Chlorpropham distribution in potato stores and evaluation of environmental issues relating to its use
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.