, Ni, Pb and Zn were 0.28, 70.0, 17.0, 4.48 × 10 .4, 13.5, 32.3 and 229 mg kg^{− 1}, respectively. The geoaccumulation index results indicated that most of the drain sediments were from unpolluted to slightly polluted by heavy metals for most of the sites, with the exception of Cu which had seven sites Class 3, two sites Class 4 and two sites Class 5 and 6, respectively. Similarly, the enrichment factors showed that most of the sites had minimum enrichment.