Understanding the persistence, transformation and fate of CIPC (Chlorpropham) in commercial potato stores to help guard against cross-contamination.

The fate and distribution of the sprout suppressant chlorpropham (CIPC) in potato stores is uncertain. Detectable amounts of CIPC in any commodity exceeding the Maximum Residue Limit (MRL) renders it unfit for use in the EU. The MRL for CIPC on cereals is set at the limit of quantification (LOQ, 0.01 mg kg-1) because it is not permitted for use on these crops. Cross-contamination of cereals with CIPC is an emerging concern in the UK. Grain cross-contamination may have occurred during storage in buildings with a history of CIPC use, however, the retention of CIPC residues in the fabric of stores and the effect on grain cross-contamination is poorly understood. Unfortunately, even extensive cleaning of a store is not sufficient to remove CIPC residues from the infrastructure. Sensitive analytical methods are therefore required to detect CIPC in building materials to allow informed recommendations to be made to farmers about the re-use of stores for other crop commodities. Decontamination strategies are urgently required to allow valuable storage facilities to be used for the purpose they were intended. This project provides an understanding of the persistence, transformation and fate of CIPC in commercial potato stores to help guard against cross-contamination. An initial step in tackling the cross contamination was the development of sensitive analytical methods to detect CIPC and its degradation product 3 chloroaniline (3-CA) in the fabric of potato stores. Robust High- Performance Liquid Chromatography with Ultraviolet Detection (HPLC UV/VIS) and Gas Chromatography Mass Spectrometry (GCMS) methods were developed for quantifying and confirming the presence of CIPC and 3-CA in building material (concrete) and crop commodity (grains). The methods were successfully used in stores to determine: the degree of CIPC and 3-CA contamination in the concrete flooring; the degree and route of CIPC and 3-CA cross contamination of grains and the effectiveness of a sealant to prevent cross contamination. The distribution of CIPC and 3-CA in the concrete flooring of stores with histories between 1 and 25 years of application was determined. The degree of chemical penetration into the flooring was dependent on the physical composition of the concrete, with >90% in the top centimetre layer of less porous concrete. CIPC was persistent in all stores to a depth of at least 3 cm and this was irrespective of the date of the last CIPC application. The accumulation of residues in the flooring was also influenced by the quantities of applied CIPC, the point of CIPC entry into the store and the type of circulatory system used. The levels of contamination were more likely to be higher in areas closest to the point of entry into the stores. Of the stores studied, the magnitude of contamination was increased with the number of applications in research stores and vice versa in commercial stores. The degree of contamination in stores was influenced by air circulation causing heterogeneity of CIPC distribution. 3-CA was persistent in commercial stores with the distribution varying in the flooring. The methods developed in this project are invaluable for the detection of residues in stores and the knowledge gained on the magnitude of contamination is significant for risk assessment prior to the storage of non-potato crops in buildings with a history of CIPC use. In addition, this study provides invaluable information for decontamination strategies since it provides an indication on the depth of concrete that would require removal or treatment to allow stores to be re-used. The degree and route of cross contamination of grains was examined in commercial stores with histories of 16 and 25 years since the final application of CIPC. Cross contamination was feasible irrespective of the CIPC levels in the concrete flooring and provided evidence that the headspace in the general store, the headspace above the concrete flooring and dislodged contaminated dust particles in a store environment are all important routes of cross contamination. The duration of storage of grain influenced the magnitude of cross contamination, with an increase in magnitude for longer storage duration. The magnitude of cross contamination was increased in the vicinities of the points of CIPC entry into the stores because accumulation of residues in the concrete flooring and dust was higher in these areas. Therefore, the heterogeneity of CIPC distribution in the concrete flooring may influence the magnitude of cross contamination, with an increase in magnitude at higher levels of CIPC in the flooring. The storage of grains and other commodities with MRLs set at the LOQ for CIPC are at risk of cross contamination in contaminated buildings. Therefore, the reuse of potato stores for other commodities is not recommended. Decontamination strategies for removal of CIPC residues were explored. A xylene based sealant was ineffective in retaining residues and thus permitted cross contamination of grains in contact with the concrete flooring of the store. However, useful information with respect to the method of sealant application was gathered, with future benefits for other trials. Chemical degradation of CIPC with 3-decen-2-one was not observed, instead, a non-covalent complex involving a N-H…O hydrogen bond was formed. The reaction was reversible due to the type of bonding; suggesting decenone was not effective for the decontamination of CIPC on concrete. The complexes formed from the reaction, however, were unlikely to change the properties of CIPC present on building materials; preventing the formation of 3-CA. Therefore, decenone can be an alternative solvent for CIPC application in stores. Titanium dioxide incorporated in sealants or pillared clays and ozone are other promising decontamination strategies that require exploring