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PubMed2004

Comparison of two particulate hexavalent chromium compounds: Barium chromate is more genotoxic than lead chromate in human lung cells.

Particulate hexavalent chromium [Cr(VI)] compounds are well-established human lung carcinogens. However, their carcinogenic mechanisms are poorly understood as most investigators have used soluble Cr(VI) compounds. Recent work from our laboratory has found that barium chromate (BC) is also cytotoxic and clastogenic. To understand how BC relates to existing data on other particulate Cr(VI) compounds, we compared its cytotoxicity and clastogenicity with lead chromate (LC), which has been used as a prototypical particulate Cr(VI) compound, in WTHBF-6 cells, a near-normal human lung cell line. We found that BC is a more potent cytotoxicant, inducing 67%, 12%, 3%, and 0% relative survival at concentrations of 0.1, 0.5, 1, and 5 microg/cm2, respectively, while LC induced 90%, 71%, 43%, and 15% survival at these same concentrations. We found that BC was also more clastogenic, damaging 22% and 49% of metaphase cells at 0.1 and 0.5 microg/cm2, and causing complete cell cycle arrest at 1 and 5 microg/cm2. By contrast, 0.1, 0.5, and 1.0 microg/cm2 LC damaged 10%, 27%, and 37% of metaphase cells, respectively, and complete cell cycle arrest was not observed until a concentration of 5 microg/cm2 was reached. We found that BC and LC both partially dissolved in complete medium in the presence of cells, producing similar extracellular concentrations. Both compounds were also comparable with respect to particle uptake and the amount of intracellular Cr ions. Considering previous reports showing that lead ions were inactive and that sodium chromate and LC have similar clastogenic potencies, these data suggest that BC genotoxicity may not be solely mediated by Cr ions, but also involve some clastogenic activity of barium ions.

Barium Compounds↗

PubMed1990

Chromate-resistance in a chromate-reducing strain of Enterobacter cloacae.

Resistance to toxic hexavalent chromium (chromate: CrO4(2)) in Enterobacter cloacae strain HO1, isolated from an activated sludge sample, was investigated under aerobic and anaerobic conditions. Decreased uptake of 51CrO4(2-) in E. cloacae strain HO1 was observed under aerobic conditions, when compared with a standard laboratory E. cloacae strain (IAM 1624). Under anaerobic conditions E. cloacae strain HO1 was able to reduce hexavalent chromium to the less toxic trivalent form. When E. clocacae strain HO1 was grown with nitrate anaerobically, the cells were observed to lose simultaneously their chromate-reducing ability and chromate-resistance under anaerobic conditions.

Anaerobiosis↗

PubMed1983

[Penetration of chromate ions in damaged and undamaged skin of sensitized and nonsensitized individuals occupationally exposed to chromates].

The importance of oversensitivity to chromate within the framework of occupational dermatoses is sufficiently well known. Questions still remained unanswered as to which substances and solutions in which form and quantity sensitivity to chromate occurs. Further, it is unclear why one worker reacts allergically and another remains unaffected carrying out the same work. In spite of all attempts it is as a rule still impossible to predict who will be affected. By investigating the penetration of chromate ions, we wanted to draw attention to possible dangers those beginning work are exposed to. We are aware that a complex series of questions exists but that only a small part can be approached at once. It appeared appropriate to determine whether the level of penetration of the metal ions differs between individuals, in particular whether the rate is higher in sensitive than in non-sensitive people. To handle this question a method had to be found to determine metal ions with and without exposure in the skin.

Chromates↗

PubMed2002

Accommodation to simulations of defocus and chromatic aberration in the presence of chromatic misalignment.

Previous studies have demonstrated that accommodation will respond to sine gratings in which the relative modulations of red, green and blue image components have been altered to simulate the effects of defocus and longitudinal chromatic aberration. The present study aimed to determine the tolerance of the accommodative system to relative phase shifts in those components induced by chromatic misalignment. It was found that accommodation can tolerate moderate amounts of chromatic misalignment (6'), but responds adversely when misalignments are large. Applications to visual display terminals and spectacle lens and instrument design are discussed.

Accommodation, Ocular↗

PubMedDate not supplied

Chromatic contrast detection in spatial chromatic noise.

The spectral properties of chromatic-detection mechanisms were investigated using a noise-masking paradigm. Contrast-detection thresholds were measured for a signal with a Gaussian spatial profile, modulated in the equiluminant plane in the presence of spatial chromatic noise. The noise was distributed within a sector in the equiluminant plane, centered on the signal direction. Each stimulus consisted of two adjacent fields, one of which contained the signal, separated horizontally by a gap with the same average chromaticity as the uniform background. Observers were asked to judge on which side of the central fixation point the signal was displayed via a two-alternative, forced-choice (2AFC) paradigm. Contrast thresholds were measured for four color directions and three sector widths at increasing levels of the average energy of the axial component of the noise. Results show that contrast thresholds are unaffected by the width of the noise sector, as previously found for temporally modulated stimuli (D'Zmura & Knoblauch, 1998). The results are consistent with the existence of spectrally broadband linear-detection mechanisms tuned to the signal color direction and support the hypothesis of the existence of higher-order color mechanisms with sensitivities tuned to intermediate directions in color space.

Acoustic Stimulation↗

PubMed2002

The influence of chromatic and achromatic variability on chromatic induction and perceived colour.

Judgments of the colour of a surface are influenced by the colour of the surrounding. To determine whether only the average colour of the surrounding matters, or also the chromatic variability, judgments in colourful scenes are often compared with ones in which a target is surrounded by a plain background that provides the same average physical illumination of the retina as the colourful scene. The variability sometimes makes a difference (eg Shevell and Wei, 1998 Vision Research 38 1561-1566), and sometimes it does not (eg Brenner and Cornelissen, 1998 Vision Research 38 1789-1793). Is this because of the nonlinearity in cone responses? We designed scenes that stimulated the cones in an equivalent manner, both on average and in terms of variability, and yet differed markedly in chromatic variability. The more colourful surroundings had considerably less influence on subjects' colour judgments. We conclude that early cone-specific regulation of sensitivity cannot be responsible for the change in perceived colour, and deduce that chromatic induction takes place after contrast gain control.

Color Perception↗

PubMed2002

Chromate reduction in Serratia marcescens isolated from tannery effluent and potential application for bioremediation of chromate pollution.

Pollution of aquatic systems by heavy metals has resulted in increasing environmental concern because they cannot be biodegraded. One metal that gives reason for concern due to its toxicity is chromium. Cr(VI) and Cr(III) are the principal forms of chromium found in natural waters. A chromate-resistant strain of the bacterium S. marcescens was isolated from tannery effluent. The strain was able to reduce Cr(VI) to Cr(III), and about 80% of chromate was removed from the medium. The reduction seems to occur on the cell surface. Transmission electron microscopic examination of cells revealed that particles were deposited on the outside of bacterial cells. A stable biofilm was formed in less than 10 h, reaching around 1010 cfu attached per milligram of activated carbon. These findings demonstrate that immobilized S. marcescens might be used in industrial waste treatment processes.

Biodegradation, Environmental↗

PubMed1992

The effect of pupil size on chromostereopsis and chromatic diplopia: interaction between the Stiles-Crawford effect and chromatic aberrations.

Several studies have reported that the magnitude of chromostereopsis changes as the pupil size changes. Einthoven's theory, that chromostereopsis is determined by interocular differences of monocular transverse chromatic aberration, can not easily explain this change. Therefore, several alternative hypotheses have been introduced, most notably by Vos [(1960) Vision Research, 6, 105-107], who argues that shifts in chromostereopsis with pupil size are due to decentration of the peak of the Stiles-Crawford effect (SCE) with respect to the pupil. We tested this hypothesis by measuring chromostereopsis under both scotopic (no SCE) and photopic conditions with centered and decentered artificial pupils. The results show that the SCE plays an important role in the effect of pupil size on chromostereopsis. Similar changes were also measured in monocular chromatic diplopia which supports the hypothesis that the effect of pupil size on chromostereopsis is due to monocular mechanisms.

Adult↗

PubMed1997

A dissociation between brain activity and perception: chromatically opponent cortical neurons signal chromatic flicker that is not perceived.

When two isoluminant colors alternate at frequencies > 10 Hz, we perceive only one fused color with a minimal sensation of brightness flicker. In spite of the perception of color fusion, color opponent (CO) cells at early stages of the visual pathway are known to respond to chromatic flicker at frequencies far exceeding the perceptual fusion frequency. To explain color fusion, several groups have predicted that CO cells in V1-unlike the retina and lateral geniculate nucleus-should not follow high-frequency flicker. To test this prediction we recorded from 12 CO cells in various V1 layers. We found, contrary to expectations, that these neurons follow high frequency flicker well above heterochromatic fusion frequencies. All followed 15 Hz flicker and 10/12 followed 30 Hz flicker. For three cells, we tested 60 Hz luminance flicker and found clear responses. We thus present evidence of cortical activity in alert, trained monkeys that is clearly representing visual stimulation, yet is not perceived. Our data call into question explanations of perceptual phenomena that invoke a low temporal frequency cut-off of CO cells in V1 to account for the failure to perceive fast temporal changes in the chromatic domain.

Animals↗

PubMed1991

Relation between the chromatic difference of refraction and the chromatic difference of magnification for the reduced eye.

We provide a simple model for calculating the chromatic difference of magnification for the human eye. Spectral differences in image size are proportional to the eye's longitudinal chromatic aberration and the axial distance between the entrance pupil and nodal point. We verify that the model provides magnification estimates equal to previously published predictions, and we show the significant increase in this aberration produced by experimental use of artificial pupils.

Humans↗

PubMed1965