Sustainable Ocean Resources Network

Abstract

Marine sediment analysis for heavy metal contamination elicits a better picture on pollution level than sea water analysis since pollutants can be accumulated in deposits. Present study was to investigate heavy metal contamination in relation to sediment characteristics in Colombo port. Site selection was based on specific site characteristics as well as present and historical usage. Sediment samples were collected from ten sampling sites using large (18 cm) core sampler between June and October 2013. Samples were analyzed for five heavy metals namely Cadmium, Chromium, Zinc, Lead and Nickel. Samples were digested using concentrated Sulfuric acid and Nitric acid and heavy metal content was determined using Atomic Absorption Spectrophotometer (AAS). Particle size was determined by sieving dry samples and organic content was analyzed by loss of ignition (LoI) method. Sea Surface Temperature (SST) and Sea Surface Salinity (SSS) were measured using meters. GIS tools were used to create heavy metal dispersion maps. Mean concentrations of heavy metals (μg/g dry weight) in bottom sediment were as follows: Cd (0.610–5.858), Cr (90.313–169.06), Zn (288.06–1230.95), Pb (41.25– 189.99) and Ni (67.24–90.29). Mean SST and SSS ranged from 28–29.5 0 C, 15.5–33.5 ppt and organic content and sediment texture ranged from 6.63–14.02% and very fine sand (63-125µm) to coarse sand (500µm-1mm) respectively. Zn and Ni concentrations exceeded the high level standard of Interim Sediment Quality Guidelines (ISQG) whereas other metals were below the ISQG-high level standard. Relatively high levels of Zn, Pb and Cd concentrations in sediments could be due to oil contamination, cement packaging or ship corrosion. According to one way ANOVA; Cd, Cr and Ni concentrations were not significantly different (p>0.05) within sampling sites. However, Zn and Pb concentrations were significantly different (p<0.05) among the sites. Pearson correlation coefficient revealed a positive relationship between organic content and Cd, Cr, Zn and Pb concentrations and a negative relationship with Ni. However, no relationship was observed between heavy metal concentrations and particle size.