Heavy metals in sediment cores from a tropical estuary affected by anthropogenic discharges: Coatzacoalcos estuary, Mexico

Large scale industrial development has taken place in the Coatzacoalcos river estuary, SE Mexico, over the last 32 years, and the area is now regarded as the most polluted coastal area of Mexico. A series of sediment cores were taken from the lower Coatzacoalcos river and the estuary, and the concentrations of trace elements (Zn, Co, Cu, Cr, Ni, Pb, V), major elements (Al, Si, Mn, Fe, Ti, Ca, Mg, Na, K, P) and organic matter determined. Heavy metal concentration seems to be largely dependant on proximity to industrial areas, with highest metal concentrations (particularly for Zn, Ni and Cu) found at Teapa, the most heavily industrialized site, and lowest values found at Jicaro, upstream of the main industrial areas. At all of the sites examined, heavy metals either show a relatively uniform distribution with depth, or subsurface maxima, which reflect changes in sediment composition. There is little evidence for significant early-diagenetic remobilization at any of the sites studied. 210Pb and 137Cs data at Teapa indicate that the sediments have accreted rapidly and may be vigorously mixed, and so these sediment cores cannot be used to reliably reconstruct temporal changes in pollutant input.