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Archives of Environmental Contamination and Toxicology (v.39, #1)
Roe Deer Antlers as Monitoring Units for Assessing Temporal Changes in Environmental Pollution by Fluoride and Lead in a German Forest Area over a 67-Year Period by H. Kierdorf; U. Kierdorf (pp. 1-6).
Fluoride and lead concentrations were analyzed in antlers of adult roe bucks (Capreolus capreolus) collected between 1932 and 1998 in a forest area of 800 ha, that directly borders on the eastern suburbs of Cologne (Germany). Values ranged between 158 and 3,713 mg/kg dry weight for fluoride and from 0.4 to 12.0 mg/kg dry weight for lead, and varied significantly between periods (1932–49, 1950–59, 1960–69, 1970–79, 1980–89, 1990–98). Antler bone levels of both contaminants decreased markedly during the 1980s and 1990s. As a consequence, mean fluoride and lead concentrations in antlers collected in the 1990s were significantly lower than those from all preceding periods. These findings indicate a pronounced decline in fluoride and lead pollution of the study area, which is attributed to reduced emissions from stationary sources and, in the case of lead, to the introduction of unleaded gasoline and the subsequent phasing out of leaded gasoline in Germany. Because antlers are replaced annually, grow during a seasonally fixed period of some months, and are regularly collected and kept by hunters, they are useful monitoring units for recording past and present environmental pollution by “bone-seeking” pollutants in a cost-effective way. Due to its relative abundance and its rather narrow home range, the roe deer is well suited as a monitoring species for assessing changes in ambient contaminant levels on a local scale.
Mediation of Oxidative Stress in HCH-Induced Neurotoxicity in Rat by A. Sahoo; L. Samanta; G. B. N. Chainy (pp. 7-12).
Effect of repeated oral administration of hexachlorocyclohexane (HCH) (10 and 20 mg/kg body weight/day for 7 and 30 days) on the antioxidant defense system and lipid peroxidation (LPX) of rat cerebral hemisphere (CH) was evaluated. The level of LPX was elevated after 7 days of treatment in crude homogenate (endogenous and FeSO4- and ascorbic acid–stimulated) and subcellular fractions except the nuclear fraction in which induction was seen after 30 days. The pesticide elicited a significant decrease in the activities of cytosolic total and CN−-sensitive superoxide dismutase (SOD) after 7 and 30 days of HCH treatment, but failed to evoke any change in CN−-resistant SOD. Catalase activity decreased throughout the treatment period. Cerebral glutathione peroxidase activity (both selenium-dependent and -independent isoenzymes) and the level of glutathione content were decreased after 7 and 30 days of treatment, respectively. Activity of glutathione reductase and content of ascorbic acid, however, were enhanced following the pesticide exposure. The results suggest that repeated HCH administration induced oxidative stress in rat CH.
Accumulation of Butyltin and Phenyltin Compounds in Various Fish Species by H. Harino; M. Fukushima; S. Kawai (pp. 13-19).
Concentrations of organotins (OTs) were measured in the muscle of 11 species of fishes from the Port of Osaka and Yodo River, Japan. Tributytin (TBT) and triphenyltin (TPT) compounds were detected in the range of 0.011–0.182 mg/kg wet weight and < 0.001–0.130 mg/kg wet weight, respectively. Concentrations of TBT were higher than those of TPT in the muscle of fish. Concentrations of OTs in fish from sea areas were higher than those from rivers, and the ratios of TBT to total butyltins (BTs) in fish from sea areas were also higher than those from rivers. A similar trend was found for TPT. Logarithm of bioconcentration factor (BCF) of TBT in fish was in the range of 2.7–3.9. No sex differences in TBT and TPT concentrations in Japanese sea perch were observed, and the concentrations of TBT and TPT were not related to total length of fish. No correlation was also observed between the concentration of TBT or TPT and lipid content. The concentrations of BTs and phenyltins (PTs) in organs and tissues of three fish species were determined. TBT was higher concentration in liver, brain, and muscle of white croaker and yellowtail. The ratios of TBT to the total BTs were 30–40%, and the ratios of TPT to total PTs in these fishes were greater than 50% of the total PT concentrations.
Development and Evaluation of Consensus-Based Sediment Quality Guidelines for Freshwater Ecosystems by D. D. MacDonald; C. G. Ingersoll; T. A. Berger (pp. 20-31).
Numerical sediment quality guidelines (SQGs) for freshwater ecosystems have previously been developed using a variety of approaches. Each approach has certain advantages and limitations which influence their application in the sediment quality assessment process. In an effort to focus on the agreement among these various published SQGs, consensus-based SQGs were developed for 28 chemicals of concern in freshwater sediments (i.e., metals, polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and pesticides). For each contaminant of concern, two SQGs were developed from the published SQGs, including a threshold effect concentration (TEC) and a probable effect concentration (PEC). The resultant SQGs for each chemical were evaluated for reliability using matching sediment chemistry and toxicity data from field studies conducted throughout the United States. The results of this evaluation indicated that most of the TECs (i.e., 21 of 28) provide an accurate basis for predicting the absence of sediment toxicity. Similarly, most of the PECs (i.e., 16 of 28) provide an accurate basis for predicting sediment toxicity. Mean PEC quotients were calculated to evaluate the combined effects of multiple contaminants in sediment. Results of the evaluation indicate that the incidence of toxicity is highly correlated to the mean PEC quotient (R2= 0.98 for 347 samples). It was concluded that the consensus-based SQGs provide a reliable basis for assessing sediment quality conditions in freshwater ecosystems.
Increase in Dopamine Metabolites in Murine Striatum After Oral Exposure to Inorganic But Not Organic Form of Selenium by M. Tsunoda; V. J. Johnson; R. P. Sharma (pp. 32-37).
Selenium (Se) is an essential as well as a toxic trace element. Se intoxication has been reported in both livestock and humans. The central nervous system is sensitive to Se poisoning; exposure to Se causes blind staggers in cattle, poliomyelomalacia in pigs, and nervous system disorders in humans. Differences in neurotoxicity between inorganic and organic Se have been demonstrated. In this study, groups of five male BALB/c mice each were administered sodium selenite or selenomethionine in drinking water ad libitum at 0, 1, 3, and 9 ppm as Se for 14 days. At the end of Se exposure, their brains were removed and dissected into different regions. The concentration of norepinephrine (NE), dopamine (DA), dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), serotonin (5-HT), and 5-hydroxyindolacetic acid (5-HIAA) were determined in each brain region. Food and water consumption and body weight gain were significantly decreased in the group treated with the highest concentration of sodium selenite. In mice administered sodium selenite at 3 and 9 ppm, DOPAC was significantly higher in the striatum than in the control group. The striatal HVA was also increased in the group treated with 3 ppm Se; the DA showed a similar pattern, but the increase was not statistically significant. No alterations of NE, 5-HT, or 5-HIAA levels were detected in any brain region of mice treated with sodium selenite. No significant differences in any parameter among the groups treated with selenomethionine were observed indicating that inorganic Se was more neurotoxic than organic Se via drinking water. The alterations of DA metabolites by inorganic Se in DA-rich striatum suggested a Se-specific increased neural activity of dopaminergic pathways. Results may be useful in further elucidation of neurotoxicity of Se and in establishing a safe level of intake for this element.
Organochlorine and Metal Contaminant Exposure and Effects in Hatching Black-Crowned Night Herons (Nycticorax nycticorax) in Delaware Bay by B. A. Rattner; D. J. Hoffman; M. J. Melancon; G. H. Olsen; S. R. Schmidt; K. C. Parsons (pp. 38-45).
Pea Patch Island in Delaware Bay is the site of the largest heronry north of Florida. From 1989–93, the population of nine species of wading birds numbered approximately 12,000 pairs, but has recently declined to about 7,000 pairs. Because Delaware Bay is a major shipping channel and receives anthropogenic releases of toxic substances from agricultural, industrial, and municipal point and nonpoint sources, contaminant exposure and effects to the heronry have been an ongoing concern. In 1997, pipping (early hatching stage) black-crowned night herons (Nycticorax nycticorax) were collected from separate nests at Pea Patch Island and from a coastal reference site, Middle Island in Rehoboth Bay, Delaware. There was no evidence of malformations or hepatic histopathological lesions in embryos, and their body and liver weights did not differ between sites. Biomarkers of petroleum hydrocarbons, polyhalogenated contaminant, and metal exposure (cytochrome P450 induction and oxidative stress responses) did not differ (p > 0.05) between sites, although activities of benzyloxy-O-dealkylase and ethoxyresorufin-O-dealkylase were somewhat elevated in 3 of the 15 embryos collected from Pea Patch Island. Concentrations of 21 organochlorine pesticides and metabolites were relatively low at both sites, with p,p′-DDE values well below the threshold associated with eggshell thinning. Although total PCB concentration was modestly elevated (p < 0.05) in Pea Patch Island heron embryos, levels of arylhydrocarbon receptor-active PCB congeners, polychlorinated dibenzodioxins and dibenzofurans, and toxic equivalents were low and did not differ between sites. Concentrations of Cd and Mn in pipping embryos from Pea Patch Island were slightly greater (p < 0.05) than values observed in Middle Island embryos, but levels of these and the other metals and metalloids (e.g., Hg and Se) were below values associated with toxicity. In conclusion, it seems unlikely that chlorinated hydrocarbon and metal contaminant exposure constitutes a direct threat to the reproductive success of black-crowned night herons at Pea Patch Island. However, low-level exposure to these contaminants may constitute one of many stressors that in combination could adversely affect the stability of the wading bird population at this large heronry.
The Effect of Bioaccumulated Selenium on Mortalities and Deformities in the Eggs, Larvae, and Fry of a Wild Population of Cutthroat Trout (Oncorhynchus clarki lewisi) by C. J. Kennedy; L. E. McDonald; R. Loveridge; M. M. Strosher (pp. 46-52).
To determine if elevated concentrations of waterborne selenium (Se), caused by coal mining, in the Elk River in southeastern British Columbia, may be causing reproductive or teratogenic effects in wild cutthroat trout (Oncorhynchus clarki lewisi), fertilized eggs from exposed and reference fish were raised in the laboratory. Eggs from each female were reared separately and the percent mortalities and deformities were related to the selenium content of the eggs. Selenium concentrations in females from the exposed site were highest in the liver (36.6 ± 22.5 μg/g dry weight, range: 18.3 to 114), followed by the eggs (21.0 ± 18.3 μg/g, range: 8.7 to 81.3) and the muscle (12.5 ± 7.7 μg/g, range: 6.7 to 41). Despite these elevated egg Se concentrations, there was no significant effect on fertilization; time to hatch; percent hatch; or egg, larvae, and fry deformities or mortalities. Reproductive failure and embryonic terata have been reported at much lower egg Se concentrations in other fish species. The lack of any toxic response in this study may be due to an evolved tolerance to higher tissue Se concentrations in a population of fish living in a seleniferous river system.
A Survey of Size-Specific Mercury Concentrations in Game Fish from Maryland Fresh and Estuarine Waters by C. C. Gilmour; G. S. Riedel (pp. 53-59).
A survey of size-specific mercury (Hg) concentrations in game fish from a subset of Maryland fresh and estuarine waters was conducted, in which Hg concentrations in 112 fish from seven freshwater impoundments and three tidal and four estuarine locations in Chesapeake Bay and its tributaries were measured. Striped bass (Morone saxatilis) was the most intensively examined species. Of the fish examined, the largest freshwater sportfish contained the highest Hg concentrations. Striped bass and largemouth bass (Micropterus salmoides) from Chesapeake Bay and its tributaries contained less Hg at the same size than the same species in fresh waters. Large striped bass, chain pickerel (Esox niger), and walleye (Stizostedion vitreum) from Deep Creek Lake and Liberty Reservoir exceeded the FDA action level of 1 mg Hg/kg. Striped bass, largemouth bass, and white crappie (Pomoxis annularis) in other impoundments equaled or exceeded a common advisory level of 0.5 mg Hg/kg. Large differences in size-normalized Hg concentrations among lakes and particularly between fresh and salt waters highlight the large differences in MeHg production and bioaccumulation among ecosystems. This work indicates that a more comprehensive study of Hg in Maryland fish is warranted to protect human and wildlife health.
Soil Dissipation of Diuron, Chlorotoluron, Simazine, Propyzamide, and Diflufenican Herbicides After Repeated Applications in Fruit Tree Orchards by J. Rouchaud; O. Neus; R. Bulcke; K. Cools; H. Eelen; T. Dekkers (pp. 60-65).
In a pear tree orchard planted on loam soil, each plot was treated in April 1998 with either one of the ureas diuron or chlorotoluron, or triazine simazine herbicides applied at 3, 4, and 2 kg AI ha−1, respectively. Some plots had not been previously treated with one of these herbicides. Other plots had been treated annually during the past 12 years with the same herbicide. One herbicide, and always the same, was thus applied to each plot. In the plots treated for the first time with either diuron, chlorotoluron, or simazine, the soil half-lives of these herbicides in the 0–10 cm surface soil layer were 81, 64, and 59 days, respectively. In the plots treated with the same herbicide for 12 years, the corresponding soil half-lives were 37, 11, and 46 days. Diuron thus produced a moderately enhanced biodegradation, chlorotoluron a high one, and simazine a low but significant one. In another pear tree orchard planted on sandy loam soil, each plot was treated in April 1998 with one of the amide propyzamide (1.25 or 1.0 AI kg ha−1) or diflufenican (250 g AI ha−1) herbicides. In the plots not previously treated with propyzamide, the propyzamide soil half-life was the same for both doses, i.e., about 30 days. In the plots treated annually for 3 or 14 years with propyzamide, the soil half-life was 12 and 10 days, respectively. In the plots treated for the first time with diflufenican and in those treated annually with diflufenican for 3 years, the diflufenican soil half-life was the same, i.e., 65 days. Propyzamide thus already showed a highly accelerated biodegradation after 3 years of repeated annual applications. Diflufenican, however, did not show enhanced biodegradation after 3 years of repeated annual applications.
Chemistry of Rain Water in Riyadh, Saudi Arabia by A. I. Alabdula'aly; M. A. Khan (pp. 66-73).
Twenty-three rain water samples were collected from 15 sampling locations in Riyadh during four rain events in 1994 and analyzed for pH, conductivity, TDS, alkalinity, Cl, NO3, F, SO4, Na, Mg, Ca, and 12 trace metals. The pH ranged between 6.83 and 8.21. The major cation and anion were Ca and SO4, contributing with 30.5% and 20.8%, respectively, to TDS. Moderate variation in major ions concentration was found to occur between different sites. The concentrations of different metals varied considerably from one sampling location to another. The dominant trace metal ions in the rain water samples were Zn, Pb, and Al. Samples collected from a site near a cement factory in Riyadh showed maximum concentrations of most of the major ions and metals. The concentrations of various ions in the first rain event were comparatively higher than the concentrations of these ions in the later rain events.
The Effect of pH on the Kinetics of Intra- and Extracellular Uptake of Al in Fontinalis antipyretica: Changes in the Cellular Contents of K, Mg, and Ca by M. D. Vázquez; J. López; S. Díaz; A. Carballeira (pp. 74-85).
The effect of acidity on the accumulation of Al in the aquatic bryophyte Fontinalis antipyretica was studied. The main interest of this study was in characterizing the relationship between the two parameters, as Al is typically mobilized in acidic environments, where it becomes extremely toxic. With this aim, a series of laboratory experiments were carried out where samples of F. antipyretica were held in tanks of water with different concentrations of Al (0.1–3 mg L−1) and levels of acidity (pH 3–5.8). The incubation time varied between 1 and 24 h. In general, the greatest accumulations of both intra- and extracellular Al were found at a pH of 4.4. With the results obtained, the kinetics of both intra- and extracellular Al uptake was characterized, and models constructed for different combinations of Al and acidity.The study was completed by examining the relationship between the pH of the holding water and bioaccumulation of Al and the variation in concentration of cations essential to plant life, which are also indicators of changes in cellular physiology (K, Mg, Ca). In general, losses of these elements were found at intra- and extracellular locations, especially at high pH.
Increased Abundance of Terrestrial Isopod Populations in Terrestrial Ecosystems Contaminated with Petrochemical Wastes by B. C. Faulkner; R. L. Lochmiller (pp. 86-90).
Arthropods are integral components of the food chain, and because many reside in close association to the soil and its contaminants, their communities may be sensitive indicators of ecotoxicity. We examined the influence of petrochemical contaminants on the abundance of several taxonomic groups of macroarthropods, with an emphasis on isopods, residing on two reference sites and three petrochemical-contaminated sites at an abandoned oil refinery site in southwestern Oklahoma. Relative densities of surface-dwelling macroarthropod assemblages were significantly greater on contaminated sites than reference sites. Differences in terrestrial isopod populations were particularly remarkable and consistent across study sites, with densities approaching 180-fold greater on contaminated than reference sites. Similarity comparisons indicated that abundances and composition of macroarthropod assemblages sampled on the contaminated sites were more similar to one another than to the communities residing on reference sites. Although preliminary, these initial results support the hypothesis that macroarthropod assemblages, in particular isopods, are sensitive to soil contaminants and could be a valuable approach to evaluating the effects of petrochemical contamination of soils on terrestrial ecosystems.
Long-Term Effects of Pesticide Exposure at Various Life Stages of the Southern Leopard Frog (Rana sphenocephala) by C. M. Bridges (pp. 91-96).
Amphibian larvae are commonly exposed to low levels of pesticides during their development. Chronic studies generally examine the effects of long-term exposure, but they often disregard the importance of the individual life stage at which tadpoles are exposed. I determined the point during development at which carbaryl effects are manifested by exposing southern leopard frog tadpoles (Rana sphenocephala) to the pesticide carbaryl at five different times during development. Metamorphs exposed throughout the tadpole stage and throughout development (egg, embryo, tadpole) experienced significant mortality at all chemical levels. Although the length of the larval period was the same for all experimental groups, metamorphs exposed during the egg stage were smaller than their corresponding controls, independent of whether they were exposed at any other stage. Nearly 18% of individuals exposed to carbaryl during development exhibited some type of developmental deformity (including both visceral and limb malformities), compared to a single deformed (< 1%) control tadpole, demonstrating that a chemical hypothesis for amphibian deformities remains viable. Because exposure to nonpersistent chemicals may last for only a short period of time, it is important to examine the long-term effects that short-term exposure has on larval amphibians and the existence of any sensitive life stage. Any delay in metamorphosis or decrease in size at metamorphosis can impact demographic processes of the population, potentially leading to declines or local extinction.
Field Evaluation of Lead Effects on Canada Geese and Mallards in the Coeur d'Alene River Basin, Idaho by C. J. Henny; L. J. Blus; D. J. Hoffman; L. Sileo; D. J. Audet; M. R. Snyder (pp. 97-112).
Hatch year (HY) mallards (Anas platyrhynchos) in the Coeur d'Alene (CDA) River Basin had higher concentrations of lead in their blood than HY Western Canada geese (Branta canadensis moffitti) (geometric means 0.98 versus 0.28 μg/g, wet weight). The pattern for adults of both species was similar, although geometric means (1.77 versus 0.41 μg/g) were higher than in HY birds. HY mallards captured in the CDA River Basin in 1987 contained significantly lower lead concentrations in their blood than in 1994–95 (0.36 versus 0.98 μg/g); however, some very young mallards were sampled in 1987, and concentrations in adults were not significantly different in 1987, 1994, or 1995 (1.52, 2.07, 1.55 μg/g, respectively). Both species in the CDA River Basin in 1994–95 showed significantly reduced red blood cell delta-aminolevulinic acid dehydratase (ALAD) activity compared to the reference areas: Canada geese (HY −65.4 to −86.0%, adults −82.3%), and mallards (HY −90.7 to −95.5%, adults −94.1%). Canada goose goslings were divided into size classes, and the two smaller classes from the CDA River Basin had significantly elevated free erythrocyte protoporphyrin (protoporphyrin) levels compared to the reference area (15.2× and 6.9×). HY and adult mallards both had significantly elevated protoporphyrin (5.9× and 7.5×). Recognizing that interspecific differences exist in response and sensitivity to lead, it appears (at least for hemoglobin and hematocrit) that Canada geese were more sensitive to lead than mallards, i.e., adverse hematologic effects occur at lower blood lead concentrations. Only Canada geese from the CDA River Basin, in spite of lower blood lead concentrations, had significantly reduced mean hemoglobin and hematocrit values. No euthanized Canada geese (all HYs) from CDA River Basin were classified as clinically lead poisoned, but 38 Canada geese found dead in the CDA River Basin during a concurrent study succumbed to lead poisoning between 1992 and 1997. Only 6 (15.8%) of these 38 contained ingested lead shot, which contrasts greatly with the 75–94% incidence of ingested lead shot when mortality was due to lead shot ingestion. Lead from other contaminated sources (i.e., sediments and vegetation) in the CDA River Basin was strongly implicated in most Canada goose deaths. Based on the 31 live mallards and Canada geese collected in the CDA River Basin, which were representative of the live populations blood sampled only, the prevalence of subclinical and clinical lead poisoning (as determined by liver lead concentrations, excluding birds with ingested lead shot) was higher in mallards: subclinical (4 of 8, 50% HYs and 6 of 11, 55% adults); clinical (0% HYs and 4 of 11, 36% adults), with less data available for Canada geese (only 1 of 9, 11% HYs marginally subclinical). The clinically lead-poisoned mallards had extremely high concentrations of lead in blood (2.69–8.82 μg/g) and liver (6.39–17.89 μg/g). Eight mallards found dead in the CDA River Basin during a concurrent study were diagnosed as lead poisoned, and only one (12.5%) contained ingested lead shot, which again strongly implicates other lead sources. The finding of dead lead poisoned Canada geese together with the high percentage of live mallards classified as subclinically or clinically lead poisoned, in combination with the low incidence of ingested lead shot causes us concern for both of these species, which live in association with lead-contaminated sediment in the CDA River Basin.
Utility of Caenorhabditis elegans for Assessing Heavy Metal Contamination in Artificial Soil by C. L. Peredney; P. L. Williams (pp. 113-118).
There is an increasing need for the development of soil bioassay protocols. Currently the only internationally standardized soil test organism is the lumbricid earthworm Eisenia fetida. Many alternate soil test organisms have been proposed. This work compares Caenorhabditis elegans to several other test organisms, including E. fetida, for heavy metals in soil. In this evaluation, such factors as ease of testing and culturing, duration of testing, soil volume needed, and the sensitivity of the organism were considered. Results show that C. elegans is more sensitive than most other organisms evaluated and is similar in response to E. fetida. The second issue compares C. elegans LC50 values to heavy metals criteria specified in the US EPA regulations for land application of sewage sludge. Currently, the regulations are set on total metals in the soil and do not consider bioavailability of the metals. Regulations do not consider soil physiochemical properties, such as organic matter content, clay content, and cation exchange capacity, which have been shown to affect the availability of metals to soil organisms. While the C. elegans LC50 values are above standard values in artificial soil, work in our lab indicates that the LC50s are below regulation values for other soil types. Due to the ease of culturing and testing, good sensitivity, along with the wealth of biological information and ecological relevance, C. elegans is a good organism for use in soil bioassays.
Variability of Mercury and Selenium Levels in Clutches of Audouin's Gulls (Larus audouinii) Breeding at the Chafarinas Islands, Southwest Mediterranean by C. Sanpera; M. Morera; X. Ruiz; L. Jover (pp. 119-123).
We determined mercury and selenium in 43 eggs (eggshell, albumen, and yolk) which belong to different clutch sizes of Audouin's gull from the Chafarinas Islands. The results were compared with those obtained previously with the same species at the Ebro Delta. Both, the intra- and the interclutch sources of variability have been examined. There is an effect of the female on mercury and selenium concentrations in a clutch, which supports the use of eggs as monitoring tools. The distribution pattern of mercury among albumen, yolk and eggshell, the dynamics of this element during the laying process, as well as data concerning egg formation strategies suggest that the mercury in the albumen corresponds mainly to the mercury acquired by the female while feeding in the breeding area. The mercury and selenium levels of the eggs from the Chafarinas Islands were lower than those of the Ebro Delta, which can be due to differences in both the marine contamination and the diet in the two colonies.
Effects of Mercury on the Isolated Perfused Rat Tail Vascular Bed Are Endothelium-Dependent by V. da Cunha; H. P. Souza; L. V. Rossoni; A. S. França; D. V. Vassallo (pp. 124-130).
The effects of mercury on vascular smooth muscle results in vasoconstriction, but the mechanism of this action is not elucidated yet. To investigate this issue we examined the effects of HgCl2 in the isolated rat tail vascular bed. The tail artery was dissected, cannulated, and perfused at a constant flow (2.5 ml/min) with Krebs solution plus EDTA 0.03 mM at 36°C. After equilibration for 30 min the effects of increasing concentrations of HgCl2 (0.5, 1, 2, 5, and 10 μM) on the perfusion pressure were investigated. Concentrations of HgCl2, 2 μM and above, significantly increased perfusion pressure. Blockade of α receptors (prazosin 84 ng/ml) did not alter the responses to HgCl2, suggesting that the metal does not induce the release of neurotransmitters from sympathetic nerve terminals. To investigate the possible role of endothelium on the vasoconstriction produced by HgCl2, preparations were precontracted with 10−7 M phenylepherine or perfused with 5 μM HgCl2 for 20 min. Acetylcholine-vasodilated preparations precontracted with phenylepherine demonstrating the integrity of the endothelial nitric oxide–releasing mechanism. In contrast, after perfusion with 5 μM HgCl2, the vasodilation produced by acetylcholine was abolished. In the presence of either phenylephrine or HgCl2 the effects of sodium nitroprusside remained unchanged. Pretreatment with 30 μM indomethacin fully prevented the HgCl2-induced vasoconstriction. However, the endothelium-dependent vasodilation in response to acetylcholine was significantly reduced after indomethacin plus HgCl2 treatment, meanwhile the vasodilation produced by nitroprusside remained unchanged. Pretreatment with L-arginine (1 mM) did not prevent the vasoconstriction induced by HgCl2, nor did it restore the ability of acetylcholine to produce vasodilation, and it did not alter the response to sodium nitroprusside. The possibility of HgCl2's actions mediated by the formation of free radicals was also investigated. The administration of 10 mM histidine significantly reduced the vasoconstrictor response if used before HgCl2 treatment without improving the reduced vasodilation produced by acetylcholine. These results are consistent with the hypothesis that the vasoconstriction produced by HgCl2 may be mediated by the formation of superoxide anions, stimulating the production of a COX-derived vasoconstrictor agent and by reducing the endothelial vasodilator activity.