Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) are highly hydrophobic compounds that have been implicated as carcinogens and, more recently, as estrogen disrupters. An occurrence and distribution study of these compounds in the Willamette Basin, Oregon, was conducted by the U.S. Geological Survey as part of the National Water-Quality Assessment Program. Bed sediment was collected from 22 sites; fish tissue was collected from eight sites. PCDD/F were found to be ubiquitous in Willamette Basin sediment. A distinct homolog profile, dominated by octachlorodibenzo-p-dioxin, was observed in sediment throughout the basin. The PCDD homolog profile was consistent at all sites, regardless of total PCDD/F concentration, presence of point sources, subbasin size, geographic location or land use. Principal components analysis revealed a gradient among the homolog profiles that showed increasing dominance of highly chlorinated congeners where human and industrial activity increased. Tissue and bed sediment obtained from the same site did not have similar PCDD/F concentrations or homolog profiles. Fish tissue showed enrichment in less chlorinated congeners and congeners with chlorine substitutions in the 2, 3, 7 and 8 positions.
The results for my blanks were reported as less than a concentration that was greater than some of my field samples-do I have a contamination problem?.
A discontinuous acidimetric titration method incorporating ultrafiltration was developed to measure the association of a soil humic acid with Lit, Na+ and K+ (pH 3 to 8). In addition, possible site-specific binding of these alkali metal cations was investigated using desorption experiments at pH 1. Li, Na and K cations behavedequivalently in the titrations and the amounts of these cations associated with the humic acid was measurable at all pH values between 3 and 8. Up to 90% of the total alkali metal cation was humate-associated at pH 8. The absolute amount of humic-associated cation did not depend on the alkali metal cation concentration, but rather on the solution alkalinity. In addition, the net charge of the humate polyanion made a negligible contribution to the electroneutrality of the bulk solution under all conditions. These results are consistent with a diffuse layer model of hydrated humic acid in which the alkali metal cations neutralize the humic charge. The association of Na+ and K + with humic acid at pH 1 was successfully described by a Langmuir adsorption model. The number of sites per g of humic acid was very small, and greater for K + than for Nat. Lithium cations exhibited no detectable humic association at pH 1 . These differences suggest that humic acids may have a small number of specific binding sites for which the size of the hydrated cation is important. I N T R O D U C T I O NMost studies of the association between metal cations and natural organic matter focus on the complexation of a few select trace metals. Interactions between humic substances and the major cations such as Na' and K + have often been either ignored or assumed to be negligible. The need to characterize such interactions is evidenced by the sheer number of systems, both environmental and experimental, which contain appreciable quantities of these cations. In highly organic soils, association with humic matter may decrease the K t availability, increasing the need for amendment with K fertilizers (Kononova, 1966). In estuaries, aquatic humic substances are subjected to strong salinity gradients that can influence humic binding of trace metals. In the laboratory, experiments with aqueous humic material often utilize a background electrolyte containing Na+ or K+ to control the ionic strength. The extent to which Na+ or K + affect the humate conformation, the electrostatic charge or the binding of other cations is unknown.Aqueous alkalimetric titration has been used to investigate the association of fulvic and humic acids with Na+ or K + (Gamble, 1973;Frizado, 1979). Gamble (1973) showed that the amount of fulvic-associated Na+ and K + increased as the titration progressed. However, alkalimetric titrations present an ambiguous picture of cation-humate association. Because NaOH and KOH were used as titrants the increase in cation association with rising pH may have been due to the greater charge of the dissociating fulvate, the increasing alkali metal cation concentration, or both. Interestingly, between pH 5 and 10, Na+ ...
The potential sources of organic matter to bed sediment of the Tualatin River in northwestern Oregon were investigated by comparing the isotopic fractionation of carbon and nitrogen and the carbon/nitrogen ratios of potential sources and bed sediments. Samples of bed sediment, suspended sediment, and seston, as well as potential source materials, such as soil, plant litter, duckweed, and wastewater treatment facility effluent particulate were collected in 1998-2000. Based on the isotopic data, terrestrial plants and soils were determined to be the most likely sources of organic material to Tualatin River bed sediments. The δ 13 C fractionation matched well, and although the δ 15 N and carbon/ nitrogen ratio of fresh plant litter did not match those of bed sediments, the changes expected with decomposition would result in a good match. The fact that the isotopic composition of decomposed terrestrial plant material closely resembled that of soils and bed sediments supports this conclusion. Phytoplankton probably was not a major source of organic matter to bed sediments. Compared to the values for bed sediments, the δ 13 C values and carbon/nitrogen ratios of phytoplankton were too low and the δ 15 N values were too high. Decomposition would only exacerbate these differences. Although phytoplankton cannot be considered a major source of organic material to bed sediment, a few bed sediment samples in the lower reach of the river showed a small influence from phytoplankton as evidenced by lower δ 13 C values than in other bed sediment samples. Isotopic data and carbon/nitrogen ratios for bed sediments generally were similar throughout the basin, supporting the idea of a widespread source such as terrestrial material. The δ 15 N was slightly lower in tributaries and in the upper reaches of the river. Higher rates of sediment oxygen demand have been measured in the tributaries in previous studies and coupled with the isotopic data may indicate the presence of more labile organic matter in these areas. Results from this study indicate that strategies to improve oxygen conditions in the Tualatin River are likely to be more successful if they target sources of soil, leaf litter, and other terrestrially derived organic materials to the river rather than the instream growth of algae.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.