The accumulation of mercury by the thornback ray, Raja clavata L.

The accumulation of inorganic and organic mercury by the thornback ray has been studied using ²⁰³HgCl₂ and CH₃²⁰³HgCl. Observations have been made on the rates of intake and loss of ²⁰³Hg, from both labelled food and sea water, and the internal distributions of the isotope compared with that of total mercury. Both forms were readily absorbed from sea water. Retention of the two forms from food was, however, dissimilar in that, in contrast to inorganic mercury, methylmercury was readily absorbed and only slowly eliminated. The results are compared with data on the accumulation of mercury by the plaice.     

The accumulation of inorganic mercury from sea water by the plaice, Pleuronectes platessa L

The accumulation of inorganic mercury from sea water by plaice eggs, larvae, and adult fish has been studied using ²⁰³HgCl₂ as a tracer. The isotope was rapidly accumulated and the levels of accumulation have been related to stable element concentrations. High concentration factors were attained by many organs, but the distribution of the ²⁰³Hg was markedly different from that of the stable element. Whereas the largest fraction of the body burden of mercury is contained by muscle, only a slow rate of accumulation into this tissue was observed. In addition, the mercury in fish muscle is of the methyl form: no evidence for the methylation of the tracer was obtained.     

Laboratory Study of Chemical Speciation of Mercury in Lake Sediment and Water under Aerobic and Anaerobic Conditions

Chemical speciation and partitioning of radiolabeled HgCl₂ were studied in model aquatic systems consisting of undisturbed eutrophic lake sediment and water in plastic cylinders. The cylinders were either gradually made anaerobic by a gentle flow of N₂-CO₂ or kept aerobic by air flow. The proportion of methylated ²⁰³Hg was significantly higher, in both water and sediment, in the anaerobic systems than in the aerobic systems. The composition and total concentration of fatty acids originating from bacterial phospholipids, as well as the concentration of vitamin B₁₂, including related cobalamins, were similar in sediments from the anaerobic and aerobic systems. Bacterial cell numbers were, on average, 3.6 times higher in the anaerobic water columns than in the aerobic ones. Volatilization of ²⁰³Hg occurred in all systems except in an autoclaved control and was of similar magnitudes in the anaerobic and aerobic systems. Incorporation of ²⁰³Hg into the sediment was significantly faster in the aerobic systems than in the anaerobic systems. These results suggest that episodes of anoxia in bottom waters and sediment cause an increase in net mercury methylation and, hence, an increase in bioavailable mercury.     

Mercury translocation in and evaporation from soil. I. soil lysimeter experiments with 203Hg‐radiolabeled compounds

Due to a considerable increase of anthropogenic mercury emissions, the mercury load of many soils has risen significantly, for instance in northern Europe. Understanding the fate of mercury in soils is a prerequisite for assessing the effects of ecotoxicological concern. This paper presents a method for obtaining qualitative and quantitative information about mercury translocation in and evaporation from soil. Soil lysimeters were treated with ²⁰³Hg‐labeled HgCl₂ and CH₃HgCl and irrigated with artificial rain. It was demonstrated that the leaching of Hg can be detected by measuring the relative y‐activity throughout the soil profile by means of Na(TI)I detectors. Furthermore, the set‐up was designed to allow detection of Hg volatilization from soil by using traps of iodized charcoal, followed by a potassium peroxodisulfate solution and measuring the γ‐activity. The amount of radioactive Hg in soil leachate was measured by a Na(Tl)I well‐type detector after upconcentration. The determination of monomethyl ²⁰³Hg was been performed by extraction procedures that isolate the methyl mercury compounds. The amount of ²⁰³Hg retained in the soil profile and the real depth of leaching were determined by stratifying the soil profile at the end of the experiment and measuring the y‐activity. With control of all pathways of Hg, the experimental design allows performance of a mass balance analysis.     

Mode of in vitro interaction of mercuric mercury with selenite to form high-molecular weight substance in rabbit blood

Mode of interaction of mercuric mercury and selenite in rabbit blood was investigated in vitro. After the incubation of rabbit blood with 10^?5 M each of ²⁰³HgCl₂ and Na₂⁷⁵SeO₃, the amounts of both ²⁰³Hg and ⁷⁵Se incorporated into erythrocytes were markedly larger than the case where the blood was treated separately with one of these compounds. Most of ²⁰³Hg and ⁷⁵Se distributed into plasma and erythrocytes were found in high-molecular weight substance(s) (HMWS) fractionated by gel filtration at a molar ratio of 1:1. The ²⁰³Hg and ⁷⁵Se in HMWS found in plasma and erythrocytes were hardly diffusable through the erythrocytes membrane. The formation of the HMWS containing mercury and selenium was observed in stroma-free hemolysate incubated with mercuric chloride and selenite, but not in plasma. Addition of reduced glutathione (GSH) to the plasma, however, gave the HMWS as reaction products containing equimolar amounts of mercury and selenium. Further the binding properties of selenium to proteins were studied in the plasma incubated with selenodiglutathione (GSSeSG) or with selenite in the presence of GSH. The results indicated that GSH, a cellular component, is essential for the formation of an active selenium compound from selenite and that the interaction of mercuric mercury and selenite in plasma in the presence of GSH may occur through the other mechanism than the formation of GSSeSG.     

Mercury distribution and renal metallothionein induction after subchronic oral exposure in rats

The effects of long-term daily intake of low and high levels of mercury on its organ distribution and binding to renal metallothionein (MT) in male rats were studied. The animals were exposed to mercuric chloride labelled with²⁰³Hg via drinking water for 8 weeks (5, 50 and 500 m Hg). The greatest concentration of mercury was found in the kidneys. Similar levels of radioactivity in the buccal cavity and oesophagus were also observed by whole-body autoradiography. In the kidneys, the mercury was accumulated in the outer stripe of the outer zone of the medulla and, to a minor degree, in the renal cortex. Almost 50% the total renal mercury was associated to MT. The binding capacity of the renal MT for mercury tends to saturate with increasing doses, thus this means that the capacity of the kidneys to accumulate mercury is limited.     

Comparative Study of Uptake and Cellular Distribution of Hg203-Labeled Phenyl-Mercuric Acetate and Mercuric Acetate by Pea Roots

Uptake and cellular distribution of mercury²⁰³ from dilute mercuric acetate or phenylmercuric acetate solutions by excised pea roots (Pisum sativum) have been investigated. The time course of uptake showed that the amount of mercury uptake was increased with the time of incubation, and was similar for inorganic mercury or phenylmercuric acetate. The trend of mercury²⁰³ incorporation into cellular components from mercuric acetate and phenylmercuric acetate differed greatly as the time of incubation increased. The concentrations of mercuric acetate and phenylmercuric acetate solutions or the temperature of incubation also affected the mercury²⁰³ uptake as well as its cellular distribution. Longer time of exposure or higher concentration resulted in a greater mercury incorporation into mitochondrial fraction from phenylmercuric acetate than from inorganic mercury. This difference in intracellular distribution may be responsible for the degree of toxicity between inorganic mercury and phenylmercuric acetate in biological systems.     

Photosynthetic limitations of a halophyte sea aster (<Emphasis Type="Italic">Aster tripolium</Emphasis> L) under water stress and NaCl stress

To understand the mechanisms of salt tolerance in a halophyte, sea aster (Aster tripolium L.), we studied the changes of water relation and the factors of photosynthetic limitation under water stress and 300 mM NaCl stress. The contents of Na⁺ and Cl^- were highest in NaCl-stressed leaves. Leaf osmotic potentials (Ψ _s) were decreased by both stress treatments, whereas leaf turgor pressure (Ψ _t) was maintained under NaCl stress. Decrease inΨ _s without any loss ofΨ _t accounted for osmotic adjustment using Na⁺ and Cl^- accumulated under NaCl stress. Stress treatments affected photosynthesis, and stomatal limitation was higher under water stress than under NaCl stress. Additionally, maximum CO₂ fixation rate and O₂ evolution rate decreased only under water stress, indicating irreversible damage to photosynthetic systems, mainly by dehydration. Water stress severely affected the water relation and photosynthetic capacity. On the other hand, turgid leaves under NaCl stress have dehydration tolerance due to maintenance of Ψ _t and photosynthetic activity. These results show that sea aster might not suffer from tissue dehydration in highly salinized environments. We conclude that the adaptation of sea aster to salinity may be accomplished by osmotic adjustment using accumulated Na⁺ and Cl^-, and that this plant has typical halophyte characteristics, but not drought tolerance. Electronic Publication     

Methods for Measuring Specific Rates of Mercury Methylation and Degradation and Their Use in Determining Factors Controlling Net Rates of Mercury Methylation

A method was developed to estimate specific rates of demethylation of methyl mercury in aquatic samples by measuring the volatile ¹⁴C end products of ¹⁴CH₃HgI demethylation. This method was used in conjunction with a ²⁰³Hg²⁺ radiochemical method which determines specific rates of mercury methylation. Together, these methods enabled us to examine some factors controlling the net rate of mercury methylation. The methodologies were field tested, using lake sediment samples from a recently flooded reservoir in the Southern Indian Lake system which had developed a mercury contamination problem in fish. Ratios of the specific rates of methylation/demethylation were calculated. The highest ratios of methylation/demethylation were calculated. The highest ratios of methylation/demethylation occurred in the flooded shorelines of Southern Indian Lake. These results provide an explanation for the observed increases in the methyl mercury concentrations in fish after flooding.     

Mercury bioremediation by mercury accumulating Enterobacter sp. cells and its alginate immobilized application

The effective microbial remediation of the mercury necessitates the mercury to be trapped within the cells without being recycled back to the environment. The study describes a mercury bioaccumulating strain of Enterobacter sp., which remediated mercury from the medium simultaneous to its growth. The transmission electron micrographs and electron dispersive X-ray analysis revealed the accumulation of remediated mercury as nano-size particles in the cytoplasm as well as on the cell wall. The Enterobacter sp. in the present work was able to accumulate mercury, without being engineered in its native form. The possibility of recovering the accumulated mercury from the cells is also indicated. The applicability of the alginate immobilized cells in removing mercury from synthetic and complex industrial effluent in a batch mode was amply demonstrated. The initial load of 7.3 mg l⁻¹ mercury in the industrial effluent was completely removed in 72 h. The cells immobilized in calcium alginate were similarly effective in the complete removal of 5 mg l⁻¹ HgCl₂ of mercury from the synthetic effluent in less than 72 h. The immobilized cells could be reused for multiple cycles.     

Quenching of a proton gradient and concomitant increase of intragranular calcium in interstitial cells of Mytilus retractor muscle

Summary The content of specific glio-interstitial granules in situ was studied in Mytilus retractor muscle using fluorescent probes and X-ray microanalysis. The granules readily take up the fluorescent monoamine dye acridine orange added to sea water (2.7×10^-6 M) and appear red in fluorescence microscopy. The addition of ammonium chloride (10 mM) or various proton ionophores results in extinction of the granule fluorescence. In addition, a step-wise decrease in granule fluorescence is observed when the tissue is perfused with artificial sea water of decreasing pH. These granules thus appear to be acidic inside. The animals were maintained in artificial sea water containing 8.36 mM Ca²⁺ and 528.90 mM Na⁺, the ratio R=[Ca²⁺]₀/[Na⁺]² ₀ being thus equal to 3x10^-5. Perfusions of the tissue with artificial sea water containing a higher calcium concentration (12.2 mM) and/or a higher [Ca²⁺]₀/[Na⁺]² ₀ ratio (R=4.5×10^-5) result in a drastic reduction of the proton gradient, evidenced by a quenching of the acridine orange fluorescence. Under the same conditions, a significant increase of the total intragranular calcium concentration was demonstrated by quantitative X-ray micro-analysis of the tissue processed by quick freezing and freeze-substitution in the presence of oxalic acid. The fluorescence of the probe Fluo-3/AM, indicative of ionized calcium, is higher in the granules than in the surrounding cytoplasm; this suggests that calcium is accumulated in the granule against its concentration gradient. The acidic gradient of specific glio-interstitial cell granules could provide the energy needed for this calcium accumulation through a Ca²⁺/H⁺ exchange. These results are discussed with regard to the hypothesis that the glio-interstitial tissue can regulate pericellular calcium and/or hydrogen ion ioncentration in the vicinity of nerve and muscle cells.     

UPTAKE AND RELEASE OF METHYLMERCURY-203 BY CLADOPHORA GLOMERATA1

Cladophora glomerata was exposed to CH₃²⁰³HgCl at concentrations of 10, 50, and 100 μg/liter of water. Formalin-killed alga was exposed to a concentration of 50 μg CH₃²⁰³HgCl/liter. Uptake was monitored at 2 and 12 hr, and days 1, 2, 4, 8, and 16. At the end of this period, the Cladophora was placed in uncontaminated water, and release of methylmercury was monitored at 1, 2, 4, 8, and 16 days. Sorption occurred at all concentrations, and the live algal material accumulated more methylmercury than the dead alga, at equal exposure concentrations. Accumulation of methylmercury by the live Cladophora peaked on or near the second day for all exposure concentrations, suggesting that the uptake rate was independent of methylmercury concentration in the water. Uptake was greatest at the 50 μg/liter exposure. Desorption was nominal during the 16-day release period. The mechanisms of methylmercury uptake by Cladophora are discussed.     

The cycling of cadmium and mercury between substrate and fruiting bodies of Agrocybe aegerita (a fungal model system)

Summary The cycling of cadmium and mercury between substrate and fruiting bodies in a model system with wood colonizing basidiomycete Agrocybe aegerita was studied. When radiolabeled ¹⁰⁹CdCl₂ and ²⁰³HgCl₂ were applied to the fruiting bodies of the first flush, they were translocated via substrate into successive harvests. Cadmium and mercury displayed different patterns of distribution in the system. On a percent basis, more cadmium went from the fruiting bodies into the substrate and was retained there. Only minor portions of the metal were translocated into consecutive crops. In contrast, more mercury was retained in the treated fruiting bodies. The fraction which had penetrated into the substrate, however, was more easily translocated into fruiting bodies of successive crops. When calculated on a dry weight basis, the amount of both metals decreased in consecutive harvests.At the end of the experiment, in following distribution patterns for cadmium and mercury were observed: Cd²⁺: first crop (treated), 9.5%; substrate, 77%; combined successive crops (untreated), 9.5%; Hg²⁺: first crop (treated), 36.5%; substrate 21.5%; combined successive crops (untreated), 37%. The patterns reveal that mercury is more mobile in the substrate and therefore more easily translocated to successive fruiting body generations. Hence, from a nutritional point of view, mercury would seem to be more hazardous than cadmium.     

Two modes of bicarbonate utilization in the marine green macroalga Ulva lactuca

The green marine macroalga Ulva lactuca L. was found to be able to utilize HCO₃^? from sea water in two ways. When grown in flowing natural sea water at 16°C under constant dim irradiance, photosynthesis at pH8.4 was suppressed by acetazolamide but unaffected by 4,4′-diisothiocyanostilbene-2,2′-disulphonate. These responses indicate that photosynthetic HCO₃^? utilization was via extracellular carbonic anhydrase (CA) -mediated dehydration followed by CO₂ uptake. The algae were therefore described as being in a ‘CA state’. If treated for more than 10 h in a sea water flow-through system at pH9.8, these thalli became insensitive to acetazolamide but sensitive to 4,4′-diisothiocyanostilbene-2,2′-disulphonate. This suggests the involvement of an anion exchanger (AE) in the direct uptake of HCO₃^?, and these plants were accordingly described as being in an ‘AE state’. Such thalli showed an approximately 10-fold higher apparent affinity for HCO₃^? (at pH9.4) than those in the ‘CA state’, while thalli of both states showed a very high apparent affinity for CO₂. These results suggest that the two modes of HCO₃^? utilization constitute two ways in which inorganic carbon may enter the Ulva lactuca cells, with the direct entry of HCO₃^?, characterizing the ‘AE state’, being inducible and possibly functioning as a complementary uptake system at high external pH values (e.g. under conditions conducive to high photosynthetic rates). Both mechanisms of entry appear to be connected to concentrating CO₂ inside the cell, probably via a separate mechanism operating intracellularly.     

Effects of phosphorus and iron fertilizers on the growth of two soybean varieties at two soil temperatures

The influence of FeEDDHA (0, 0.2 and 2 μg Fe g⁻¹ soil) and NaH₂PO₄·H₂O (0 and 120 μg Pg⁻¹ soil) on the growth of two Fe-ineffective soybean (Glycine max L. Merr.) varieties (anoka and T203) on a calcareous soil at two soil temperatures (16 and 24°C) was compared under greenhouse conditions. The two soybean varieties differed in the following respects: (a) T203 accumulated smaller concentrations of Fe in washed tops than Anoka under comparable conditions; (b) T203 was more susceptible to Fe deficiency and its accentuation by high levels of fertilizer P than Anoka; (c) T203 accumulated lower quantities of Mn in tops than Anoka under comparable conditions; (d) T203, but not Anoka, developed Mn deficiency symptoms when treated with P and 2 μg Fe g⁻¹ at 16°C. Fe deficiency was more severe in both varieties at the higher soil temperature due apparently to: (a) greater plant concentration of P in tops at 24°C; and/or (b) an increased rate of plant growth and greater dilution of Fe in young tissue at 24°C. Foliar P concentration was increased much more than foliar Fe concentration by an increase in soil temperature. Severely Fe deficient T203 plants grown without FeEDDHA at 24°C accumulated less foliar Mn than their FeEDDHA counterparts. Comparisons of Fe effectiveness of various soybean cultivars based on relative responses to FeEDDHA can be influenced by differential effects on Mn nutrition.     

The relationships of Hg(II) volatilization from a freshwater pond to the abundance ofmer genes in the gene pool of the indigenous microbial community

The role of biological activities in the reduction and volatilization of Hg(II) from a polluted pond was investigated. Elemental mercury was evolved from pond water immediately following spiking with²⁰³Hg(NO₃)₂, whereas an acclimation period of 36 hours was required in control samples collected from a nearby, unpolluted river before onset of volatilization. Genes encoding the bacterial mercuric reductase enzyme (mer genes) were abundant in DNA fractions extracted from biomass of the pond microbial community, but not in samples extracted from control communities. Thus, evolution of Hg⁰ was probably due to activities mediated by the bacterial mercuric reductase. Of four characterizedmer operons, the system encoded by transposon 501 (mer(Tn501)) dominated and likely contributed to the majority of the observed Hg(II) volatilization. Thus,mer-mediated reduction and volatilization could be used to reduce Hg(II) concentrations in polluted waters, in turn decreasing rates of methylmercury formation by limiting substrate availability.     

Efficiency of autometallographic detection of mercury in the rat kidney

Summary The autometallographic silver enhancement method is a method for subcellular localization of some heavy metals, such as mercury. However, no quantitative estimate has been made of the amount of mercury demonstrated by the method. In this study, pellets of autometallographic silver grains were prepared from unfixed kidney slices of rats exposed i.p. to mercury chloride containing trace amounts of ²⁰³Hg. The slices were silver-enhanced, and subsequently all organic material was removed by enzymatic digestion. During all stages of the experiment the solutions and tissue were gamma-counted. The analysis showed that the final pellets contained approximately 30% of the mercury compared to that found in the slices prior to development and that the mercury was probably located in lysosomes.     

Experimental study of the combined effects of pH and salinity on the bioaccumulation of inorganic mercury in the crayfish Astacus leptodactylus

ABSTRACT

The combined effects of pH and salinity were investigated on the bioaccumulation of inorganic mercury in the Turkish crayfish Astacus leptodactylus, at the whole organism and organ levels. Effects on the ionic balance were also analysed during the acclimatization phase and after 3 and 15 days of exposure, via the direct route. The experimental protocol, based on a complete factorial design, took into account nine experimental conditions, resulting from the combination of three levels for pH (6, 7.5 and 9) and for salinity (1, 10 and 100 mM Cl-). The results showed an important Hg accumulation in the organs or tissues in direct contact with the surrounding medium, e.g. gills and carapace. The effects of the nine pH and salinity conditions were complex and variable from one organ to another. Correlations were studied between chemical species concentrations in the water (HgCl₂, HgOHCl, HgCl₃-,HgCl₄², Hg(OH)₂) and amounts of metal accumulated in the different organs. A positive correlation was found between the neutral species HgCl₂ and metal accumulated in the gills and in the carapace. Perturbations of the haemolymph ionic concentrations were no significant, except for Na⁺ after 3 days of exposure.     

Biosorption of inorganic and methyl mercury by a biosorbent from Aspergillus niger

A biosorbent prepared by alkaline extraction of Aspergillus niger biomass was evaluated for its potential to remove mercury species – inorganic (Hg²⁺) and methyl mercury (CH₃Hg⁺) – from aqueous solutions. Batch experiments were carried out to determine the pH and time profile of sorption for both species in the pH range 2–7. The Hg²⁺ exhibited more rapid sorption and higher capacity than the CH₃Hg⁺. Further, removal of both mercury species from spiked ground water samples was efficient and not influenced by other ions. Sorption studies with esterified biosorbent indicated loss of binding of both mercury species (>80%), which was regained when the ester groups were removed by alkaline hydrolysis, suggesting the involvement of carboxyl groups in binding. Further, no interconversion of sorbed species occurred on the biomass. The biosorbent was reusable up to six cycles without serious loss of binding capacity. Our results suggest that the biosorbent from Aspergillus niger can be used for removal of mercury and methyl mercury ions from polluted aqueous effluents.     

Are Root Hydraulic Conductivity Responses to Salinity Controlled by Aquaporins in Broccoli Plants?

Broccoli (Brassica oleracea L. var. Italica) is a recognised health-promoting vegetable, which is moderately sensitive to salinity. In this study, the primary response of broccoli plants (cv. Marathon) to salinity has been characterised. For this, leaf water relations, nutrient composition, root hydraulic conductivity (L ₀) and the effect of mercury (an aquaporin blocker) on L ₀ were determined for plants grown with 0, 20, 40, 60, 80 or 100 mM NaCl for 2 weeks. During the 2 weeks of treatment, the plants showed a two-phase growth response to salinity. During the first phase (1 week), growth reduction was high, probably related to water stress as no osmotic adjustment occurred and reductions of L ₀, the mercury effect and Gs were observed. After 2 weeks, the growth reduction could have resulted from internal injury caused by Na⁺ or Cl⁻, since osmotic adjustment was achieved and water relations plus the mercury effect were re-established to a high degree, indicating high aquaporin functionality. The fact that aquaporin functionality fits well with the overall water relations response is very relevant, since the two-phase adaptation to salinity may imply two types of aquaporin regulation.