Environmental impact of heavy metal concentration in the Coatzacoalcos River, Veracruz, Mexico

Abstract

A quantitative environmental impact study on heavy metal concentration (Cr, Cu, Mn, Cd, Pb, Co and Ni) in the water, sediments and benthic fauna of the Coatzacoalcos River, Mexico was carried out to establish relationships between heavy metal concentration and human activity (urban and agricultural activities). The Coatzacoalcos River is characterized by one of the largest estuarine systems in the eastern coast of Mexico, and exhibits a large diversity of mangroves, palm trees and terrestrial invertebrates. However, the river has suffered from impacts of petrochemical activities in the past. Sediments, water and benthic fauna were collected during four sampling periods in September 1996 (rainy season), January 1997 (dry season), April 1997 (dry season) and August 1997 (rainy season). Dry sieving of the sediments was carried out. Also in situ measurements of organic matter content and heavy metal concentration were determined for seventeen river stations. The first and fourth samplings showed that most sediment in the Coatzacoalcos River is transported by suspension during the rainy season. The second and third sampling showed saltation as the main mode of transport during the dry season. Nine stations in the river were environmentally impacted by industrial and urban discharges leading to high Cu and Cr concentration values in water and sediments. Poor recovery of benthic organisms was observed for most Coatzacoalcos River stations. Depletion of benthic organisms was due to intensive dredging activity in the past decades as well as low O2 values in the water column. Bivalves, Rangia concentrate 1.1 times more Cu than Cr than others Polimesoda from sediments. Polimesoda carolineana, Rangia cuneata and Rangia flexuosa concentrate 2.2 times more Cr than Cu from water. Rangia also concentrates 4.2 times more Cu than Cr in sediments. This suggests that the three species have an efficient excretory system to tolerate and eliminate the excess of Cu. A varimax rotated factor analysis showed that the highest impacted stations of the Coatzacoalcos River area Página 1 de 21