Mapping of industrial effluent on coastal sediments using EDX

Abstract

Marine pollution monitoring surveys often include the measurement of heavy metals and other trace elements in sediments from multiple stations around marine outfalls. EDX may offer a supplementary, relatively cheap and rapid screening method where 'signature' elements in effluent can be traced on the sea-bed. 'Hot-spots' so identified, may subsequently be examined by more sensitive spectroscopic techniques and trace metals quantified. This paper describes the methodology for EDX evaluation of both effluent and sediments, establishes control criteria and applies these criteria to samples of sediment obtained from near the Huntsman Tioxide and Richards Bay A and B pipelines. Tioxide effluent was rich in Ti and Fe and Richards Bay, A and B pipelines, rich in Ca and P. Sediments obtained from near the outfalls were screened for these elements using EDX. Excess concentrations (EC) of signature elements in sediments near pipelines were determined by calculating the wt. % difference of each element in samples from near pipelines with its expected value, based on the measured wt. % in the coarse fraction, and the correlation established from the pristine control areas. Surfer 16 software was employed to create plots of EC for each element. The resultant contour plots confirmed that EDX offers a rapid means of delimiting the spatial distribution of effluent fallout and identifying the position of signature element 'hot-spots' on the sea-bed.