The content and pollution evaluation of heavy metals in surface seawater in Dalian Bay

Surface seawater samples at 23 sites in the offshore area of Dalian Bay were collected in November 2014 and May 2015, to investigate the concentration and pollution characteristics of the six heavy metals (Cu, Pb, Zn, Cd, Hg and As) in that area. The heavy metals pollution condition was evaluated using single factor pollution index evaluation method and comprehensive pollution evaluation method, the variation coefficient method was used to analyze the dispersion degree of pollutants on the spatial scale between the stations, and the correlation analysis and PCA method was used to study the main resources of heavy metals pollutants. The results showed that the average value of Cu, Pb, Zn, Cd, Hg and As met the I water quality requirements of the seawater water quality standard The single factor pollution index values of the six heavy metals in the two seasons were in the following order: Cu>Pb> Zn > Hg > Cd > As. The evaluation result of the comprehensive pollution index method showed the average value was less than 1, so the study area was clean. The result of the variation coefficient showed that the heavy metal content in the water body between the stations was small in the investigation area, and the pollution degree of the heavy metal pollution factors in the sea area was basically the same. The results of correlation analysis and principal component analysis indicated the correlation coefficient of Cu, Pb, Zn, Cd, Hg and As was small and the positive load of heavy metals was low. Therefoere, there were no similar pollution level or common source of pollution between six metals, that is, the probability of common sources was lower among the elements.