Physical and biochemical aspects of the flow across the Mascarene Plateau in the Indian Ocean.

This paper presents results from a detailed hydrographic survey of the Mascarene Plateau and surrounding area undertaken by the RRS Charles Darwin in June-July 2002. We examine how the westward-flowing South Equatorial Current (SEC) crosses the plateau, and how the structure of the flow determines the supply of nutrients to the surface waters. We find that the flow of the SEC across the plateau is highly dependent on the complex structure of the banks which make up the plateau, and that a large part of the flow is channelled between the Saya de Malha and Nazareth Banks. Furthermore, the SEC forms a sharp boundary between subtropical water masses from further south, which are low in nutrients, and waters from further north, which are relatively nutrient rich. Overall, the SEC delivers relatively high levels of nutrients to the near-surface waters of the central and northern regions of the plateau, compared with the southern regions of the plateau. This is partly due to uplifting of density surfaces through Ekman suction on the northern side of the SEC, and partly due to the higher levels of nutrients on those density surfaces on the northern side of the SEC. This may drive increased production of phytoplankton in these areas, which would in turn be expected to fuel increased abundances of zooplankton and higher levels of the food chain.

Halocarbon and dimethyl sulphide studies around the Mascarene Plateau.

Air-sea exchange is thought to be one of the major routes by which halocarbons and dimethyl sulphide reach the troposphere and stratosphere. Once there, in different ways, they participate in chemical reactions that have implications for ozone depletion and climate change. The gases are released by phytoplankton and other algae, but our present understanding of the sources and sinks is insufficient to establish a balanced global budget. Published data suggest that there are regions of coastal and ocean waters that constitute a major source, but, for halocarbons, in other regions the ocean is a net sink. For example, in many open oceanic areas, the rate of degradation of methyl bromide outweighs production. Here we present data from the Central Indian Ocean, a region considered to be low in terms of biological productivity. Little is known about trace-gas release from the Central Indian Ocean and without such data it is impossible to even hazard a guess at the global ocean source to the atmosphere.

Urinary homovanillic acid (HVA) and vanillymandelic acid (VMA) in workers exposed to manganese dust.

The neurotoxicity of manganese (Mn) is well known, however, the neurochemical effect caused by this metal is less well investigated. In this study, urinary homovanillic acid (HVA) and vanillymandelic acid (VMA), two end products of catecholamine metabolism, were measured in 39 workers chronically exposed to Mn in a manganese smelting plant. The average duration of Mn exposure was 17.4 yr. Nineteen nonexposed workers were also studied. Concentrations of Mn in serum (MnS) and in urine (MnU) were measured by Zeeman graphite furnace atomic absorption spectrophotometry (ZAAS), and HVA and VMA determined by high performance liquid chromatography (HPLC). For Mn-exposed workers, the concentration of MnS was nearly 2.8 times (1.61 +/- 0.16 mg/L vs 0.56 +/- 0.16 mg/L) and MnU about 4.5 times higher (7.62 +/- 0.17 mg/L vs 1.69 +/- 0.16 mg/L) than the nonexposed. Although the geometric mean concentration of HVA in exposed workers was similar to that of the nonexposed (3.09 +/- 1.39 mg/g cre. vs 2.99 +/- 1.40 mg/g cre.), the VMA concentration was significantly higher (3.02 +/- 1.43 mg/g cre. vs 2.49 +/- 1.58 mg/g cre., p = 0.033). Multiple regression analysis showed that although there were no correlations between any of these parameters with the duration of exposure to Mn, both HVA and VMA showed significant correlations with increase in MnS and MnU. These data provide evidence that exposure to Mn was associated with measurable increase in catecholamine metabolites. This finding is compatible with recent observations in laboratory animals that Mn interferes with neurochemical metabolism.

Plasma vitamins A, C and E in the general population of Singapore, 1993 to 1995.

The National University of Singapore Heart Study measured cardiovascular risk factors, including selected plasma vitamins, on a random sample of the general population aged 30 to 69 years. Plasma vitamins A and E were normal and similar by ethnic group. Mean plasma vitamin A levels were: Chinese (males 0.68 and females 0.52 mg/L), Malays (males 0.67 and females 0.54 mg/L), and Indians (males 0.66 and females 0.51 mg/L). Mean plasma vitamin E levels were: Chinese (males 12.6 and females 12.6 mg/L), Malays (males 13.6 and females 13.3 mg/L), and Indians (males 12.9 and females 12.8 mg/L). No person had plasma vitamin A deficiency (< 0.01 mg/L) and only 0.1% had vitamin E deficiency (< 5.0 mg/L). In contrast, plasma vitamin C was on the low side and higher in Chinese than Malays and Indians. Mean plasma vitamin C levels were: Chinese (males 6.3 and females 8.4 mg/L), Malays (males 5.1 and females 6.4 mg/L), and Indians (males 5.7 and females 6.9 mg/L). Likewise, the proportions with plasma vitamin C deficiency (< 2.0 mg/L) were lower in Chinese (males 14.4 and females 0.7%), than Malays (males 19.7 and females 7.2%), and Indians (males 17.8 and females 11.0%). Relatively low levels of plasma vitamin C may contribute to the high rates of coronary heart disease and cancer in Singapore. In particular, lower plasma vitamin C in Malays and Indians than Chinese may contribute to their higher rates of coronary heart disease. However, plasma vitamin C does not seem to be involved in the higher rates of cancer in Chinese than Malays and Indians. The findings suggest a relatively low intake of fresh fruits and a higher intake is recommended. Also, food sources of vitamin C may be destroyed by the high cooking temperatures of local cuisines, especially the Malay and Indian ones.

Detection of oxidative DNA damage in human sperm and the association with cigarette smoking.

The present study aims to evaluate oxidative DNA damage in human sperm and the association with cigarette smoking. The level of 8-hydroxydeoxyguanosine (8-OHdG) in sperm DNA, cotinine concentration in seminal plasma, and conventional seminal parameters such as semen volume, sperm density, viability, motility, and normal morphology were determined in 60 healthy subjects. It was found that the sperm DNA of smokers contained a significantly higher amount of 8-OHdG than that of nonsmokers (6.19 +/- 1.71 vs. 3.93 +/- 1.33 8-OHdG/10(5) dG, P < 0.001). The level of 8-OHdG in sperm DNA was also closely correlated to seminal cotinine concentration (r = 0.38, P < 0.05). These findings suggest that cigarette smoking enhances the extent of DNA damage in sperm. In contrast, no significant difference was observed for conventional parameters between smokers and nonsmokers, suggesting that the level of 8-OHdG in sperm may reflect the deleterious effect of cigarette smoking on sperm quality more accurately than conventional seminal parameters. Further investigation is required to understand the exact biologic and pathologic significance of oxidative damage to sperm DNA and the possibility of using 8-OHdG for the assessment of sperm quality.

Comparative analysis of conjugated bile acids in human serum using high-performance liquid chromatography and capillary electrophoresis.

This paper describes the analysis of conjugated bile acids in human serum using reversed-phase high-performance liquid chromatography (HPLC) and micellar electrokinetic capillary electrophoresis (CE). Samples of healthy subjects and patients with different hepatic diseases were pretreated with a simple preparation procedure using a solid-phase extraction technique. The optimal analytical conditions of both chromatographic methods were investigated for the convenience and reliability for routine analysis. Both HPLC and CE methods were found to be reliable and compatible. The recoveries of nine bile acid conjugates using both methods were generally >85% and reproducibility >90%. The day-to-day variation of retention time was <5% for HPLC, while the variation of migration time for CE was <3%. Although the detection limit of the HPLC method (1 nmol/ml) was five times more sensitive than that of the CE method, the CE method was considered to be more time and cost effective.

Urinary homovanillic acid and vanillylmandelic acid in workers exposed to carbon disulfide.

Homovanillic acid (HVA) and vanillylmandelic acid (VMA), two end products of dopamine metabolism, were measured in 60 workers exposed to carbon disulfide (CS(2)) in a rayon factory and in 48 unexposed workers. The airborne CS(2) concentrations in eight major exposure zones of the plant were measured monthly over a period of 4 years, from 1990 to 1994. In addition, the exposure concentrations and exposure history of each worker were integrated to estimate the overall lifetime exposure. Industrial hygiene data showed that the geometric mean concentrations of CS(2) in the plant ranged from 2.68 to 20.19 ppm, and more than 15% of the studied population had been repeatedly exposed to CS(2) at concentrations exceeding the ACGIH recommended time-weighted average of 10 ppm. The results showed that there was a significantly lower level and a higher proportion of CS(2) workers with decreased HVA and VMA excretion. However, there were no statistical correlations between the two dopaminergic metabolites and the mean CS(2) concentration, and years of employment. In contrast, significant dose-effect relationships were observed between these two metabolites and the integrated cumulative exposure (ICE) variable. The correlation coefficients for ICE and HVA, and ICE and VMA were -0.35 (p < 0.01) and -0.20 (p <0.05), respectively. These data suggest that chronic exposure to CS(2) was associated with measurable reduction in catecholamine metabolite concentrations. This finding is compatible with the earlier observations in laboratory animals that CS(2) exposures interfere with neurochemical metabolism.

Liquid chromatographic determination of urinary 2-thiothiazolidine-4-carboxylic acid, a biomarker of carbon disulphide exposure.

An effective gradient high-performance liquid chromatographic method for baseline separation of urinary 2-thiothiazolidine-4-carboxylic acid (TTCA), with photodiode array detection at 271 nm was described. o-Methylhippuric acid was used as an internal standard (I.S.). A 1-ml urine sample was saturated with 300 mg of sodium sulphate, acidified with 100 microliters of 6 M hydrochloric acid, extracted twice with 2 ml of diethyl ether, and after evaporation, the residue was taken up in 1 ml of 0.1% (v/v) phosphoric acid. The two mobile phases used for gradient elution were: (A) 10 mM ammonium dihydrogenphosphate (pH 3.5) and (B) same concentration of buffer but containing 20% (v/v) of methanol (pH 4.8). The flow-rate was set at 1.0 ml/min. TTCA and I.S. were detected at 2.2 and 9.1 min, respectively. The method was validated with urine samples collected from normal subjects and workers occupationally exposed to carbon disulphide. The present method enables the detection of urinary TTCA at a concentration of 0.025 mg/l. Analytical recovery and reproducibility generally exceeded 90%. The proposed method is considered more sensitive, specific and reliable than other existing methods.

Urinary trans,trans-muconic acid determined by liquid chromatography: application in biological monitoring of benzene exposure.

We describe a sensitive and specific high-performance liquid-chromatographic method for determining the benzene metabolite, trans,trans-muconic acid (ttMA) in urine by measuring ultraviolet absorbance at 265 nm. We mix 1 mL of urine sample with 2 mL of Tris buffer containing vanillic acid as internal standard (IS) and percolate this through a preconditioned ion-exchange column. After rinsing the column with phosphoric acid solution, acetate buffer, and deionized water, we elute the analytes with 2 mL of an equivolume solution of 1.5 mol/L sodium chloride and methanol. Of this, 5 microL is injected into the HPLC column. The mobile phase used consists of, per liter, 10 mL of acetic acid, 100 mL of methanol, and the rest 5 mmol/L sodium acetate. The flow rate was started at 1 mL/min and increased to 1.5 mL/min after 6 min. ttMA and IS were detected at 5.2 and 10.2 min, respectively. The lowest detection limit is 125 pg. Analytical recovery and reproducibility generally exceeded 90%. We validated the method with urine samples collected from normal persons and from refinery workers exposed to benzene concentrations < 1 microL/L. The results show that urinary ttMA is a promising biological marker for risk assessment of low-concentration benzene exposure.

Determination of plasma ascorbic acid by high-performance liquid chromatography with ultraviolet and electrochemical detection.

A convenient and reliable reversed-phase liquid chromatographic method for the routine determination of ascorbic acid with ultraviolet detection is described. This system avoids the use of modifier and ion-pairing reagent. The mobile phase consists of 20 mM ammonium dihydrogenphosphate with 0.015% metaphosphoric acid. This method enables the detection of plasma ascorbic acid at a concentration of 120 ng/ml within 5 min. The recovery and reproducibility were above 95%. A comparative study was also performed using ultraviolet and electrochemical detectors. Excellent agreement was observed between the two detection modes, with a correlation coefficient of 0.99. In addition, the storage conditions and stability of ascorbic acid in plasma and whole blood were investigated. The results showed that ascorbic acid was more stable in whole blood when stored below 4 degrees C.