The possibility of developing amperometric biosensors for the measurement of SO2 in flowing gas streams has been examined. Screen-printed carbon electrodes (SPCEs) were tailored with the enzyme sulfite oxidase and cytochrome c and the response is generated through the resulting enzymatic and electrocatalytic reactions involving SO32−, formed when SO2 gas is dissolved in the supporting electrolyte. Two methods of integrating the enzyme and cytochrome c with the SPCE were investigated. In one design (b-type biosensor), the components were mixed thoroughly with the same ink used to produce the SPCEs, then the modified ink was spread over the working electrode. In the second approach the bio-components were dissolved in the supporting electrolyte and simply deposited on top of the transducer (s-type biosensor). Both devices gave linear responses over the range 4–50 ppm but the sensitivity of the s-type was approximately twice that of the b-type biosensor. In addition, the time taken to reach 90% of the maximum response (t90%) was 110 s for the s-type biosensor compared with 200 s for the b-type biosensor. These studies illustrate the successful use of biosensors for the detection of sulfur dioxide at the relatively low potential of +0.3 V versus Ag.AgCl and should provide useful alternatives for decentralised environmental studies.

An amperometric biosensor for sulfite has been developed. The enzyme sulfite oxidase (SOD) and electron acceptor cytochrome c are mixed into the carbon ink that is deposited onto the working electrode of a screen-printed strip. A silver–silver chloride electrode is printed alongside the working electrode and serves as reference/counter electrode. The electrochemical behaviour of the biosensor surface in plain buffer has been investigated by cyclic voltammetry. In the voltage range −0.5 to +0.5 V, a well-defined anodic peak appeared at −0.15 V and a less well-defined anodic peak at about +0.2 V. In the presence of SO32−, the cyclic voltammogram obtained with the biosensor exhibited an increase in magnitude of the more positive peak; this was considered to result from the electrocatalytic oxidation of SO32− involving SOD and the heme (Fe2+/Fe3+) centre of cytochrome c. Amperometry in stirred solution was used to construct a hydrodynamic voltammogram for SO32− using the biosensor; this exhibited a single wave with a plateau beginning at +0.3 V. This wave corresponds to the electrocatalytic response observed by cyclic voltammetry. The pH and concentration of buffer components have been optimised for the determination of SO32− by amperometry in stirred solution. Using these conditions, a detection limit of 4 ppm was obtained. The stability of the biosensors was examined after storage in 0.05 M phosphate buffer pH 7.4 at 4°C; it was found that the initial response was retained for at least 45 days. The proposed biosensors were evaluated on samples of unspiked and spiked estuarine, river and tap waters. The recovery and precision data indicated that the devices could be expected to give reliable data in these waters.

Bacteria and fungi can contribute to the flavour of our foodstuff and improve the product. The presence of these micro-organisms is more often an undesirable one and indeed it is well known that these micro-organisms are mainly the cause of the ultimate decay of foodstuffs. The flavour of cheese and game results from microbial breakdown of the foodstuff which produce a more desirable product. The availability of sensors for detecting the state of the product would be useful as they would forego the need for an organoleptics panel of experts whose sense of taste and smell is subjective. It is for these reasons that there has been a considerable interest in commercial electronic noses by certain areas of the food industry. These 'noses' operate on a sensor array basis coupled to a pattern recognition system. A range of relatively non-specific sensors are able to detect the vapours which may, for instance, come from fungi, generally as alcohols, esters, aldehyde or ketones. The vapours from bacteria generally come from the breakdown of protein as well as carbohydrates, and consist of the products of decarboxylation and deamination of amino acids which have been formed by the proteolytic degradation of proteins. These vapours I,2.3 are generally methylamine, dimethylamine, trimethylamine and ammonia. They can also be sulphur based, e.g., hydrogen sulphide, methyl mercaptan, dimethyl disulphide, derived from sulphur containing amino acids such as cysteine and methionine. Amines such as histamine are released from bacterial metabolism of the amino acid histidine; this is particularly a problem in fish such as mackerel and tuna. Bacteria tend to produce vapours which are obnoxious to human beings e.g. sulphides and amines, such as cadavarine and putrescine. Furthermore amine based compounds such as indole produce a faecal like smell. The bacterial break down ofproteins does not necessarily produce obnoxious smelling compounds with a variety of ketones and aldehydes being produced such as acetone, butanone, diacetyl, methyl butanal and acetaldehyde. Esters such as methyl acetate and low molecular weight fatty acids are often produced as well. It should also be noted that some sulphur compounds, although obnoxious, at very low concentrations can often give a desirable flavour to foods. The fungi tend to attack foodstuffs with a high carbohydrate content producing alcohols and esters, such as ethanol and ethyl acetate which are considered to be pleasant smelling by humans. Some secondary metabolites, i.e. compounds not essential for mainstream metabolic processes, are responsible for the mouldy smell associated with fungi e.g., 3-octanol. It should be noted that our sense of smell to some compounds produced by fungi e.g. geosmin and trans-oct-2-enal, is very acute. For example, trans-oct2-enal has an odour threshold of 3 parts per trillion and is considered to possess a sweet phenolic smell. Another secondary metabolite often produced by fungi is 2-phenylethanol which has a rose like smell. It is not necessary to know the volatiles that are being emitted for assessing the quality of a certain foodstuff as long as one has standards i.e. produce of known high quality assessed by a sensory panel which can be presented to an array of sensors and used to 'teach' a pattern recognition system. This procedure has been adopted recently by a number of companies e.g., Alphamos, AromaScan and Neotronics, to produce commercially viable electronic noses based on this principle. The sensors involved to some extent depends on the expertise of the relative company e.g. AromaScan tends to use conducting polymers" whereas Alphamos, have used ceramic heated sensors• At present these systems require careful control of the environment, are expensive and are not hand held instruments. However they can speed up analysis considerably i.e. what might once have been carried out by GCMS in a laboratory, can now effectively be done very near the production of the produce itself and with relatively untrained personnel. At the University of the West of England (UWE) we have not adopted the approach of a large sensor array associated with electronic interfacing and pattern recognition, we have chosen to identify the major components of the vapours using gas chromatography and mass spectroscopy (GCMS) techniques as appropriate from such produce as citrus fruit and air cured salted hams. (See figure 1). The most significant volatiles are then identified and sensors sourced from commercial suppliers such as City Technology and Figaro or fabricated in-house. Sensors which we have recently been working on have been in the areas of fluorescence, electrochemical, polymer and ceramic based technologies. Our objectives have been to produce hand held devices which are economical, reliable and specific for the task, based on single or relatively small numbers of sensor devices.

The 1994 Oslo Protocol for reduction of sulphur dioxide emissions was developed in the context of transboundary air pollution and its effects on acidification of natural ecosystems. However there are additional benefits of such emission abatement which are concentrated closer to the source in the country of origin. This paper dicussses the damage to buildings and materials which may be avoided as a result of the Oslo Protocol, and gives an approximate indication of the economic value of this saving.

Damage to buildings and materials caused by acidifying atmospheric pollution imposes considerable socioeconomic costs across much of Europe. The aim of this study was to attempt a first estimate of the cost savings which will result from the implementation of the second Sulphur Protocol, The methodology and damage functions were adapted from a joint Nordic project which calculated damage costs in Stockholm, Prague and Sarpsborg, in Norway [Kucera er al. (1993). In Progress in the Understanding of Corrosion, Vol. 1. Institute of Materials, London]. For evaluation at this scale population data was used as the only available indicator of the distribution of stock al risk. Sulphur dioxide was used as a proxy for all acidifying pollutants, and urban and rural concentration data provided by WHO and EMEP, respectively. Results show that the cost savings are potentially very large, particularly in Eastern Europe, and may compensate for a considerable proportion of abatement costs. Ln addition, the mainly local nature of effects could shift the economic emphasis from transboundary to domestic benefits, and thus affect the political decision-making process. Copyright (C) 1996 Elsevier Science Ltd

European emissions of reduced nitrogen, arising principally from agriculture, are comparable with those of oxidised nitrogen from mobile and stationary combustion sources. It is therefore important to include ammonia emissions in working towards a new protocol on nitrogen under the programme of the UN Economic Commission for Europe on the control of transboundary air pollution. However the nature of the sources and the subsequent atmospheric transport and chemistry are very different from other acidifying pollutants. This paper describes work in hand under the MARACCAS project to compare agricultural activities in different European countries and to assess the applicability and efficacy of potential abatement measures. The aim is to derive abatement costs for each country relating successive emission reductions to the costs of achieving them, to be used by the UN ECE Task Force on Integrated Assessment Modelling (TFIAM) — in particular with our Abatement Strategies Assessment Model, ASAM. The paper will also address the large uncertainties involved in integrated assessment modelling with respect to ammonia, and suggest how these may be allowed for in deriving cost-effective abatement strategies.

In spite of the considerable interest which has been shown in the use of screening procedures, and the increasing use of at least some counselling techniques by teaching staff concerned with pastoral care, the notion of devising a screening procedure to identify pupils who may benefit from help seems to have attracted surprisingly little attention. Even the multitude of studies of disruption in schools and how it might be managed have indicated few positive steps in this direction.