Analytical and environmental studies on some dissolved trace metals in sea water

Statham, Peter John (1983) Analytical and environmental studies on some dissolved trace metals in sea water. University of Southampton, Doctoral Thesis.

Abstract

A method has been developed for the determination of dissolved Mn and Fein open ocean waters in which the metals are chelated by a mixed dithiocarbamate reagent, solvent extracted into Freon TF (1,1,2-trichloro-1,2,2trifluoroethane), and back extracted into a small volume of dilute nitric acid. The metals were determined by graphite furnace atomic absorption spectrophotometry. The technique is also applicable to the determination of Cd, Co, Cu, Ni, Pb and Zn. Procedures were adopted or developed to control adventitious and systematic contamination during analysis and sample handling. Dissolved Cd and Mn were determined in samples taken at 13 stations in the equatorial and North Atlantic Ocean using the developed technique. Attempts to measure dissolved iron were negated by contamination. Dissolved Cd was highly correlated with dissolved phosphate at all stations. The overall regression equation for the whole data set (n=186) was Cd(nmol/l)=0.03+0.25P (umol/1), r=0.942. Dissolved Mn concentrations were highest in thee surface mixed layer (1 .26-3.17 nmol/l); there was a rapid decrease to about 0.25 nmolyl in the deep water. The coincidence of high atmospheric dust loadings and high surface dissolved Mn suggests that inputs of this element may be principally aeolian in this region. Small maxima of dissolved Mn superimposed on the general distribution may be caused by in situ biological and inorganic processes. The concentrations of dissolved Mn and Cd in Mediterranean Outflow Water were not elevated relative to eastern North Atlantic Ocean waters. Dissolved Al and As were determined in waters from the Cape Basin area of the South Atlantic Ocean. Mean concentrations of inorganic As above and below 110 m were 19.9 and 21.1 nmol/l respectively. Dissolved Al data showed considerable scatter, probably reflecting analytical and sampling inadequacies, with most concentrations in the range 4-15 nmbl/l. An analytical technique for the determination of dissolved Cd, Cu, Ni and Zn in estuarine and coastal waters was examined. The sensitivity of colorimetric methods for the determination of dissolved Fe was not increased sufficiently for their' application to open ocean waters. More than 85% of ionic 59Fe(III) added to natural and organic-free sea water at natural pH was removed on passage through XAD-2 resin, whilst at pHs about 3 less than 1O% was lost. Ionic 59Fe(III) added to sea water samples at natural pH and stored in polyethylene bottles was rapidly lost from solution. Removal was fastest in organic-free sea water *suggesting significant 59Fe-organic associations. Iron-59 remained in solution for at least 30 days at pHs less than 3. Ionic 54Mn added to sea water appears to be stable in dissolved forms, even at high pH, for periods up to at least 30 d. No losses of As(V) dissolved in sea water at natural pH and stored in polyethylene bottles, was observed over an 8 hr period. Acidification of samples was required to prevent losses of Mn and Fe during ultra-violet (uv) irradiation.The use of a low power ultra-violet lamp for photo-decomposition of dissolved organic matter in sea water was critically evaluated. A dissolved organic carbon analyser, which uses a high power uv lamp, was adapted for continuous use. Dissolved organic carbon was determined in samples taken at 10 stations in the equatorial and North Atlantic Ocean; concentrations were highest in surface waters (up to 83 pmol/1) and decreased rapidly below the mixed layer to consistent deep water levels in the eastern and western stations of about 37 and 46 pmol/l respectively.

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