The provision of crops of a light fry colour, from store, is of the utmost importance to processors. Poor fry colour leads to rejection of crops on a quality basis. The application of Chlorpropham (CIPC) sprout suppressant, as a thermal fog is associated with a deterioration in fry colour. The BPC funded project at the University of Glasgow and its collaborator Sutton Bridge Experimental Unit investigates the effects of CIPC use on the processing quality of stored potatoes. CIPC is the only sprout suppressant available for medium and long-term storage for processing in Britain. In the UK the majority of CIPC treatments are conducted as thermal fog applications. This is considered to be the most practical means of achieving successful sprout control. The introduction of a hot fog into potato stores has a disruptive influence. It can physiologically alter the potatoes by creating a stressful environment. Tuber respiration rate increases and so the crop will age. Experimental trials conducted as part of this project have shown that it is the fogging process itself that is responsible for the decrease in crop quality following application, not the CIPC formulation applied. Studies revealed that both carbon dioxide and ethylene were produced naturally by crop and from the combustion of petrol used to generate thermal fogs. Initially the fry colour problems were linked with carbon dioxide in combustion gases and from increased respiration. However, carbon dioxide output from thermal fogger machines was less significant than expected. The levels were consistently lower than concentrations shown to have a deleterious effect in previous BPC funded work. Ethylene is present in thermal fogs as a by-product of burning the hydrocarbon fuel used to generate fog. The concentration of ethylene produced is associated with the running conditions of the fogger machine I.e. burner temperature, type and volume of fuel used etc. The ethylene created in a standard CIPC thermal-fog application is sufficient to induce a physiological response in tubers. Exposure of crop to ethylene effects respiration, dormancy period, sprout morphology, reducing sugar concentration and hence fry colour. The extent of the outcome depends on exposure time and concentration. Following assessment of the fogging situation, various means of reducing the impact of CIPC application on fry colour were evaluated. Different approaches were undertaken and included both attempting to control and remove the contaminants present in thermal fogs. By ventilating stores earlier than the recommended twenty-four hour period after treatment a vast improvement in fry colour was observed. In doing this the exposure time of crop to contaminants was greatly reduced. In the experimental work the stores were ventilated eight hours after treatment. This allowed adequate time for the effective fraction of the thermal god to settle.

Work described in this thesis was designed to address a number of environmental issues relating to the use of chlorpropham (CIPC) as a sprout suppressant in potato stores. Studies considered the behaviour of CIPC during the application process and storage and also the potential for it to be released into the environment. All commercial studies were carried out in box stores, rather than bulk stores. A survey of potato growers was carried out to provide up-to-date industry information on store management practice and to determine the extent of chlorpropham use in the UK. Results confirmed that the vast majority of crop held in the UK for both pre-packing and processing is treated with chlorpropham. In most cases, several applications are necessary to maintain sprout control throughout the season, which highlights the inefficiency of the application process. Thermal fog application (the industry standard) is known to be inefficient, and to result in uneven distribution of chlorpropham around the store. This can lead to unacceptably high chemical residues in crop at certain locations, and poor sprout control in places that do not receive the correct dose. The imminent introduction of a Maximum Residue Level (MRL) for chlorpropham means that store managers must be able to predict with confidence the amount of chemical reaching each tuber. Analysis of crop from commercial stores found chemical levels ranging from 0-50 mg kg-1 following conventional application. Washing significantly reduced these very high levels in most cases. Improvements in chemical distribution (and a lowering of the highest chemical levels) were seen when the movement of air and fog around the store were manipulated using fans or by restricting air flow using polythene sheeting. A method for the collection and analysis of air samples was developed and used to quantify CIPC in samples of air from treated stores. Vapour concentrations were found to be of the order of mg l-1 (parts per billion), and to increase linearly with air temperature. 3-chloroaniline (a metabolite of CIPC) was also identified in the air samples, suggesting significant breakdown of the CIPC molecule may occur during chemical application or storage. The mechanism of breakdown was not identified. Contaminated fabrics within the store are believed to provide a reservoir of chemical that can readily volatilise and be found in the vapour phase. The presence of chlorpropham in the air has implications for crop contamination and the extent of chemical loss from the store. Samples of effluent from potato washing plants were collected and analysed on several occasions. The CIPC concentration to liquid effluent (after removal of all suspended material) was found to range from several mg/l (parts per million) in untreated samples to <0.01 mg l-1 following filtration and digestion.