Μg Ag Research Articles

The physiology of waterborne silver toxicity in freshwater rainbow trout ( Oncorhynchus mykiss) 1. The effects of ionic Ag +

Adult rainbow trout, fitted with arterial catheters, were exposed to AgNO 3 for 6 days at a concentration (10 μg Ag l −1, flow-through) close to the 7 day LC50 in moderately hard freshwater. Approximately 35% of total Ag occurred as free ionic Ag +, and the remainder as silver chlorides. Ag accumulated on the gills and increased about 4-fold above control levels in blood plasma, stabilizing by 48 h. Much greater concentrations of Ag accumulated in the liver, but not the kidney, at 6 days. Metallothionein induction did not occur. Plasma [Na +] and [Cl −] declined steadily to 70% of control levels by day 6, accompanied by a progressive metabolic acidosis, a 5-fold increase in blood [glucose], a 40% decrease in relative plasma volume, contraction of the spleen, and marked hemoconcentration. Plasma [Ca 2+] and [K +] were largely unaffected. Respiratory suffocation did not occur: plasma [lactate] remained constant, arterial P O 2 increased and P CO 2 decreased, the latter compensating the metabolic acidosis so arterial pH fell only moderately. Comparably sampled control fish exhibited negligible disturbance. Unidirectional Na + influx from the water, measured in juvenile trout, was inhibited by 42% immediately, and abolished by 48 h of AgNO 3 exposure. These symptoms suggested a similar toxic mechanism of action to that of low environmental pH. We speculate that Ag + interferes with net Na + and Cl − uptake at the gills, and causes death by secondary fluid volume disturbance, hemoconcentration, and eventual cardiovascular collapse.

TOXICITY, SILVER ACCUMULATION AND METALLOTHIONEIN INDUCTION IN FRESHWATER RAINBOW TROUT DURING EXPOSURE TO DIFFERENT SILVER SALTS

Static-renewal 168-h toxicity tests of silver nitrate (AgNO3), silver chloride (AgCln), and silver thiosulfate (Ag(S2O3)n) with juvenile rainbow trout (Oncorhyncus mykiss) were performed by standard methods. Because of low solubility of AgCl(s), bioassays for AgCln were performed in two separate ways. In one test series, AgCl(s) was added to freshwater and in another, AgCln(aq) was generated by adding AgNO3 to freshwater supplemented with 50 mM NaCl. Concentrations of Ag and metallothionein (MT) were analyzed in gills and livers offish that survived the exposures. Although Ag added as AgNO3 was found to be highly toxic to rainbow trout (168-h LC50 = 9.1 μg Ag L−1), the toxicities of the other Ag salts were low. The 168-h LC50 for Ag(S2O3)n was 137,000 μg Ag L−1 and no mortality was observed in AgCln (100,000 μg Ag L−1). Exposure to AgNO3, Ag(S2O3)n, or AgCln caused accumulation of Ag and induction of MT. Highest Ag levels were found in livers of trout exposed to 164,000 μg Ag L−1 as Ag(S2O3)n. In these fish, the hepatic Ag concentration was increased 335 times from the control value. The MT levels in gills and liver increased with the water Ag concentration and the highest level of MT was found in liver of fish exposed to Ag(S2O3)n.

Effect of the TRH analogue, CG 3703, on prolactin secretion in the pseudopregnant rat

The effect of the TRH analogue, CG 3703 (AG), on secretion of prolactin (Prl) was studied in pseudopregnant rats. AG stimulated Prl secretion of incubated pituitary glands in the presence of 5.10 −8 M dopamine (DA) but not in the presence of 0 or 10 −6 M DA. AG did not inhibit the in vitro secretion of Prl. AG postponed the peaks of Prl which were generated between 0100 and 1200 h (delay after 500 μg AG: 3–4 h); the height of these nocturnal Prl peaks was not affected by AG. AG did not induce Prl secretion during the phase of low Prl secretion (the interphase) between 2000 and 0100 h. The DA-release blocking drug, HA 966, induced peaks of Prl during the interphase. These peaks were as high as spontaneous nocturnal Prl peaks and were blocked by AG. The results show that AG has two opposite effects on Prl secretion: a direct, stimulating effect, which is modulated by DA, and an indirect inhibitory effect, which is probably executed by DA, released by AG from the tuberoinfundibular DA neurons.

Variations inter-spécifiques de la bioaccumulation et de la toxicité de l'argent á l'égard de trois mollusques bivalves marins

Previous data about silver in marine molluscs have shown a high variability of both accumulation and toxicity of this metal. A potential relationship between these factors has been examined. In a preliminary experiment, three species of bivalves ( Crassostrea gigas, Mytilus galloprovincialis, Chlamys varia) were exposed to silver concentrations varying from 1 to 1000 μg Agl −1 in order to determine parameters of lethal toxicity. Then, specimens of the same species were exposed to sub-lethal levels of silver through food (groups 2), water (groups 3) or both food and water (groups 4). In this main experiment, the level of silver was identical (20 μg Ag1 −1 in the culture medium of algae used as food and in the rearing medium of bivalves. Since the nominal levels of silver in water decreased during the experiment (Tables 1 and 2), seawater and contaminant were renewed every day. The species-related variations of mean lethal time (Table 3) revealed that the most resistant species was the oyster and the lesser one was the scallop. The resistance of oysters was mentioned previously by Martoja et al. (1988) who did not observe any cytological lesion in individuals exposed to silver in experimental conditions similar to those applied in the present study. The susceptibility of scallops has been confirmed since a moderate level of silver of 20 μg Ag l −1 was sufficient to disturb their attachment to the substratum (Table 4) as a consequence of a heavy accumulation of silver sulphide in glandular cells which secrete byssus threads (Martoja et al., 1990). The patterns of bioaccumulation in soft tissues were different in oysters—in which the maximal concentration was reached within 2 weeks (Fig. 1)—and in mussels—which this maximum was not reached after 4 weeks (Fig. 2). Exposure to silver via food induced a significant uptake of this metal in soft tissues of bivalves but it was low compared to uptake from seawater and to the contamination due to the double way of exposure (Table 5). However, the biomass of molluses per unit volume of culture medium varied from species to species. In order to compare strictly the specific ability to concentrate silver, we have determined the quantity of metal available (from food and/or water) per unit weight of filter-feeding organism over a definite period. Then we calculated the percentage of available silver retained by each species (Table 6). These results, as well as the literature data (Brooks and Rumsby, 1965; Folsom and Young, 1965; Preston et al., 1968; Bryan, 1973; Pouvreau and Amiard, 1974), show that Pectinidae and Ostreidae are able to retain very high levels of silver compared to Mytilidae. The species-related behaviour of silver may be interpreted from the point of view of ecotoxicological consequences: • -Species such as the oyster, with a low susceptibility and high ability to concentrate silver, could have an important role as the vector of contamination in food webs. • -Species such as the scallop, able to concentrate high levels of silver and very susceptible, could be eliminated from polluted ecosystens but, in these conditions, their role in trophic transfer will be limited. • -Species such as the mussel, which accumulate only low quantities of silver, will not have any role in food chain contamination and their intermediate susceptibility could have consequences only in highly polluted environments.

Substoichiometric determination of silver by Neutron Activation Analysis

A rapid and selective method has been developed for the determination of Ag in biological samples and mineral ores by thermal neutron activation analysis employing substoichiometric extraction with 1,2,3-benzotriazole /1,2,3-BT/ into chloroform. The time required for the radiochemical purification and counting of two samples was 1 h. 4.84 μg Ag can be determined with an accuracy of 7.44% and a precision of 3.57%.

Silver in Welsh soils: Physical and chemical distribution studies

Profile distributions of Ag and other metals (Cd, Cu and Pb) in contaminated and uncontaminated soils from west Wales, U.K. are presented. Background Ag levels were <0.1 μg Ag g −1, whilst profiles contaminated by past mining activities contained up to 9 μg Ag g −1. Silver showed a marked surface enrichment in all cases. Adsorption of AgNO 3 by various soil samples was satisfactorily modelled by the Freundlich isotherm equation. Values for k (a constant related to the binding capacity) ranged between 50 and 1450. The Langmuir isotherm equation gave a less satisfactory summary of the adsorption behaviour. Radioactive 110mAg added to intact cores of an alluvial and a peat soil and subjected to leaching over one year (at the annual precipitation rate) remained in the surface layers; after this time 110mAg was not leached appreciably below 40 mm. A chemical fractionation procedure for soil Ag was applied to the contaminated soils. In soils contaminated between 80 and 150 years ago there were negligible amounts of readily exchangeable Ag; nearly half the total Ag was “residual” (i.e., solubilised only in concentrated nitric acid). The two intact soil columns still contained a considerable proportion of the 110mAg in the readily exchangeable form after one year, but most was bound in ‘acid-reducible’ or ‘oxidisable-organic’ forms. The evidence for a strong association between soil organic matter and Ag indicates that humus may control the availability of Ag in the short term and that mineral prospecting for Ag by the chemical analysis of soil humus may be a useful reconnaissance technique. Fixation in a residual fraction may be a mechanism which reduces the bioavailability of the element in the long term.

Determination of silver and thallium in nickel-base alloys by atomic absorption spectrometry with introduction of solid samples into an induction furnace

Atomic absorption spectrometry with an induction furnace is used for the determination of silver (0.03–12 μg g -1) and thallium (0.004–12 μg g -1) in 1–40-mg samples of nickelbase alloys dropped into the furnace. Calibration graphs of peak absorbance versus mass of element were constructed by use of standardised alloys. The accuracy, precision and limits of detection of the method are described for numerous nickel-base alloys. With alloys containing more than 0.2 μg Ag g -1 and 0.4 μg Tl g -1, relative standard deviations are usually <15% and <12%, respectively. The limits of detection for silver and thallium are 0.014 μg g -1 and 0.004 μg g -1, respectively.

Use of blotting-paper collectors for the separation and X-ray fluorescent determination of traces of heavy metals (Cu, Hg, Ag) in water and waste water

Traces of Hg, Ag and Cu were separated in the range of 0.5–500 Μg with blotting-paper collectors and were subsequently determined directly with energy dispersive X-ray fluorescence. For comparison, spectrophotometric determinations were carried out as well. The results were in good agreement. The collectors contained 0.2 mM ZnS, in case of Ag a thioureide collector was also employed. Limits of detection were 0.2 Μg Hg, 0.4 Μg Cu and 0.15 Μg Ag for the ZnS collector and 0.13 Μg Ag for the thioureide collector.

Spectrophotometric determination of trace amounts of silver(I) by formation of dicyanoargentate(I) and solvent extraction with methylene blue

The spectrophotometric method proposed for the determination of micro amounts of silver(I) is based on the formation of dicyanoargentate(I) and its extraction into 1,2-di-chloroethane as an ion pair with méthyléne blue. The absorbance of the extract is stable for at least 3 days in a glass-stoppered tube. The apparent molar absorptivity for silver at 657 nm is 99500 l mol -1 cm -1 and the Sandell sensitivity is 0.0011μg Ag cm -2 for 0.001 absorbance. Linear calibration graphs are obtained over the range 2.8 × 10 -7–1.0 × 10 -5 M silver(I) (0.3–10.8μg Ag in 10 ml; at the 6 × 10 -6 M silver(I) level, the relative standard deviation is 0.3%. Very high selectivity is achieved with EDTA as masking agent.

Toxicity of silver to rainbow trout ( Salmo gairdneri)

The mean 96-h LC 50's of silver with rainbow trout were 6.5 μg l −1 and 13.0 μg l −1 in soft water (approximately 26 mg l −1 hardness as CaCO 3) and hard water (350 mg l −1 hardness as CaCO 3), respectively. The long-term, “no effect” concentration for silver, added to the water as silver nitrate, was between 0.09 and 0.17 μg l −1 after 18 months exposure in soft water. The “no effect” concentration is that concentration range which defines no observed effect. Based on mortalities different from the control, no mortalities attributable to silver occurred at 0.09 μg Ag l −1, whereas 17.2% mortality occurred to fish exposed to 0.17 μg ll −1. The “no effect” concentration does not reflect possible effects of silver on spawning behavior or reproduction, since female rainbow trout will not generally reach sexual maturity before 3 yr. At silver concentrations of 0.17 μg l −1 or greater, silver caused premature hatching of eggs and reduced growth rate in fry. In one experiment, the eggs were completely hatched within 10 days of exposure; whereas, control eggs completed hatching after 42 days. The prematurely erupted fry were not well developed and frequently died. The growth rate of surviving fry was greatly reduced.

2,3-Naphthotriazole as a gravimetric, spectrophotometric, and fluorimetric reagent for the determination of silver

2,3-Naphthotriazole is suitable for the determination of macro- and muquantities of silver. The gravimetric (for 5–100 mg Ag) and spectrophotometric (ε=1,000; 1–30 μg Ag ml ) methods are rapid and free of halide and foreign ion interferences; excellent selectivity is attained by means of masking agents. The fluorimetric method (0.025–0.1 μg Ag ml ) is much more sensitive than the spectrophotometric method but is more subject to interferences.