Sorption and degradation characteristics of phosmet in two contrasting Australian soils

The organophosphate insecticide phosmet [phosphorodithioic acid, s-((1,3-dihydro-1,3-dioxo-2H-isoindol-2yl)methyl), o,o-dimethyl ester] is used to control red-legged earth mites (Halotydeus destructor), lucerne flea (Sminthurus viridis), and Oriental fruit moth (Cydia molesta) in horticulture and vegetable growing. This study was undertaken with two soils of contrasting properties to determine the extent to which sorption and degradation of the insecticide might influence its potential to leach from soil into receiving waters. Two soils were used: a highly organic, oxidic clay soil (Ferrosol) and a sandy soil low in organic matter (Podosol), sampled to 0.3 m depth. The extent of sorption and decomposition rate of a phosmet commercial formulation were measured in laboratory experiments. Sorption followed a Freundlich isotherm at all depths. The Freundlich coefficient K was significantly correlated (p = 0.005) with organic C content in the Podosol, and significantly correlated (p = 0.005) with organic C and clay content in the Ferrosol. K was highest (48.8 L kg-1) in the 0- to 0.05-m depth of the Ferrosol, but lowest (1.0 L kg-1) at this depth in the Podosol. Degradation followed first-order kinetics, with the phosmet half-life ranging from 14 h (0-0.05 m depth) to 187 h (0.2-0.3 m depth) in the Ferrosol. The half-life was much longer in the sandy Podosol, ranging from 462 to 866 h, and did not change significantly with depth. Soil organic C and to a lesser degree clay content influenced phosmet sorption and degradation, but the interaction was complex and possibly affected by co-solvents present in the commercial formulation.

Soil factors affecting the sustainability and productivity of perennial and annual pastures in the high rainfall zone of south-eastern Australia

A field study was carried out in the high rainfall zone (HRZ, >600 mm p.a.) of southern Australia from March 1994 to August 1997 to test the hypothesis that sown perennial grasses and liming could make the existing pastures more sustainable through better use of water and nitrogen. The site, on an acid duplex soil at Book Book near Wagga Wagga in southern New South Wales, was typical of much of the HRZ grazing country in southern New South Wales and north-east Victoria. The experiment consisted of 4 replicate paddocks (each 0.135 ha) of 4 treatments: annual pasture (mainly ryegrass Lolium rigidum, silver grass Vulpia spp., subterranean clover Trifolium subterraneum and broadleaf weeds) without lime, annual pasture with lime, perennial pasture (phalaris Phalaris aquatica, cocksfoot Dactylis glomerata and subterranean clover T. subterraneum) without lime, and perennial pasture with lime. Soil pH (0–10 cm) in the limed treatments was maintained at 5.5 (0.01 mol/L CaCl2), compared to 4.1 in the unlimed treatments. The pastures were rotationally grazed with Merino ewe or wether hoggets at a stocking rate which varied with the season, but was 10–25% higher on the limed pastures [14.8–17.3 dry sheep equivalent (dse)/ha] than the unlimed pastures. One replicate set of pasture treatments was intensively monitored for surface runoff, subsurface flow (at the top of the B horizon), water potential gradients and ammonium volatilisation. Other measurements of nitrogen inputs, transformations and losses were made on all paddocks. In a normal to wet year, surface runoff, subsurface flow and deep drainage (>180 cm depth) were about 40 mm less from the perennial than the annual pastures. The reduction in deep drainage under the perennials was about one-third to one-half (20–29 mm/year). The smaller loss of solution NO3– from the perennial pastures (up to 12 kg N/ha.year) suggested soil acidification under perennials was reduced by about 1 kmol H+/ha.year. Denitrification and volatilisation losses of N were small (1–12 kg N/ha.year). Nitrogen fixed by subterranean clover (above ground parts) ranged from 2–8 kg N/ha in the drought of 1994–95 to 128 kg N/ha in a normal year (1996). The soil-pasture nitrogen balance was positive for all treatments and averaged 76 kg N/ha.year over 2 years. The abundance of introduced and native earthworms increased from 85 to 250/m2 in the limed pastures between 1994 and 1997. Introduced species, such as Aporrectodea trapezoides, were especially responsive to lime. Animal production per hectare was 10–25% higher on pastures with lime. Critical gross margins per dse were lowest ($16/ha) for a long-lived perennial pasture (>15 years), and highest ($20/ha) for a short-lived perennial (5 years). Overall, there were substantial benefits in animal production, improved soil quality and water use from establishing perennial grass pastures with lime on these strongly acid soils.

Obtaining soil hydraulic properties for water balance and leaching models from survey data. 1. Water retention

A physico-empirical 2-parameter power law model of the draining water retention curve (WRC) based solely on clay content is described and further developed using 6 datasets obtained from Australian and New Zealand soils. The slope of the WRC, or pore-size distribution index, is well described by the model but the bubbling pressure, or inflection point is poorly described. Without a good estimation of the bubbling pressure it is not possible to scale the physico-empirical model to the WRC. To achieve the scaling, a single measured point on the WRC in the unsaturated range is required. The resulting estimated water contents may be satisfactory for application within broad-scale leaching risk models and for generalised extrapolation of results from detailed experimental sites but caution is still required for quantitative applications of nitrate leaching models at a particular site. It is concluded that soil surveys could usefully include a single WRC measurement in the field at each sampling location to improve their utility for water and chemical transport modelling.

Perfluorocarbon liquids (perfluorodecalin) in vitreoretinal surgery--a local experience

A low viscosity perfluorocarbon liquid (perfluorodecalin) known commercially as DKLine was used intraoperatively as a temporary vitreous substitute in 20 patients undergoing vitrectomy surgery for a variety of complicated vitreoretinal conditions. The indications for its use included giant retinal tears (9), proliferative vitreoretinopathies (2), dislocated lenses (2), dislocated posterior chamber implant (1), endophthalmitis with retinal detachment (2), traction retinal detachment (1), pseudophakic retinal detachment (2) and exudative retinal detachment (1). In all cases with retinal detachment, perfluorodecalin was successful in flattening the retina intraoperatively. It was also successful in permitting the safe removal of dislocated lenses that were lying on the retina. In all except four cases, removal of perfluorodecalin was complete. We observed no toxic effects from remnant bubbles of perfluorocarbon in the eye.

Secondary syphilis presenting with optic perineuritis and uveitis

We describe a 40 year-old man with optic perineuritis due to secondary syphilis. This condition which is due to inflammation of the optic nerve sheath is often mistaken for papilloedema or papillitis. We discuss its diagnosis and stress the importance of recognising it because it is easily treated by a course of Penicillin.

Idiopathic subretinal neovascularization

Idiopathic subretinal neovascularization is a potentially blinding condition and often strikes patients in their prime of life. It appears to be seen in more females, at an earlier age than males. Treatment is possible by photoablation of the subretinal new vessel by Argon or Yag laser. There is a clinical impression that Argon laser is more effective than the Yag laser for this purpose.

Current and future trends in the correction of aphakia: a local perspective

Over the last 20 years, the correction of aphakia has moved from spectacles and contact lens to intraocular lenses. Advances in lens design and implantation techniques are now in the exciting process of refinement--the aim being bionic perfection.

Scanning electron microscopic evaluation of posterior chamber intraocular lenses

A great variety of Intraocular Lenses (IOLs) made by various manufacturers are now available to the Implant Surgeon. The Surgeon must decide which IOLs are better than others, and be aware of physical characteristics of IOLs that would be potentially dangerous to the intraocular structures. The Scanning Electron-Microscope (SEM) is now recognised as a powerful tool in providing detailed information of the physical characteristics of Intraocular lenses. We randomly selected five posterior chamber intraocular lenses from each of five different manufacturers and subjected them to scanning with the SEM to evaluate their physical qualities as well as to assess the consistency of manufacture. Striking differences in quality of finish of the intraocular lenses were revealed. The consistency of quality of good or of defective characteristics was high amongst manufacturers.

Implantation and diabetes: analysis of 525 cases

This is a retrospective study of 525 posterior chamber implants in diabetics performed by A S M Lim and B C Ang of Singapore. The patients were reviewed by visiting ophthalmologists--J E Kennedy (Sydney), M Ngui (East Malaysia) and P M Hart (Belfast). This study did not show any significant difference in the complication of post-operative visual acuity between diabetics and non-diabetics. 95% obtained 6/12 vision or better when pre-existing disease was excluded. It also showed that posterior chamber implants can be inserted in eyes with maculopathy or proliferative retinopathy if laser treatment was effectively done before or after surgery.

Eye diseases in the elderly in Singapore

Ocular disorders in the elderly have become more important because of increased longevity and the demand for good vision. Many serious ocular conditions are age-related and they include cataract, glaucoma, diabetic retinopathy and other retinal conditions. The most important ocular disorder is cataract which fortunately is curable with excellent results when a posterior chamber implant is inserted. Angle closure glaucoma is common in the elderly Singapore Chinese and can be effectively treated with microscopic peripheral iridectomy or trabeculectomy. Blindness from diabetic retinopathy can be prevented with argon laser photocoagulation. In most cases blindness is preventable with early diagnosis e.g. in glaucoma and diabetic retinopathy. Severe visual loss in the elderly requires careful explanation and compassion by doctors and social workers.