Heavy metals in the fine fraction of coastal sediments from Baja California (Mexico) and California (USA)

The concentrations of heavy metals in the fine fraction ( < 63 mu m) of 19 surficial sediment samples from the border region of Baja California (Mexic o) and California (USA) were determined. The concentration ranges (in mu g g(-1)) of the metals were: Cu, 4.9-23; Zn, 39-188; Ni, 16-44; Cr, 56-802; P b, 6-21; Cd, 0.08-0.64; Ag, 0.01-0.28; and Mn, 392-1506; the intervals (per centage) for Fe and Al were 1.36-4.6 and 3.61-8.55, respectively. The heavy metals in these sediments indicate a relative enrichment of Cr (> 3000%), Zn (> 350%), Ni (> 300%) and Cu (> 150%) off the wastewater outfall at Punt a Bandera in Tijuana, Baja California, with respect to non-polluted sedimen ts of the region. Pb, Cd and Ag have low concentrations off the same outfal l and enrichment factors are generally lower than 300% (Pb) and lower than 150% (Cd and Ag). This suggests that these metals have a different origin, or that they are controlled by a different geochemical mechanism than the f ormer. The concentrations of Mn, Fe and Al occurred within ranges typical f or coastal areas and probably reflect the mineralogical composition of the sediments of the region. (C) 2000 Elsevier Science Ltd. All rights reserved .