Comparative assessment of the global fate of α- and β-hexachlorocyclohexane before and after phase-out

Technical hexachlorocyclohexane (HCH) was one of the most widely used pesticides during the 20th century. Although production and use were phased-out during the 1990s, two of its major components, α- and β-HCH, are still ubiquitous in the environment. Here, we have collected and analyzed data on concentrations of α- and β-HCH in the atmosphere and oceans, including spatial and temporal trends and seasonalities. We apply a global fate and transport model to both isomers over the period 1950 to 2050 to rationalize current levels and trends at remote locations with estimated emissions and to forecast into the near future. Our model results indicate that secondary emissions from soils and oceans are currently controlling the observed rates of decline in the atmosphere. β-HCH is declining more slowly than α-HCH due to its higher persistence, and we hypothesize that it will eventually become the predominant isomer of HCH in the environment. The model reproduces over 70% of measured concentrations of α-HCH in air and ocean water within factors of 3 and 5, respectively, and over 70% of measured concentrations of β-HCH within factors of 8 and 20, respectively. The model results are only weakly sensitive to climate change-induced trends in Arctic sea-ice cover and temperature.

BETR global--a geographically-explicit global-scale multimedia contaminant fate model

We present two new software implementations of the BETR Global multimedia contaminant fate model. The model uses steady-state or non-steady-state mass-balance calculations to describe the fate and transport of persistent organic pollutants using a desktop computer. The global environment is described using a database of long-term average monthly conditions on a 15°×15° grid. We demonstrate BETR Global by modeling the global sources, transport, and removal of decamethylcyclopentasiloxane (D5).

The use of the Internet in dentistry

With internet connectivity, a new horizon of scientific co-operation and collaboration at global level has been opened. Anyone can have easy access to information on not only public health and hygiene matters, but also on more esoteric aspects of dental practice. This article points out the use of the internet in dentistry.

Two case reports of delayed skin burns from methylisothiazolines used in water treatment

Kathon CG and Kathon WT are biocides containing 5-Chloro-2-Methyl-4-Isothiazoline-3-One (MCI) and 2-Methyl-4-Isothiazoline-3-One (MI) in a 3:1 ratio. These compounds are used as preservatives in skin care products and there have been many reports of allergic contact dermatitis due to Kathon used in this context. They are also widely used in industry as preservatives in metal working fluids, latex emulsions and for water treatment. Two cases of severe irritant contact dermatitis through accidental exposure to high concentrations of Kathon in industrial settings are reported to highlight the importance of worker education and the use of personal protective equipment when handling this corrosive chemical.

Severe noise-induced deafness--a 10-year review of cases

Noise Induced Deafness (NID) is the leading occupational disease in Singapore. Every year, over 500 new cases of NID are detected by the Department of Industrial Health (DIH). Severe NID is a disabling disease which is compensable under the law. A retrospective study was conducted to elicit the profile of workers with severe, disabling NID. From 1 January 1985 to 31 December 1994, the DIH confirmed 127 of such cases. Of these, 57 (44.9%) were involved in the building and repair of ships and boats, 30 (23.6%) with the basic steel industries, manufacture and fabrication of metal products and storage batteries, 9 (7.2%) with the transport and allied support industries, 7 (5.5%) in granite quarrying, 7 (5.5%) in the manufacture of food and drinks, 5 (3.9%) in the manufacture of wooden furniture and 7 (5.5%) in other industries such as manufacture of glass, electricity generation, construction, textiles, printing and so on. The mean age of these workers upon diagnosis of severe NID was 48 years (SD 8.07). The mean duration of exposure to noise was 24 years (SD 9.11). The mean of the average hearing thresholds at 1, 2 and 3 kHz for these workers was found to be 61.5 dBA (SD 4.26). The main jobs at risk were grit blasters, steel workers, fitters, boiler fabricators, panel beaters and carpenters. Noise dosimetry was performed on 46 of the cases and the mean time-weighted exposure level was 90 dBA (SD 10.00). Finally, 82.7% of cases already had audiometric evidence of severe deafness at the time of notification.

Fatal gassing due to methylene chloride - a case report

Methylene chloride is a major component of paint and varnish strippers. Due to its high volatility, its use in unventilated or poorly ventilated confined spaces poses a serious health hazard as a result of accumulation of the solvent vapour. At high levels, methylene chloride can cause severe central nervous system depression and ultimately death, as illustrated in this case report. The importance of adequate forced ventilation, utilisation of proper personal protective equipment and enforcement of a permit-to-work system during work with solvents in confined spaces is emphasised.

Environmental and biological monitoring of occupational exposure to 1,1,1-trichloroethane

Fifty workers involved in various degreasing and cleaning processes using 1,1,1-trichloroethane (1,1,1-TCE) were studied with respect to personal and static exposures. In addition, end-of-shift expired air and venous blood samples were taken for analysis of the parent compound. Urinary samples were also obtained at the same time for analysis of its metabolites-trichloroethanol (TCOH) and trichloracetic acid (TCA). The results show that open/manual degreasing processes generate the highest environmental solvent levels (mean = 819.9 mg/m3; SD = 781.9 mg/m3) followed by jet-spray cleaning (mean = 460.5 mg/m3; SD = 292.4 mg/m3), vapour degreasing (mean = 365.3 mg/m3; SD = 279.9 mg/m3) and ultrasonic degreasing (mean = 134.7 mg/m3; SD = 121.0 mg/m3). Personal exposure levels were well correlated with concentrations of 1,1,1-TCE in end-of-shift expired air (r = 0.81) and venous blood samples (r = 0.88) but only moderately correlated with concentrations of its metabolites in urine (r = 0.49 for TCOH; r = 0.58 for TCA). Static (area) samples were poorly correlated with the biological exposure indices studied.

Organophosphate poisoning in a factory: relationship to workload and production volume

In Singapore, all workers exposed to organophosphate compounds are required to undergo Statutory Medical Examinations. In this paper, the relationship between workload and worker exposure to these compounds is illustrated. In addition, the importance of performing detailed clinical examinations and baseline red blood cell acetylcholinesterase estimations for all organophosphate exposed workers is emphasised.