Construction and evaluation of a metal ion biosensor

Escherichia coli, genetically engineered with a mercury(II)-sensitive promoter and the lux genes from Vibrio fischeri, were used as microbial bioluminescent sensors for the detection of mercury. Evaluation of this genetic construction was carried out by determining the effects of various parameters on cell suspensions maintained at constant conditions in a small 100-mL vessel. The strongest light intensities and quickest induction times occurred with cells in the midexponential growth phase maintained at 28 degrees C, concentrated to 1 x 10(9) cells/mL, mixed at very fast speeds, and aerated at 2 vvm (volume of air per volume of culture per minute) during light measurement in the small vessel. The cells were sensitive to the mercuric ion in the range of 20 nM to 4 muM (4 to 800 ppb), and the total response time was on the order of 1 hour, depending on the above parameters. The cells exhibited great specificity for mercury. The cells had almost equal specificity for organic and inorganic forms of the mercuric ion and responded more weakly to the mercurous ion. A simple, inexpensive, durable miniature probe (3 mL) was constructed and operated using the optimum parameters found in the small vessel as a guide. The range of sensitivity to the mercuric ion detected in the probe was 10 nM to 4 muM when aeration was provided. (c) 1993 John Wiley & Sons, Inc.     

The relationship between the seed bank and species composition of plant communities in two British salt marshes

The composition of the seed bank was compared with that of the above-ground vegetation in two British salt marshes. Vegetation and seed banks were sampled in autumn and spring. There was a relatively low correlation between seed bank and vegetation in most perennial-dominated zones. Percentage annual plant cover was significantly positively correlated to percentage similarity value between vegetation and seed bank. Cluster analysis indicated that the zones dominated by annuals and by Suaeda vera on the ungrazed Nod Marsh in Norfolk formed groups between seed bank and vegetation, whereas on the Llanrhidian Marsh in Wales the seed bank of four of the six zones formed a group.     

Mercury translocation in and evaporation from soil. III. quantification of evaporation of mercury from podzolized soil profiles treated with Hg Cl

Mercury evaporation from undisturbed iron‐humus podzol lysimeters was measured over 3 months after treatment with HgCl₂ spiked with radioactive ²⁰³Hg. The relative evaporation rate from HgCl₂ treated soils followed the sum of two exponential functions. Because evaporation asymptotically approaches zero with time, the integral of the fit curve represents the evaporative loss in percent of atmospheric deposition. For the soil investigated, about 5% of atmospheric Hg deposition was reemitted into the atmosphere. It is hypothesized that mercury evaporation can decrease the leaching of mercury in and from soil significantly; this effect is probably increasing with decreasing rain acidity or soil acidity. Mercury deposited as soluble salt remains susceptible to reemission to air for 300 d after incorporation into the soil matrix. Indications are found that Hg evaporation from soils in geological background areas predominantly derives from recent atmospheric Hg deposition and not from geological sources.     

Soft-tissue accumulation of lead in the blue tilapia,Oreochromis aureus (steindachner), and the modifying effects of cadmium and mercury

The interaction of mercury and cadmium with lead was investigated by exposingOreochromis aureus to two heavy metals simulataneously. The chronic accumulation prolife of lead was determined by analyzing the liver, brain, gill filaments, intestine, caudal muscle, spleen, trunk kidney, and gonads following exposure to lead alone and in mixtures with mercury and cadmium. Nominal exposure concentrations of lead were 0.05, 0.10, 0.50, and 1.00 mg/L. Mixtures of lead (0.50 or 0.05 mg/L) with cadmium (0.05 mg/L) and lead (0.50 or 0.05 mg/L) with mercury (0.05 mg/L) were also used. Following 140 d of exposure to lead, the highest concentrations of lead consistently accumulated in the trunk kidney. The concentration of lead in the kidney was decreased by coexposure to mercury or cadmium, but increased in the muscle and liver. Under all exposure regimes, the median concentration of lead in the muscle exceeded safety levels recommended for human consumption. In a food fish, such asO. aureus, a knowledge of toxic metal accumulation patterns is of great importance.     

Circadian and seasonal variation of the body temperature of sheep in a tropical environment

Nychthemeral and annual rhythms of the rectal temperature were determined for Corriedale sheep in a tropical climate. The minimum rectal temperature averaged 39.55° C at 0500 hours in summer, and 38.87° C at 0600 hours in winter. The maximum was 40.03° C in summer (1700 hours) and 39.33° C in winter (1830 hours). Annual cycle of the rectal temperature showed a minimum in July and maximum in December.     

Effects of methylmercury and inorganic mercury on periphytic diatom communities in freshwater indoor microcosms

The effects of inorganic mercury (HgII) and methylmercury (MeHg) on the colonization of artificial substrates by periphytic diatoms were studied using indoor freshwater microcosms. These consisted of a mixed biotope– water column + natural sediment – with rooted macrophyte cuttings (Elodea densa) and benthic bivalve molluscs (Corbicula fluminea).The periphyton was collected on glass slides in the water column after 34and 71 days. The two Hg sources were introduced either by daily additions to the water column, or once at the beginning into the sediment, using two nominal concentrations: water column, 0.5 μgL^-1 and 2 μg L^-1 for both compounds: sediment, 0.5 mg kg^-1 (fw) and 2 mgkg^-1 (fw) for MeHg and 1 mg kg^-1 (fw) and 10 mgkg^-1 (fw) for HgII. Several complementary criteria were used to analyse the structural and functional perturbations induced: cell density, species richness, diatom size, relative abundance. Exposure to MeHg added to the water column resulted in reduced cell density and changes in species composition with enhancement of e.g. Fallacia pygmaea or Nitzschia palea; inorganic Hg had less effect on the population structure. After contamination via the sediment, the effects of the two compounds were less pronounced than for the water source. This revised version was published online in August 2006 with corrections to the Cover Date.     

Urinary excretion of mercury, copper and zinc in subjects exposed to mercury vapour

The excretion of mercury, copper and zinc in urine, and mercury in whole blood andplasma, was determined in 40 chloralkali workers exposed to mercury vapour and 40age-matched referents. The Hg concentrations in whole blood, plasma and urine werehigher in the exposed group (35 nmol l, 30 nmol l,and 11.5 nmol mmol creatinine, respectively) in comparison with thereference group (15 nmol l, 6.3 nmol l, and 1.8nmol mmol creatinine, respectively). The urinary copper excretionwas similar in the two groups, while U-Zn excretion was significantly higher (P = 0.04)in the exposed group, median 0.83 mmol mmol creatinine versus 0.76mnmol mmol creatinine in the reference group. In a subgroup of exposedworkers with current U-Hg above 11.5 nmol lmmolcreatinine (20 mg g creatinine) the medianU-Zn was 1.1 mmol mmol creatinine. In both groups smokers had highU-Zn levels than non smokers. When both U-Hg and smoking were taken into account in alinear regression model, there was a significant association between U-Hg and U-Zn inthe combined group of exposed and referents (P = 0.002). This study indicates thatmercury exposure in humans, as in animals, causes increased urinary excretion of zinc.The mechanisms may be induced synthesis of metallothionein in the kidneys, displacementof Zn from preexisting metallothionein by Hg, or a decreased reabsorption of zinc in thekidneys owing to a slight tubular dysfunction.     

Immunological properties of low molecular-weight proteins binding heavy metals in rat kidney and liver

Two homogenous fractions of hepatic metallothioneins ((Cd,Zn) MT-1 and (Cd,Zn) MT-2) and renal metal binding proteins ((Bi,Cu) BP-1 and (Bi,Cu) BP-2) were isolated from rats exposed to heavy metals and specific antisera to them were produced in rabbits.These antisera were tested by immunodiffusion and immunoelectrophoresis for their ability to bind different fractions of hepatic Cd,Zn -metallothionein and renal (Bi,Cu)-, (Hg,Cu)- and (Cd,Cu)-binding proteins. It was found that anti (Bi,Cu) BP antisera did not cross-react with hepatic (Cd,Zn) MT-1 and (Cd,Zn) MT-2. Strong immunological cross-reactions were detected between anti (Bi,Cu) BP antisera and individual forms of (Cd,Cu)-, (Hg,Cu)- and (Bi,Cu)-binding proteins isolated from rat kidneys.