The measurement and evaluation of certain trace metal concentrations in the nearshore environment of the northwest Gulf of Mexico and Galveston Bay.
MetadataShow full item record
As a study preliminary to a future long-range program to establish water quality standards, this research was directed towards the determination of manganese, nickel, copper, zinc, and lead in the nearshore environment. A method utilizing filtration, ion exchange, persulfate oxidation and hydrofluoric acid digestion in conjunction with atomic absorption spectroscopy was developed. A total of 66 water and 20 sediment samples from Galveston Bay, the Gulf of Mexico, and the Mississippi River were analyzed. The data indicate that these metals are distributed in at least three definable fractions. They are (1) soluble-reactive (ionic) -- that fraction available for direct uptake by the ion exchange resin without prior alteration of their chemical state, (2) filterable-nonreactive (particulate) -- that fraction retained by a 0.3 micro pore size glass fiber filter, and (3) soluble-non- reactive -- the fraction which penetrates both the filter and the ion exchange resin. The only metals which yielded a consistent soluble-nonreactive fraction were nickle and copper. The method was not effective for soluble- nonreactive manganese and lead. No values were obtained for particulate zinc due to an intense silicon interference encountered in the atomic absorbtion phase of the determinations. In Galveston Bay the ranges of the observed ionic values were: <0.1 to 174 ug/1 manganese, <0.1 to 5.92 ug/1 nickle, <0.1 to 1.00 ug/1 copper, 2.5 to 25 ug/1 zinc, and <0.1 ug/1 lead. The ranges of the particulate values were: 5.04 to 84 ug/1 manganese, <0.1 to 3.74 ug/1 nickle, 0.24 to 5.94 ug/1 copper and 1.62 to 4.80 ug/1 lead. Estimated soluble-nonreactive nickle ranged from 0.88 to about 5.92 ug/1 in Galveston Bay. Lower values were found in the nearshore Gulf of Mexico with similar to higher values obtained in the Mississippi River. From the data obtained it was concluded that the particulate form predominates over the ionic form for all the metals with a significant portion of nickel and copper existing as soluble-nonreactive complexes. This has been attributed to solubilization by organic complex formation (e.g. chelation). The ineffectiveness of the method for soluble-nonreactive manganese and lead was attributed to several factors. The existence of higher oxidation states such as Mn (IV) and particulate Pb(IV) coupled with ion pair formation, hydrolysis, isopolycationic complexes are thought to be responsible for the observed discrepancies. No definite distribution patterns of the forms were established. It was inferred from the data that removal of the metals from suspected input points results from adsorption by suspended organic and inorganic materials (e.g. clay minerals).