Evaluation of heavy metal enrichment in Cochin estuary and its adjacent coast: multivariate statistical approach

摘要

Temporal and spatial variations of heavy metals in the Cochin estuary and its adjacent coastline during three seasons were studied to investigate the impact of anthropogenic heavy metal pollution. Total organic carbon, sand, silt, clay and 10 metals (Cd, Pb, Cr, Ni, Co, Cu, Zn, Mn, Mg and Fe) in the surface sediments were analysed. Multivariate statistical analyses like canonical correspondence analysis, principal component analysis and cluster analysis were used for source identification, integration of geochemical data and clustering of stations based on similarities. Enrichment factor, contamination factor and geoaccumulation index were used to assess the contamination level. From the study, it can be understood that estuary and coast are highly polluted especially with Cd, Zn, Pb and Ni. Anthropogenic influence of heavy metals was evidenced from both the principal component analysis and cluster analysis. Finer fractions (mud) of the sediment and the associated Fe oxy hydroxides might be playing major role in the transport of heavy metals in the system. Very high enrichment factor value observed suggested high anthropogenic pressure in the study area. All the stations in the northern part of the estuary showed very high enrichment factors indicating heavy load of Zn and Cd in this area which might have reached from the industrial area lying to the north side of the Cochin estuary. Pollution indices suggested that both the estuary and its adjacent coast were showing low contamination with respect to Cr, Mg, Mn and Fe; all other metals were causing low to extremely high levels of pollution in the study area.