Biomonitoring of low levels of mercurial derivatives in water and soil by Allium micronucleus assay

The Allium micronucleus (MNC) assay was developed to monitor low levels of mercury in aquatic and terrestrial environments. Four mercurial derivatives namely mercuric chloride (MC), methyl mercuric chloride (MMC), phenyl mercuric acetate (PMA) and a methoxy ethyl mercuric chloride based fungicide, Emisan-6, were tested to assess the sensitivity and versatility of the Allium MNC assay. Allium bulbs were set directly on water and soil contaminated with known levels of mercurial derivatives (0.0001-10.00 ppm). On the 5th day the endpoints measured were root length, mitoses with spindle abnormality and cells with MNC in root meristems. The effective concentrations of the test chemicals that cause 50% of root length as compared to control (EC50) were determined from dose-response curves so obtained. The lowest effective concentration tested (LECT) and highest ineffective concentration tested (HICT) for each of the mercurial derivatives for the induction of spindle malfunction and MNC were determined. It was found that EC50, LECT and HICT values for mercurial derivatives in soil were higher than those in water. The frequencies of cells with MNC and mitoses with spindle abnormality were highly correlated indicating that MNC is a good parameter of spindle malfunction. The present approach increased the sensitivity of the Allium assay by 10-fold, the detection limit being 0.001-0.1 ppm and 0.1-1.0 ppm in aquatic and terrestrial environments respectively, depending on the species of mercury.     

Water hyacinth (Eichhornia crassipes) to biomonitor genotoxicity of low levels of mercury in aquatic environment

The mitotic cell-cycle duration of root meristematic cells of Eichhornia crassipes as determined by the colchicine labelling method was approximately 24 h at 30 +/- 1 degrees C. In one experiment the intact root meristems of E. crassipes were subjected to 1 h acute exposure to water contaminated with maleic hydrazide (MH), 56 ppm, or methyl mercuric chloride (MMCl), 0.1-0.5 ppm, followed by recovery in tap water for 4-48 h. In a second experiment the roots were subjected to 96 h exposure to water contaminated with MH, 56 ppm, or MMCl, 0.0001-0.1 ppm. In both experiments the cytological end-point measured was the frequency of cells with micronuclei (MNC). In the first experiment, while in the MH-exposed root meristems the frequency of MNC was significant at 40 h of recovery, MMCl induced significant MNC at 12, 20, 24, 40, and 40 h of recovery depending on the concentration. In the second experiment both test chemicals induced MNC which was concentration-dependent in case of MMCl. The highest ineffective concentration tested (HICT) and lowest effective concentration tested (LECT) for MMC determined in this experiment were 0.0005 ppm and 0.001 ppm, respectively. The present work provides evidence that E. crassipes could be a promising in situ environmental biomonitoring assay system.     

Cultivation of mercury resistent microorganisms

A strain of bacteria was isolated from soil samples. The resistance of these microorganisms to mercury ions was proved by means of discontinuous and continuous fermentations. Continuous fermentation was carried out also at a mercury ion concentration of 250 mg/l. A balance of mercury distributions demonstrates the capability of these bacteria to accumulate a great amount of mercury.     

Evaluation of mercury level in waters, bottom sediments and soils in selected rural areas

The studies carried out aimed at evaluation of the mercury level in waters, bottom sediments and soils in selected rural areas, during the season of mercury biocides application and after their withdrawal from agricultural use. Generally, in the period between 1976-1980 the mercury level in 1268 environmental samples has been examined. Shallow dug wells of bad technical state and wrong location particularly exposed to contamination, have been selected for the studies. Mercury level has been determined after mineralization with concentrated acids by means of flameless method of atomic absorption spectrophotometry. The results have been compared with standards for mercury level in drinking waters (1 microgram/l) and in surface waters (5 micrograms/l), with the Warren-Devault criterion for soils (0.25 mg/kg) and with the value 1 mg/kg adopted as maximum natural mercury level in bottom sediments. The results have also been the subject to statistical analysis by means of the Tsao-Fei method and t-test. Mercury level in well waters, surface waters, bottom sediments and soils varied according to the region and the year of study and were respectively: 0.08-26.00 micrograms/l; 0.00-25.20 micrograms/l; 0.02-91.91 mg/kg; 0.01-24.94 mg/kg. Mercury levels of several dozen micrograms/l (waters) and several dozen mg/kg (bottom sediments and soils) have been recorded only in a few cases. A statistically significant decrease of mercury level in the environment of the regions investigated coincided with mercury biocides withdrawal from agricultural practice in our country.     

Luminescent bacteria toxicity assay in the study of mercury speciation

The toxicities of solutions of 10 mercury compounds to luminescent bacteria were measured using the Microtox Toxicity Bioassay. The aim of this study was to assess the influence that the counter-ions have on the aquatic toxicity of mercury salts. The toxicities of these mercury compounds were very similar, except for mercurous tannate and mercuric salicylate. This can be attributed to differences in the ionization and speciation patterns of these compounds relative to the other compounds tested. In general, the toxicity of the solutions at pH 5 was not significantly different from the toxicity of these solutions at pH 6, but a clear reduction in toxicity was observed when the pH of the solution was adjusted to pH 9. Significant differences were found between the toxicity of Hg(I) and Hg(II) salts of the same anion at pH 9. When cysteine was added to a mercuric nitrate solution (at pH 6), a reduction in the toxicity was observed. This can be explained in terms of the strong binding of mercury to cysteine, thus reducing the concentration of mercury species available to cause an observable toxic effect to the bioluminescent bacteria.     

Development of microbial mercury detoxification processes using mercury-hyperresistant strain of Pseudomonas aeruginosa PU21

A mercury-hyperresistant strain of Pseudomonas aeruginosa PU21 harboring plasmid Rip64 was utilized to develop bioprocesses able to detoxify and recover soluble mercuric ions in aquatic systems. The kinetics of mercury detoxification was investigated to determine the parameters needed for the design of the bioprocesses. Batch, fed-batch, and continuous bioreactors were utilized to evaluate the efficiency and feasibility of each mode of operation. The results showed that the specific mercury detoxification rate was dependent on cell growth phases, as well as the initial mercury concentrations. Cells at the lag growth phase exhibited the best specific detoxification rate of approximately 1.1 x 10(-6) microg Hg/cell/h, and the rate was optimal at an initial mercury concentration of 8 mg/L. In batch operations with initial mercuric ions ranging from 2 to 10 mg/L, the mercuric ions added were rapidly volatilized from the media in less than 2-3 h. With periodic feeding of 3 or 5 mg Hg/L at fixed time intervals, the fed-batch processes had mercury removal efficiencies of 2.9 and 3.3 mg Hg/h/L, respectively. For continuous operations, the effluent cell concentration (Xe) was essentially invariant at 527 and 523 mg/L with the dilution rates (D) of 0.18 and 0.325 h-1, respectively. The increase in mercury feeding concentrations (Hgf) from 1.0 to 6.15 mg Hg2+/L did not affect the steady-state cell concentration (Xe) but forced the effluent mercury concentration (Hge) to increase. The decrease in the dilution rate, however, resulted in lower Hge values. It was also found that sequential mercury vapor absorption columns recovered over 80% of the Hg degrees released from the bioreactor while the residual mercury vapor was subsequently immobilized by an activated carbon trap in the down stream of the absorption column.     

Genotoxicity biomarkers in occupational exposure to formaldehyde--the case of histopathology laboratories

Oxidative stress-mediated genotoxicity of wastewaters taken from two different cities, Saharanpur (SWW) and Aligarh (AWW), were compared with a battery of short-term assays namely the Allium cepa genotoxicity test, the plasmid-nicking assay, and the Ames fluctuation test. Both test-water samples - when used undiluted - increased the frequency of chromosomal abnormalities and/or micronuclei and alterations in the mitotic index of root cells of Allium cepa. Bridges and fragmentation of the chromosome were the predominant effects of the Saharanpur water sample while the Aligarh sample induced mainly chromosome fragmentation. Single- and double-strand breaks were also observed in plasmid DNA treated with these test wastewaters. The plasmid-nicking assay performed on SWW resulted in linearization of plasmid DNA when 18μl was tested (in a total reaction volume of 20μl). However, with the same amount of AWW, all three forms of plasmid, viz. supercoiled, open circular and linear were observed. Supplementation with specific scavengers of reactive oxygen species (ROS) caused a significant decline in mutagenicity of test-water samples in all the tests, pointing at oxidative stress as the mediator of the observed genotoxicity. The role of heavy metals in the AWW-induced oxidative stress and that of phenolics in SWW cannot be ruled out.     

Indicative value of mercury concentration in adipose fin of brown trout, Salmo trutta L.

Investigation of adipose fin and axial muscle mercury concentration in brown trout, Salmo trutta , from Lake Tyrifjorden, south-east Norway showed that these were highly correlated ( r = 0.93, P<0.001), but adipose fin mercury concentrations were approximately 80% lower. Analysis of adipose fin mercury concentration may prove helpful in documenting mercury contamination in aquatic environments. Conflicts regarding the highly-priced salmonids are reduced when sampling from living individuals.     

Exploring the structural basis for selenium/mercury antagonism in Allium fistulosum

While continuing efforts are devoted to studying the mutually protective effect of mercury and selenium in mammals, few studies have investigated the mercury-selenium antagonism in plants. In this study, we report the metabolic fate of mercury and selenium in Allium fistulosum (green onion) after supplementation with sodium selenite and mercuric chloride. Analysis of homogenized root extracts via capillary reversed phase chromatography coupled with inductively coupled plasma mass spectrometry (capRPLC-ICP-MS) suggests the formation of a mercury-selenium containing compound. Micro-focused synchrotron X-ray fluorescence mapping of freshly excised roots show Hg sequestered on the root surface and outlining individual root cells, while Se is more evenly distributed throughout the root. There are also discrete Hg-only, Se-only regions and an overall strong correlation between Hg and Se throughout the root. Analysis of the X-ray absorption near edge structure (XANES) spectra show a "background" of methylselenocysteine within the root with discrete spots of SeO(3)(2-), Se(0) and solid HgSe on the root surface. Mercury outlining individual root cells is possibly binding to sulfhydryl groups or plasma membrane or cell wall proteins, and in some places reacting with reduced selenium in the rhizosphere to form a mercury(ii) selenide species. Together with the formation of the root-bound mercury(ii) selenide species, we also report on the formation of cinnabar (HgS) and Hg(0) in the rhizosphere. The results presented herein shed light on the intricate chemical and biological processes occurring within the rhizosphere that influence Hg and Se bioavailability and will be instrumental in predicting the fate and assisting in the remediation of these metals in the environment and informing whether or not fruit and vegetable food selection from aerial plant compartments or roots from plants grown in Hg contaminated soils, are safe for consumption.     

Cytogenetic effects of silver and gold nanoparticles on Allium cepa roots

The present study evaluates the cytogenetic effects of both silver and gold nanoparticles on the root cells of Allium cepa. In this study, the root cells of Allium cepa were treated with both gold and silver nanoparticles of different concentrations (1?mg/L, 5?mg/L and 10?mg/L) along with control for 72?h. Experimental results revealed that after 72?h of exposure, a significant decrease in mitotic index (MI) from 68% (control) to 52.4% (1?mg/L), 47.3% (5?mg/L) and 41.4% (10?mg/L) for gold nanoparticles and 57.1% (1?mg/L), 53% (5?mg/l), 55.8% (10?mg/L) for silver nanoparticles. Through minute observation of the photograph, it was recorded that some specific chromosomal abnormalities such as stickiness of chromosome, chromosome breaks, nuclear notch, and clumped chromosome at different exposure conditions. Therefore, present results clearly suggest that Allium cepa root tip assay could be a viable path through which negative impact of both gold and silver nanoparticles can be demonstrated over a wide range of concentrations.     

Immunological profiles in workers occupationally exposed to inorganic mercury.

Forty-one male mercury-exposed workers were examined for the serum concentration levels of immunoglobulins (IgG, IgA, IgM), alpha-1-antitrypsin (A1AT), alpha-2-macroglobulin (A2M), ceruloplasmin (CPL) and orosomucoid (ORO). In the period preceding this investigation the mercury concentrations in workplace air ranged from 0.106 to 0.783 mg.m-3, the range of urinary mercury concentrations was from 0.029 to 0.545 mg.1(-1). All but two (IgG and A1AT) of the immune parameters tested were at the levels that were evidently higher than those found in a control group of 55 workers matched by age who lived in a relatively clean area. The percentage of individuals with no value out of the range of normal physiological limits was in the controls almost 80%, in the exposed 36.6% only. These findings confirm the literature data which show that an inhalation exposure to inorganic mercury may evidently have a stimulating effect on some serum proteins in humans.     

The influence of urinary flow rate on mercury excretion in children

ProjectThere is limited literature concerning the effect of urinary flow rate on mercury excretion at low-level exposure. The aim of the present study is to examine the influence of urinary flow rate on mercury excretion in children. Also of interest is the influence of flow rate on creatinine excretion and creatinine-corrected mercury, which arisearises with spot urine samples.ProcedureA substudy of the New England Children's Amalgam Trial collected pairs of urine samples from children aged 10–16 years: a timed overnight collection and a spot daytime sample collected the following day. These samples were analyzed for mercury and creatinine concentration. Regression analysis was used to model the effect of urinary flow rate in the timed overnight samples. A paired t-test compared concentrations and creatinine-corrected mercury between overnight and daytime samples.ResultsCreatinine excretion rate (mg/h) increased significantly with urinary flow rate (mL/h), whereas creatinine concentration (g/L) decreased with flow rate. We found a non-significant increase in mercury excretion rate (ng/h) with flow rate, and mercury concentration decreased with flow rate. Mercury and creatinine concentrations were significantly higher in the overnight compared to daytime samples. For creatinine-corrected mercury, no significant impact of urinary flow rate was found.ConclusionsAlthough the creatinine excretion rate, and probably the mercury excretion rate, increased with urinary flow rate, the mercury/creatinine ratio seemed relatively unaffected by urinary flow rate.     

Bioaccumulation of mercury from wastewater by genetically engineered Escherichia coli

Genetically engineered E. coli, which express both a Hg2+ transport system and metallothionein, were tested for their ability to remove mercury from wastewater. The wastewater contained more than ten different ions, including 2.58 mg/l mercury, and its pH was 9.6. Mercury uptake was faster from the wastewater than from distilled water, probably because of the higher ionic strength, as the high pH had little effect on mercury accumulation. EDTA also stimulated mercury uptake rather than inhibiting it. A hollow-fiber bioreactor was used to retain induced cells for continuous mercury uptake. The cells removed more than 99% of the mercury in the wastewater and the final amount of mercury accumulated was 26.8 mg/g cell dry weight, while none of the other ions were removed from the water. These results indicated that the induced cells had a high affinity and specificity for mercury.     

Metallic mercury in the arterial blood of normal and acatalasemic mice exposed to metallic mercury vapor

Concentration of metallic mercury in the arterial blood was higher in acatalasemic mice after exposure to 3.45 mg/m3 for 10 minutes in comparison with normal mice, whereas concentration of mercuric ion was lower in acatalasemic mice than in normal mice. Thus, the ratio of metallic mercury to total mercury in the arterial blood of acatalasemic mice was 5.86 +/- 3.61%, which was statistically significantly higher than the value (1.36 +/- 0.65%) of corresponding normal mice. The mercury concentration and distribution in the brain and liver of acatalasemic mice were higher than those in normal mice. Data indicate that the concentration of metallic mercury in the arterial blood of acatalasemic mice was higher than that of normal mice and that metallic mercury soluble in lipids is likely transferred to the brain and liver from the blood. Conclusively, metallic mercury in the arterial blood is the biologically active form for transferring mercury from blood to organs.     

Habitat use and trophic position determine mercury concentration in the straight fin barb Barbus paludinosus, a small fish species in Lake Awassa, Ethiopia

The diet, habitat use and mercury concentration of the small fish species, the straight fin barb Barbus paludinosus , were studied in Lake Awassa, Ethiopia, for a period of 1 year from February 2003 to January 2004. Stable isotope signatures of nitrogen and carbon in different total length ( L _T) classes were used to determine trophic positions and organic carbon sources, respectively. Barbus paludinosus mainly occupied the protected benthic habitats (littoral and profundal) of the lake. The δ¹³C values were in the range from −24 to −19‰, indicating that the carbon source for B. paludinosus was benthic, as well. Small individuals (≤ 60 mm L _T) mainly preyed upon ostracods, intermediate sizes (60–100 mm) on aquatic insects and gastropods, while a tiny cyprinodont fish Aplocheilichthys antinorii dominated the diet of large individuals (100–160 mm). The progressively increase in δ¹⁵N with increasing L _T also indicated a diet shift towards piscivory in larger individuals. The mercury concentration ranging from 0·02 to 0·74 mg kg⁻¹ wet mass (wm), was unexpectedly high in this small species, and was significantly positively related to L _T, as well as to δ¹⁵N. Some large individuals had mercury concentrations < 0·1 mg kg⁻¹ wm, and low δ¹⁵N, indicating substantial variations in diet between individuals of same size. The study suggests that other piscivorous species which include B. paludinosus in their diet may have a high mercury intake risk.     

Comparative study on the inhibition of acetylcholinesterase activity in the freshwater fish Cyprinus carpio by mercury and zinc.

The effects of sublethal concentrations of mercury (0.1mg/l) and zinc (6 mg/l) on acetylcholinesterase activity and acetylcholine content of gill, kidney, intestine, brain, liver and muscle of the freshwater fish Cyprinus carpio at 1, 15 and 30 days of exposure were studied. A significant suppression in acetylcholinesterase activity was recorded in all the organs from both mercury and zinc intoxicated fish at all the exposure periods. Concurrently, a significant increase in the content of acetylcholine in the organs was observed. These changes observed in the organs of mercury treated fish in different exposure periods were in the order 1 greater than 15 less than 30 days and in zinc treated fish 1 greater than 15 greater than 30 days. Further, these changes were greater in magnitude in the brain, liver and muscle (non-osmoregulatory organs) than in the gill, kidney and intestine (osmoregulatory organs) in both metal media.     

芦竹修复镉汞污染湿地的研究

以湿土盆栽方法研究了芦竹在Cd和Hg污染模拟湿地中的富集能力及其在植株中的分布.结果表明,芦竹在101mg·kg^-1Hg污染环境中生长8个月后,对Hg的富集量是根系>茎>叶片,植物地上部分对Hg富集量为200±20mg·kg^-1DW;而在115mg·kg^-1Cd污染环境中生长8个月后,其对Cd的富集量是叶片>根系>茎,芦竹叶片对Cd的富集量在160±26mg·kg^-1DW.重金属在芦竹各器官内的含量随种植时间的延长而增加,8个月生长期富集量比4个月生长期富集量高30%～50%.芦竹生物富集系数(Bio concentrationfactorBCF)随土壤中重金属含量增加而减小.在污染土壤中,芦竹叶、茎对Hg的BCF为1.9和2.1、对Cd为1.5和0.3;在未受污染的空白对照湿土中(含Hg6.8mg·kg^-1,Cd8.5mg·kg^-1),芦竹叶、茎对Hg的BCF为6.8和12.2,对Cd为7.0和2.7,表明芦竹具有生物量大、根系发达、适应性强等特点,对Cd、Hg有较大富集量和较好的耐受性.     

Mutagenicity and genotoxicity of suspended particulate matter in the Seine river estuary

Highly mutagenic compounds such as some PAHs have been identified in surface waters and sediments of the Seine river estuary. Suspended particulate matter (SPM) represents a dynamic medium that may contribute to the exposure of aquatic organisms to toxic compounds in the water column of the estuary. In order to investigate major sources of mutagenic contaminants along the estuary, water samples were taken at 25 m downstream of the outlet of an industrial wastewater-treatment plant (WWTP). SPM samples were analyzed for their genotoxicity with two short-term tests, the Salmonella typhimurium mutagenicity assay (TA98+S9 mix) and the comet assay in the human HepG2 cell line. Sampling sites receiving effluents from a chemical dye industry and WWTP showed the highest mutagenic potencies, followed by petrochemical industries, petroleum refinery and pulp and paper mills. These data indicate that frame-shift mutagens are present in the Seine river estuary. Furthermore, the comet assay revealed the presence of compounds that were genotoxic for human hepatocytes (HepG2 cells). We also observed a high level of mutagenic potency in the sediment of the lower estuary (3 × 10? revertants/g). The source of mutagenic and genotoxic compounds seems to be associated with various types of effluents discharged in the Seine river estuary. Both test systems resulted in the same assessment of the genotoxicity of particulate matter, except for three of the 14 samples, underlying the complementarity of bioassays.     

Histochemical demonstration of mercury induced changes in rat neurons.

A histochemical method modified for ultrastructural studies of mercury induced changes is described. Rat neurons from areas known to be influenced by mercury are used as examples. The histochemical reaction, suggested to be caused by polymercury sulphide complexes, is localized to "dense bodies" where it is visible 14 days after initiation of peroral mercury treatment (20 mg HgCl2/l drinking water).