Histochemical demonstration of mercury in the olfactory system of salmon (Salmo salar L.) following treatments with dietary methylmercuric chloride and dissolved mercuric chloride

The deposition of organic and inorganic mercury compounds was studied histochemically in the salmon (Salmo salar L.) olfactory system. One group of salmon was given fodder pellets containing methylmercuric chloride (CH3HgCl, 99 micrograms Hg/g) for 4 weeks. Other groups of fish were exposed to dissolved mercuric chloride (HgCl2, 270 micrograms Hg/liter) for 2, 6, and 12 hr, respectively. In both series of experiments, the radioisotope 203Hg was included in order to determine the accumulation of mercury in the olfactory system. Gamma-spectrometry showed that both mercury compounds accumulated in the olfactory rosettes and their nerves. Tissue sections from the rosettes and olfactory nerves were subjected to autometallographic silver enhancement, thereby rendering mercury deposits visible for light and electron microscopy. Microscopic analysis demonstrated an intense and comprehensive Hg deposition in the axons and Schwann cells of both methylmercury- and inorganic mercury-exposed fish. On the other hand, the two mercury compounds showed different staining patterns in the sensory epithelium. The silver grains evoked by methylmercury were localized predominantly in lysosome-like inclusions within the receptor cells, while those produced by HgCl2 exposure were situated mainly along the borders of neighboring cells. The present findings that organic and inorganic mercury compounds were deposited in the olfactory system along its whole length, from the receptor cell apices to the brain, support the electrophysiological results presented elsewhere (Baatrup et al., 1990, Ecotoxicol. Environ. Safety 20, 269-276).     

The effect of Cu (II) on the electro-olfactogram (EOG) of the Atlantic salmon (Salmo salar L) in artificial freshwater of varying inorganic carbon concentrations.

The effect of inorganic copper species was studied by recording the receptor potential, electro-olfactogram (EOG), from the olfactory epithelium of Atlantic salmon (Salmo salar L). In a series of experiments, the olfactory organ was irrigated with aqueous copper solutions with concentrations of the free cupric ion (Cu2+) ranging from 0.2 to 9.7 microM. The diverse copper species were created by varying the amount of bicarbonate (NaHCO3) in artificial freshwater solutions of equal total copper concentrations. In general, these copper solutions induced a slow depolarization of the baseline followed by a hyperpolarization. The amplitudes of these variations in baseline potentials increased with increasing concentrations of Cu2+ ion, i.e., decreasing concentrations of NaHCO3. Stimulating the olfactory epithelium with L-alanine during the copper exposure evoked atypical EOG responses. The amplitudes and form of the EOGs changed drastically with increasing Cu2+ concentrations, with significant correlation between the reduction in EOG amplitudes and the Cu2+ concentration. The results indicate that among the copper species tested the toxic effect is caused mainly by the dissolved Cu2+ ion. The results also suggest that the Cu2+ ion exerts its toxic effects on the transduction mechanisms of the olfactory receptor cells. The different EOG profiles obtained in response to varying Cu2+ concentrations indicate that this ion affects the transduction mechanisms at different stages.     

Changes in juvenile coho salmon electro-olfactogram during and after short-term exposure to current-use pesticides

For anadromous salmonids, olfaction is a critical sense, enabling return migration. In recent years, several pesticides have been identified that interfere with salmonid olfaction at concentrations in the microg/L range; thus, they may pose a risk to species longevity. In the present study, we investigated the acute effects of five agricultural pesticides on juvenile coho salmon (Oncorhynchus kisutch) olfaction using the electro-olfactogram (EOG), a measure of odorant-evoked field potentials. Electro-olfactogram responses to the odorant L-serine were measured during and following a 30-min exposure of the left olfactory rosette to chlorothalonil, endosulfan, glyphosate acid, iodocarb (IPBC), trifluralin, and 2,4-dichlorophenoxyacetic acid. With the relatively insoluble pesticides endosulfan and trifluralin, decreases in EOG amplitude were only apparent at relatively high concentrations (100 and 300 microg/L, respectively) following 20 min of exposure and were absent for chlorothalonil (1 mg/L). With the water-soluble herbicide glyphosate, significant EOG reductions occurred within 10 min of exposure to 1 mg/L and more rapidly with higher concentrations. Recovery of EOG post-glyphosate exposure was concentration-dependent, and complete recovery was not observed with some concentrations at 60 min postexposure. Dichlorophenoxyacetic acid only affected EOG at high concentration (100 mg/L), where it eliminated EOG within 2 min of exposure. With IPBC, EOG was decreased at 25 min of exposure to 1 microg/L; higher concentrations caused decreases to occur more rapidly. Excluding IPBC and glyphosate, all EOG reductions occurred at concentrations greater than the current Canadian water-quality guidelines and reported 96-h lethality values. Our results show that olfactory neurons can be impaired rapidly by some current-use pesticides, even at exposures in the low-microg/L range.     

Initial events in stimulation of taste and smell receptor cells.

Analysis of the initial interactions of chemicals with olfactory and taste receptor cells is complicated by problems in controlling stimulus presentation. These interactions arise from chemicals diffusing through an unstirred layer to reach the cell surfaces and, in the case of olfaction, partitioning into mucus from air. In many instances, the odorants are metabolized to products that may be stimulants. In such cases, the analysis is further complicated by uncertainty about which chemical species actually stimulate. Stimulation of chemoreceptors can be thought of as originating from specific and nonspecific interactions of stimuli with the cells. Specific interactions involve receptor proteins in or on the cell membranes. These interactions are probably important in initiating sweet taste but not in detecting salty or sour stimuli. There are many reported preparations including putative olfactory receptor proteins, and evidence exists that the proteins comprise a structurally similar class. In some, the proteins are demonstrated to have olfactory function, but blocking their interaction with odorants only partially inhibits olfactory responses. The remainder of the responses presumably occur by general irritant effects of odorants and their metabolites.     

Copper deficiency alters vasodilation in the rat cremaster muscle microcirculation.

The effects of copper deficiency on smooth muscle relaxation were studied in the cremaster muscle microcirculation. Male Sprague-Dawley rats were fed either a copper-adequate diet (CuA, 5 micrograms copper/g diet) or copper-deficient diet (CuD, no added copper) for 17-27 d before experimentation. In vivo television microscopy was used to quantify agonist-induced diameter changes in third-order arterioles. Endothelium-dependent relaxation, which is hypothesized to be mediated by nitric oxide, was attenuated by copper deficiency. Both receptor (acetylcholine, 10(-7) to 10(-4) mol/L) and nonreceptor (calcium ionophore A23187, 10(-8) to 10(-7) mol/L) relaxation was decreased. Nitric oxide-mediated dilation, which was endothelium-independent (10(-7) to 10(-5) mol/L sodium nitroprusside), was also attenuated by copper deficiency. Maximal responses were as follows: for acetylcholine, 136 +/- 16% CuA vs. 45 +/- 15% CuD; for A23187, 104 +/- 16% CuA vs. 21 +/- 11% CuD; and for nitroprusside, 125 +/- 12% CuA vs. 46 +/- 13% CuD. There was no difference in microvascular dilation between groups treated with 10(-6) to 10(-4) mol/L of the phosphodiesterase inhibitor papaverine (e.g., CuA 109 +/- 11% vs. CuD 133 +/- 21% with 10(-4) mol/L). These results suggest that copper deficiency inhibits the nitric oxide-mediated mechanism of vascular smooth muscle relaxation without altering the capacity of the smooth muscle to relax. We suggest that copper deficiency either decreases nitric oxide radical availability or disrupts the nitric oxide-guanylate cyclase interaction.     

Development of flow cytometry-based algal bioassays for assessing toxicity of copper in natural waters

Copper toxicity to the freshwater algae Selenastrum capricornutum and Chlorella sp. and the marine algae Phaeodactylum tricornutum and Dunaliella tertiolecta was investigated using different parameters measured by flow cytometry: cell division rate inhibition, chlorophyll a fluorescence, cell size (i.e., light-scattering), and enzyme activity. These parameters were assessed regarding their usefulness as alternative endpoints for acute (1-24 h) and chronic (48-72 h) toxicity tests. At copper concentrations of 10 micrograms/L or less, significant inhibition (50%) of the cell division rate was observed after 48- and 72-h exposures for Chlorella sp., S. capricornutum, and P. tricornutum. Bioassays based on increases in algal cell size were also sensitive for Chlorella sp. and P. tricornutum. Copper caused both chlorophyll a fluorescence stimulation (48-h EC50 of 10 +/- 1 micrograms Cu/L for P. tricornutum) and inhibition (48-h EC50 of 14 +/- 6 micrograms Cu/L for S. capricornutum). For acute toxicity over short exposure periods, esterase activity in S. capricornutum using fluorescein diacetate offered a rapid alternative (3-h EC50 of 90 +/- 40 micrograms Cu/L) to growth inhibition tests for monitoring copper toxicity in mine-impacted waters. For all the effect parameters measured, D. tertiolecta was tolerant to copper at concentrations up to its solubility limit in seawater. These results demonstrate that flow cytometry is a useful technique for toxicity testing with microalgae and provide additional information regarding the general mode of action of copper (II) to algal species.     

Dissolved organic carbon modulates the effects of copper on olfactory-mediated behaviors of chinook salmon

The modulation of Cu effects on olfactory-mediated behaviors by dissolved organic carbon (DOC) and Fe was examined in juvenile chinook salmon. Chinook were exposed to several concentrations of Cu, DOC, and Fe alone or in combination in a flow-through system for either 4 d (acute exposure) or 14 d (subchronic exposure) and tested for their ability to detect and avoid the odorant L-histidine in an avoidance/preference trough assay. In both acute and subchronic exposures, Cu inhibited the ability of fish to detect this amino acid in a concentration-dependent manner, and Cu toxicity (olfactory inhibition) decreased with increasing DOC concentration. In both acute and subchronic experiments including DOC, Cu-induced olfactory inhibition decreased in a linear fashion with increasing DOC concentration, although the modulation was lower in subchronic exposures. The protective effect of DOC on Cu olfactory inhibition was reduced only slightly in the presence of Fe, indicating that other metals can potentially affect the modulation of the olfactory inhibition of Cu through competition for DOC binding sites. The results of the present study clearly show the amelioration by DOC of the effects of Cu on juvenile chinook salmon olfaction at a behavioral level. These data further indicate that DOC concentrations should be considered when evaluating the potential impact of Cu on fish olfaction. Environ. Toxicol. Chem. 2012; 31: 2281-2288. ? 2012 SETAC.     

Exposure to a Mixture of Zinc and Copper Decreases Survival and Fecundity of Discocotyle sagittata (Leuckart) Parasitizing Juvenile Atlantic Salmon, Salmo salar L.

We assessed the effects of zinc and copper on freshwater monogenean ectoparasites (Discocotyle sagittata Leuckart) infecting juvenile Atlantic salmon (Salmo salar L.). Exposure to 47 μg/L zinc and 3 μg/L copper reduced survival and fecundity of adult D. sagittata, while egg hatching success was only reduced at high exposure concentrations (2704 μg/L zinc and 164 μg/L copper). Parasitized salmon had decreased plasma chloride, but this was negated in infected fish exposed to metals. No other effects on Atlantic salmon survival and physiology (plasma osmolality, hematocrit) were noted, suggesting that D. sagittata may be more susceptible to metal toxicity than its host fish.     

Detection of Odorants through the Main Olfactory Epithelium and Vomeronasal Organ of Mice

Previous research has indicated that volatile odorants are detected through the main olfactory epithelium (MOE), whereas pheromones are detected via the vomeronasal organ (VNO). Gene disruption studies have established that olfactory signaling through the MOE is mediated through receptor stimulation of type 3 adenylyl cyclase (AC3). Mice lacking AC3 cannot detect odorants through the MOE. Recently, it was discovered using olfactory-based behavioral assays that AC3 mutant mice can detect some volatile odorants. An analysis of these mutant mice led to the surprising discovery that some odorants are detected through the VNO .     

Studies in human lactation: zinc, copper, manganese and chromium in human milk in the first month of lactation

Zinc, copper, manganese and chromium were measured in a total of 259 samples of human milk from 11 women from day of delivery to 31 days postpartum. Milk intakes by their fully breast-fed infants were calculated from 24-h test-weighing measurements. Zinc was analyzed by flame atomic absorption spectrophotometry, and the other elements by graphite furnace atomic absorption. Mean (+/- SD) concentrations declined from a maximum of 11.5 +/- 4.7 micrograms/ml at 2 days to 2.98 +/- 0.78 micrograms/ml at 28 +/- 3 days. Changes in the other three elements were irregular. The average copper concentration declined from 0.6 +/- 0.12 micrograms/ml on day 5 to 0.41 +/- 0.04 micrograms/ml at 28 days. Manganese levels decreased from a mean of 5.4 +/- 1.6 ng/ml on day 1 to 2.7 +/- 1.6 ng/ml on day 5; from 8 to 28 days there was little change, the overall mean being 3.7 +/- 2.2 ng/ml. The average concentration of chromium over the whole period was 0.27 +/- 0.10 ng/ml. Average daily intakes of the elements, by the infants, over the one month period were: zinc, 2.0 mg; copper, 0.25 mg; manganese, 2.0 micrograms; chromium, 150 ng.     

Differential effects of mercurial compounds on the electroolfactogram (EOG) of salmon (Salmo salar L.)

The effects on the salmon (Salmo salar L.) electroolfactogram (EOG) of the two mercurials, mercuric chloride (HgCl2) and methylmercuric chloride (CH3HgCl), were studied. The EOG responses were evoked by stimulating the olfactory epithelium with 340 microM L-alanine for 10 sec every second minute during a 1-hr period. Each EOG response consisted of an initial peak component followed by a sustained component with an amplitude about 40% below the peak value. Three experimental series, each comprising six fish, were carried out. In the first series, the rosette was irrigated solely with artificial "fresh water." In the two other series, a 5-min exposure to mercury (HgCl2 or CH3HgCl, at 10(-5) M) was included after 10 min and a 15-min exposure after 45 min. The mercuric ion (Hg2+) eliminated the peak response within 2 min and suppressed the sustained response to about 35%. During the subsequent irrigation with mercury-free fresh water, both EOG components regained about 50% of their initial amplitudes. In contrast, methylmercury induced a steady and parallel decline of both the peak and the sustained responses, which were not reversed by rinsing the epithelium with fresh water. The results of this study demonstrate the vulnerability of the olfactory receptor function in fish to mercury exposure. Also, they show the very different effects of inorganic and organic mercurials upon the EOG.     

Adverse effects of high dietary iron and ascorbic acid on copper status in copper-deficient and copper-adequate rats

The effects of elevated dietary ascorbic acid and iron on copper utilization were examined. Male Sprague-Dawley rats were fed one of two levels of Cu (deficient, 0.42 microgram Cu/g, or adequate, 5.74 micrograms Cu/g), Fe (moderate, 38 micrograms Fe/g or high, 191 micrograms Fe/g), and ascorbic acid (low, 0% or high, 1% of the diet) for 20 d. High Fe decreased (p less than 0.05) Cu absorption only in Cu-deficient rats. High ascorbic acid significantly decreased tissue Cu levels in Cu-adequate rats. High Fe with ascorbic acid caused severe anemia in Cu-deficient rats and decreased plasma ceruloplasmin by 44% in Cu-adequate rats. Cu,Zn-superoxide dismutase activity in erythrocytes was decreased (p less than 0.05) by 14% during Cu deficiency but was not affected by Fe or ascorbic acid. These results may be important to individuals with high intakes of Fe and ascorbic acid.     

Dissolved copper triggers cell death in the peripheral mechanosensory system of larval fish

Dissolved copper is an increasingly common non-point source contaminant in urban and urbanizing watersheds. In the present study, we investigated the sublethal effects of dissolved copper on the peripheral mechanosensory system, or lateral line, of larval zebrafish (Danio rerio). Zebrafish larvae were exposed to copper (0-65 microg/L), and the cytotoxic responses of individual lateral line receptor neurons were examined using a combination of in vivo fluorescence imaging, confocal microscopy, scanning electron microscopy, and conventional histology. Dissolved copper triggered a dose-dependent loss of neurons in identified lateral line neuromasts at concentrations > or = 20 microg/L. The onset of cell death in the larval mechanosensory system was rapid (< 1 h). When copper-exposed zebrafish were transferred to clean water, the lateral line regenerated over the course of 2 d. In contrast, the lateral line of larvae exposed continuously to dissolved copper (50 microg/L) for 3 d did not recover. Collectively, these results show that peripheral mechanosensory neurons are vulnerable to the neurotoxic effects of copper. Consequently, dissolved copper in non-point source storm-water runoff has the potential to interfere with rheotaxis, schooling, predator avoidance, and other mechanosensory-mediated behaviors that are important for the migration and survival of fish.     

Interaction of dietary carbohydrate, ascorbic acid and copper with the development of copper deficiency in rats

The effects of dietary carbohydrate and ascorbic acid on the development of copper deficiency were investigated. Male Sprague-Dawley rats (n = 48) were fed one of eight diets in a 2 X 2 X 2 factorial design for 21 d. These diets varied in copper (1.11 or 8.96 micrograms Cu/g diet), carbohydrate (sucrose or cornstarch, 62.3%) and ascorbic acid (0 or 1%). Compared to controls, copper-deficient rats had lower hematocrit and ceruloplasmin levels, lower levels of copper and iron in several tissues, higher heart weights and lower spleen weights. During copper deficiency, liver iron levels were higher than control levels when cornstarch, but not sucrose, was the carbohydrate source, while liver and gastrointestinal tract weights were higher with sucrose compared to cornstarch. Copper-deficient rats fed ascorbic acid had significantly (P less than 0.05) lower hematocrits when fed sucrose compared to starch [29.6 +/- 1.2 vs. 36.8 +/- 1.2 g/dl (mean +/- SEM), respectively]. In copper-deficient rats, sucrose tended to lower the apparent absorption of copper compared to cornstarch, while ascorbic acid reduced the apparent absorption of iron. Thus, sucrose and ascorbic acid appeared to reduce hematocrit levels through effects on mineral absorption.     

Zinc and copper status in children with bronchial asthma and atopic dermatitis

The study comprised 40 children of both sexes aged from 2 to 12 years, 22 suffering from bronchial asthma and 18 suffering from atopic dermatitis. Twenty healthy children of comparable age and sex to the patients were studied as controls. All the children were subjected to full history including dietetic questionnaire, thorough examination, and to estimation of serum IgE, serum ceruloplasmin, and zinc and copper levels in both serum and hairs. The mean concentrations of zinc in serum and hairs were respectively 70.3 +/- 13.2 micrograms/100 ml and 167.5 +/- 23.0 micrograms/gm in asthmatic cases and 65.9 +/- 11.7 micrograms/100 ml and 164.8 +/- 23.6 micrograms/gm in those with atopic dermatitis. These levels were significantly (p less than 0.001) decreased in comparison to the control values (88.4 +/- 11.0 micrograms/100 ml and 194.5 +/- 18.6 micrograms/gm). On the other hand, a significant (p less than 0.001) increase in serum and hairs copper was demonstrated in both allergic groups compared to the controls. Mean copper values were respectively 79.5 +/- 8.06 micrograms/100 ml and 18.7 +/- 1.9 micrograms/gm in the asthmatic cases and 81.4 +/- 8.4 micrograms/100 ml and 17.8 +/- 2.08 micrograms/gm in cases with atopic dermatitis. The control mean concentrations were 67.95 +/- 6.37 micrograms/100 ml and 14.5 +/- 2.53 micrograms/gm respectively. Significant (p less than 0.001) higher levels of serum ceruloplasmin were observed in the allergic patients compared to the controls and were correlated with the hypercupremia. The results were discussed and a good dietetic intake of high biological value protein and zinc supplement was recommended to these patients in order to correct their disturbances especially the hypozincemia which could lead to exaggeration of their allergic conditions. The field of trace elements metabolism has grown rapidly over the past few years, particularly after the development of novel techniques as the atomic absorption spectrophotometry which had allowed the reliable measurements of several trace elements in tissues and so had opened a new field for many researches (Henkin, 1976). Zinc and copper are involved in cell and tissue growth. Zinc plays an important role in DNA and protein synthesis and is intimately involved with copper as cofactors in several important enzyme systems. The effects of many pathological conditions as congestive heart failure, pneumonia, rheumatic heart diseases, bronchitis, recurrent infection, hemolytic anemia, psoriasis, and malnutrition on the levels of serum zinc, copper, and other trace elements have been of interest to investigators for a number of years (Sinha and Gabrieli, 1970; David et al., 1984).(ABSTRACT TRUNCATED AT 400 WORDS)     

Effects of low-level lead and arsenic exposure on copper smelter workers

An analysis of reported symptoms and their relationship with indicators of lead absorption--blood lead (Pb-B) and zinc protoporphyrin (ZPP)--and of arsenic absorption--urinary arsenic (As-U)--was undertaken among 680 active copper smelter workers. Lead and arsenic absorption in the copper smelter employees were characterized by the median values of 30.4 micrograms/dl for Pb-B, 41.5 micrograms/dl for ZPP, and 26 micrograms/L for As-U. Blood lead was 40 micrograms/dl or higher in 16.7% of cases, ZPP was 50 micrograms/dl or higher in 31.2%, and urinary arsenic was 50 micrograms/L or higher in 16.4% of currently active copper smelter workers. The number of reported symptoms (from a total of 14 symptoms) increased with ZPP levels; the relationship with Pb-B was less marked. Arsenic contributed relatively little. Mean Pb-B, ZPP, and As-U levels for subjects reporting each of the 14 symptoms were compared with those of subjects who did not report the symptoms. Mean Pb-B was found to differ significantly for one symptom, fatigue. Significant differences in mean ZPP levels were found for fatigue, sleep disturbances, weakness, paresthesia, and joint pain. Prevalence rates for these symptoms rose more markedly with increasing ZPP than with Pb-B levels. The results indicate a relationship between certain CNS and musculo-skeletal symptoms and increased lead absorption in this population. Adherence to exposure standards that preclude undue lead absorption and appropriate biological monitoring including ZPP levels, are necessary to prevent adverse, especially long-term, health effects.     

Effects of dissolved organic carbon on the toxicity of copper to the developing embryos of the Pacific oyster (Crassostrea gigas)

The effects of humic acid (HA) on copper speciation and its subsequent toxicity to the sensitive early life stages of the Pacific oyster (Crassostrea gigas) are presented. Differential pulse anodic stripping voltammetry with a hanging mercury drop electrode was used to measure the copper species as labile copper (LCu; free ion and inorganic copper complexes) and total copper (TCu) with respect to increasing HA concentration. The TCu and LCu 50% effect concentrations (EC50s) in the absence of HA were 20.77 microg/L (95% confidence interval [CI], 24.02-19.97 microg/L) and 8.05 microg/L (95% CI, 9.6-5.92 microg/L) respectively. A corrected dissolved organic carbon (DOC) concentration (HA only) of 1.02 mg/L was required to significantly increase the TCu EC50 to approximately 41.09 microg/L (95% CI, 44.27-37.52 microg/L; p < 0.05), almost doubling that recorded when DOC (as HA) was absent from the test media. In contrast, the LCu EC50 was unaffected by changes in DOC concentration and was stable throughout the corrected DOC concentration range. The absence of change in the LCu EC50, despite increased HA concentration, suggests that the LCu fraction, not TCu, was responsible for the observed toxicity to the oyster embryo. This corresponds with the current understanding of copper toxicity and supports the free-ion activity model for copper toxicity.     

Histochemical demonstration of mercury in the olfactory system of salmon (Salmo salar L.) following treatments with dietary methylmercuric chloride and dissolved mercuric chloride

The deposition of organic and inorganic mercury compounds was studied histochemically in the salmon Salmo salar L. olfactory system. One group of salmon was given fodder pellets containing methylmercuric chloride (CH₃HgCl, 99 μg Hg/g) for 4 weeks. Other groups of fish were exposed to dissolved mercuric chloride (HgCl₂, 270 μg Hg/liter) for 2, 6, and 12 hr, respectively. In both series of experiments, the radioisotope ²⁰³Hg was included in order to determine the accumulation of mercury in the olfactory system. Gamma-spectrometry showed that both mercury compounds accumulated in the olfactory rosettes and their nerves. Tissue sections from the rosettes and olfactory nerves were subjected to autometallographic silver enhancement, thereby rendering mercury deposits visible for light and electron microscopy. Microscopic analysis demonstrated an intense and comprehensive Hg deposition in the axons and Schwann cells of both methylmercury- and inorganic mercury-exposed fish. On the other hand, the two mercury compounds showed different staining patterns in the sensory epithelium. The silver grains evoked by methylmercury were localized predominantly in lysosome-like inclusions within the receptor cells, while those produced by HgCl₂ exposure were situated mainly along the borders of neighboring cells. The present findings that organic and inorganic mercury compounds were deposited in the olfactory system along its whole length, from the receptor cell apices to the brain, support the electrophysiological results presented elsewhere (Baatrup et al., 1990, Ecotoxicol. Environ. Safety 20, 269–276).     

Dissolved organic carbon reduces the toxicity of copper to germlings of the macroalgae, Fucus vesiculosus

This study investigates the effects of waterborne copper exposure on germling growth in chemically defined seawater. Germlings of the macroalgae, Fucus vesiculosus were exposed to a range of copper and dissolved organic carbon (DOC as humic acid) concentrations over 14 days. Germling growth was found to be a sensitive indicator of copper exposure with total copper (TCu) and labile copper (LCu) EC(50) values of approximately 40 and 20 microg/L, respectively, in the absence of added DOC. The addition of DOC into the exposure media provided germlings with protection against copper toxicity, with an increased TCu EC(50) value of 117.3 microg/L at a corrected DOC (cDOC from humic acid only) concentration of 2.03 mg/L. The LCu EC(50) was not affected by a cDOC concentration of 1.65 mg/L or less, suggesting that the LCu concentration not the TCu concentration was responsible for inhibiting germling growth. However, at a cDOC concentration of approximately 2mg/L an increase in the LCu EC(50) suggests that the LCu concentration may play a role in the overall toxicity to the germlings. This is contrary to current understanding of aquatic copper toxicity and possible explanations for this are discussed.     

Effects of copper on olfaction of Colorado pikeminnow

Effects of copper on olfaction of Colorado pikeminnow (Ptychocheilus lucius) were investigated by exposing fish for 24 or 96 h, then evaluating olfactory ability using a behavioral assay and observing olfactory structures using scanning electron microscopy (SEM). The behavioral assay measured a response known as fright reaction. Failure of exposed fish to demonstrate a fright reaction in the presence of skin homogenate assumed to contain fright pheromone was considered evidence of copper-induced loss of olfactory ability. Regression analysis was used to describe the response of fish as a function of copper concentration at each exposure duration. Olfactory ability declined with increasing copper concentration. For copper concentrations less than 66 microg/L, olfaction was more sensitive to exposure at 24 h than at 96 h. This result suggests that physiological adaptation and recovery of sensory ability occurred despite continuous exposure in the 96-h treatment. Protective mechanisms induced by exposure may have reduced sensitivity to copper by 96 h. Systematic surveys using SEM to detect presence or absence of olfactory receptors confirmed results of behavioral assays. Copper concentrations in one river inhabited by Colorado pikeminnow were compared with effective concentrations estimated by regression. Comparisons suggest that ambient copper concentrations may occasionally inhibit olfaction of wild fish.