Occurrence of Cu-ATPase in Dictyostelium: possible role in resistance to copper

Dictyostelium discoideum amoebae showed an uncommon resistance to Cu(2+), as pointed out through cell growth rate (EC(50) = 469 +/- 30 microM) and the neutral red cytotoxicity assay (EC(50) = 334 +/- 45 microM). Although no evidence of Cu-inducible metallothionein was found, Cu-dependent ATPase activity was cytochemically detected on pelletted, resin-embedded amoebae. This activity required Cu(2+) in the incubation medium, was sensitive to TPEN, vanadate and temperature, and showed dose-dependent increase after exposure of amoebae to 10-500 microM Cu(2+) for 7 days. Accordingly, immunofluorescence and Western blotting revealed the occurrence of a Cu-inducible, putative homologue of human Menkes (MNK) Cu-P-type ATPase. To verify if Cu-ATPase is involved in copper resistance, amoebae were exposed to low concentrations of Cu(2+) and vanadate followed by the neutral red assay. Exposure to either treatment showed no effect, while a combination caused a dramatic increase of Cu toxicity, possibly depending on Cu-ATPase inhibition.     

Heavy metal concentrations in the breast milk of Saudi women

Lead, cadmium, and mercury concentrations were determined in breast milk of Saudi lactating mothers from Riyadh and Al-Ehssa regions in Saudi Arabia who were not occupationally exposed. The mean levels for cadmium, lead, and mercury were 1.732 μg/L, 31.671 μg/L, and 3.100 μg/L, respectively. In contrast to mercury, mothers living in the Al-Ehssa region had significantly higher cadmium and lead concentrations in their breast milk than those in the Riyadh region. The estimated weekly intakes of cadmium, lead, and mercury of breast-fed infants in this study were in some cases higher than the Provisional Tolerance Weekly Intake (PTWI) recommended by FAO/WHO, which pose a threat to their health. This necessitates the urgent need to undertake a comprehensive study to determine the sources of exposure to these heavy metals. Breast-feeding is of great benefical value for the infant’s development; therefore, efforts should be made to prevent its contamination with environmental pollutants.     

New Facts about CdCl2 Action on the Photosynthetic Apparatus of Spinach Chloroplasts and Its Comparison with HgCl2 Action

Using EPR spectroscopy it was found that CdCl₂ and HgCl₂ interact (1) with the intermediates , i.e. with the tyrosine radicals on the donor side of photosystem (PS) 2 situated in the 161^st position in D₁ and D₂ proteins; (2) with the primary donor of PS1 (P700) whereby the oxidation of chlorophyll (Chl) a dimer in the reaction centre of PS1 occurs yet in the dark; (3) with the manganese cluster which is situated in the oxygen evolving complex. Due to these interactions of investigated metal chlorides with the photosynthetic apparatus, the interruption of the photosynthetic electron transport through photosynthetic centres occurs. Monitoring of time dependence of EPR signal I of chloroplasts treated with CdCl₂ or HgCl₂ after switching off the light suggests that all mechanisms, i.e. direct, cyclic, and non-cyclic reductions of P700⁺ are damaged. The formation of complexes between mercury or cadmium ions and amino acid residues constituting photosynthetic peptides was suggested as possible mechanism of their inhibitory action. The higher HgCl₂ efficiency in comparison with that of CdCl₂ was explained by higher ability of mercury ions to form complexes with amino acids, what was demonstrated by their apparent binding constants: K = 10 200 M^–1 for Hg²⁺ ions, and K = 3 700 M^–1 for Cd²⁺ ions.     

Genes for all metals—a bacterial view of the Periodic Table

Bacterial chromosomes have genes for transport proteins for inorganic nutrient cations and oxyanions, such as NH₄ ⁺, K⁺, Mg²⁺, Co²⁺, Fe³⁺, Mn²⁺, Zn²⁺ and other trace cations, PO₄ ^3-, SO₄ ^2- and less abundant oxyanions. Together these account for perhaps a few hundred genes in many bacteria. Bacterial plasmids encode resistance systems for toxic metal and metalloid ions including Ag⁺ AsO₂ ^-, AsO₄ ^3-, Cd²⁺, Co²⁺, CrO₄ ²⁻, Cu²⁺, Hg²⁺, Ni²⁺, Pb²⁺, TeO₃ ²⁻, TI⁺ and Zn²⁺. Most resistance systems function by energy-dependent efflux of toxic ions. A few involve enzymatic (mostly redox) transformations. Some of the efflux resistance systems are ATPases and others are chemiosmotic ion/proton exchangers. The Cd²⁺-resistance cation pump of Gram-positive bacteria is membrane P-type ATPase, which has been labeled with ³²P from [γ-³²P]ATP and drives ATP-dependent Cd²⁺ (and Zn²⁺) transport by membrane vesicles. The genes defective in the human hereditary diseases of copper metabolism, Menkes syndrome and Wilson’s disease, encode P-type ATPases that are similar to bacterial cadmium ATPases. The arsenic resistance system transports arsenite [As(III)], alternatively with the ArsB polypeptide functioning as a chemiosmotic efflux transporter or with two polypeptides, ArsB and ArsA, functioning as an ATPase. The third protein of the arsenic resistance system is an enzyme that reduces intracellular arsenate [As(V)] to arsenite [As(III)], the substrate of the efflux system. In Gram-negative cells, a three polypeptide complex functions as a chemiosmotic cation/protein exchanger to efflux Cd²⁺, Zn²⁺ and Co²⁺. This pump consists of an inner membrane (CzcA), an outer membrane (CzcC) and a membrane-spanning (CzcB) protein that function together. Received 08 August 1997/ Accepted in revised form 01 November 1997     

Responses of Glutathione and Glutathione S-Transferase to Cadmium and Mercury Exposure in Pedunculate Oak (Quercus robur) Leaf Discs

Changes in chlorophyll, non-protein thiol and glutathione (GSH) levels, and the activity of glutathione S-transferase (GST) were investigated in cadmium(ll) and mercury(ll) cchloride treated leaf discs of mature pedunculate oak trees (Quercus robur). Both heavy metals caused decreases in chlorophyll content, but mercury was more toxic than cadmium. Cadmium treatments (30–250μiM) resulted in increasing non-protein thiol levels after 3d, but GSH contents decreased. Mercury (1–20μM) led to a concentration-dependent decline in both non-protein thiol and GSH levels. GST activities were not modified significantly by cadmium, but mercury treatments caused a dose- and time-dependent enzyme induction. Both the phytotoxic- and GST-inducing effect of mercury could be prevented by the cysteine precursor L-2-oxo-4-thiazolidinecarboxylic acid.     

An examination of current Hg deposition and export in Fenno-Scandian catchments

The input and output flux data of total Hg (THg) and methylmercury (MeHg) from three catchments located in different geographical regions in Sweden and one catchment in southern Finland were compared to elucidate the role of current atmospheric Hg/MeHg deposition with regard to waterborne Hg/MeHg output.There was a negative co-variaton between the open field THg inputs and the ratio of THg output to open field input. The highest ratio (and lowest input) occurring in N. Sweden and S. Finland, while the lowest output ratio (and highest inputs) occurred in southwest Sweden. A much larger variation was found in the ratio of output to open field input for MeHg (14 to 160%). Examinations of MeHg input/output data in relation to catchment charateristics suggest that riparian peat, mires and wet organic soil contributed to the large MeHg output from certain catchments, probably due to in situ production of MeHg. This finding is consistent with other studies which have found that catchment characteristics such as wetland area, flow pathways, seasonal temperature and water flow are important in controlling the output of MeHg. These catchment characteristics govern the fate of the contemporary input of Hg and MeHg as well as the mobilization of the soil pools.     

Fluxes of mercury to lake sediments in central and northern Canada inferred from dated sediment cores

Sediment cores were collected from lakes in central and northern Canada and from Hudson Bay to compare current and historic net depositions of mercury. Cores from most locations were enriched in mercury in the upper layers deposited recently relative to deeper, historic layers. The lakes with the greatest enrichments in mercury were located in central/southern Canada. This enrichment was interpreted as being of anthropogenic origin. Mercury inputs at the Experimental Lakes Area (ELA) in northwestern Ontario inferred from a core profile agreed well with inputs calculated independently from precipitation and runoff data. Anthropogenic inputs of mercury to northwestern Ontario were calculated to be about 9 µg m^-2 y^-1. Considering all the locations over the geographic range, the core profiles infer that fluxes of mercury have increased on average by about 2 fold over the past half century. This is consistent with results from other sites in North America and Europe.     

Effect of urban sewage treatment on total and methyl mercury concentrations in effluents

The purpose of this study was to investigate the effect of sewage treatment on total mercury (THg) and methylmercury (MeHg) concentrations in domestic effluents and the contribution of urban sewage treatment facilities to THg and MeHg in rivers. We determined the concentrations of THg and MeHg in unfiltered samples of untreated and treated domestic sewage from the three treatment facilities and receiving river water within the City of Winnipeg. The concentrations of THg in the Red and Assiniboine rivers ranged from 3–31 ng/L. THg was related positively to suspended sediment concentrations in the rivers. The concentrations of MeHg in these rivers were usually 0.2–0.3 ng/L. THg concentrations in raw sewage varied widely, from 2–150 ng/L. Treatment removed an average of 88% of this mercury. MeHg concentrations in raw sewage were 0.5–4.3 ng/L, however, after treatment at two treatment facilities, MeHg was greatly reduced, usually to 0.1–0.4 ng/L. Most treated sewage, therefore, had MeHg concentrations that were similar to levels in the receiving rivers and the effect of discharged effluent was usually a change of about 2% or less on concentrations in the rivers. However, one of the facilities (the West End plant) was discharging higher concentrations of MeHg, up to 2 ng/L, causing calculated increases of up to 11% in the concentration of MeHg in the Assiniboine River.     

Synanthropic primates in Asia: Potential sentinels for environmental toxins

Macaques are similar to humans both physiologically and behaviorally. In South and Southeast Asia they are also synanthropic, ecologically associated with humans. Synanthropy with humans raises the possibility that macaques come into contact with anthropogenic toxicants, such as lead and mercury, and might be appropriate sentinels for human exposures to certain toxic materials. We measured lead (Pb) and mercury (Hg) levels and characterized the stable isotopic compositions of δ¹⁵N and δ¹³C in hair from three groups of free‐ranging macaques at the Swoyambhu temple in Kathmandhu, Nepal, an urban population that has abundant contact with humans. Hair lead levels were significantly higher among young macaques and differed among the three groups of macaques that were sampled. Hair Hg levels were low. No statistical association was found between stable isotopic compositions (δ¹⁵N and δ¹³C) and Pb and Hg levels. Our data did not find evidence that lead levels were associated with diet. We conclude that, in this population of macaques, behavioral and/or physiologic factors may play a significant role in determining exposure to lead. Chemical analysis of hair is a promising, noninvasive technique for determining exposure to toxic elements in free‐ranging nonhuman primates. Am J Phys Anthropol, 2010. © 2009 Wiley‐Liss, Inc.     

DNA barcodes reveal species-specific mercury levels in tuna sushi that pose a health risk to consumers

Excessive ingestion of mercury—a health hazard associated with consuming predatory fishes—damages neurological, sensory-motor and cardiovascular functioning. The mercury levels found in Bigeye Tuna (Thunnus obesus) and bluefin tuna species (Thunnus maccoyii, Thunnus orientalis, and Thunnus thynnus), exceed or approach levels permissible by Canada, the European Union, Japan, the US, and the World Health Organization. We used DNA barcodes to identify tuna sushi samples analysed for mercury and demonstrate that the ability to identify cryptic samples in the market place allows regulatory agencies to more accurately measure the risk faced by fish consumers and enact policies that better safeguard their health.