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PubMed2005

Octanol-water partitioning of chemical constituents in river water and treated sewage effluent.

A shake-flask approach has been employed to determine the n-octanol-water partitioning of chemical constituents in various river waters and in treated sewage effluent. The bulk inorganic composition of the water samples (conductivity, pH and the concentrations of major solutes: Ca, K, Mg, Na) was unaffected by the presence of solvent. Boron, however, exhibited increasing partition with decreasing sample pH, because its dominant form in freshwaters, B(OH)3, is neutral, covalent and acidic. Constituents having significant association with dissolved organic matter (DOM), including components of DOM itself (C, S) and trace metals that form complexes with organic ligands (Al, Cu, Fe, Pb, Zn), exhibited measurable partition into the solvent in most cases, with conditional partition coefficients, D(ow), in the region 0.03-2.5. Significant differences in the partitioning among these constituents and among the environments studied did not appear to be related to bulk sample characteristics or the degree of association of the constituent with DOM. These observations suggest that partition is sensitive to the nature of the organic matter (C, S) and the availability of specific binding ligands (trace metals). Thus, although D(ow) is critical for defining the biogeochemical behaviour and potential impacts of chemical constituents in the environment, it appears to be a difficult parameter to model or predict.

1-Octanol↗

PubMed2006

Composition of a protein-like fluorophore of dissolved organic matter in coastal wetland and estuarine ecosystems.

This study demonstrates the compositional heterogeneity of a protein-like fluorescence emission signal (T-peak; excitation/emission maximum at 280/325 nm) of dissolved organic matter (DOM) samples collected from subtropical river and estuarine environments. Natural water samples were collected from the Florida Coastal Everglades ecosystem. The samples were ultrafiltered and excitation-emission fluorescence matrices were obtained. The T-peak intensity correlated positively with N concentration of the ultrafiltered DOM solution (UDON), although, the low correlation coefficient (r(2)=0.140, p<0.05) suggested the coexistence of proteins with other classes of compounds in the T-peak. As such, the T-peak was unbundled on size exclusion chromatography. The elution curves showed that the T-peak was composed of two compounds with distinct molecular weights (MW) with nominal MWs of about >5 x 10(4) (T(1)) and approximately 7.6 x 10(3) (T(2)) and with varying relative abundance among samples. The T(1)-peak intensity correlated strongly with [UDON] (r(2)=0.516, p<0.001), while T(2)-peak did not, which suggested that the T-peak is composed of a mixture of compounds with different chemical structures and ecological roles, namely proteinaceous materials and presumably phenolic moieties in humic-like substances. Natural source of the latter may include polyphenols leached from senescent plant materials, which are important precursors of humic substances. This idea is supported by the fact that polyphenols, such as gallic acid, an important constituent of hydrolysable tannins, and condensed tannins extracted from red mangrove (Rhizophora mangle) leaves exhibited the fluorescence peak in the close vicinity of the T-peak (260/346 and 275/313 nm, respectively). Based on this study the application of the T-peak as a proxy for [DON] in natural waters may have limitations in coastal zones with significant terrestrial DOM input.

Chromatography, Gel↗

PubMed2000

Proliferative activity of intratumoral fibroblasts is closely correlated with lymph node and distant organ metastases of invasive ductal carcinoma of the breast.

Mitotic figures of fibroblasts are seen within invasive ductal carcinoma (IDC) of the breast. This suggests that the proliferative activity of fibroblasts may play an important role in IDC tumor progression. The purpose of this study was to examine whether the proliferative activity of fibroblasts can predict lymph node metastasis (LNM) or distant-organ metastasis (DOM) of IDCs. Two hundred four consecutive patients with IDC of the breast surgically treated at the National Cancer Center Hospital East constituted the basis of this study. Proliferative activity of fibroblasts was immunohistochemically evaluated by the mouse MIB-1 monoclonal antibody against Ki-67 antigen. The MIB-1 labeling index was the percentage of fibroblasts with positively stained nuclei, and fields for cell counting were selected in inner and outer areas within IDCs. In both areas, 300 fibroblasts were counted in each high-power field. The significance of proliferative activity of fibroblasts on LNM or DOM was compared with well-known prognostic parameters. Multivariate analyses demonstrated that a MIB-1 labeling index of more than 10% of fibroblasts in the inner area of IDCs significantly increased the relative risk of LNM and hazard rate of DOM (P < 0.001 and P = 0.007, respectively). The present study indicated that the metastatic ability of IDCs is closely dependent on proliferative activity of fibroblasts in the inner area.

Adult↗

PubMed1999

Delayed onset muscle soreness: lack of effect of therapeutic ultrasound in humans.

OBJECTIVE: To investigate the effects of two dosages of pulsed ultrasound therapy (1 MHz, spatial averaged peak intensity 0.8 W/cm2, mark space ratio of 1:4) on acute-stage delayed onset muscle soreness (DOMS). DESIGN: Double-blind, placebo-controlled, randomized trial. SETTING: Laboratory of a university physiotherapy department. PARTICIPANTS: Forty-eight healthy volunteers (24 men, 24 women) with no arm pathology or pain at the time of the study. INTERVENTIONS: Subjects were randomly allocated to one of four treatment groups: control, placebo (sham insonation), low-dosage pulsed ultrasound (mean dosage 172.8 J), or high-dosage pulsed ultrasound (mean dosage 345.6 J). DOMS was induced in the nondominant elbow flexors in a standardized fashion through repeated eccentric exercise until exhaustion. MAIN OUTCOME MEASURES: Elbow extension, flexion, and resting angles (universal goniometer), pain (visual analogue scale), mechanical pain threshold/tenderness (pressure algometer), and a McGill pain questionnaire. Measurements were taken before and after treatment each day except for the McGill pain questionnaire, which was completed at the end of the trial. RESULTS: Significant differences were seen between groups in relation to range of flexion (p = .0032), with the control group losing least range of flexion. There were no other significant differences between the groups. CONCLUSION: No convincing evidence was found to support the use of pulsed ultrasound therapy in the management of DOMS at the parameters discussed here.

Adult↗

PubMed2003

Characterization of a novel effect of serotonin 5-HT1A and 5-HT2A receptors: increasing cGMP levels in rat frontal cortex.

Elucidating the mechanisms of action of hallucinogens has become an increasingly important area of research as their abuse has grown in recent years. Although serotonin receptors appear to play a role in the behavioral effects of the phenethylamine and indoleamine hallucinogens, the signaling pathways activated by these agents are unclear. Here it is shown that administration of serotonin (5-hydroxytryptamine, 5-HT) increased cyclic guanosine monophosphate (cGMP) production in frontal cortical slices of rat brain. The effect of 5-HT was greater than that of N-methyl-D-aspartate (NMDA), a stimulant of cGMP formation in the central nervous system. The 5-HT(2A/2C) receptor phenethylamine agonist, 2,5-dimethoxy-4-methylamphetamine (DOM), increased cGMP content in the slices. Additionally 8-hydroxy-2-(di-n-propylamino)tetralin (DPAT), a 5-(HT1A/7) receptor agonist also increased cGMP production. Stimulation of cGMP formation by DOM was prevented by a 5-HT(2A/2C) receptor antagonist, pirenperone, as well as by a 5-HT2A receptor selective antagonist, MDL100907. A 5-HT2C receptor antagonist, SB242084, did not block the effect of DOM. Stimulation of cGMP production by DPAT was blocked by the 5-HT1A receptor antagonist, WAY100635. Stimulation of cGMP formation by serotonin could be prevented by pirenperone or WAY100635. In summary, activation of serotonin 5-HT1A and 5-HT2A receptors increase brain cGMP levels.

Animals↗

PubMed2001

Characterization of isolated fractions of dissolved organic matter from natural waters and a wastewater effluent.

Dissolved organic matter (DOM) was concentrated from natural waters and the effluent of a wastewater treatment plant using a portable reverse osmosis (RO) system. The humic acid (HA), fulvic acid (FA) and hydrophilic (HyI) fractions were isolated and purified by the XAD-8 resin combined with the cation exchange resin method. The FA fractions predominated in natural waters and accounted for 54-68% of the total amount of dissolved organic carbon (DOC), whereas the HA and HyI fractions constituted, respectively, 13-29 and 9-30% of the total DOC. The effluent of wastewater was almost devoid of HA and the HyI fraction exceeded FA. The elemental compositions of HA and FA were in the ranges typical for natural humic materials, but the HyI fractions did not exhibit humic character. 1H NMR spectra revealed that the HyI fractions were almost devoid of aromatic protons and the aliphatic region featured more sharp signals than HA and FA fractions, indicating that HyI fractions were consisted of more simple compounds and less complex mixtures. The aliphatic functional groups in these fractions of DOM samples followed the order HA < FA HyI. The rate of Cu complexation with the HyI fraction was faster than the rate with the HA or FA fraction of the Suwannee River DOM, implying that copper reacted with relatively weak ligands faster than with strong ligands.

Benzopyrans↗

PubMed2002

Aluminum speciation in natural waters: measurement using Donnan membrane technique and modeling using NICA-Donnan.

The study of Al speciation is of interest for the assessment of soil and water quality. For the measurement of "free" aluminum (Al3+), a recently developed Donnan membrane technique was tested by measuring Al3+ in aluminum-fluoride solutions and gibbsite suspensions. It shows that the Donnan membrane technique can measure free Al3+ reliably up to 10(-9) M and the equilibration takes 3-4 days. Next, Al binding to humic acid (HA) purified from a forest soil was measured using either the Donnan membrane technique or gibbsite suspension. Results were compared with those predicted with the non-ideal consistent competitive adsorption (NICA)-Donnan model. The predictions using the generic parameters without fitting were in reasonable agreement with the measured data. Finally, the Donnan membrane technique was used to determine Al binding to dissolved organic matter (DOM) in the solutions of 24 soil samples at pH interval of 3-7. Measurements agree well with the predictions using the NICA-Donnan model assuming 30% of DOM is HA and 30% is fulvic acid. With this model, the effects of pH and DOM changes on the concentration of Al in 81 soil solutions were predicted reasonably without adjustment of model parameters. The comparison between the results of analysis and the modeling provides a mutual validation for the two methods.

Adsorption↗

PubMed2003

Trihalomethane formation potential of dissolved organic matter in a shallow eutrophic lake.

Dissolved organic matter (DOM) in water samples from the shallow eutrophic Lake Kasumigaura, the second largest lake in Japan, was fractionated and characterized by using resin adsorbents into 5 classes: aquatic humic substances (AHS), hydrophobic neutrals, hydrophilic acids (HiA), bases (BaS) and hydrophilic neutrals (HiN). Subsequently, the trihalomethane formation potential (THMFP), ultraviolet absorbance to dissolved organic carbon (UV:DOC) ratio, and molecular size distribution of the DOM, AHS and hydrophilic fractions (HiF) (HiF=HiA+BaS+HiN) were examined. The THMFP of HiF, normalized on a DOC basis, was found to be comparable to that of AHS (0.176 microM THM mg C(-1) vs. 0.195 microM THM mg C(-1), respectively). The importance of HiF over AHS as a THM precursor became more pronounced when THMFP was evaluated in terms of concentration. In this case, the THMFP of HiF was much greater than that of AHS (0.374 microM THM l(-1) vs. 0.229 microM THM l(-1), respectively). Molecular size distributions all exhibited a narrow size range and relatively low molecular weights. The weight-averaged molecular weights of DOM, AHS and HiF were 780, 957 and 606 g M(-1), respectively.

Environmental Monitoring↗

PubMed2002

Study of chlorothalonil photodegradation in natural waters and in the presence of humic substances.

Photodegradation of chlorothalonil was studied in different natural waters (sea, river and lake) as well as in distilled water under natural and simulated solar irradiation. The effect of dissolved organic matter (DOM) such as humic and fulvic substances on the photodegradation rate of chlorothalonil was also studied in simulated sunlight. The presence of DOM enhanced the photodegradation of chlorothalonil with the exception of seawater. The kinetics were determined through gas chromatography electron capture detection (GC/ECD) and the photodegradation proceeds via pseudo-first-order reaction in all cases. Half-life ranged from 1 to 48 h. In natural and humic water chlorothalonil photodegradation gave rise to two different intermediates compared to distilled water demonstrating that the transformation of chlorothalonil depend on the constitution of the irradiated media and especially from DOM. The byproducts identified by GC/MS techniques were: chloro-1,3-dicyanobenzene, dichloro-1,3-dicyanobenzene, trichloro-1,3-dicyanobenzene and benzamide.

Fungicides, Industrial↗

PubMed2002

Copper complexation by dissolved organic matter and uncertainty assessment of their stability constants.

The interaction of Cu with dissolved organic matter (DOM, extracted from an organic forest floor) was investigated and the resulting data was evaluated in terms of their uncertainty. The speciation of Cu over 'free' Cu (as analysed by diffusive gradients in thin films (DGT)), dissolved Cu-DOM complexes and precipitated Cu-DOM was determined as a function of pH (3.5, 4.0 and 4.5) and Cu/C ratio. The dissolved organically bound fraction was highest at pH 4.5, but this fraction decreased with increasing Cu/C ratio, which was observed for all pH levels. In the range of Cu/C = 7 x 10(-5) -2.3 x 10(-2) (mol/mol) the precipitated fraction was very small. The speciation of both Al and Fe was not affected by increasing Cu concentrations. From a continuous distribution model using the Scatchard approach, we calculated the optimal fit and corresponding upper and lower 95% uncertainty bounds of the overall stability constants (K(o)) with the shuffled complex evolution Metropolis (SCEM) algorithm. Although the optimal equation fitted the data very well, the uncertainty of the, according to literature, most reliable approach to establish stability constants, was still large. Accordingly, the usually reported intrinsic stability constants exhibited large uncertainty ranging from log K(i) = 6.0-7.1 (optimal 6.7) for pH 3.5, log K(i) = 6.5-7.1 (optimal 6.8) for pH 4.0, and log K(i) = 6.4-7.2 (optimal 6.8) for pH 4.5 and showed only little effect of pH.

Chemical Precipitation↗

PubMed2002

Further characterization of the stimulus properties of 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline.

This investigation is based on the premise that conformational restriction of abused phenylalkylamines in a tetrahydroisoquinoline conformation alters their pharmacology in such a manner that their original action is lost and that a new action emerges. TDIQ or 5,6,7,8-tetrahydro-1,3-dioxolo[4,5-g]isoquinoline, is a conformationally constrained phenylalkylamine that serves as a discriminative stimulus in animals. Although TDIQ bears structural resemblance to phenylalkylamine stimulants (e.g., amphetamine), hallucinogens (e.g., 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane [DOM]), and designer drugs (e.g., N-methyl-1-(3,4-methylenedioxyphenyl)-2-aminopropane [MDMA], N-methyl-1-(4-methoxyphenyl)-2-aminopropane [PMMA]), the TDIQ stimulus failed to generalize to (+)amphetamine or MDMA. In the present investigation, further evaluations were made of the stimulus nature of TDIQ. Specifically, the stimulus similarities of TDIQ, PMMA, and DOM were examined. In no case was stimulus generalization (substitution) observed. The results confirm that TDIQ produces stimulus effects distinct from those of the abovementioned phenylalkylamines. We also examined the structure-activity relationships of a series of TDIQ analogs, including several that might be viewed as conformationally restricted (CR) analogs of phenylalkylamine hallucinogens, stimulants, and designer drugs. These agents were examined in rats trained to discriminate either DOM (1.0 mg/kg), (+)amphetamine (1.0 mg/kg), MDMA (1.5 mg/kg), or TDIQ (5.0 mg/kg) from saline vehicle. Whereas we have demonstrated that none of these agents retains their respective phenylalkylamine stimulus actions, several of these agents were found to substitute for TDIQ. N-Methylation abolished TDIQ-stimulus action. These results, coupled with previous findings, imply that TDIQ derivatives represent a novel class of phenylalkylamines analogs with unique stimulus properties. Preliminary radioligand binding studies suggest that an alpha2-adrenergic mechanism might underlie the stimulus effects produced by TDIQ.

Animals↗

PubMed2002

Effect of 1-(3,4-methylenedioxyphenyl)-2-aminopropane and its optical isomers in PMMA-trained rats.

1-(3,4-Methylenedioxyphenyl)-2-aminopropane (MDA) is a drug of abuse that is known to produce stimulus effects similar to those of the stimulant phenylalkylamine (+)amphetamine and the hallucinogenic phenylalkylamine 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM). Earlier, a working model was described to account for the stimulus effects produced by phenylalkylamines. Such agents can produce one or more of three distinct effects: an amphetamine effect, a DOM effect and a third effect that is typified by the agent N-methyl-1-(4-methoxyphenyl)-2-aminopropane (PMMA). Because MDA is known to produce two of the three effects, in the present investigation, we sought to determine if racemic MDA or either of its optical isomers could produce a PMMA-like effect in animals. Administration of S(+)MDA, R(-)MDA and (+/-)MDA to rats trained to discriminate 1.25 mg/kg of PMMA from saline vehicle under a VI 15-s schedule of reinforcement resulted in substitution in each case. (+/-)MDA and S(+)MDA were nearly equipotent and several fold more potent than R(-)MDA. The results are not only consistent with the proposed model but also identify (+/-)MDA as the first phenylalkylamine shown to produce all three types of stimulus effects (i.e., amphetamine-like, DOM-like and PMMA-like) in rats.

3,4-Methylenedioxyamphetamine↗

PubMed2000

Rapid delineation of humic and non-humic organic matter fractions in water.

Dissolved organic matter (DOM) in water is often characterized by aggregate parameters like dissolved organic carbon (DOC). DOM from conventional surface water treatment plant in Northern New Jersey was isolated and fractionated using resin adsorption chromatography into six different fractions, which were operationally categorized as hydrophobic acid, hydrophobic neutral, hydrophobic base, hydrophilic acid, hydrophilic neutral and hydrophilic base. The spectral fluorescent signatures (SFS) technique was developed for the quantitative identification of the six fractions by post-processing analysis that includes a statistical model. The SFS is the total sum of emission spectra of a sample at different excitation wavelengths, recorded as a matrix of fluorescent intensity in coordinates of excitation and emission wavelengths, in a definite spectral window. High sensitivity and rapid identification and quantification of DOM fractions are among the main features of the technique. Since hydrophobic and hydrophilic substances are considered more humic and non-humid in nature, respectively, the technique provided an opportunity to rapidly delineate source waters in terms of such categories.

Adsorption↗

PubMed2000

The variation of mass and disinfection by-product formation potential of dissolved organic matter fractions along a conventional surface water treatment plant.

Dissolved organic matter (DOM) influences many aspects of water treatment, including the formation of potentially harmful disinfection by-products (DBPs) when disinfectants are applied. DOM from a conventional surface water treatment plant (WTP) in Northern New Jersey was isolated and fractionated using resin adsorption chromatography into six different fractions. These fractions are operationally categorized as hydrophobic acid, hydrophobic neutral, hydrophobic base, hydrophilic acid, hydrophilic neutral and hydrophilic base. The hydrophilic acid fraction was found to be the most abundant fraction in the source water. The hydrophilic neutral, hydrophilic acid and hydrophobic acid fractions had the highest removal efficiency through the WTP (about 65%). The variation and removal effectiveness of each fraction along the WTP was studied. Seven-day chlorine DBP formation potential (FP) tests were performed on all DOM fractions through the WTP. For the source water studied, the hydrophilic acid fraction was found to be the most reactive precursor to the trihalomethane (THM) formation. The hydrophobic neutral fraction was found to be the fraction of concern with respect to the FP of haloacetic acids (HAAs) class of DBPs. The FP of each fraction's class of DBPs was found to be amenable for reduction along the treatment train, specifically by coagulation/sedimentation. The fractionated approach concept showed to be very beneficial in the study of DBP precursors and their effective removal by physical and chemical treatment.

Adsorption↗

PubMed1998

Cobalt binding to gills of rainbow trout (Oncorhynchus mykiss): an equilibrium model.

Rainbow trout (Oncorhynchus mykiss, 1-5 g) were exposed to approximately 7.5 microM Co in soft water for 2-3 hr at pH approximately 6.5. The water contained either complexing ligands such as nitrilotriacetic acid and natural dissolved organic matter (DOM) or competing cations such as Ca, Na, or H. After exposure, gills were excised and analyzed for total bound Co using a graphite furnace atomic absorption spectrophotometer. A Langmuir isotherm was used to calculate the conditional equilibrium binding constant (K) for Co binding to trout gills plus the concentrations of gill Co binding sites. The calculated binding constant for Co to trout gills was log KCo-gillCo = 5.1, with 88 nmol Co binding sites per g of wet gill tissue. Conditional equilibrium binding constants were also calculated for Ca, Na, and H binding to the gill Co sites and for Co binding to DOM. The experimentally determined binding constants were entered into an aquatic equilibrium chemistry program, MINEQL+, to predict Co binding by fish gills. Predicted and observed results indicate that Co would not accumulate on or in gills of trout held in a series of natural and 1:1 diluted natural waters supplemented with approximately 8.7 microM Co. Model analysis of the reasons for Co being kept off gills of trout held in natural waters indicated that Ca competition and DOM complexation were the most important factors in preventing Co binding by trout gills.

Animals↗

PubMed2003

Atmospheric pressure mass spectrometry: a new analytical chemical characterization method for dissolved organic matter in rainwater.

The complex mixture of organic compounds in the atmosphere influences climate, air quality, and ecosystem processes. Atmospheric pressure electrospray ionization mass spectrometry (APESI-MS) was evaluated as a potential tool for direct measurement of the total suite of individual dissolved organic matter (DOM) compounds in rainwater. The APESI-MS response was linear to all DOM compounds of atmospheric significance examined as standard solutions. Urban precipitation samples from New Brunswick, NJ (USA) were analyzed by APESI-MS over the mass-to-charge (m/z) range 50-3,000. Over 95% of the m/z ions detected were in the low m/z range (50-500). Over 300 unique m/z ions were detected across the 11 rainwater samples indicating the complexity of the mixture of DOM in rainwater. Forty percent of the organic bases (positive mode detection) and 22% of the organic acids (negative mode) occurred in at least 6 of the 11 rainwater samples. Ions corresponding to the m/z of carboxylic acids standards (nonanedioic acid; 1,4-butanedicarboxylic acid; pentanedioic acid; hydroxybutanedioic acid; and butanedioic acid) and to reduced N standards (allylurea; caffeine; imidazole; and N-2-propenylurea) occurred in at least one of the 11 rainwater samples. Total dissolved organic carbon (DOC) estimated from the APESI-MS analysis and measured by standard DOC methods were not statistically different.

Air Pollutants↗

PubMed2004

Ultrafiltration of nonionic surfactants and dissolved organic matter.

A brownwater sample with a high content of humic substances (HS) was fractionated by multistage ultrafiltration (mst-UF) into five fractions with nominal molecular weights ranging from >30 to <1 kDa. Fractions were characterized with respect to molecular size distribution and structure. Size exclusion chromatography with online DOC detection revealed that mst-UF yielded fractions with decreasing Mp (molecular weight at peak maximum) and polydispersities from nominally large to small mst-UF fractions. 13C MAS NMR analysis showed that the content of carbohydrate structures decreased from the original sample toward smaller molecular weight (MW) fractions, which in turn contained more carboxylic groups and branched aliphatic structures. Specific UV absorbances (SUVA254) were highest in the >30 kDa fraction and decreased with decreasing MW. To evaluate whether separation mechanisms other than size exclusion were of importance during the fractionation, the behavior of low molecular weight model compounds (MC) with a range of polarities was studied. Recoveries decreased with increasing hydrophobicity of the MC. For selected nonylphenol ethoxylates and 4-nonylphenol the recovery correlated well with the hydrophile-lipophile balance value. The presence of dissolved organic matter (DOM) caused an additional loss of hydrophobic MC, possibly because of sorption of the compounds onto DOM fouling layers. The hydrophilic MC caffeine was recovered almost completely (85-86%) regardless of the DOM content of the model solution. It was concluded that size exclusion was the dominant fractionation mechanism for caffeine, whereas hydrophobic interactions played a major role during the mst-UF fractionation of nonpolar contaminants. For a better understanding of the behavior of polyfunctional molecules such as HS, the effect of other physicochemical properties needs to be investigated in further studies.

Caffeine↗

PubMed2004

Cadmium bioavailability and accumulation in the presence of humic acid to the zebra mussel, Dreissena polymorpha.

Metal speciation in aquatic systems is mainly determined by the type and concentration of ligands present in solution. A very important group of complexing agents is dissolved organic matter (DOM), e.g., humic and fulvic acids. According to the free-ion activity model, only the free metal ion is available to biota. Nevertheless, DOM has been reported to decrease or increase metal uptake, leading to uncertainty concerning the bioavailability of metal-DOM complexes. In this work the effect of Aldrich humic acid on cadmium accumulation by the zebra mussel, Dreissena polymorpha, was studied under laboratory conditions. Mussels, collected in a drinking water reservoir, were exposed to varying environmentally relevant concentrations of cadmium in the presence and absence of humic acid. Cadmium concentrations in the mussel tissues were analyzed, and measurements with a cadmium-ion-selective electrode were made to determine the free cadmium ion activity in the exposure waters. The uptake of humic acid by the zebra mussels was measured by the decrease of the total organic carbon (TOC) concentration in the water over time. The free cadmium ion activity in the water decreased from 51.6% to 19.9% of the total cadmium concentration in the presence of humic acid. This decrease by a factor of 2.6 resulted in a decrease in the cadmium uptake rate in the soft tissue of zebra mussels from 12.9 to 7.9 nmol/g dry wt/day, which corresponds to a decrease by a factor of 1.6. This implies that cadmium uptake rates were higher than predicted by the free-ion activity model and indicates that cadmium-humic acid complexes are partly available to zebra mussels.

Animals↗