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PubMed1994

Perception of green and red under chromatic adaptation: the effects of stimulus size and eccentricity.

We measured thresholds for the perception of green and red light added to white, blue, green, yellow, or red adaptation fields presented at eccentricities of 0 to 70 degrees in the temporal visual field of two subjects. A series of stimulus sizes was used at each eccentricity to determine size-scaling factor E2--the eccentricity at which stimulus diameter has to be doubled in order to maintain foveal performance. For green light added to white or yellow, E2 varied from 3.1 to 41.5 degrees. When red light was added to white, yellow, or blue, E2 varied from 0.1 to 11.8 degrees. For red color in green and green color in blue or red there was no spatial scaling factor that would make performance independent of eccentricity. Our results suggest that E2 value for green and red perception depends on the state of chromatic adaptation and also shows marked interindividual differences.

Adaptation, Ocular↗
PubMed1995

Small amounts of chromatic aberration influence dynamic accommodation.

The prevailing view of accommodation is that the eye changes focus to maximize luminance contrast by trial and error. Negative feedback is considered essential in this view because luminance contrast provides no directional information. Fincham proposed an alternate view in which longitudinal (axial) chromatic aberration (LCA) provides a directional stimulus for accommodation. For spatial frequencies above approximately 0.5 cpd contrast of the retinal image is different for long, middle, and short spectral waveband components of the image. We varied the amount of LCA in small steps (0.25 D) to determine how much LCA is needed to enhance or impair the response. An infrared optometer monitored accommodation continuously while subjects viewed a yellow/black square-wave grating (3.5 cpd) in a Badal stimulus system. The yellow/black grating was produced by superimposing red (600 nm) and green (520 nm) gratings, and LCA was increased, decreased, neutralized, and reversed by repositioning the red grating component along the axis of the optical system. Target vergence was modulated sinusoidally (0.2 Hz) over a 1 D range (1.5 to 2.5 D) and gain and phase-lag of the accommodation response were determined by Fourier analysis. Subjects accommodated well as long as a normal amount of LCA was present--0.5 D in the correct direction enhanced accommodative gain, and 0.25 D in the reverse direction markedly inhibited the response. We conclude that the contrast of the retinal image in different spectral wavebands specifies focus of the eye, and provides a powerful directional stimulus for reflex accommodation.

Accommodation, Ocular↗
PubMed2005

Low-level hexavalent chromium exposure and rate of mortality among US chromate production employees.

OBJECTIVE: Although numerous studies have reported an elevated lung cancer risk among chromium chemical production employees, few studies have focused on employees hired after major process changes and enhanced industrial hygiene controls were implemented. METHODS: This study examines the mortality experience of two post-change cohorts of chromate production employees constituting the current US chromium chemical industry. RESULTS: Mortality among chromium chemical workers generally was lower than expected on the basis of national and state-specific referent populations. Lung cancer mortality was 16% lower than expected, with only three lung cancer deaths (3.59 expected). CONCLUSION: The absence of an elevated lung cancer risk may be a favorable reflection of the post-change environment. However, longer follow-up allowing an appropriate latency for the entire cohort will be needed to confirm this conclusion.

Carcinogens, Environmental↗
PubMed1973

Action Spectra for Chromatic Adaptation in Tolypothrix tenuis.

The dark synthesis of biliproteins in the blue-green alga Tolypothrix tenuis is controlled by brief light treatments. Green light potentiates synthesis of phycoerythrin and red light potentiates synthesis of phycocyanin. Red reverses the effect of green and vice versa. Action spectra for the red and green effects were obtained for the wavelength region 320 nanometers to 710 nanometers, at 10-nanometer intervals. The principal action band in the red peaks at 660 nanometers, with a half-band width of 58 nanometers and an accompanying shortwave band at 360 nanometers. The green action band peaks at 550 nanometers, with a half-band width of 76 nanometers, and a shortwave band at 350 nanometers. Chromatic adaptation and another photomorphogenic response in the blue-green algae are discussed in terms of possible regulation by a photoreversible pigment recently isolated from Tolypothrix.

Journal Article↗
PubMed1985

Constant Phycobilisome Size in Chromatically Adapted Cells of the Cyanobacterium Tolypothrix tenuis, and Variation in Nostoc sp.

Phycobilisomes of Tolypothrix tenuis, a cyanobacterium capable of complete chromatic adaptation, were studied from cells grown in red and green light, and in darkness. The phycobilisome size remained constant irrespective of the light quality. The hemidiscoidal phycobilisomes had an average diameter of about 52 nanometers and height of about 33 nanometers, by negative staining. The thickness was equivalent to a phycocyanin molecule (about 10 nanometers). The molar ratio of allophycocyanin, relative to other phycobiliproteins always remained at about 1:3. Phycobilisomes from red light grown cells and cells grown heterotrophically in darkness were indistinguishable in their pigment composition, polypeptide pattern, and size. Eight polypeptides were resolved in the phycobilin region (17.5 to 23.5 kilodaltons) by isoelectric focusing followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Half of these were invariable, while others were variable in green and red light. It is inferred that phycoerythrin synthesis in green light resulted in a one for one substitution of phycocyanin, thus retaining a constant phycobilisome size. Tolypothrix appears to be one of the best examples of phycobiliprotein regulation with wavelength. By contrast, in Nostoc sp., the decrease in phycoerythrin in red light cells was accompanied by a decrease in phycobilisome size but not a regulated substitution.

Journal Article↗
PubMed2004

Hexavalent chromium and lung cancer in the chromate industry: a quantitative risk assessment.

The purpose of this investigation was to estimate excess lifetime risk of lung cancer death resulting from occupational exposure to hexavalent-chromium-containing dusts and mists. The mortality experience in a previously studied cohort of 2,357 chromate chemical production workers with 122 lung cancer deaths was analyzed with Poisson regression methods. Extensive records of air samples evaluated for water-soluble total hexavalent chromium were available for the entire employment history of this cohort. Six different models of exposure-response for hexavalent chromium were evaluated by comparing deviances and inspection of cubic splines. Smoking (pack-years) imputed from cigarette use at hire was included in the model. Lifetime risks of lung cancer death from exposure to hexavalent chromium (assuming up to 45 years of exposure) were estimated using an actuarial calculation that accounts for competing causes of death. A linear relative rate model gave a good and readily interpretable fit to the data. The estimated rate ratio for 1 mg/m3-yr of cumulative exposure to hexavalent chromium (as CrO3), with a lag of five years, was RR=2.44 (95% CI=1.54-3.83). The excess lifetime risk of lung cancer death from exposure to hexavalent chromium at the current OSHA permissible exposure limit (PEL) (0.10 mg/m3) was estimated to be 255 per 1,000 (95% CI: 109-416). This estimate is comparable to previous estimates by U.S. EPA, California EPA, and OSHA using different occupational data. Our analysis predicts that current occupational standards for hexavalent chromium permit a lifetime excess risk of dying of lung cancer that exceeds 1 in 10, which is consistent with previous risk assessments.

Adult↗
PubMed1994

A phosphorylated DNA-binding protein is specific for the red-light signal during complementary chromatic adaptation in cyanobacteria.

Complementary chromatic adaptation is a mechanism by which some cyanobacteria that are able to synthesize phycoerythrin can adapt their pigment (phycobiliprotein) content to the incident wavelengths of the light. In Calothrix sp. PCC 7601 it concerns phycoerythrin (cpe operon), synthesized under green light, and phycocyanin-2 (cpc2 operon), expressed under red light, and involves transcriptional controls. With cell-free extracts from Calothrix sp. PCC 7601 grown under various light regimes, a protein designated RcaD was found by gel retardation experiments to specifically bind to the cpc2 promoter region and to be present only in red-light-grown cells. This protein was partially purified and its binding activity was shown to be sensitive to an alkaline phosphatase treatment. RcaD can protect two regions of the cpc2 promoter sequence against degradation by DNase I. Because its activity is detected only under the conditions required for cpc2 expression, we propose that RcaD is a positive effector of transcription.

Adaptation, Physiological↗
PubMed1981

Effects of chromatic illumination on cyanobacterial phycobilisomes. Evidence for the specific induction of a second pair of phycocyanin subunits in Pseudanabaena 7409 grown in red light.

Pseudanabaena 7409 is a chromatically cyanobacterium which photocontrols the synthesis of both phycoerythrin and phycocyanin [Tandeau de Marsac (1977) J. Bacteriol. 130, 82--91]. Phycobilisomes, isolated from cells grown in either green or red light, have been dissociated and the component biliproteins purified and characterized. Phycobilisomes isolated from cells grown in green light were composed of allophycocyanin B, allophycocyanin, two phycocyanin subunits (one alpha-type and one beta-type subunit), phycoerythrin and eight uncolored polypeptides. When dissociated phycobilisomes were chromatographed on DEAE-cellulose at pH 5.5, most of the phycocyanin was recovered as part of a large (17.3 S) multiprotein complex with phycoerythrin (molar ratio 1 : 1). This complex also contained five of the uncolored polypeptides found in intact phycobilisomes isolated from cells grown in green light. Phycobilisomes isolated from cells grown in red light were composed of allophycocyanin B, allophycocyanin, four phycocyanin subunits (two alpha-type and two beta-type subunits), and six uncolored polypeptides. When these phycobilisomes were dissociated, the phycocyanin was recovered as a large (21.0 S) multiprotein complex which was composed of the four phycocyanin subunits types and four uncolored polypeptides. This complex was morphologically identical to the rod-like stacks of discs about 6 x 12 nm which form the peripheral rods of intact phycobilisomes. Each of the four phycocyanin subunits found in the complex isolated from the phycobilisomes of cells grown in red light was purified to homogeneity and characterized. Amino acid compositions of the four subunits indicated that each subunit was a unique gene product. Two of the subunits of the complex were apparently identical to those of the phycocyanin purified from phycobilisomes isolated from cells grown in green light. These studies suggest that one pair of phycocyanin subunits was synthesized constitutively (i.e. irrespective of the light wavelength to which the cells were exposed during growth) while the synthesis of the second pair of phycocyanin subunits was specifically induced during growth in red light.

Amino Acids↗
PubMed1995

Chromate allergy from 'antifreeze-antiboil'.

A diesel mechanic developed hand dermatitis after more than 3 years in the trade. Patch testing showed positive reactions to chromate and cobalt. Potassium dichromate is added to antifreeze-antiboil as a corrosion inhibitor.

Adult↗
PubMed1989

Axial chromatic aberration of the human eye: frequency or wavelength?

The axial chromatic aberration of the human eye is nearly perfectly described by a linear function when expressed in terms of frequency rather than wavelength. Since linear functions are simple to work with and more readily understood, there are advantages for the expression of these data in terms of frequency.

Analysis of Variance↗
PubMed1990

A comparison of sclerosing agents: clinical and histologic effects of intravascular sodium tetradecyl sulfate and chromated glycerin in the dorsal rabbit ear vein.

The dorsal marginal rabbit ear vein was injected with 0.25 ml of 0.1% or 0.25% sodium tetradecyl sulfate (STS) (Sotradecol Injection) or undiluted or 50% Scleremo (Scl) (chromated glycerin). Only the 50% Scl solution failed to produce clinical or histologic thrombosis at 1 hour. Clinical fading was observed in STS-treated vessels at 10 days postinjection. Histologically, early thrombus formation with focal endothelial necrosis was replaced by fibrosis and microangiopathic recanalization. Although undiluted Scl caused similar, yet milder histologic findings, luminal recanalization after 10 days resulted in a clinically unfaded vessel. The use of 50% Scl produced no endothelial damage with no subsequent change in vessel appearance. Cutaneous necrosis or extravasation of erythrocytes was not observed.

Animals↗
PubMed2004

Single-blind, randomized study comparing chromated glycerin, polidocanol solution, and polidocanol foam for treatment of telangiectatic leg veins.

BACKGROUND: A single-blind, randomized, comparative study was performed to evaluate the efficacy of pure chromated glycerin (CG), polidocanol (POL) 0.25% solution, and POL 0.25% foam (Monfreux technique) for treatment of telangiectasias and reticular leg veins. OBJECTIVE: To determine the relative efficacy and safety of two sclerosing agents and foam. METHOD: Of 150 randomized patients presenting comparable areas (lateral face of thigh) of telangiectasias and reticular leg veins, 147 could be evaluated by photographic assessment, patients' satisfaction score, and pain at injection sites. Internal and external agreement for the photographic assessment was good for two independent blinded experts. RESULTS: CG cleared vessels significantly better than POL solution or foam (p<0.002). The patients' satisfaction score was also higher in the CG group, although the difference did not reach statistical significance. CG was significantly more painful at injection sites. Other side effects were very few, precluding any statistical comparison. Foam was associated with more side effects (microthrombi, matting) than CG or POL solution. Three patients treated with POL foam experienced a transient visual disturbance. CONCLUSION: This study shows that CG is superior to POL solution and foam for sclerotherapy of leg telangiectasias.

Adolescent↗
PubMed2006

A probabilistic arsenic exposure assessment for children who contact chromated copper arsenate (CCA)-treated playsets and decks, Part 2: Sensitivity and uncertainty analyses.

A probabilistic model (SHEDS-Wood) was developed to examine children's exposure and dose to chromated copper arsenate (CCA)-treated wood, as described in Part 1 of this two-part article. This Part 2 article discusses sensitivity and uncertainty analyses conducted to assess the key model inputs and areas of needed research for children's exposure to CCA-treated playsets and decks. The following types of analyses were conducted: (1) sensitivity analyses using a percentile scaling approach and multiple stepwise regression; and (2) uncertainty analyses using the bootstrap and two-stage Monte Carlo techniques. The five most important variables, based on both sensitivity and uncertainty analyses, were: wood surface residue-to-skin transfer efficiency; wood surface residue levels; fraction of hand surface area mouthed per mouthing event; average fraction of nonresidential outdoor time a child plays on/around CCA-treated public playsets; and frequency of hand washing. In general, there was a factor of 8 for the 5th and 95th percentiles and a factor of 4 for the 50th percentile in the uncertainty of predicted population dose estimates due to parameter uncertainty. Data were available for most of the key model inputs identified with sensitivity and uncertainty analyses; however, there were few or no data for some key inputs. To evaluate and improve the accuracy of model results, future measurement studies should obtain longitudinal time-activity diary information on children, spatial and temporal measurements of residue and soil concentrations on or near CCA-treated playsets and decks, and key exposure factors. Future studies should also address other sources of uncertainty in addition to parameter uncertainty, such as scenario and model uncertainty.

Arsenates↗
PubMed1992

Differential effect of ultraviolet-B radiation on certain metabolic processes in a chromatically adapting Nostoc.

The impact of UV-B radiation on growth, pigmentation and certain physiological processes has been studied in a N2-fixing chromatically adapting cyanobacterium, Nostoc spongiaeforme. A brownish form (phycoerythrin rich) was found to be more tolerant to UV-B than the blue-green (phycocyanin rich) form of N. spongiaeforme. Continuous exposure to UV-B (5.5 W m-2) for 90 min caused complete killing of the blue-green strain whereas the brown strain showed complete loss of survival after 180 min. Pigment content was more strongly inhibited in the blue-green strain than in the brown. Nitrogenase activity was completely abolished in both strains within 35 min of UV-B treatment. Restoration of nitrogenase occurred upon transfer to fluorescent or incandescent light after a lag of 5-6 h, suggesting fresh synthesis of nitrogenase. Unlike the above processes, in vivo nitrate reductase activity was stimulated by UV-B treatment, the degree of enhancement being significantly higher in the blue-green strain. Like the effect of UV-B on nitrogenase, 14CO2 uptake was also completely abolished by UV-B treatment in both strains. Our findings suggest that UV-B may produce a deleterious effect on several metabolic activities of cyanobacteria, especially in cells lacking phycoerythrin. Strains containing phycoerythrin appear to be more tolerant to UV-B, probably because of their inherent property of adapting to a variety of light qualities.

Adaptation, Physiological↗
PubMed1992

Responses of macaque ganglion cells to movement of chromatic borders.

1. We have measured responses of macaque ganglion cells to moving borders under conditions designed to simulate the minimally distinct border (MDB) task. 2. Extending previous results, we show that minimization of responses of phasic ganglion cells of the magnocellular (MC)-pathway obey the photometric laws of transitivity and additivity. 3. To equal luminance borders, a residual response was present in MC-pathway cells analogous to the second harmonic response seen in these neurones with temporal chromatic modulation. It was proportional to the tritanopic purity difference (magnitude of delta Pt, the rectified middle- to long-wavelength cone opponent signal) between the two colours on either side of the border. For a delta Pt of one, the mean residual response was equivalent to the response evoked by achromatic borders of about 14% luminance contrast. Both these properties of the MC-pathway closely resemble psychophysical estimates as to the distinctness of equal luminance borders. 4. We show how MC-pathway cell responses could be used centrally to support the MDB task. It was difficult to generate a model from responses of tonic ganglion cells of the parvocellular (PC)-pathway which would support the task. 5. The MDB task is still possible psychophysically after blurring the retinal image. Although blurring the border spatially smeared the responses of MC-pathway ganglion cells and reduced their amplitude, responses still went through a minimum close to equal luminance. Thus, blurring the image did not affect the ability of MC-pathway cells to support the task. Blurring the retinal image decreased the 'sharpness' of the border response of tonic, PC-pathway ganglion cells, but response amplitude was unaffected. Response features indicative of centre-surround organization were attenuated. A central mechanism reliant on centre-surround field structure of PC-pathway cells would thus not be able to support the task after blurring. 6. Taken together, these results strongly suggest that the MC-pathway forms the sole physiological substrate of the MDB task, and any contribution of the PC-pathway is, indeed, minimal.

Animals↗
PubMed1963

Adaptation to chromatic aberration by the human visual system.

Prolonged exposure to the chromatic dispersion produced by prism spectacles leads to a perceptual adaptation. The adaptation develops rapidly in the first two days of the wearing of the spectacles, and seems to be a special reac ion to the relative change in illuminance at intensity gradients on the retina.

Adaptation, Ocular↗
PubMed1984

The wood preservative chromated copper arsenate is a substrate for trimethylarsine biosynthesis.

The wood preservative chromated copper arsenate (CCA) is a very widely used product. As it contains both copper and arsenic, it is not dissimilar to the pigments Scheele's green and Schweinfurter's green which were found to be biologically convertible to the toxic Gosio gas (B. Gosio, Ber. 30:1024-1026, 1897) later identified by Challenger and co-workers as trimethylarsine (F. Challenger, Adv. Enzymol. 12:429-491, 1951). Thus, it was of interest to determine whether microbiological action on CCA and wood treated with CCA could result in the production of trimethylarsine. We report that the fungus Candida humicola will produce this arsine from dilute solutions of CCA and from wood soaked in CCA.

Air Pollutants↗
PubMed2001

Chromatic adaptation in marine Synechococcus strains.

Characterization of two genetically distinct groups of marine Synechococcus sp. strains shows that one, but not the other, increases its phycourobilin/phycoerythrobilin chromophore ratio when growing in blue light. This ability of at least some marine Synechococcus strains to chromatically adapt may help explain their greater abundance in particular ocean environments than cyanobacteria of the genus Prochlorococcus.

Adaptation, Physiological↗