Humic acids freshwater

Conditional stability constants have been determined for cadmium binding to humic acid in freshwater, log Kk 6.5 [27], which may be comparable to binding to humic acid coated particles. The experiments demonstrated the importance of cadmium uptake from particles rather than from the dissolved phase. The authors recognised that the overall conclusion was similar to previous studies [28], but there remain inconsistencies in the uptake levels which may be related to the heterogeneity of the systems. Uptake from the intestine into the mucosal cells was not investigated. It was presumed that the material was digested extracellularly by hydrolytic enzymes and the released metal was taken up by facilitated diffusion. 

The aim of this study was to investigate the effect of high but environmentally realistic concentrations of humic acid on the relative long-term accumulation of Cd in the freshwater mussel D. polymorpha under controlled laboratory conditions. We assessed whether the long-term uptake of Cd is in agreement with the free-ion activity model and if Cd accumulation is related to the Cd -jon activity in the water. 

Freshwater cyanobacterium, Synechocystls aquatllls 1000-10,000 of Sn+2 or Sn- " Inhibited growth and chlorophyll a content in 96 h, but only under alkaline conditions Sn was more toxic than Sn + toxicity of both tin species increased with increased tin concentration, increased exposure, and increased pH of the medium humic acid reduced the toxicity of tin 43... 

Organic matter in unpolluted freshwater is usually in the form of humic acids (Section 13.6), which may discolor drinking water, foul ion-exchange resins, transport toxic metal ions, or generate carcinogenic chlorocarbons if the water is chlorinated (see below). Humic compounds may be removed by coagulation. Low levels of organic solutes can be removed by sorption on activated charcoal. 

Laboratory microcosms with Little Rock Lake sediments inoculated with 35S042- also show a gradual increase in organically bound 35S (< 1% to > 30% of reduced S over three months) and "CRS (20% to > 50%) whether incubated anaerobically or under oxic water columns. Sediments incubated under oxic water columns showed increasing incorporation of 3SS into fulvic and humic acids after a one-month delay (up to 30% of reduced S). Whether incorporation into fulvic and humic acids followed partial oxidation to polysulfides or elemental S (cf. 46-491 is not known. However, AVS accounted for < 10% of reduced 35S in our microcosms. Recent marine studies have also shown that H S (50-521 can be directly incorporated into acrylate, a breakdown product of i-mmethylsulphoniopropionate (DMSP), but the significance of this reaction in freshwater sediments has not been examined. 

The bioconcentration factor (BCF) for chromium(VI) in rainbow trout (Salmo gairdneri) is 1. In bottom-feeder bivalves, such as the oyster (Crassostrea virginica), blue mussel (Mytilus edulis), and soft shell clam (Mya arenaria), the BCF values for chromium(III) and chromium(VI) may range from 86 to 192 (EPA 1980, 1984a Fishbein 1981 Schmidt and Andren 1984). The bioavailability of chromium(ni) to freshwater invertebrates (Daphnia pulex) decreased with the addition of humic acid (Ramelow et al. 

Figure 19 Ecosystem-level differences in the ability of humic substances to accept electrons. Samples were taken from the water column of freshwater lakes and rivers, aquatic sediments and soils (FA = fulvic acid, HA = humic acid) (after Scott et al., 1998).

Foams form where surface-active chemicals or "surfactants" are present. Surfactants also are called amphipathic agents and are characterized by the presence of both hydrophilic and hydrophobic functional groups (7). Surface-active agents that may be present in natural waters include fulvic and humic acids, collectively termed humic substances, (2,3), fatty acids and lipids (4), and proteins (5), and all have been identified as contributing surfactants in the few characterization studies that have been conducted on natural foams in freshwater environments (5-70) and marine surface layers (77-76). 

Despite these limitations, there are advantages of fluorescence measurements of dissolved humic substances. For example, Ghosh and Schnitzer (1980a) were able to differentiate between soil fulvic acids and humic acids, since fulvic acids exhibited additional excitation bands at 360 nm. Further studies are needed to reveal if this phenomenon also occurs in freshwater humic substances. 

No further H NMR studies have been conducted for freshwater lake humic substances. However, reeent H NMR spectra of marine humie aeid appear similar to those of lake humic acid. Hatcher et al. (1980b) estimated H aromaticity of marine humic acid to be 2-3% and the C aromaticity to be 9-14%. They also estimated C aromaticity of marine humim to be 7% (Hatcher et al., 1980c). 

Karavaev, N. M. and Budyak, N. F. (1960). Investigation of so-called humic acids from freshwater sapropels. Dokl. Akad. Nauk SSSR 132, 192-194. 

Martin, D. E. and Pierce, R. A. (1975). A convenient method of analysis of humic acids in freshwater. Environ. Lett. 1, 49-52. 

The addition of UV-absorbing organic matter was also discussed to match the presence of humic acids. An attempt to add humic acids to the samples failed, owing to a decomposition of these acids during autoclave sterilisation. It was hence decided to add lauryl sulphate as a compromise for matching the presence of these acids, as was successfully performed for the certification of nitrate in artificial freshwater [5]. The short-term stability study demonstrated that the samples remained stable under the conditions tested. 

Values for 0 doc,320 computed from available data (Table 2) range from 0.3 to 3.2 m g for both marine and freshwater sites (converted to 320 nm from other wavelengths as needed using reported S values and equation (13)). Data from a study of 61 lakes [60] reveal that DOC-specific absorption increases together with DOC concentration with an exponent of 1.12 and doc,320= 1-2 (Table 2). CDOM from surface waters in the Gulf of Mexico was concentrated and separated into fulvic and humic fractions [69] to indicate their relative contributions to absorption. Fulvic acids have a much lower specific absorption than humic acids. While shifting proportions of the fulvic and humic fractions in... 

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