Elevated Zinc Research Articles

Barnacles as biomonitors of trace metal availabilities in Hong Kong coastal waters: changes in space and time

The use of selected organisms as biomonitors of trace metal bioavailabilities allows comparisons to be made over space and time. The concentrations of 11 trace metals (arsenic, cadmium, chromium, cobalt, copper, iron, lead, manganese, nickel, silver, zinc) were measured in the bodies of two barnacle species, Balanus amphitrite and Tetraclita squamosa, from up to 18 littoral sites from Hong Kong coastal waters in April 1998. These data provide evidence on the geographical variation in metal bioavailabilities at this time, and are compared selectively against historical data sets for 1986 and 1989. Geographical variation in bioavailabilities is clear for several metals, with hotspots for arsenic, copper, nickel and silver at Chai Wan Kok, and for lead in Junk Bay. Victoria Harbour sites head the rankings for silver and arsenic, and Tolo Harbour sites exhibit relatively elevated cobalt, manganese and zinc. Many bioavailabilities of trace metals to barnacles are lower in Hong Kong coastal waters in 1998 than in 1986. The two barnacle species are widespread and the extensive data set presented is a benchmark which can be compared to the results of similar biomonitoring programmes elsewhere in the Indo-Pacific and beyond.

The distribution of heavy metals in an abandoned mining area; a case study of Strauss Pit, the Drake mining area, Australia: implications for the environmental management of mine sites

Surface water samples from the Drake mining area show elevated metal concentrations, notably cadmium, iron and zinc. A detailed study of a sphalerite /quartz vein from Strauss Pit and chalcopyrite and pyrite from the Adeline mine and Strauss Pit indicate that micro-scale analyses of ores are necessary for environmental management of mine sites. Analyses show that Cd is elevated, up to 2.1 % by weight, and is associated with sphalerite, replacing Zn, or to a lesser extent replacing Pb within small galena grains. High concentrations of Cu are also associated with the Strauss Pit ore as small chalcopyrite grains along the margins of the sphalerite vein, within the central quartz zone of the vein system, and as replacement rims on sphalerite grains. Chalcopyrite from the Adeline mine area, is by comparison, metal poor, but still contains elevated heavy metal concentrations. Whereas, pyrite and chalcopyrite, from Strauss Pit have variable heavy metal concentrations, with chalcopyrite from within sphalerite veins having higher Cd and Zn concentrations than chalcopyrite distal to the veins. Cadmium and other heavy metals within the ores are mobilised during sulphide weathering and enter the drainage network; precipitation of secondary oxidation minerals act as temporary stores for many heavy metals. The complexity of the mineral and heavy metal associations at Strauss Pit suggest that a detailed knowledge of these associations and distributions within ore bodies, and associated waste rocks, are needed by environmental managers of mine sites because the presence of havy metals may greatly affect the decision making process, and management strategies employed.

Metallothionein Expression Protects against Carbon Tetrachloride-Induced Hepatotoxicity, but Overexpression and Dietary Zinc Supplementation Provide No Further Protection in Metallothionein Transgenic and Knockout Mice

Metallothionein and zinc have been implicated in cellular defense against a number of cytotoxic agents. With respect to the free radical-generating hepatotoxin carbon tetrachloride, conclusions about a defensive role were reached from in vitro studies, in vivo studies using inducers of metallothionein and studies using injections of pharmacological amounts of zinc. Metallothionein knockout (null) and metallothionein transgenic mice are more direct models to examine the effects of metallothionein expression on induced cytotoxicity. Similarly, zinc presented via the diet is a more physiological model than that presented via injection. We examined whether metallothionein-overexpressing mice or metallothionein knockout mice had altered sensitivity to carbon tetrachloride and whether supplemental dietary zinc reduced sensitivity to carbon tetrachloride in these genotypes. Metallothionein knockout mice produced no metallothionein and were unable to sequester additional hepatic zinc in response to elevated dietary zinc. Hepatotoxicity, as measured by serum alanine aminotransferase activity, histological analyses and hepatic thiol levels, was greater in the knockout mice than in controls 12 h after carbon tetrachloride treatment but not at later time points (up to 48 h). In contrast, metallothionein-overexpressing mice produced more metallothionein and sequestered more liver zinc than control mice, but hepatotoxicity was similar between genotypes. Supplemental dietary zinc had no effect on hepatotoxicity with either genotype. These data suggest metallothionein null mice were more susceptible to carbon tetrachloride-induced hepatotoxicity than were control mice. However, neither metallothionein overexpression nor supplemental dietary zinc provided further protection.

Zinc inhibits the mixed lymphocyte culture.

The mixed lymphocyte culture (MLC) is an established clinical method for bone marrow transplantation, as it serves as an in vitro model for allogenic reaction and transplantation. We previously showed that cytokine release into the supernatant is a more specific and sensitive parameter for cross-reactivity in the MLC than the common measurement of cell proliferation. Therefore we tried to find an inhibitor of the MLC in vitro with the least side effects in vivo, measuring interferon (IFN)-gamma as one of the most important cytokines in posttransplant medicine. Earlier studies showed that zinc is an important trace element for immune function with both stimulatory and inhibitory effects on immune cells. We found that slightly elevated zinc concentrations (three to four times the physiological level), which do not decrease T-cell proliferation in vitro nor produce immunosuppressive effects in vivo, suppress alloreactivity in the mixed lymphocyte culture. In this report we analyzed the mechanism whereby zinc influences the MLC to possibly find a nontoxic way of immunosuppression.

Epilepsy-associated plasticity in γ-aminobutyric acid receptor expression, function, and inhibitory synaptic properties

Although epilepsy is fundamentally a circuit phenomenon, the most basic manifestation of the hyperexcitability characteristic of epilepsy must be evident at the level of a single neuron. Furthermore, in the future, manipulations of surviving neurons within the epileptic focus will constitute one of the best therapeutic targets for intervention to cure this devastating disease. Therefore, the more that can be learned about epileptogenic alterations in this population of surviving focal neurons, the more potential avenues for therapeutic intervention will emerge. This chapter has summarized one aspect of postsynaptic neuronal function that undergoes dramatic alterations in the epileptic brain: the properties of inhibitory neurotransmitter (i.e., GABA) receptors in surviving focal neurons. GABARs in these neurons undergo significant alterations in their function and pharmacology, which appear to be mediated, at least in part, by alterations in the transcriptional production of GABAR subunits. These GABAR alterations fulfill many of the requirements for an epileptogenic mechanism: they are consistent with the hyperexcitability characteristic of epilepsy; the changes develop prior to the onset of recurrent spontaneous seizures; and the elevated zinc sensitivity of epileptic GABARs combined with epilepsy-associated mossy fiber sprouting (a zinc "delivery mechanism") can account for the existence of a prolonged latent period. Although GABAR alterations in DGCs of the epileptic hippocampus may be consistent with hyperexcitability and therefore contribute to epileptogenesis, many other processes undoubtedly also contribute, including (but not limited to) neuronal loss, circuit rearrangements, alterations in other membrane proteins, and birth of new neurons. Assuming any single change is both necessary and sufficient to fully account for epilepsy is undoubtedly an oversimplification. The initial precipitating events associated with the subsequent development of epilepsy are often traumatic events and associated with changes in many processes in widespread areas of the brain. Some of these processes may contribute to excitability changes, some may resist the development of epilepsy, and some may be unrelated to epileptogenesis. Characterizing the critical processes initiated during epileptogenesis remains an important and challenging research endeavor for the foreseeable future.

Weight loss and net abnormalities of Hydropsyche betteni (caddisfly) larvae exposed to aqueous zinc

AbstractCaddisfly larvae (Hydropsyche betteni) were collected near a zinc mining operation and exposed to elevated concentrations of zinc in an attempt to determine the efficacy of using weight change and capture net architecture for assessing the toxicological impact of metal exposure. One group of larvae was collected near the mine site (Adjacent) with another collected upstream and away from the mine (Remote). Weight change and capture net architecture was monitored on 400 individually identifiable larvae. The threshold‐observed‐effect concentration after 13 d was 7.6 mg/L for the Remote group and 30.2 mg/L for the Adjacent group. After 48 d, the highest test concentration of 42 mg/L resulted in a 23 and 19% loss in live‐body weight in the Remote and Adjacent groups, respectively, while control larvae from both groups gained 6% in comparison to initial pre‐exposure weights. Five weeks of exposure at 22 mg Zn/L or greater was required by both larval groups to statistically reduce the frequency of normal nets, indicating that the sensitivity of the net response was less sensitive than weight loss. Relative differences in weight changes and net architecture strongly suggest that the Adjacent larval group was slightly more tolerant than the Remote and that this increased tolerance may be related to chronic pre‐exposure to zinc prior to collection of larvae. This study demonstrates the utility of using weight loss, net architecture, and tissue burdens for assessing the impact of elevated zinc.

THE INFLUENCE OF ELEVATED DIETARY ZINC, SELENIUM, AND THEIR COMBINATION ON THE SUPPRESSIVE EFFECT OF DIETARY AND INTRAPERITONEAL CADMIUM ON EGG PRODUCTION IN LAYING HENS

The influence of elevated dietary zinc and/or selenium on the suppressive effect of cadmium on egg production in hens has not been previously established. To address this question, two models of cadmium administration were used to differentiate protective effects of zinc or selenium that may result from a reduced absorption of cadmium from those resulting from an elevated nutritional status of these minerals. First, cadmium-induced suppression of egg production was produced in White Leghorn hens using intraperitoneal injections of Cd in order to determine protective effects that result from prefeeding diets supplemented with 803 ppm Zn, 0.91 ppm Se, or their combination relative to a basal diet (control). Feeding elevated dietary selenium throughout the experiment, including a 6-day prefeeding period before Cd administration, resulted in significant protection from the egg suppression produced by 2 injections of cadmium (0.27 mg/ kg each) given 1 d apart. Feeding elevated dietary zinc alone or combined with +0.91 ppm Se for a similar period did not markedly protect against cadmium-induced egg suppression. After a 0.54- mg/ kg dose of Cd was administered, for a cumulative dose of 1.08 mg/ kg, no significant protection was observed from any of the supplemented diets. In a second experiment, the protective effect of the same dietary treatments on the egg-suppressive effect of dietary cadmium was determined. In contrast to cadmium injection, the suppressive effect of 153 ppm dietary cadmium was not mitigated by selenium supplementation, while supplemental zinc protected against this effect of dietary cadmium regardless of the amount of selenium in the diet. There was no significant change in plasma estrogen and vitellogenin levels as a result of cadmium administration in either model, with the exception of significant reduction in both these parameters in the dietary cadmium-exposed birds fed the basal diet. Together, the data suggest that the level of dietary zinc in food sources may be more important in influencing cadmium-induced egg suppression than the nutritional status of zinc in cadmium-exposed birds. In contrast, the nutritional status of selenium in cadmiumexposed birds may have the potential to mitigate this effect, but high exposures to dietary cadmium or zinc may preclude such protection.

Metallothionein is expressed in adipocytes of brown fat and is induced by catecholamines and zinc.

Metallothionein (MT) is thought to have an antioxidant function and is strongly expressed during activation of thermogenesis and increased oxidative stress in brown adipose tissue (BAT). Localization and regulation of MT expression in BAT was therefore investigated in rats and mice. Immunohistochemical analysis of BAT from rats exposed to 4 degrees C for 24 h showed that MT and uncoupling protein 1 (UCP1) were coexpressed in differentiated adipocytes, and both cytoplasmic and nuclear localization of MT was observed. Cold induction of MT-1 expression in BAT was also observed in mice. Administration of norepinephrine to rats and isoproterenol to mice stimulated MT and UCP1 expression in BAT, implying a sympathetically mediated pathway for MT induction. In mice, zinc, and particularly dexamethasone, induced MT-2 expression in BAT and liver. Surprisingly, zinc also induced UCP1 in BAT, suggesting that elevated zinc may induce thermogenesis. We conclude that expression of MT in mature brown adipocytes upon beta-adrenoceptor activation is consistent with a role in protecting against physiological oxidative stress or in facilitating the mobilization or utilization of energy reserves.

Increased risk of preterm delivery with elevated maternal alpha-fetoprotein and plasma zinc levels in African-American women

This study evaluated the relationship of maternal serum alpha-fetoprotein (MSAFP) and plasma zinc levels (PZn) to pregnancy outcome. The subjects for this investigation consisted of 917 African-American women, who on registration for prenatal care between 7-22 weeks gestational age (GA), had PZn levels determined and also had MSAFP recorded in their charts. MSAFP levels greater than the 90th percentile significantly increased the risk of PTD (adjusted odds ratio or AOR=2.5, 95% C.I.=1.5-4.2) but not of IUGR. There was no significant relationship between maternal PZn level and PTD or IUGR. When subjects were stratified by MSAFP levels, in women with MSAFP greater than the 90th percentile, the AOR for PTD was 4.0 (95% C.I.=1.2-13.5) for women with PZn levels greater than the median vs. those with PZn equal to or less than the median. In women with MSAFP equal to or less than the 90th percentile, there was no such difference. Multiple regression analyses, using GA at birth as the dependent variable, indicated an interaction between MSAFP and PZn levels. In this population, the adverse pregnancy outcome associated with elevated MSAFP was seen only in women with PZn levels greater than the median. The reason for this association is not currently apparent.

Increased risk of preterm delivery with elevated maternal alpha-fetoprotein and plasma zinc levels in African-American women

Increased risk of preterm delivery with elevated maternal alpha-fetoprotein and plasma zinc levels in African-American women

Influence of zinc on protein metabolism in various lung cell lines

Toxic cellular effects after exposure to elevated zinc concentrations affect protein metabolism. We separated proteins by 2D-PAGE after cellular zinc exposure in order to decide whether changes in protein metabolism of specific proteins by elevated zinc might be a main critical cellular effect. The investigation was performed with fibroblast-like (11Lu, 16Lu) and alveolar epithelial (L2, A549) lung cell lines. Silver staining and autoradiography after radiolabelled methionine incorporation of 2D gels of cellular proteins was executed in order to look for specific changes in protein content. Methionine incorporation decreased in a concentration- and time-dependent manner to values of 10% with 100 μ mzinc chloride for 3 hr in the non-malignant cell lines, while about 20% was reached with 200 μ m after 4 hr of incubation in the malignant A549 cells. In silver stained 2D gels of zinc-exposed cells only few differences as compared to controls were detectable. Autoradiograms of 2D gels after methionine incorporation showed few additional spots that could be heat shock proteins in alveolar epithelial cell lines after zinc exposure. Autoradiographically detectable methionine in 2D-gels obtained after exposure of cells to high zinc concentrations for time intervals greater than 1 hr showed a time-dependent decrease in all cell lines. This decrease was accompanied by an increase of three characteristic spots at 28/9 (kDa/pI), 32/8 and 42/7.5 respectively, amounting to 15–30% of all incorporated radioactivity after 2–4 hr of zinc exposure. When cells were allowed to recover from zinc poisoning, similar 2D gel spot patterns as compared to controls without zinc exposure were obtained in all cell lines tested.

Water and sediment chemistry of a wetland treating municipal wastewater

The effects of wastewater discharge in an artificially confined wetland, Turangi land treatment facility, New Zealand, were investigated by measuring the changes in water and sediment chemistry in the land treatment facility. Analysis of surface water shows that the treatment facility is effective at removing BOD5 (85%), but not NH4‐N, SO4, PO4‐P, and total suspended solids. Surface flow measurements indicate that the effluent flows through the confined wetland in less than a day. The retention time is too short to allow exchange between wetland vegetation and effluent, thus preventing efficient contaminant removal. The change in land use c. 30 years ago associated with the construction of the land treatment facility is reflected in a change in stratigraphy and sediment chemistry. Elevated sulphur and zinc concentrations in sediments are attributed to sewage effluent discharge, and indicate that soil uptake is taking place.

Extractive Decontamination of Metal-Polluted Soils Using Oxalate

Oxalate (Ox) was investigated as an extractant for decontaminating two metal-polluted soils, one with elevated total zinc (ZnT = 2700 mg kg-1) from the Palmerton, Pennsylvania smelter site and the other from a grossly contaminated (PbT = 210 000 mg kg-1) automobile battery recycling facility in Indiana. Metal retention within the soils was substantially different as shown by sequential fractionation experiments. High Zn removal (>80%) was achieved with 1.0 M Ox when Zn existed predominantly in non-detrital metal fractions. However, Ox was an unsuitable Pb extractant due to the sparing solubility of PbOx(s). Despite the dramatically higher stability of ZnEDTA2- (log K = 16.5) compared to ZnOx° (log K = 3.4), Ox released more Zn than EDTA from the Palmerton soil because 40% of ZnT was associated with the oxide fraction. Extract analysis indicated that Ox, but nor EDTA, dissolved soil Fe oxides in the 24 hr extraction period. When contaminating metals are associated with soil oxides, Ox may be a superior extractant to powerful chelants like EDTA. It is essential to establish thoroughly metal solution chemistry and fixation behavior within the soil when extractive decontamination is proposed for site remediation.

Placental Copper Transport in Rats: Effects of Elevated Dietary Zinc on Fetal Copper, Iron and Metallothionein

We hypothesized that the competition between zinc (Zn) and copper (Cu) during fetal accretion of copper could be discriminated at either the dam-to-placenta or placenta-to-fetus stage. This premise was tested by feeding dams a high Zn diet (1000 mg/kg, HZn) during the second half of gestation. One day before delivery, dams were anesthetized, fetuses removed and both maternal and fetal tissues and plasma obtained and assayed. Other rats were fed a normal Zn concentration diet (32.4 mg/kg, ND) throughout pregnancy. There were significantly lower fetal liver Cu concentrations and greater plasma Fe concentrations, but not plasma Cu concentrations or liver Fe concentrations in the HZn group. Both dam and fetal Zn liver concentrations were greater in the HZn than in the ND group. Plasma Cu levels were lower in the HZn-fed than in the ND-fed dams. Placental tissue from the HZn litters had a greater concentration of Zn and Fe than did the ND group, whereas no effect was noted for Cu concentration. Metallothionein (MT) levels were elevated in dam livers and placenta in the HZn group, but there were no differences in fetal liver MT. The dynamic assessment of placental transport was conducted by injecting 2.5 mg/kg Cu acetate intravenously into dams of both groups. Sequential samplings of dam and fetal blood and placentas were taken from 0 to 60 min. After the Cu bolus, there was a consistently higher plasma Cu concentration in the HZn than in the ND dams, but no alteration in the concentration of Cu in the placenta or fetal plasma. This study indicates that placental Cu uptake is not affected by a high Zn diet in the dam. In addition, the greater Zn concentration in the placenta of HZn than in ND litters results in abnormal fetal Cu, Fe and Zn concentrations, suggesting that an imbalanced maternal mineral consumption is deleterious to normal divalent metal accretion.

Zinc binding to the gills of rainbow trout: the effect of long-term exposure to sublethal zinc

The effects of sublethal waterborne Zn (2·28 μmol l−1) on Zn binding kinetics to the apical gill surface were studied in juvenile rainbow trout (Oncorhynchus mykiss). Two separate radiotracer techniques were employed to ascertain this information. First, in vitro binding kinetic experiments were performed at extremely elevated zinc concentrations (up to 20 mmol l−1) to measure relatively low-affinity binding sites at the gill epithelium. There were no differences in Zn binding parameters (Km and Bmax) for fish sublethally exposed to Zn for 21 days and their simultaneous controls. Nevertheless, Ca did have an increased inhibitory effect on Zn binding in Zn-exposed fish suggesting that the anionic groups on the gill epithelium of these fish had been altered in some manner. Additionally, in vivo Zn binding kinetics were investigated using environmentally relevant waterborne Zn concentrations (low μmol l−1 range) to isolate high-affinity Zn binding sites (Ca transporters). No appreciable alterations in the Km and Bmax values for Zn binding were seen between the Zn-exposed group and its simultaneous control following 15 days of exposure. Furthermore, no significant differences in CC morphometry were observed between treatments. Despite these lack of treatment effects, there were temporal alterations in Km, Bmax and CC fractional surface area in both groups. It is proposed that these fluctuations are controlled by hormonal factors (such as stanniocalcin), believed to play a role in Ca influx.

Zinc binding to the gills of rainbow trout: the effect of long‐term exposure to sublethal zinc

The effects of sublethal waterborne Zn (2·28 μmol l−1) on Zn binding kinetics to the apical gill surface were studied in juvenile rainbow trout (Oncorhynchus mykiss). Two separate radiotracer techniques were employed to ascertain this information. First, in vitro binding kinetic experiments were performed at extremely elevated zinc concentrations (up to 20 mmol l−1) to measure relatively low‐affinity binding sites at the gill epithelium. There were no differences in Zn binding parameters (Km and Bmax) for fish sublethally exposed to Zn for 21 days and their simultaneous controls. Nevertheless, Ca did have an increased inhibitory effect on Zn binding in Zn‐exposed fish suggesting that the anionic groups on the gill epithelium of these fish had been altered in some manner. Additionally, in vivo Zn binding kinetics were investigated using environmentally relevant waterborne Zn concentrations (low μmol l−1 range) to isolate high‐affinity Zn binding sites (Ca transporters). No appreciable alterations in the Km and Bmax values for Zn binding were seen between the Zn‐exposed group and its simultaneous control following 15 days of exposure. Furthermore, no significant differences in CC morphometry were observed between treatments. Despite these lack of treatment effects, there were temporal alterations in Km, Bmax and CC fractional surface area in both groups. It is proposed that these fluctuations are controlled by hormonal factors (such as stanniocalcin), believed to play a role in Ca influx.

Metallothionein Knockout and Transgenic Mice Exhibit Altered Intestinal Processing of Zinc with Uniform Zinc-Dependent Zinc Transporter-1 Expression

A role for metallothionein in intestinal zinc absorption has been the subject of considerable debate. If metallothionein affects zinc absorption, then those factors that induce metallothionein synthesis (e.g., heavy metals, hormones) should alter zinc absorption and homeostasis. The present studies used metallothionein transgenic mice (overexpressing) and metallothionein knockout mice (no expression of metallothionein-1 or metallothionein-2) to examine directly the effects of metallothionein on zinc absorption, independent of secondary effects that could be caused by metallothionein inducers. Zinc absorption was examined by administering a single oral zinc dose (0.5 mmol/kg) by feeding tube to metallothionein transgenic and metallothionein knockout mice and measuring the serum zinc concentration. Two hours after the dose, the serum zinc concentration was 2.3 times higher in metallothionein knockout mice than in their control strain. Conversely, the concentration was elevated only one third as much in the metallothionein transgenic mice as in their controls after the zinc dose. We found that the serum zinc concentration was inversely related to the level of metallothionein protein. The intestinal zinc content was higher in the metallothionein knockout mice, however, suggesting that metallothionein did not reduce zinc absorption by simply sequestering zinc in the mucosa. The expression of the zinc transporter ZnT-1 was directly related to the serum zinc level and was independent of the level of metallothionein. These results further support metallothionein as an important component for reducing the efficiency of zinc absorption at elevated zinc intakes.

Metallothionein Expression Is Increased in Monocytes and Erythrocytes of Young Men during Zinc Supplementation , ,

The metallothionein gene is transcriptionally regulated by zinc. Consequently, metallothionein has potential for serving as an index of dietary zinc status in humans. To examine this possibility, an enzyme-linked immunoassay (ELISA) based on a sandwich approach that utilizes monoclonal and chicken egg yolk antibodies was used to compare the response of erythrocyte metallothionein protein levels with the response of monocyte metallothionein mRNA levels as measured by competitive reverse transcriptase–polymerase chain reaction (CRT-PCR) during zinc supplementation. Young male subjects participated in an 18-d supplementation study in which zinc was provided at 50 mg/d. Control subjects received a placebo. The zinc supplement resulted in significantly greater erythrocyte metallothionein levels by d 8 of supplementation compared with controls. Monocyte metallothionein mRNA levels were significantly greater than those of controls by d 2 of supplementation. Both remained elevated through d 18. They returned to base line by 8 and 4 d after supplementation, respectively. The plasma zinc concentration was significantly greater than in controls by d 6 and had returned to control levels by d 22 of supplementation. The results presented here show that both monocyte metallothionein mRNA and erythrocyte metallothionein protein concentrations change in human subjects in response to elevated dietary zinc intake and that monocyte metallothionein mRNA responds more rapidly to elevation of dietary zinc status than erythrocyte metallothionein protein. Consequently, both erythrocyte metallothionein and monocyte metallothionein mRNA may prove to be measures useful for assessment of either zinc depletion or the bioavailability of zinc supplements.

Chemical speciation of dissolved Cu, Zn, Cd, Pb in Narragansett Bay, Rhode Island

The chemical speciation of `dissolved' Cu, Zn, Cd, and Pb was determined by differential pulse anodic stripping voltammetry (DPASV) at three sampling sites in the high salinity region (24–30 psu) of the Narragansett Bay estuary. Speciation results show that organic chelates of these four trace metals are the dominant forms in conventionally filtered ( 99% for Cu in these estuarine waters. Dissolved Zn ([ZnT]) varied from 72 nM at the Upper Bay site to 16 nM at the Lower Bay site, the concentration of the Zn-binding ligands ([LT]) varied from 48 to 11 nM with a relatively uniform conditional stability constant (KZnL,Zn′cond=109.0 M−1). At the Upper and Lower Bay sites, where [ZnT]>[LT], there was less organic complexation (50 to 60%) of [ZnT] as compared to the Mid-Bay (bloom) station, where [ZnT]<[LT] and the degree of organic complexation was considerably higher (97%). The concentration of Cd-binding ligands was nearly constant throughout the bay (ca. 4 nM with mean KCdL,Cd′cond=108.9 M−1) and present at much higher levels than the dissolved Cd ([CdT]=0.80–0.29 nM, decreasing down bay). Titration results for Pb were modeled by two classes of Pb-binding ligands. Dissolved Pb ranged from 0.32 to 0.13 nM and the strong class of Pb-binding ligands (L1) was in slight excess of these values (ca. 0.8 nM) with a mean KcondPbL1,Pb′=1010.0 M−1. A weaker class of Pb-binding ligands (L2) existed at 4.0–8.2 nM with a mean KcondPbL2,Pb′=108.8 M−1. Titration data for Cu were interpreted as being influenced by three classes of Cu-binding ligands (L1, L2, L3), whose sum was always in excess of the dissolved [CuT] (12.7–27.9 nM). Our DPASV estimates of [L1] were 16–38 nM with a KcondCuL1,Cu′≥1012 M−1. There were higher concentrations of intermediate and weaker classes of Cu-binding ligands: [L2]=40 to 15 nM with a mean KcondCuL2,Cu′=108.8 M−1 and [L3]=100 to 54 nM with a mean KcondCuL3,Cu′=107.7 M−1. The two stronger classes of Cu-binding ligands (L1 and L2) resulted in CuL1 and CuL2 as the dominant dissolved Cu species. Free ion concentrations were calculated for all four metals at the three sampling sites: [Cu2+]≤10−12 M, [Cd2+]≤2×10−12 M, [Pb2+]∼10−12 M, while [Zn2+] ranged from 0.3–13×10−9 M. For Cu, Pb, and Cd, these ambient values are below the concentrations of toxic responses reported from laboratory studies of marine microorganisms. At the Upper Bay site, any toxic effect of the elevated free zinc ion concentration is likely to be alleviated by the antagonistic effect of high dissolved Mn.

CHANGES IN CONCENTRATION OF TRACE ELEMENTS IN URINE, SERUM, AND SALIVA AS INDICES OF GENTAMICIN NEPHROTOXICITY IN MALE WISTAR RATS

Male Wistar rats were treated with gentamicin in repeated doses (5 2 100 mg/kg) intraperitoneally. The concentrations of trace elements (zinc and copper) in urine, serum, and pure saliva obtained from submandibular glands were determined 24 h and 20 d after the last administration of the drug. At the same time, kidneys and submandibular glands were examined histopathologically by electron microscopy. Rats receiving gentamicin demonstrated phospholipidosis at the end of 5 d of administration. At the same time, elevated zinc and copper levels in urine, increased zinc levels in serum, and decreased copper levels in serum and zinc levels in saliva were observed. Twenty days after the last injection, the levels of these metals were comparable to the control group and none of the sections demonstrated phospholipidosis. Based on these results, it may be concluded that certain changes in the levels of these metals in serum and saliva could also be an indicator of acute gentamicin nephrotoxicity.