Historical trends of metal pollution recorded in the sediments of the Culiacan River Estuary, Northwestern Mexico

The accumulation of selected trace metals (Cd, Co, Cu, Ni, Pb and Zn) was studied in a sediment core collected in a shallow sandy area at the upper estuary of the Culiacan River. The chronology was developed by using the accumulation rates determined previously from 210Pb analyses of the same core. Trace metal concentration began to increase over background levels at depths corresponding to the late 40s and reached a maximum at the present time, excepting for Cd and Pb. The observed profile trends were related to population growth, and significant relationships between organic C and Cd, Cu and Zn indicated that such metals are mainly delivered to the estuarine sediments from a common source, identified as sewage wastes. Excess metal inventories and metal concentration factors indicated a slight pollution by all the trace metals examined, although levels of enrichment for Ni and Pb (Concentration Factors less-than-or-equals, slant1.5) were considerably less than those found for Co, Cd, Zn and Cu (CFʹsnot, vert, similar3). However, the concentrations of Cu, Pb and Ni were considered as potentially toxic and therefore, these metals must be considered pollutants of concern and further investigation (e.g. biological and chemical testing) is strongly recommended.